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a0d0e21e LW |
1 | =head1 NAME |
2 | ||
8e07c86e | 3 | perlxs - XS language reference manual |
a0d0e21e LW |
4 | |
5 | =head1 DESCRIPTION | |
6 | ||
7 | =head2 Introduction | |
8 | ||
beb31b0b GS |
9 | XS is an interface description file format used to create an extension |
10 | interface between Perl and C code (or a C library) which one wishes | |
11 | to use with Perl. The XS interface is combined with the library to | |
12 | create a new library which can then be either dynamically loaded | |
13 | or statically linked into perl. The XS interface description is | |
14 | written in the XS language and is the core component of the Perl | |
15 | extension interface. | |
16 | ||
17 | An B<XSUB> forms the basic unit of the XS interface. After compilation | |
18 | by the B<xsubpp> compiler, each XSUB amounts to a C function definition | |
19 | which will provide the glue between Perl calling conventions and C | |
20 | calling conventions. | |
21 | ||
22 | The glue code pulls the arguments from the Perl stack, converts these | |
23 | Perl values to the formats expected by a C function, call this C function, | |
24 | transfers the return values of the C function back to Perl. | |
25 | Return values here may be a conventional C return value or any C | |
26 | function arguments that may serve as output parameters. These return | |
27 | values may be passed back to Perl either by putting them on the | |
28 | Perl stack, or by modifying the arguments supplied from the Perl side. | |
29 | ||
30 | The above is a somewhat simplified view of what really happens. Since | |
31 | Perl allows more flexible calling conventions than C, XSUBs may do much | |
32 | more in practice, such as checking input parameters for validity, | |
33 | throwing exceptions (or returning undef/empty list) if the return value | |
34 | from the C function indicates failure, calling different C functions | |
35 | based on numbers and types of the arguments, providing an object-oriented | |
36 | interface, etc. | |
37 | ||
38 | Of course, one could write such glue code directly in C. However, this | |
39 | would be a tedious task, especially if one needs to write glue for | |
40 | multiple C functions, and/or one is not familiar enough with the Perl | |
41 | stack discipline and other such arcana. XS comes to the rescue here: | |
42 | instead of writing this glue C code in long-hand, one can write | |
43 | a more concise short-hand I<description> of what should be done by | |
44 | the glue, and let the XS compiler B<xsubpp> handle the rest. | |
45 | ||
46 | The XS language allows one to describe the mapping between how the C | |
47 | routine is used, and how the corresponding Perl routine is used. It | |
48 | also allows creation of Perl routines which are directly translated to | |
49 | C code and which are not related to a pre-existing C function. In cases | |
50 | when the C interface coincides with the Perl interface, the XSUB | |
51 | declaration is almost identical to a declaration of a C function (in K&R | |
52 | style). In such circumstances, there is another tool called C<h2xs> | |
53 | that is able to translate an entire C header file into a corresponding | |
54 | XS file that will provide glue to the functions/macros described in | |
55 | the header file. | |
56 | ||
57 | The XS compiler is called B<xsubpp>. This compiler creates | |
58 | the constructs necessary to let an XSUB manipulate Perl values, and | |
59 | creates the glue necessary to let Perl call the XSUB. The compiler | |
a0d0e21e | 60 | uses B<typemaps> to determine how to map C function parameters |
beb31b0b GS |
61 | and output values to Perl values and back. The default typemap |
62 | (which comes with Perl) handles many common C types. A supplementary | |
63 | typemap may also be needed to handle any special structures and types | |
64 | for the library being linked. | |
65 | ||
66 | A file in XS format starts with a C language section which goes until the | |
67 | first C<MODULE =Z<>> directive. Other XS directives and XSUB definitions | |
68 | may follow this line. The "language" used in this part of the file | |
7817ba4d NC |
69 | is usually referred to as the XS language. B<xsubpp> recognizes and |
70 | skips POD (see L<perlpod>) in both the C and XS language sections, which | |
71 | allows the XS file to contain embedded documentation. | |
a0d0e21e | 72 | |
cb1a09d0 | 73 | See L<perlxstut> for a tutorial on the whole extension creation process. |
8e07c86e | 74 | |
beb31b0b | 75 | Note: For some extensions, Dave Beazley's SWIG system may provide a |
b3b6085d | 76 | significantly more convenient mechanism for creating the extension |
21b40ab4 | 77 | glue code. See L<http://www.swig.org/> for more information. |
7b8d334a | 78 | |
8e07c86e AD |
79 | =head2 On The Road |
80 | ||
a5f75d66 AD |
81 | Many of the examples which follow will concentrate on creating an interface |
82 | between Perl and the ONC+ RPC bind library functions. The rpcb_gettime() | |
83 | function is used to demonstrate many features of the XS language. This | |
84 | function has two parameters; the first is an input parameter and the second | |
85 | is an output parameter. The function also returns a status value. | |
a0d0e21e LW |
86 | |
87 | bool_t rpcb_gettime(const char *host, time_t *timep); | |
88 | ||
89 | From C this function will be called with the following | |
90 | statements. | |
91 | ||
92 | #include <rpc/rpc.h> | |
93 | bool_t status; | |
94 | time_t timep; | |
95 | status = rpcb_gettime( "localhost", &timep ); | |
96 | ||
97 | If an XSUB is created to offer a direct translation between this function | |
98 | and Perl, then this XSUB will be used from Perl with the following code. | |
99 | The $status and $timep variables will contain the output of the function. | |
100 | ||
101 | use RPC; | |
102 | $status = rpcb_gettime( "localhost", $timep ); | |
103 | ||
104 | The following XS file shows an XS subroutine, or XSUB, which | |
105 | demonstrates one possible interface to the rpcb_gettime() | |
106 | function. This XSUB represents a direct translation between | |
107 | C and Perl and so preserves the interface even from Perl. | |
108 | This XSUB will be invoked from Perl with the usage shown | |
109 | above. Note that the first three #include statements, for | |
110 | C<EXTERN.h>, C<perl.h>, and C<XSUB.h>, will always be present at the | |
111 | beginning of an XS file. This approach and others will be | |
112 | expanded later in this document. | |
113 | ||
114 | #include "EXTERN.h" | |
115 | #include "perl.h" | |
116 | #include "XSUB.h" | |
117 | #include <rpc/rpc.h> | |
118 | ||
119 | MODULE = RPC PACKAGE = RPC | |
120 | ||
121 | bool_t | |
122 | rpcb_gettime(host,timep) | |
8e07c86e AD |
123 | char *host |
124 | time_t &timep | |
beb31b0b | 125 | OUTPUT: |
a0d0e21e LW |
126 | timep |
127 | ||
128 | Any extension to Perl, including those containing XSUBs, | |
129 | should have a Perl module to serve as the bootstrap which | |
130 | pulls the extension into Perl. This module will export the | |
131 | extension's functions and variables to the Perl program and | |
132 | will cause the extension's XSUBs to be linked into Perl. | |
133 | The following module will be used for most of the examples | |
134 | in this document and should be used from Perl with the C<use> | |
135 | command as shown earlier. Perl modules are explained in | |
136 | more detail later in this document. | |
137 | ||
138 | package RPC; | |
139 | ||
140 | require Exporter; | |
141 | require DynaLoader; | |
142 | @ISA = qw(Exporter DynaLoader); | |
143 | @EXPORT = qw( rpcb_gettime ); | |
144 | ||
145 | bootstrap RPC; | |
146 | 1; | |
147 | ||
148 | Throughout this document a variety of interfaces to the rpcb_gettime() | |
149 | XSUB will be explored. The XSUBs will take their parameters in different | |
150 | orders or will take different numbers of parameters. In each case the | |
151 | XSUB is an abstraction between Perl and the real C rpcb_gettime() | |
152 | function, and the XSUB must always ensure that the real rpcb_gettime() | |
153 | function is called with the correct parameters. This abstraction will | |
154 | allow the programmer to create a more Perl-like interface to the C | |
155 | function. | |
156 | ||
157 | =head2 The Anatomy of an XSUB | |
158 | ||
beb31b0b GS |
159 | The simplest XSUBs consist of 3 parts: a description of the return |
160 | value, the name of the XSUB routine and the names of its arguments, | |
161 | and a description of types or formats of the arguments. | |
162 | ||
8e07c86e AD |
163 | The following XSUB allows a Perl program to access a C library function |
164 | called sin(). The XSUB will imitate the C function which takes a single | |
165 | argument and returns a single value. | |
a0d0e21e LW |
166 | |
167 | double | |
168 | sin(x) | |
8e07c86e | 169 | double x |
a0d0e21e | 170 | |
9e24e6f2 IZ |
171 | Optionally, one can merge the description of types and the list of |
172 | argument names, rewriting this as | |
beb31b0b | 173 | |
9e24e6f2 IZ |
174 | double |
175 | sin(double x) | |
176 | ||
177 | This makes this XSUB look similar to an ANSI C declaration. An optional | |
178 | semicolon is allowed after the argument list, as in | |
179 | ||
180 | double | |
181 | sin(double x); | |
182 | ||
183 | Parameters with C pointer types can have different semantic: C functions | |
184 | with similar declarations | |
beb31b0b | 185 | |
9e24e6f2 IZ |
186 | bool string_looks_as_a_number(char *s); |
187 | bool make_char_uppercase(char *c); | |
188 | ||
189 | are used in absolutely incompatible manner. Parameters to these functions | |
190 | could be described B<xsubpp> like this: | |
beb31b0b GS |
191 | |
192 | char * s | |
9e24e6f2 | 193 | char &c |
beb31b0b GS |
194 | |
195 | Both these XS declarations correspond to the C<char*> C type, but they have | |
9e24e6f2 IZ |
196 | different semantics, see L<"The & Unary Operator">. |
197 | ||
198 | It is convenient to think that the indirection operator | |
beb31b0b | 199 | C<*> should be considered as a part of the type and the address operator C<&> |
9e24e6f2 IZ |
200 | should be considered part of the variable. See L<"The Typemap"> |
201 | for more info about handling qualifiers and unary operators in C types. | |
a0d0e21e | 202 | |
a0d0e21e | 203 | The function name and the return type must be placed on |
beb31b0b | 204 | separate lines and should be flush left-adjusted. |
a0d0e21e LW |
205 | |
206 | INCORRECT CORRECT | |
207 | ||
208 | double sin(x) double | |
8e07c86e AD |
209 | double x sin(x) |
210 | double x | |
a0d0e21e | 211 | |
7817ba4d NC |
212 | The rest of the function description may be indented or left-adjusted. The |
213 | following example shows a function with its body left-adjusted. Most | |
214 | examples in this document will indent the body for better readability. | |
c07a80fd | 215 | |
216 | CORRECT | |
217 | ||
218 | double | |
219 | sin(x) | |
220 | double x | |
221 | ||
beb31b0b GS |
222 | More complicated XSUBs may contain many other sections. Each section of |
223 | an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:. | |
224 | However, the first two lines of an XSUB always contain the same data: | |
225 | descriptions of the return type and the names of the function and its | |
226 | parameters. Whatever immediately follows these is considered to be | |
227 | an INPUT: section unless explicitly marked with another keyword. | |
228 | (See L<The INPUT: Keyword>.) | |
229 | ||
230 | An XSUB section continues until another section-start keyword is found. | |
231 | ||
a0d0e21e LW |
232 | =head2 The Argument Stack |
233 | ||
beb31b0b | 234 | The Perl argument stack is used to store the values which are |
a0d0e21e | 235 | sent as parameters to the XSUB and to store the XSUB's |
beb31b0b GS |
236 | return value(s). In reality all Perl functions (including non-XSUB |
237 | ones) keep their values on this stack all the same time, each limited | |
238 | to its own range of positions on the stack. In this document the | |
a0d0e21e LW |
239 | first position on that stack which belongs to the active |
240 | function will be referred to as position 0 for that function. | |
241 | ||
8e07c86e AD |
242 | XSUBs refer to their stack arguments with the macro B<ST(x)>, where I<x> |
243 | refers to a position in this XSUB's part of the stack. Position 0 for that | |
a0d0e21e LW |
244 | function would be known to the XSUB as ST(0). The XSUB's incoming |
245 | parameters and outgoing return values always begin at ST(0). For many | |
246 | simple cases the B<xsubpp> compiler will generate the code necessary to | |
247 | handle the argument stack by embedding code fragments found in the | |
248 | typemaps. In more complex cases the programmer must supply the code. | |
249 | ||
250 | =head2 The RETVAL Variable | |
251 | ||
beb31b0b GS |
252 | The RETVAL variable is a special C variable that is declared automatically |
253 | for you. The C type of RETVAL matches the return type of the C library | |
254 | function. The B<xsubpp> compiler will declare this variable in each XSUB | |
255 | with non-C<void> return type. By default the generated C function | |
256 | will use RETVAL to hold the return value of the C library function being | |
257 | called. In simple cases the value of RETVAL will be placed in ST(0) of | |
258 | the argument stack where it can be received by Perl as the return value | |
259 | of the XSUB. | |
a0d0e21e LW |
260 | |
261 | If the XSUB has a return type of C<void> then the compiler will | |
beb31b0b GS |
262 | not declare a RETVAL variable for that function. When using |
263 | a PPCODE: section no manipulation of the RETVAL variable is required, the | |
264 | section may use direct stack manipulation to place output values on the stack. | |
e7ea3e70 IZ |
265 | |
266 | If PPCODE: directive is not used, C<void> return value should be used | |
267 | only for subroutines which do not return a value, I<even if> CODE: | |
54310121 | 268 | directive is used which sets ST(0) explicitly. |
e7ea3e70 IZ |
269 | |
270 | Older versions of this document recommended to use C<void> return | |
271 | value in such cases. It was discovered that this could lead to | |
c2611fb3 | 272 | segfaults in cases when XSUB was I<truly> C<void>. This practice is |
e7ea3e70 IZ |
273 | now deprecated, and may be not supported at some future version. Use |
274 | the return value C<SV *> in such cases. (Currently C<xsubpp> contains | |
c2611fb3 | 275 | some heuristic code which tries to disambiguate between "truly-void" |
e7ea3e70 IZ |
276 | and "old-practice-declared-as-void" functions. Hence your code is at |
277 | mercy of this heuristics unless you use C<SV *> as return value.) | |
a0d0e21e | 278 | |
c4e79b56 MHM |
279 | =head2 Returning SVs, AVs and HVs through RETVAL |
280 | ||
281 | When you're using RETVAL to return an C<SV *>, there's some magic | |
282 | going on behind the scenes that should be mentioned. When you're | |
283 | manipulating the argument stack using the ST(x) macro, for example, | |
284 | you usually have to pay special attention to reference counts. (For | |
285 | more about reference counts, see L<perlguts>.) To make your life | |
286 | easier, the typemap file automatically makes C<RETVAL> mortal when | |
287 | you're returning an C<SV *>. Thus, the following two XSUBs are more | |
288 | or less equivalent: | |
289 | ||
290 | void | |
291 | alpha() | |
292 | PPCODE: | |
293 | ST(0) = newSVpv("Hello World",0); | |
294 | sv_2mortal(ST(0)); | |
295 | XSRETURN(1); | |
6421dfac | 296 | |
c4e79b56 MHM |
297 | SV * |
298 | beta() | |
299 | CODE: | |
300 | RETVAL = newSVpv("Hello World",0); | |
301 | OUTPUT: | |
302 | RETVAL | |
303 | ||
304 | This is quite useful as it usually improves readability. While | |
305 | this works fine for an C<SV *>, it's unfortunately not as easy | |
306 | to have C<AV *> or C<HV *> as a return value. You I<should> be | |
307 | able to write: | |
308 | ||
309 | AV * | |
310 | array() | |
311 | CODE: | |
312 | RETVAL = newAV(); | |
313 | /* do something with RETVAL */ | |
314 | OUTPUT: | |
315 | RETVAL | |
316 | ||
317 | But due to an unfixable bug (fixing it would break lots of existing | |
318 | CPAN modules) in the typemap file, the reference count of the C<AV *> | |
319 | is not properly decremented. Thus, the above XSUB would leak memory | |
320 | whenever it is being called. The same problem exists for C<HV *>. | |
321 | ||
174830c7 | 322 | When you're returning an C<AV *> or a C<HV *>, you have to make sure |
c4e79b56 MHM |
323 | their reference count is decremented by making the AV or HV mortal: |
324 | ||
325 | AV * | |
326 | array() | |
327 | CODE: | |
328 | RETVAL = newAV(); | |
329 | sv_2mortal((SV*)RETVAL); | |
330 | /* do something with RETVAL */ | |
331 | OUTPUT: | |
332 | RETVAL | |
333 | ||
334 | And also remember that you don't have to do this for an C<SV *>. | |
335 | ||
a0d0e21e LW |
336 | =head2 The MODULE Keyword |
337 | ||
7817ba4d NC |
338 | The MODULE keyword is used to start the XS code and to specify the package |
339 | of the functions which are being defined. All text preceding the first | |
340 | MODULE keyword is considered C code and is passed through to the output with | |
341 | POD stripped, but otherwise untouched. Every XS module will have a | |
342 | bootstrap function which is used to hook the XSUBs into Perl. The package | |
343 | name of this bootstrap function will match the value of the last MODULE | |
344 | statement in the XS source files. The value of MODULE should always remain | |
345 | constant within the same XS file, though this is not required. | |
a0d0e21e LW |
346 | |
347 | The following example will start the XS code and will place | |
348 | all functions in a package named RPC. | |
349 | ||
350 | MODULE = RPC | |
351 | ||
352 | =head2 The PACKAGE Keyword | |
353 | ||
354 | When functions within an XS source file must be separated into packages | |
355 | the PACKAGE keyword should be used. This keyword is used with the MODULE | |
356 | keyword and must follow immediately after it when used. | |
357 | ||
358 | MODULE = RPC PACKAGE = RPC | |
359 | ||
360 | [ XS code in package RPC ] | |
361 | ||
362 | MODULE = RPC PACKAGE = RPCB | |
363 | ||
364 | [ XS code in package RPCB ] | |
365 | ||
366 | MODULE = RPC PACKAGE = RPC | |
367 | ||
368 | [ XS code in package RPC ] | |
369 | ||
a2acea2c LC |
370 | The same package name can be used more than once, allowing for |
371 | non-contiguous code. This is useful if you have a stronger ordering | |
372 | principle than package names. | |
373 | ||
a0d0e21e LW |
374 | Although this keyword is optional and in some cases provides redundant |
375 | information it should always be used. This keyword will ensure that the | |
376 | XSUBs appear in the desired package. | |
377 | ||
378 | =head2 The PREFIX Keyword | |
379 | ||
380 | The PREFIX keyword designates prefixes which should be | |
381 | removed from the Perl function names. If the C function is | |
382 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will | |
383 | see this function as C<gettime()>. | |
384 | ||
385 | This keyword should follow the PACKAGE keyword when used. | |
386 | If PACKAGE is not used then PREFIX should follow the MODULE | |
387 | keyword. | |
388 | ||
389 | MODULE = RPC PREFIX = rpc_ | |
390 | ||
391 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ | |
392 | ||
393 | =head2 The OUTPUT: Keyword | |
394 | ||
395 | The OUTPUT: keyword indicates that certain function parameters should be | |
396 | updated (new values made visible to Perl) when the XSUB terminates or that | |
397 | certain values should be returned to the calling Perl function. For | |
beb31b0b GS |
398 | simple functions which have no CODE: or PPCODE: section, |
399 | such as the sin() function above, the RETVAL variable is | |
400 | automatically designated as an output value. For more complex functions | |
a0d0e21e LW |
401 | the B<xsubpp> compiler will need help to determine which variables are output |
402 | variables. | |
403 | ||
404 | This keyword will normally be used to complement the CODE: keyword. | |
405 | The RETVAL variable is not recognized as an output variable when the | |
406 | CODE: keyword is present. The OUTPUT: keyword is used in this | |
407 | situation to tell the compiler that RETVAL really is an output | |
408 | variable. | |
409 | ||
410 | The OUTPUT: keyword can also be used to indicate that function parameters | |
411 | are output variables. This may be necessary when a parameter has been | |
412 | modified within the function and the programmer would like the update to | |
8e07c86e | 413 | be seen by Perl. |
a0d0e21e LW |
414 | |
415 | bool_t | |
416 | rpcb_gettime(host,timep) | |
8e07c86e AD |
417 | char *host |
418 | time_t &timep | |
beb31b0b | 419 | OUTPUT: |
a0d0e21e LW |
420 | timep |
421 | ||
422 | The OUTPUT: keyword will also allow an output parameter to | |
423 | be mapped to a matching piece of code rather than to a | |
ef50df4b | 424 | typemap. |
a0d0e21e LW |
425 | |
426 | bool_t | |
427 | rpcb_gettime(host,timep) | |
8e07c86e AD |
428 | char *host |
429 | time_t &timep | |
beb31b0b | 430 | OUTPUT: |
ef50df4b GS |
431 | timep sv_setnv(ST(1), (double)timep); |
432 | ||
433 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the | |
434 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired | |
435 | behavior, as it takes care of properly invoking 'set' magic on output | |
436 | parameters (needed for hash or array element parameters that must be | |
437 | created if they didn't exist). If for some reason, this behavior is | |
438 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line | |
439 | to disable it for the remainder of the parameters in the OUTPUT section. | |
440 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the | |
441 | remainder of the OUTPUT section. See L<perlguts> for more details | |
442 | about 'set' magic. | |
a0d0e21e | 443 | |
9e24e6f2 IZ |
444 | =head2 The NO_OUTPUT Keyword |
445 | ||
446 | The NO_OUTPUT can be placed as the first token of the XSUB. This keyword | |
447 | indicates that while the C subroutine we provide an interface to has | |
448 | a non-C<void> return type, the return value of this C subroutine should not | |
449 | be returned from the generated Perl subroutine. | |
450 | ||
451 | With this keyword present L<The RETVAL Variable> is created, and in the | |
452 | generated call to the subroutine this variable is assigned to, but the value | |
453 | of this variable is not going to be used in the auto-generated code. | |
454 | ||
455 | This keyword makes sense only if C<RETVAL> is going to be accessed by the | |
456 | user-supplied code. It is especially useful to make a function interface | |
457 | more Perl-like, especially when the C return value is just an error condition | |
458 | indicator. For example, | |
459 | ||
460 | NO_OUTPUT int | |
461 | delete_file(char *name) | |
375cc10d | 462 | POSTCALL: |
9e24e6f2 IZ |
463 | if (RETVAL != 0) |
464 | croak("Error %d while deleting file '%s'", RETVAL, name); | |
465 | ||
466 | Here the generated XS function returns nothing on success, and will die() | |
467 | with a meaningful error message on error. | |
468 | ||
a0d0e21e LW |
469 | =head2 The CODE: Keyword |
470 | ||
471 | This keyword is used in more complicated XSUBs which require | |
472 | special handling for the C function. The RETVAL variable is | |
beb31b0b GS |
473 | still declared, but it will not be returned unless it is specified |
474 | in the OUTPUT: section. | |
a0d0e21e LW |
475 | |
476 | The following XSUB is for a C function which requires special handling of | |
477 | its parameters. The Perl usage is given first. | |
478 | ||
479 | $status = rpcb_gettime( "localhost", $timep ); | |
480 | ||
54310121 | 481 | The XSUB follows. |
a0d0e21e | 482 | |
d1b91892 AD |
483 | bool_t |
484 | rpcb_gettime(host,timep) | |
8e07c86e AD |
485 | char *host |
486 | time_t timep | |
beb31b0b | 487 | CODE: |
a0d0e21e | 488 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 489 | OUTPUT: |
a0d0e21e LW |
490 | timep |
491 | RETVAL | |
492 | ||
c07a80fd | 493 | =head2 The INIT: Keyword |
494 | ||
495 | The INIT: keyword allows initialization to be inserted into the XSUB before | |
496 | the compiler generates the call to the C function. Unlike the CODE: keyword | |
497 | above, this keyword does not affect the way the compiler handles RETVAL. | |
498 | ||
499 | bool_t | |
500 | rpcb_gettime(host,timep) | |
501 | char *host | |
502 | time_t &timep | |
beb31b0b | 503 | INIT: |
c07a80fd | 504 | printf("# Host is %s\n", host ); |
beb31b0b | 505 | OUTPUT: |
c07a80fd | 506 | timep |
a0d0e21e | 507 | |
beb31b0b GS |
508 | Another use for the INIT: section is to check for preconditions before |
509 | making a call to the C function: | |
510 | ||
511 | long long | |
512 | lldiv(a,b) | |
513 | long long a | |
514 | long long b | |
515 | INIT: | |
516 | if (a == 0 && b == 0) | |
517 | XSRETURN_UNDEF; | |
518 | if (b == 0) | |
519 | croak("lldiv: cannot divide by 0"); | |
520 | ||
a0d0e21e LW |
521 | =head2 The NO_INIT Keyword |
522 | ||
523 | The NO_INIT keyword is used to indicate that a function | |
54310121 | 524 | parameter is being used only as an output value. The B<xsubpp> |
a0d0e21e LW |
525 | compiler will normally generate code to read the values of |
526 | all function parameters from the argument stack and assign | |
527 | them to C variables upon entry to the function. NO_INIT | |
528 | will tell the compiler that some parameters will be used for | |
529 | output rather than for input and that they will be handled | |
530 | before the function terminates. | |
531 | ||
532 | The following example shows a variation of the rpcb_gettime() function. | |
54310121 | 533 | This function uses the timep variable only as an output variable and does |
a0d0e21e LW |
534 | not care about its initial contents. |
535 | ||
536 | bool_t | |
537 | rpcb_gettime(host,timep) | |
8e07c86e AD |
538 | char *host |
539 | time_t &timep = NO_INIT | |
beb31b0b | 540 | OUTPUT: |
a0d0e21e LW |
541 | timep |
542 | ||
543 | =head2 Initializing Function Parameters | |
544 | ||
beb31b0b GS |
545 | C function parameters are normally initialized with their values from |
546 | the argument stack (which in turn contains the parameters that were | |
547 | passed to the XSUB from Perl). The typemaps contain the | |
548 | code segments which are used to translate the Perl values to | |
a0d0e21e | 549 | the C parameters. The programmer, however, is allowed to |
7ad6fb0b | 550 | override the typemaps and supply alternate (or additional) |
beb31b0b GS |
551 | initialization code. Initialization code starts with the first |
552 | C<=>, C<;> or C<+> on a line in the INPUT: section. The only | |
553 | exception happens if this C<;> terminates the line, then this C<;> | |
554 | is quietly ignored. | |
a0d0e21e LW |
555 | |
556 | The following code demonstrates how to supply initialization code for | |
353c6505 | 557 | function parameters. The initialization code is eval'ed within double |
7ad6fb0b TM |
558 | quotes by the compiler before it is added to the output so anything |
559 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] | |
19799a22 GS |
560 | must be protected with backslashes. The variables $var, $arg, |
561 | and $type can be used as in typemaps. | |
a0d0e21e LW |
562 | |
563 | bool_t | |
564 | rpcb_gettime(host,timep) | |
bfd025d9 | 565 | char *host = (char *)SvPV_nolen($arg); |
8e07c86e | 566 | time_t &timep = 0; |
beb31b0b | 567 | OUTPUT: |
a0d0e21e LW |
568 | timep |
569 | ||
570 | This should not be used to supply default values for parameters. One | |
571 | would normally use this when a function parameter must be processed by | |
572 | another library function before it can be used. Default parameters are | |
573 | covered in the next section. | |
574 | ||
beb31b0b GS |
575 | If the initialization begins with C<=>, then it is output in |
576 | the declaration for the input variable, replacing the initialization | |
577 | supplied by the typemap. If the initialization | |
578 | begins with C<;> or C<+>, then it is performed after | |
579 | all of the input variables have been declared. In the C<;> | |
580 | case the initialization normally supplied by the typemap is not performed. | |
581 | For the C<+> case, the declaration for the variable will include the | |
582 | initialization from the typemap. A global | |
c2611fb3 | 583 | variable, C<%v>, is available for the truly rare case where |
7ad6fb0b TM |
584 | information from one initialization is needed in another |
585 | initialization. | |
586 | ||
beb31b0b GS |
587 | Here's a truly obscure example: |
588 | ||
7ad6fb0b TM |
589 | bool_t |
590 | rpcb_gettime(host,timep) | |
4358a253 | 591 | time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
bfd025d9 | 592 | char *host + SvOK($v{timep}) ? SvPV_nolen($arg) : NULL; |
beb31b0b | 593 | OUTPUT: |
7ad6fb0b TM |
594 | timep |
595 | ||
beb31b0b GS |
596 | The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above |
597 | example has a two-fold purpose: first, when this line is processed by | |
598 | B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second, | |
599 | the text of the evaluated snippet is output into the generated C file | |
600 | (inside a C comment)! During the processing of C<char *host> line, | |
601 | $arg will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to | |
602 | C<ST(1)>. | |
603 | ||
a0d0e21e LW |
604 | =head2 Default Parameter Values |
605 | ||
4628e4f8 GS |
606 | Default values for XSUB arguments can be specified by placing an |
607 | assignment statement in the parameter list. The default value may | |
a104f515 | 608 | be a number, a string or the special string C<NO_INIT>. Defaults should |
a0d0e21e LW |
609 | always be used on the right-most parameters only. |
610 | ||
611 | To allow the XSUB for rpcb_gettime() to have a default host | |
612 | value the parameters to the XSUB could be rearranged. The | |
613 | XSUB will then call the real rpcb_gettime() function with | |
beb31b0b GS |
614 | the parameters in the correct order. This XSUB can be called |
615 | from Perl with either of the following statements: | |
a0d0e21e LW |
616 | |
617 | $status = rpcb_gettime( $timep, $host ); | |
618 | ||
619 | $status = rpcb_gettime( $timep ); | |
620 | ||
621 | The XSUB will look like the code which follows. A CODE: | |
622 | block is used to call the real rpcb_gettime() function with | |
623 | the parameters in the correct order for that function. | |
624 | ||
625 | bool_t | |
626 | rpcb_gettime(timep,host="localhost") | |
8e07c86e AD |
627 | char *host |
628 | time_t timep = NO_INIT | |
beb31b0b | 629 | CODE: |
a0d0e21e | 630 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 631 | OUTPUT: |
a0d0e21e LW |
632 | timep |
633 | RETVAL | |
634 | ||
c07a80fd | 635 | =head2 The PREINIT: Keyword |
636 | ||
beb31b0b | 637 | The PREINIT: keyword allows extra variables to be declared immediately |
a2293a43 | 638 | before or after the declarations of the parameters from the INPUT: section |
beb31b0b GS |
639 | are emitted. |
640 | ||
641 | If a variable is declared inside a CODE: section it will follow any typemap | |
642 | code that is emitted for the input parameters. This may result in the | |
643 | declaration ending up after C code, which is C syntax error. Similar | |
644 | errors may happen with an explicit C<;>-type or C<+>-type initialization of | |
645 | parameters is used (see L<"Initializing Function Parameters">). Declaring | |
646 | these variables in an INIT: section will not help. | |
647 | ||
648 | In such cases, to force an additional variable to be declared together | |
649 | with declarations of other variables, place the declaration into a | |
650 | PREINIT: section. The PREINIT: keyword may be used one or more times | |
651 | within an XSUB. | |
c07a80fd | 652 | |
653 | The following examples are equivalent, but if the code is using complex | |
654 | typemaps then the first example is safer. | |
655 | ||
656 | bool_t | |
657 | rpcb_gettime(timep) | |
658 | time_t timep = NO_INIT | |
beb31b0b | 659 | PREINIT: |
c07a80fd | 660 | char *host = "localhost"; |
beb31b0b | 661 | CODE: |
c07a80fd | 662 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 663 | OUTPUT: |
c07a80fd | 664 | timep |
665 | RETVAL | |
666 | ||
beb31b0b GS |
667 | For this particular case an INIT: keyword would generate the |
668 | same C code as the PREINIT: keyword. Another correct, but error-prone example: | |
c07a80fd | 669 | |
670 | bool_t | |
671 | rpcb_gettime(timep) | |
672 | time_t timep = NO_INIT | |
beb31b0b | 673 | CODE: |
c07a80fd | 674 | char *host = "localhost"; |
675 | RETVAL = rpcb_gettime( host, &timep ); | |
beb31b0b GS |
676 | OUTPUT: |
677 | timep | |
678 | RETVAL | |
679 | ||
680 | Another way to declare C<host> is to use a C block in the CODE: section: | |
681 | ||
682 | bool_t | |
683 | rpcb_gettime(timep) | |
684 | time_t timep = NO_INIT | |
685 | CODE: | |
686 | { | |
687 | char *host = "localhost"; | |
688 | RETVAL = rpcb_gettime( host, &timep ); | |
689 | } | |
690 | OUTPUT: | |
691 | timep | |
692 | RETVAL | |
693 | ||
694 | The ability to put additional declarations before the typemap entries are | |
695 | processed is very handy in the cases when typemap conversions manipulate | |
696 | some global state: | |
697 | ||
698 | MyObject | |
699 | mutate(o) | |
700 | PREINIT: | |
701 | MyState st = global_state; | |
702 | INPUT: | |
703 | MyObject o; | |
704 | CLEANUP: | |
705 | reset_to(global_state, st); | |
706 | ||
707 | Here we suppose that conversion to C<MyObject> in the INPUT: section and from | |
708 | MyObject when processing RETVAL will modify a global variable C<global_state>. | |
709 | After these conversions are performed, we restore the old value of | |
710 | C<global_state> (to avoid memory leaks, for example). | |
711 | ||
712 | There is another way to trade clarity for compactness: INPUT sections allow | |
713 | declaration of C variables which do not appear in the parameter list of | |
714 | a subroutine. Thus the above code for mutate() can be rewritten as | |
715 | ||
716 | MyObject | |
717 | mutate(o) | |
718 | MyState st = global_state; | |
719 | MyObject o; | |
720 | CLEANUP: | |
721 | reset_to(global_state, st); | |
722 | ||
723 | and the code for rpcb_gettime() can be rewritten as | |
724 | ||
725 | bool_t | |
726 | rpcb_gettime(timep) | |
727 | time_t timep = NO_INIT | |
728 | char *host = "localhost"; | |
729 | C_ARGS: | |
730 | host, &timep | |
731 | OUTPUT: | |
c07a80fd | 732 | timep |
733 | RETVAL | |
734 | ||
84287afe | 735 | =head2 The SCOPE: Keyword |
736 | ||
737 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If | |
738 | enabled, the XSUB will invoke ENTER and LEAVE automatically. | |
739 | ||
740 | To support potentially complex type mappings, if a typemap entry used | |
beb31b0b GS |
741 | by an XSUB contains a comment like C</*scope*/> then scoping will |
742 | be automatically enabled for that XSUB. | |
84287afe | 743 | |
744 | To enable scoping: | |
745 | ||
746 | SCOPE: ENABLE | |
747 | ||
748 | To disable scoping: | |
749 | ||
750 | SCOPE: DISABLE | |
751 | ||
c07a80fd | 752 | =head2 The INPUT: Keyword |
753 | ||
754 | The XSUB's parameters are usually evaluated immediately after entering the | |
755 | XSUB. The INPUT: keyword can be used to force those parameters to be | |
756 | evaluated a little later. The INPUT: keyword can be used multiple times | |
757 | within an XSUB and can be used to list one or more input variables. This | |
758 | keyword is used with the PREINIT: keyword. | |
759 | ||
760 | The following example shows how the input parameter C<timep> can be | |
761 | evaluated late, after a PREINIT. | |
762 | ||
763 | bool_t | |
764 | rpcb_gettime(host,timep) | |
765 | char *host | |
beb31b0b | 766 | PREINIT: |
c07a80fd | 767 | time_t tt; |
beb31b0b | 768 | INPUT: |
c07a80fd | 769 | time_t timep |
beb31b0b | 770 | CODE: |
c07a80fd | 771 | RETVAL = rpcb_gettime( host, &tt ); |
772 | timep = tt; | |
beb31b0b | 773 | OUTPUT: |
c07a80fd | 774 | timep |
775 | RETVAL | |
776 | ||
777 | The next example shows each input parameter evaluated late. | |
778 | ||
779 | bool_t | |
780 | rpcb_gettime(host,timep) | |
beb31b0b | 781 | PREINIT: |
c07a80fd | 782 | time_t tt; |
beb31b0b | 783 | INPUT: |
c07a80fd | 784 | char *host |
beb31b0b | 785 | PREINIT: |
c07a80fd | 786 | char *h; |
beb31b0b | 787 | INPUT: |
c07a80fd | 788 | time_t timep |
beb31b0b | 789 | CODE: |
c07a80fd | 790 | h = host; |
791 | RETVAL = rpcb_gettime( h, &tt ); | |
792 | timep = tt; | |
beb31b0b GS |
793 | OUTPUT: |
794 | timep | |
795 | RETVAL | |
796 | ||
797 | Since INPUT sections allow declaration of C variables which do not appear | |
798 | in the parameter list of a subroutine, this may be shortened to: | |
799 | ||
800 | bool_t | |
801 | rpcb_gettime(host,timep) | |
802 | time_t tt; | |
803 | char *host; | |
804 | char *h = host; | |
805 | time_t timep; | |
806 | CODE: | |
807 | RETVAL = rpcb_gettime( h, &tt ); | |
808 | timep = tt; | |
809 | OUTPUT: | |
c07a80fd | 810 | timep |
811 | RETVAL | |
812 | ||
beb31b0b GS |
813 | (We used our knowledge that input conversion for C<char *> is a "simple" one, |
814 | thus C<host> is initialized on the declaration line, and our assignment | |
815 | C<h = host> is not performed too early. Otherwise one would need to have the | |
816 | assignment C<h = host> in a CODE: or INIT: section.) | |
817 | ||
cb79badd | 818 | =head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords |
9e24e6f2 IZ |
819 | |
820 | In the list of parameters for an XSUB, one can precede parameter names | |
cb79badd IZ |
821 | by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords. |
822 | C<IN> keyword is the default, the other keywords indicate how the Perl | |
823 | interface should differ from the C interface. | |
824 | ||
825 | Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> | |
826 | keywords are considered to be used by the C subroutine I<via | |
827 | pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine | |
828 | does not inspect the memory pointed by this parameter, but will write | |
829 | through this pointer to provide additional return values. | |
830 | ||
831 | Parameters preceded by C<OUTLIST> keyword do not appear in the usage | |
832 | signature of the generated Perl function. | |
833 | ||
834 | Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as | |
835 | parameters to the Perl function. With the exception of | |
836 | C<OUT>-parameters, these parameters are converted to the corresponding | |
837 | C type, then pointers to these data are given as arguments to the C | |
838 | function. It is expected that the C function will write through these | |
839 | pointers. | |
9e24e6f2 IZ |
840 | |
841 | The return list of the generated Perl function consists of the C return value | |
842 | from the function (unless the XSUB is of C<void> return type or | |
cb79badd IZ |
843 | C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST> |
844 | and C<IN_OUTLIST> parameters (in the order of appearance). On the | |
845 | return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be | |
846 | modified to have the values written by the C function. | |
847 | ||
848 | For example, an XSUB | |
9e24e6f2 IZ |
849 | |
850 | void | |
851 | day_month(OUTLIST day, IN unix_time, OUTLIST month) | |
852 | int day | |
853 | int unix_time | |
854 | int month | |
855 | ||
856 | should be used from Perl as | |
857 | ||
858 | my ($day, $month) = day_month(time); | |
859 | ||
860 | The C signature of the corresponding function should be | |
861 | ||
862 | void day_month(int *day, int unix_time, int *month); | |
863 | ||
cb79badd IZ |
864 | The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be |
865 | mixed with ANSI-style declarations, as in | |
9e24e6f2 IZ |
866 | |
867 | void | |
868 | day_month(OUTLIST int day, int unix_time, OUTLIST int month) | |
869 | ||
870 | (here the optional C<IN> keyword is omitted). | |
871 | ||
cb79badd | 872 | The C<IN_OUT> parameters are identical with parameters introduced with |
cea6626f MS |
873 | L<The & Unary Operator> and put into the C<OUTPUT:> section (see |
874 | L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar, | |
875 | the only difference being that the value C function writes through the | |
cb79badd IZ |
876 | pointer would not modify the Perl parameter, but is put in the output |
877 | list. | |
878 | ||
879 | The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT> | |
d1be9408 | 880 | parameters only by the initial value of the Perl parameter not |
cb79badd IZ |
881 | being read (and not being given to the C function - which gets some |
882 | garbage instead). For example, the same C function as above can be | |
883 | interfaced with as | |
884 | ||
885 | void day_month(OUT int day, int unix_time, OUT int month); | |
886 | ||
887 | or | |
9e24e6f2 IZ |
888 | |
889 | void | |
890 | day_month(day, unix_time, month) | |
891 | int &day = NO_INIT | |
892 | int unix_time | |
893 | int &month = NO_INIT | |
894 | OUTPUT: | |
895 | day | |
896 | month | |
897 | ||
898 | However, the generated Perl function is called in very C-ish style: | |
899 | ||
900 | my ($day, $month); | |
901 | day_month($day, time, $month); | |
902 | ||
08ff138d IZ |
903 | =head2 The C<length(NAME)> Keyword |
904 | ||
905 | If one of the input arguments to the C function is the length of a string | |
906 | argument C<NAME>, one can substitute the name of the length-argument by | |
d7f8936a | 907 | C<length(NAME)> in the XSUB declaration. This argument must be omitted when |
08ff138d IZ |
908 | the generated Perl function is called. E.g., |
909 | ||
910 | void | |
911 | dump_chars(char *s, short l) | |
912 | { | |
913 | short n = 0; | |
914 | while (n < l) { | |
915 | printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]); | |
916 | n++; | |
917 | } | |
918 | } | |
919 | ||
920 | MODULE = x PACKAGE = x | |
921 | ||
922 | void dump_chars(char *s, short length(s)) | |
923 | ||
924 | should be called as C<dump_chars($string)>. | |
925 | ||
926 | This directive is supported with ANSI-type function declarations only. | |
927 | ||
a0d0e21e LW |
928 | =head2 Variable-length Parameter Lists |
929 | ||
930 | XSUBs can have variable-length parameter lists by specifying an ellipsis | |
931 | C<(...)> in the parameter list. This use of the ellipsis is similar to that | |
932 | found in ANSI C. The programmer is able to determine the number of | |
933 | arguments passed to the XSUB by examining the C<items> variable which the | |
934 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can | |
935 | create an XSUB which accepts a list of parameters of unknown length. | |
936 | ||
937 | The I<host> parameter for the rpcb_gettime() XSUB can be | |
938 | optional so the ellipsis can be used to indicate that the | |
939 | XSUB will take a variable number of parameters. Perl should | |
d1b91892 | 940 | be able to call this XSUB with either of the following statements. |
a0d0e21e LW |
941 | |
942 | $status = rpcb_gettime( $timep, $host ); | |
943 | ||
944 | $status = rpcb_gettime( $timep ); | |
945 | ||
946 | The XS code, with ellipsis, follows. | |
947 | ||
948 | bool_t | |
949 | rpcb_gettime(timep, ...) | |
8e07c86e | 950 | time_t timep = NO_INIT |
beb31b0b | 951 | PREINIT: |
a0d0e21e | 952 | char *host = "localhost"; |
beb31b0b GS |
953 | CODE: |
954 | if( items > 1 ) | |
1c5b513e | 955 | host = (char *)SvPV_nolen(ST(1)); |
beb31b0b GS |
956 | RETVAL = rpcb_gettime( host, &timep ); |
957 | OUTPUT: | |
a0d0e21e LW |
958 | timep |
959 | RETVAL | |
960 | ||
cfc02341 IZ |
961 | =head2 The C_ARGS: Keyword |
962 | ||
963 | The C_ARGS: keyword allows creating of XSUBS which have different | |
964 | calling sequence from Perl than from C, without a need to write | |
beb31b0b | 965 | CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is |
cfc02341 IZ |
966 | put as the argument to the called C function without any change. |
967 | ||
beb31b0b | 968 | For example, suppose that a C function is declared as |
cfc02341 IZ |
969 | |
970 | symbolic nth_derivative(int n, symbolic function, int flags); | |
971 | ||
972 | and that the default flags are kept in a global C variable | |
973 | C<default_flags>. Suppose that you want to create an interface which | |
974 | is called as | |
975 | ||
976 | $second_deriv = $function->nth_derivative(2); | |
977 | ||
978 | To do this, declare the XSUB as | |
979 | ||
980 | symbolic | |
981 | nth_derivative(function, n) | |
982 | symbolic function | |
983 | int n | |
beb31b0b | 984 | C_ARGS: |
cfc02341 IZ |
985 | n, function, default_flags |
986 | ||
a0d0e21e LW |
987 | =head2 The PPCODE: Keyword |
988 | ||
989 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used | |
990 | to tell the B<xsubpp> compiler that the programmer is supplying the code to | |
d1b91892 | 991 | control the argument stack for the XSUBs return values. Occasionally one |
a0d0e21e LW |
992 | will want an XSUB to return a list of values rather than a single value. |
993 | In these cases one must use PPCODE: and then explicitly push the list of | |
beb31b0b | 994 | values on the stack. The PPCODE: and CODE: keywords should not be used |
a0d0e21e LW |
995 | together within the same XSUB. |
996 | ||
beb31b0b GS |
997 | The actual difference between PPCODE: and CODE: sections is in the |
998 | initialization of C<SP> macro (which stands for the I<current> Perl | |
999 | stack pointer), and in the handling of data on the stack when returning | |
1000 | from an XSUB. In CODE: sections SP preserves the value which was on | |
1001 | entry to the XSUB: SP is on the function pointer (which follows the | |
1002 | last parameter). In PPCODE: sections SP is moved backward to the | |
1003 | beginning of the parameter list, which allows C<PUSH*()> macros | |
1004 | to place output values in the place Perl expects them to be when | |
1005 | the XSUB returns back to Perl. | |
1006 | ||
1007 | The generated trailer for a CODE: section ensures that the number of return | |
1008 | values Perl will see is either 0 or 1 (depending on the C<void>ness of the | |
1009 | return value of the C function, and heuristics mentioned in | |
1010 | L<"The RETVAL Variable">). The trailer generated for a PPCODE: section | |
1011 | is based on the number of return values and on the number of times | |
1012 | C<SP> was updated by C<[X]PUSH*()> macros. | |
1013 | ||
1014 | Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally | |
1015 | well in CODE: sections and PPCODE: sections. | |
1016 | ||
a0d0e21e LW |
1017 | The following XSUB will call the C rpcb_gettime() function |
1018 | and will return its two output values, timep and status, to | |
1019 | Perl as a single list. | |
1020 | ||
d1b91892 AD |
1021 | void |
1022 | rpcb_gettime(host) | |
8e07c86e | 1023 | char *host |
beb31b0b | 1024 | PREINIT: |
a0d0e21e LW |
1025 | time_t timep; |
1026 | bool_t status; | |
beb31b0b | 1027 | PPCODE: |
a0d0e21e | 1028 | status = rpcb_gettime( host, &timep ); |
924508f0 | 1029 | EXTEND(SP, 2); |
cb1a09d0 AD |
1030 | PUSHs(sv_2mortal(newSViv(status))); |
1031 | PUSHs(sv_2mortal(newSViv(timep))); | |
a0d0e21e LW |
1032 | |
1033 | Notice that the programmer must supply the C code necessary | |
1034 | to have the real rpcb_gettime() function called and to have | |
1035 | the return values properly placed on the argument stack. | |
1036 | ||
1037 | The C<void> return type for this function tells the B<xsubpp> compiler that | |
1038 | the RETVAL variable is not needed or used and that it should not be created. | |
1039 | In most scenarios the void return type should be used with the PPCODE: | |
1040 | directive. | |
1041 | ||
1042 | The EXTEND() macro is used to make room on the argument | |
1043 | stack for 2 return values. The PPCODE: directive causes the | |
924508f0 | 1044 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
a0d0e21e LW |
1045 | is this pointer which is being used in the EXTEND() macro. |
1046 | The values are then pushed onto the stack with the PUSHs() | |
1047 | macro. | |
1048 | ||
1049 | Now the rpcb_gettime() function can be used from Perl with | |
1050 | the following statement. | |
1051 | ||
1052 | ($status, $timep) = rpcb_gettime("localhost"); | |
1053 | ||
ef50df4b GS |
1054 | When handling output parameters with a PPCODE section, be sure to handle |
1055 | 'set' magic properly. See L<perlguts> for details about 'set' magic. | |
1056 | ||
a0d0e21e LW |
1057 | =head2 Returning Undef And Empty Lists |
1058 | ||
5f05dabc | 1059 | Occasionally the programmer will want to return simply |
a0d0e21e LW |
1060 | C<undef> or an empty list if a function fails rather than a |
1061 | separate status value. The rpcb_gettime() function offers | |
1062 | just this situation. If the function succeeds we would like | |
1063 | to have it return the time and if it fails we would like to | |
1064 | have undef returned. In the following Perl code the value | |
1065 | of $timep will either be undef or it will be a valid time. | |
1066 | ||
1067 | $timep = rpcb_gettime( "localhost" ); | |
1068 | ||
7b8d334a | 1069 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
e7ea3e70 | 1070 | and uses a CODE: block to indicate to the compiler |
a0d0e21e LW |
1071 | that the programmer has supplied all the necessary code. The |
1072 | sv_newmortal() call will initialize the return value to undef, making that | |
1073 | the default return value. | |
1074 | ||
e7ea3e70 | 1075 | SV * |
a0d0e21e LW |
1076 | rpcb_gettime(host) |
1077 | char * host | |
beb31b0b | 1078 | PREINIT: |
a0d0e21e LW |
1079 | time_t timep; |
1080 | bool_t x; | |
beb31b0b | 1081 | CODE: |
a0d0e21e LW |
1082 | ST(0) = sv_newmortal(); |
1083 | if( rpcb_gettime( host, &timep ) ) | |
1084 | sv_setnv( ST(0), (double)timep); | |
a0d0e21e LW |
1085 | |
1086 | The next example demonstrates how one would place an explicit undef in the | |
1087 | return value, should the need arise. | |
1088 | ||
e7ea3e70 | 1089 | SV * |
a0d0e21e LW |
1090 | rpcb_gettime(host) |
1091 | char * host | |
beb31b0b | 1092 | PREINIT: |
a0d0e21e LW |
1093 | time_t timep; |
1094 | bool_t x; | |
beb31b0b | 1095 | CODE: |
a0d0e21e | 1096 | if( rpcb_gettime( host, &timep ) ){ |
7e455f68 | 1097 | ST(0) = sv_newmortal(); |
a0d0e21e LW |
1098 | sv_setnv( ST(0), (double)timep); |
1099 | } | |
1100 | else{ | |
9cde0e7f | 1101 | ST(0) = &PL_sv_undef; |
a0d0e21e | 1102 | } |
a0d0e21e LW |
1103 | |
1104 | To return an empty list one must use a PPCODE: block and | |
1105 | then not push return values on the stack. | |
1106 | ||
1107 | void | |
1108 | rpcb_gettime(host) | |
8e07c86e | 1109 | char *host |
beb31b0b | 1110 | PREINIT: |
a0d0e21e | 1111 | time_t timep; |
beb31b0b | 1112 | PPCODE: |
a0d0e21e | 1113 | if( rpcb_gettime( host, &timep ) ) |
cb1a09d0 | 1114 | PUSHs(sv_2mortal(newSViv(timep))); |
a0d0e21e | 1115 | else{ |
beb31b0b GS |
1116 | /* Nothing pushed on stack, so an empty |
1117 | * list is implicitly returned. */ | |
a0d0e21e | 1118 | } |
a0d0e21e | 1119 | |
f27cfbbe | 1120 | Some people may be inclined to include an explicit C<return> in the above |
1121 | XSUB, rather than letting control fall through to the end. In those | |
1122 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that | |
8a2949d9 SB |
1123 | the XSUB stack is properly adjusted. Consult L<perlapi> for other |
1124 | C<XSRETURN> macros. | |
f27cfbbe | 1125 | |
beb31b0b GS |
1126 | Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can |
1127 | rewrite this example as: | |
1128 | ||
1129 | int | |
1130 | rpcb_gettime(host) | |
1131 | char *host | |
1132 | PREINIT: | |
1133 | time_t timep; | |
1134 | CODE: | |
1135 | RETVAL = rpcb_gettime( host, &timep ); | |
1136 | if (RETVAL == 0) | |
1137 | XSRETURN_UNDEF; | |
1138 | OUTPUT: | |
1139 | RETVAL | |
1140 | ||
375cc10d | 1141 | In fact, one can put this check into a POSTCALL: section as well. Together |
beb31b0b GS |
1142 | with PREINIT: simplifications, this leads to: |
1143 | ||
1144 | int | |
1145 | rpcb_gettime(host) | |
1146 | char *host | |
1147 | time_t timep; | |
375cc10d | 1148 | POSTCALL: |
beb31b0b GS |
1149 | if (RETVAL == 0) |
1150 | XSRETURN_UNDEF; | |
1151 | ||
4633a7c4 LW |
1152 | =head2 The REQUIRE: Keyword |
1153 | ||
1154 | The REQUIRE: keyword is used to indicate the minimum version of the | |
1155 | B<xsubpp> compiler needed to compile the XS module. An XS module which | |
5f05dabc | 1156 | contains the following statement will compile with only B<xsubpp> version |
4633a7c4 LW |
1157 | 1.922 or greater: |
1158 | ||
1159 | REQUIRE: 1.922 | |
1160 | ||
a0d0e21e LW |
1161 | =head2 The CLEANUP: Keyword |
1162 | ||
1163 | This keyword can be used when an XSUB requires special cleanup procedures | |
1164 | before it terminates. When the CLEANUP: keyword is used it must follow | |
1165 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The | |
1166 | code specified for the cleanup block will be added as the last statements | |
1167 | in the XSUB. | |
1168 | ||
375cc10d | 1169 | =head2 The POSTCALL: Keyword |
9e24e6f2 IZ |
1170 | |
1171 | This keyword can be used when an XSUB requires special procedures | |
375cc10d | 1172 | executed after the C subroutine call is performed. When the POSTCALL: |
9e24e6f2 IZ |
1173 | keyword is used it must precede OUTPUT: and CLEANUP: blocks which are |
1174 | present in the XSUB. | |
1175 | ||
375cc10d IZ |
1176 | See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">. |
1177 | ||
1178 | The POSTCALL: block does not make a lot of sense when the C subroutine | |
9e24e6f2 IZ |
1179 | call is supplied by user by providing either CODE: or PPCODE: section. |
1180 | ||
a0d0e21e LW |
1181 | =head2 The BOOT: Keyword |
1182 | ||
1183 | The BOOT: keyword is used to add code to the extension's bootstrap | |
1184 | function. The bootstrap function is generated by the B<xsubpp> compiler and | |
1185 | normally holds the statements necessary to register any XSUBs with Perl. | |
1186 | With the BOOT: keyword the programmer can tell the compiler to add extra | |
1187 | statements to the bootstrap function. | |
1188 | ||
1189 | This keyword may be used any time after the first MODULE keyword and should | |
1190 | appear on a line by itself. The first blank line after the keyword will | |
1191 | terminate the code block. | |
1192 | ||
1193 | BOOT: | |
1194 | # The following message will be printed when the | |
1195 | # bootstrap function executes. | |
1196 | printf("Hello from the bootstrap!\n"); | |
1197 | ||
c07a80fd | 1198 | =head2 The VERSIONCHECK: Keyword |
1199 | ||
1200 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and | |
5f05dabc | 1201 | C<-noversioncheck> options. This keyword overrides the command line |
c07a80fd | 1202 | options. Version checking is enabled by default. When version checking is |
1203 | enabled the XS module will attempt to verify that its version matches the | |
1204 | version of the PM module. | |
1205 | ||
1206 | To enable version checking: | |
1207 | ||
1208 | VERSIONCHECK: ENABLE | |
1209 | ||
1210 | To disable version checking: | |
1211 | ||
1212 | VERSIONCHECK: DISABLE | |
1213 | ||
b017ed23 NT |
1214 | Note that if the version of the PM module is an NV (a floating point |
1215 | number), it will be stringified with a possible loss of precision | |
1216 | (currently chopping to nine decimal places) so that it may not match | |
1217 | the version of the XS module anymore. Quoting the $VERSION declaration | |
1218 | to make it a string is recommended if long version numbers are used. | |
1219 | ||
c07a80fd | 1220 | =head2 The PROTOTYPES: Keyword |
1221 | ||
1222 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and | |
54310121 | 1223 | C<-noprototypes> options. This keyword overrides the command line options. |
c07a80fd | 1224 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
1225 | be given Perl prototypes. This keyword may be used multiple times in an XS | |
1226 | module to enable and disable prototypes for different parts of the module. | |
1227 | ||
1228 | To enable prototypes: | |
1229 | ||
1230 | PROTOTYPES: ENABLE | |
1231 | ||
1232 | To disable prototypes: | |
1233 | ||
1234 | PROTOTYPES: DISABLE | |
1235 | ||
1236 | =head2 The PROTOTYPE: Keyword | |
1237 | ||
1238 | This keyword is similar to the PROTOTYPES: keyword above but can be used to | |
1239 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword | |
1240 | overrides all other prototype options and keywords but affects only the | |
1241 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl | |
1242 | prototypes. | |
1243 | ||
1244 | bool_t | |
1245 | rpcb_gettime(timep, ...) | |
1246 | time_t timep = NO_INIT | |
beb31b0b GS |
1247 | PROTOTYPE: $;$ |
1248 | PREINIT: | |
c07a80fd | 1249 | char *host = "localhost"; |
beb31b0b | 1250 | CODE: |
c07a80fd | 1251 | if( items > 1 ) |
1c5b513e | 1252 | host = (char *)SvPV_nolen(ST(1)); |
c07a80fd | 1253 | RETVAL = rpcb_gettime( host, &timep ); |
beb31b0b | 1254 | OUTPUT: |
c07a80fd | 1255 | timep |
1256 | RETVAL | |
1257 | ||
dd76e73a SB |
1258 | If the prototypes are enabled, you can disable it locally for a given |
1259 | XSUB as in the following example: | |
1260 | ||
1261 | void | |
1262 | rpcb_gettime_noproto() | |
1263 | PROTOTYPE: DISABLE | |
1264 | ... | |
1265 | ||
c07a80fd | 1266 | =head2 The ALIAS: Keyword |
1267 | ||
cfc02341 | 1268 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
c07a80fd | 1269 | and to know which of those names was used when it was invoked. The Perl |
1270 | names may be fully-qualified with package names. Each alias is given an | |
1271 | index. The compiler will setup a variable called C<ix> which contain the | |
1272 | index of the alias which was used. When the XSUB is called with its | |
1273 | declared name C<ix> will be 0. | |
1274 | ||
1275 | The following example will create aliases C<FOO::gettime()> and | |
1276 | C<BAR::getit()> for this function. | |
1277 | ||
1278 | bool_t | |
1279 | rpcb_gettime(host,timep) | |
1280 | char *host | |
1281 | time_t &timep | |
beb31b0b | 1282 | ALIAS: |
c07a80fd | 1283 | FOO::gettime = 1 |
1284 | BAR::getit = 2 | |
beb31b0b | 1285 | INIT: |
c07a80fd | 1286 | printf("# ix = %d\n", ix ); |
beb31b0b | 1287 | OUTPUT: |
c07a80fd | 1288 | timep |
1289 | ||
54162f5c JP |
1290 | =head2 The OVERLOAD: Keyword |
1291 | ||
1292 | Instead of writing an overloaded interface using pure Perl, you | |
1293 | can also use the OVERLOAD keyword to define additional Perl names | |
1294 | for your functions (like the ALIAS: keyword above). However, the | |
1295 | overloaded functions must be defined with three parameters (except | |
1296 | for the nomethod() function which needs four parameters). If any | |
1297 | function has the OVERLOAD: keyword, several additional lines | |
1298 | will be defined in the c file generated by xsubpp in order to | |
1299 | register with the overload magic. | |
1300 | ||
1301 | Since blessed objects are actually stored as RV's, it is useful | |
1302 | to use the typemap features to preprocess parameters and extract | |
1303 | the actual SV stored within the blessed RV. See the sample for | |
1304 | T_PTROBJ_SPECIAL below. | |
1305 | ||
1306 | To use the OVERLOAD: keyword, create an XS function which takes | |
1307 | three input parameters ( or use the c style '...' definition) like | |
1308 | this: | |
1309 | ||
1310 | SV * | |
1311 | cmp (lobj, robj, swap) | |
1312 | My_Module_obj lobj | |
1313 | My_Module_obj robj | |
1314 | IV swap | |
1315 | OVERLOAD: cmp <=> | |
1316 | { /* function defined here */} | |
1317 | ||
1318 | In this case, the function will overload both of the three way | |
1319 | comparison operators. For all overload operations using non-alpha | |
353c6505 | 1320 | characters, you must type the parameter without quoting, separating |
54162f5c JP |
1321 | multiple overloads with whitespace. Note that "" (the stringify |
1322 | overload) should be entered as \"\" (i.e. escaped). | |
1323 | ||
30d6fba6 JP |
1324 | =head2 The FALLBACK: Keyword |
1325 | ||
1326 | In addition to the OVERLOAD keyword, if you need to control how | |
1327 | Perl autogenerates missing overloaded operators, you can set the | |
1328 | FALLBACK keyword in the module header section, like this: | |
1329 | ||
1330 | MODULE = RPC PACKAGE = RPC | |
1331 | ||
1332 | FALLBACK: TRUE | |
1333 | ... | |
1334 | ||
1335 | where FALLBACK can take any of the three values TRUE, FALSE, or | |
1336 | UNDEF. If you do not set any FALLBACK value when using OVERLOAD, | |
1337 | it defaults to UNDEF. FALLBACK is not used except when one or | |
1338 | more functions using OVERLOAD have been defined. Please see | |
89da310e | 1339 | L<overload/fallback> for more details. |
30d6fba6 | 1340 | |
cfc02341 IZ |
1341 | =head2 The INTERFACE: Keyword |
1342 | ||
1343 | This keyword declares the current XSUB as a keeper of the given | |
1344 | calling signature. If some text follows this keyword, it is | |
1345 | considered as a list of functions which have this signature, and | |
beb31b0b | 1346 | should be attached to the current XSUB. |
cfc02341 | 1347 | |
beb31b0b GS |
1348 | For example, if you have 4 C functions multiply(), divide(), add(), |
1349 | subtract() all having the signature: | |
cfc02341 IZ |
1350 | |
1351 | symbolic f(symbolic, symbolic); | |
1352 | ||
beb31b0b | 1353 | you can make them all to use the same XSUB using this: |
cfc02341 IZ |
1354 | |
1355 | symbolic | |
1356 | interface_s_ss(arg1, arg2) | |
1357 | symbolic arg1 | |
1358 | symbolic arg2 | |
1359 | INTERFACE: | |
1360 | multiply divide | |
1361 | add subtract | |
1362 | ||
beb31b0b GS |
1363 | (This is the complete XSUB code for 4 Perl functions!) Four generated |
1364 | Perl function share names with corresponding C functions. | |
1365 | ||
1366 | The advantage of this approach comparing to ALIAS: keyword is that there | |
1367 | is no need to code a switch statement, each Perl function (which shares | |
1368 | the same XSUB) knows which C function it should call. Additionally, one | |
cfc02341 | 1369 | can attach an extra function remainder() at runtime by using |
beb31b0b | 1370 | |
cfc02341 IZ |
1371 | CV *mycv = newXSproto("Symbolic::remainder", |
1372 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); | |
1373 | XSINTERFACE_FUNC_SET(mycv, remainder); | |
1374 | ||
beb31b0b GS |
1375 | say, from another XSUB. (This example supposes that there was no |
1376 | INTERFACE_MACRO: section, otherwise one needs to use something else instead of | |
1377 | C<XSINTERFACE_FUNC_SET>, see the next section.) | |
cfc02341 IZ |
1378 | |
1379 | =head2 The INTERFACE_MACRO: Keyword | |
1380 | ||
1381 | This keyword allows one to define an INTERFACE using a different way | |
1382 | to extract a function pointer from an XSUB. The text which follows | |
1383 | this keyword should give the name of macros which would extract/set a | |
1384 | function pointer. The extractor macro is given return type, C<CV*>, | |
1385 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, | |
1386 | and the function pointer. | |
1387 | ||
1388 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. | |
1389 | An INTERFACE keyword with an empty list of functions can be omitted if | |
1390 | INTERFACE_MACRO keyword is used. | |
1391 | ||
1392 | Suppose that in the previous example functions pointers for | |
1393 | multiply(), divide(), add(), subtract() are kept in a global C array | |
1394 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, | |
1395 | C<subtract_off>. Then one can use | |
1396 | ||
1397 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ | |
4ef0c66e | 1398 | ((XSINTERFACE_CVT_ANON(ret))fp[CvXSUBANY(cv).any_i32]) |
cfc02341 IZ |
1399 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ |
1400 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) | |
1401 | ||
1402 | in C section, | |
1403 | ||
1404 | symbolic | |
1405 | interface_s_ss(arg1, arg2) | |
1406 | symbolic arg1 | |
1407 | symbolic arg2 | |
beb31b0b | 1408 | INTERFACE_MACRO: |
cfc02341 IZ |
1409 | XSINTERFACE_FUNC_BYOFFSET |
1410 | XSINTERFACE_FUNC_BYOFFSET_set | |
beb31b0b | 1411 | INTERFACE: |
cfc02341 IZ |
1412 | multiply divide |
1413 | add subtract | |
1414 | ||
1415 | in XSUB section. | |
1416 | ||
c07a80fd | 1417 | =head2 The INCLUDE: Keyword |
1418 | ||
1419 | This keyword can be used to pull other files into the XS module. The other | |
1420 | files may have XS code. INCLUDE: can also be used to run a command to | |
1421 | generate the XS code to be pulled into the module. | |
1422 | ||
1423 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: | |
1424 | ||
1425 | bool_t | |
1426 | rpcb_gettime(host,timep) | |
1427 | char *host | |
1428 | time_t &timep | |
beb31b0b | 1429 | OUTPUT: |
c07a80fd | 1430 | timep |
1431 | ||
1432 | The XS module can use INCLUDE: to pull that file into it. | |
1433 | ||
1434 | INCLUDE: Rpcb1.xsh | |
1435 | ||
1436 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then | |
4db98c67 S |
1437 | the compiler will interpret the parameters as a command. This feature is |
1438 | mildly deprecated in favour of the C<INCLUDE_COMMAND:> directive, as documented | |
1439 | below. | |
c07a80fd | 1440 | |
1441 | INCLUDE: cat Rpcb1.xsh | | |
1442 | ||
4db98c67 S |
1443 | Do not use this to run perl: C<INCLUDE: perl |> will run the perl that |
1444 | happens to be the first in your path and not necessarily the same perl that is | |
1445 | used to run C<xsubpp>. See L<"The INCLUDE_COMMAND: Keyword">. | |
1446 | ||
1447 | =head2 The INCLUDE_COMMAND: Keyword | |
1448 | ||
1449 | Runs the supplied command and includes its output into the current XS | |
1450 | document. C<INCLUDE_COMMAND> assigns special meaning to the C<$^X> token | |
1451 | in that it runs the same perl interpreter that is running C<xsubpp>: | |
1452 | ||
1453 | INCLUDE_COMMAND: cat Rpcb1.xsh | |
1454 | ||
1455 | INCLUDE_COMMAND: $^X -e ... | |
1456 | ||
c07a80fd | 1457 | =head2 The CASE: Keyword |
1458 | ||
1459 | The CASE: keyword allows an XSUB to have multiple distinct parts with each | |
1460 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all | |
1461 | other XS keywords must be contained within a CASE:. This means nothing may | |
1462 | precede the first CASE: in the XSUB and anything following the last CASE: is | |
1463 | included in that case. | |
1464 | ||
1465 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: | |
1466 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable | |
1467 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the | |
1468 | B<default> case if it is not associated with a conditional. The following | |
1469 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> | |
1470 | having an alias C<x_gettime()>. When the function is called as | |
b772cb6e | 1471 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
1472 | but when the function is called as C<x_gettime()> its parameters are | |
c07a80fd | 1473 | reversed, C<(time_t *timep, char *host)>. |
1474 | ||
1475 | long | |
1476 | rpcb_gettime(a,b) | |
1477 | CASE: ix == 1 | |
beb31b0b | 1478 | ALIAS: |
c07a80fd | 1479 | x_gettime = 1 |
beb31b0b | 1480 | INPUT: |
c07a80fd | 1481 | # 'a' is timep, 'b' is host |
1482 | char *b | |
1483 | time_t a = NO_INIT | |
beb31b0b | 1484 | CODE: |
c07a80fd | 1485 | RETVAL = rpcb_gettime( b, &a ); |
beb31b0b | 1486 | OUTPUT: |
c07a80fd | 1487 | a |
1488 | RETVAL | |
1489 | CASE: | |
1490 | # 'a' is host, 'b' is timep | |
1491 | char *a | |
1492 | time_t &b = NO_INIT | |
beb31b0b | 1493 | OUTPUT: |
c07a80fd | 1494 | b |
1495 | RETVAL | |
1496 | ||
1497 | That function can be called with either of the following statements. Note | |
1498 | the different argument lists. | |
1499 | ||
1500 | $status = rpcb_gettime( $host, $timep ); | |
1501 | ||
1502 | $status = x_gettime( $timep, $host ); | |
1503 | ||
1504 | =head2 The & Unary Operator | |
1505 | ||
beb31b0b GS |
1506 | The C<&> unary operator in the INPUT: section is used to tell B<xsubpp> |
1507 | that it should convert a Perl value to/from C using the C type to the left | |
1508 | of C<&>, but provide a pointer to this value when the C function is called. | |
1509 | ||
1510 | This is useful to avoid a CODE: block for a C function which takes a parameter | |
1511 | by reference. Typically, the parameter should be not a pointer type (an | |
d1be9408 | 1512 | C<int> or C<long> but not an C<int*> or C<long*>). |
c07a80fd | 1513 | |
beb31b0b | 1514 | The following XSUB will generate incorrect C code. The B<xsubpp> compiler will |
c07a80fd | 1515 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
1516 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> | |
1517 | parameter to be of type C<time_t*> rather than C<time_t>. | |
1518 | ||
1519 | bool_t | |
1520 | rpcb_gettime(host,timep) | |
1521 | char *host | |
1522 | time_t timep | |
beb31b0b | 1523 | OUTPUT: |
c07a80fd | 1524 | timep |
1525 | ||
beb31b0b | 1526 | That problem is corrected by using the C<&> operator. The B<xsubpp> compiler |
c07a80fd | 1527 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
1528 | parameters C<(char *host, time_t *timep)>. It does this by carrying the | |
1529 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. | |
1530 | ||
1531 | bool_t | |
1532 | rpcb_gettime(host,timep) | |
1533 | char *host | |
1534 | time_t &timep | |
beb31b0b | 1535 | OUTPUT: |
c07a80fd | 1536 | timep |
1537 | ||
7817ba4d | 1538 | =head2 Inserting POD, Comments and C Preprocessor Directives |
a0d0e21e | 1539 | |
7817ba4d | 1540 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:, |
375cc10d | 1541 | PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions. |
7817ba4d NC |
1542 | Comments are allowed anywhere after the MODULE keyword. The compiler will |
1543 | pass the preprocessor directives through untouched and will remove the | |
1544 | commented lines. POD documentation is allowed at any point, both in the | |
1545 | C and XS language sections. POD must be terminated with a C<=cut> command; | |
1546 | C<xsubpp> will exit with an error if it does not. It is very unlikely that | |
1547 | human generated C code will be mistaken for POD, as most indenting styles | |
1548 | result in whitespace in front of any line starting with C<=>. Machine | |
1549 | generated XS files may fall into this trap unless care is taken to | |
1550 | ensure that a space breaks the sequence "\n=". | |
b772cb6e | 1551 | |
f27cfbbe | 1552 | Comments can be added to XSUBs by placing a C<#> as the first |
1553 | non-whitespace of a line. Care should be taken to avoid making the | |
1554 | comment look like a C preprocessor directive, lest it be interpreted as | |
1555 | such. The simplest way to prevent this is to put whitespace in front of | |
1556 | the C<#>. | |
1557 | ||
f27cfbbe | 1558 | If you use preprocessor directives to choose one of two |
1559 | versions of a function, use | |
1560 | ||
1561 | #if ... version1 | |
1562 | #else /* ... version2 */ | |
1563 | #endif | |
1564 | ||
1565 | and not | |
1566 | ||
1567 | #if ... version1 | |
1568 | #endif | |
1569 | #if ... version2 | |
1570 | #endif | |
1571 | ||
beb31b0b | 1572 | because otherwise B<xsubpp> will believe that you made a duplicate |
f27cfbbe | 1573 | definition of the function. Also, put a blank line before the |
1574 | #else/#endif so it will not be seen as part of the function body. | |
a0d0e21e LW |
1575 | |
1576 | =head2 Using XS With C++ | |
1577 | ||
beb31b0b GS |
1578 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
1579 | The generated Perl function will assume that | |
a0d0e21e LW |
1580 | its first argument is an object pointer. The object pointer |
1581 | will be stored in a variable called THIS. The object should | |
1582 | have been created by C++ with the new() function and should | |
cb1a09d0 AD |
1583 | be blessed by Perl with the sv_setref_pv() macro. The |
1584 | blessing of the object by Perl can be handled by a typemap. An example | |
1585 | typemap is shown at the end of this section. | |
a0d0e21e | 1586 | |
beb31b0b GS |
1587 | If the return type of the XSUB includes C<static>, the method is considered |
1588 | to be a static method. It will call the C++ | |
a0d0e21e | 1589 | function using the class::method() syntax. If the method is not static |
f27cfbbe | 1590 | the function will be called using the THIS-E<gt>method() syntax. |
a0d0e21e | 1591 | |
cb1a09d0 | 1592 | The next examples will use the following C++ class. |
a0d0e21e | 1593 | |
a5f75d66 | 1594 | class color { |
cb1a09d0 | 1595 | public: |
a5f75d66 AD |
1596 | color(); |
1597 | ~color(); | |
cb1a09d0 AD |
1598 | int blue(); |
1599 | void set_blue( int ); | |
1600 | ||
1601 | private: | |
1602 | int c_blue; | |
1603 | }; | |
1604 | ||
1605 | The XSUBs for the blue() and set_blue() methods are defined with the class | |
1606 | name but the parameter for the object (THIS, or "self") is implicit and is | |
1607 | not listed. | |
1608 | ||
1609 | int | |
1610 | color::blue() | |
a0d0e21e LW |
1611 | |
1612 | void | |
cb1a09d0 AD |
1613 | color::set_blue( val ) |
1614 | int val | |
a0d0e21e | 1615 | |
beb31b0b GS |
1616 | Both Perl functions will expect an object as the first parameter. In the |
1617 | generated C++ code the object is called C<THIS>, and the method call will | |
1618 | be performed on this object. So in the C++ code the blue() and set_blue() | |
1619 | methods will be called as this: | |
a0d0e21e | 1620 | |
cb1a09d0 | 1621 | RETVAL = THIS->blue(); |
a0d0e21e | 1622 | |
cb1a09d0 | 1623 | THIS->set_blue( val ); |
a0d0e21e | 1624 | |
4628e4f8 GS |
1625 | You could also write a single get/set method using an optional argument: |
1626 | ||
1627 | int | |
a104f515 | 1628 | color::blue( val = NO_INIT ) |
4628e4f8 GS |
1629 | int val |
1630 | PROTOTYPE $;$ | |
1631 | CODE: | |
1632 | if (items > 1) | |
1633 | THIS->set_blue( val ); | |
1634 | RETVAL = THIS->blue(); | |
1635 | OUTPUT: | |
1636 | RETVAL | |
1637 | ||
cb1a09d0 | 1638 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
beb31b0b | 1639 | called and C<THIS> will be given as its parameter. The generated C++ code for |
a0d0e21e | 1640 | |
d1b91892 | 1641 | void |
cb1a09d0 AD |
1642 | color::DESTROY() |
1643 | ||
beb31b0b GS |
1644 | will look like this: |
1645 | ||
1646 | color *THIS = ...; // Initialized as in typemap | |
cb1a09d0 AD |
1647 | |
1648 | delete THIS; | |
a0d0e21e | 1649 | |
cb1a09d0 AD |
1650 | If the function's name is B<new> then the C++ C<new> function will be called |
1651 | to create a dynamic C++ object. The XSUB will expect the class name, which | |
1652 | will be kept in a variable called C<CLASS>, to be given as the first | |
1653 | argument. | |
a0d0e21e | 1654 | |
cb1a09d0 AD |
1655 | color * |
1656 | color::new() | |
a0d0e21e | 1657 | |
beb31b0b | 1658 | The generated C++ code will call C<new>. |
a0d0e21e | 1659 | |
beb31b0b | 1660 | RETVAL = new color(); |
cb1a09d0 AD |
1661 | |
1662 | The following is an example of a typemap that could be used for this C++ | |
1663 | example. | |
1664 | ||
1665 | TYPEMAP | |
1666 | color * O_OBJECT | |
1667 | ||
1668 | OUTPUT | |
1669 | # The Perl object is blessed into 'CLASS', which should be a | |
1670 | # char* having the name of the package for the blessing. | |
1671 | O_OBJECT | |
1672 | sv_setref_pv( $arg, CLASS, (void*)$var ); | |
a6006777 | 1673 | |
cb1a09d0 AD |
1674 | INPUT |
1675 | O_OBJECT | |
1676 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) | |
1677 | $var = ($type)SvIV((SV*)SvRV( $arg )); | |
1678 | else{ | |
1679 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); | |
1680 | XSRETURN_UNDEF; | |
1681 | } | |
a0d0e21e | 1682 | |
d1b91892 | 1683 | =head2 Interface Strategy |
a0d0e21e LW |
1684 | |
1685 | When designing an interface between Perl and a C library a straight | |
beb31b0b GS |
1686 | translation from C to XS (such as created by C<h2xs -x>) is often sufficient. |
1687 | However, sometimes the interface will look | |
a0d0e21e | 1688 | very C-like and occasionally nonintuitive, especially when the C function |
beb31b0b GS |
1689 | modifies one of its parameters, or returns failure inband (as in "negative |
1690 | return values mean failure"). In cases where the programmer wishes to | |
a0d0e21e LW |
1691 | create a more Perl-like interface the following strategy may help to |
1692 | identify the more critical parts of the interface. | |
1693 | ||
beb31b0b GS |
1694 | Identify the C functions with input/output or output parameters. The XSUBs for |
1695 | these functions may be able to return lists to Perl. | |
1696 | ||
1697 | Identify the C functions which use some inband info as an indication | |
1698 | of failure. They may be | |
1699 | candidates to return undef or an empty list in case of failure. If the | |
1700 | failure may be detected without a call to the C function, you may want to use | |
1701 | an INIT: section to report the failure. For failures detectable after the C | |
375cc10d | 1702 | function returns one may want to use a POSTCALL: section to process the |
beb31b0b GS |
1703 | failure. In more complicated cases use CODE: or PPCODE: sections. |
1704 | ||
1705 | If many functions use the same failure indication based on the return value, | |
1706 | you may want to create a special typedef to handle this situation. Put | |
1707 | ||
1708 | typedef int negative_is_failure; | |
1709 | ||
1710 | near the beginning of XS file, and create an OUTPUT typemap entry | |
1711 | for C<negative_is_failure> which converts negative values to C<undef>, or | |
1712 | maybe croak()s. After this the return value of type C<negative_is_failure> | |
1713 | will create more Perl-like interface. | |
a0d0e21e | 1714 | |
d1b91892 | 1715 | Identify which values are used by only the C and XSUB functions |
beb31b0b GS |
1716 | themselves, say, when a parameter to a function should be a contents of a |
1717 | global variable. If Perl does not need to access the contents of the value | |
a0d0e21e LW |
1718 | then it may not be necessary to provide a translation for that value |
1719 | from C to Perl. | |
1720 | ||
1721 | Identify the pointers in the C function parameter lists and return | |
beb31b0b GS |
1722 | values. Some pointers may be used to implement input/output or |
1723 | output parameters, they can be handled in XS with the C<&> unary operator, | |
1724 | and, possibly, using the NO_INIT keyword. | |
1725 | Some others will require handling of types like C<int *>, and one needs | |
1726 | to decide what a useful Perl translation will do in such a case. When | |
1727 | the semantic is clear, it is advisable to put the translation into a typemap | |
1728 | file. | |
a0d0e21e LW |
1729 | |
1730 | Identify the structures used by the C functions. In many | |
1731 | cases it may be helpful to use the T_PTROBJ typemap for | |
1732 | these structures so they can be manipulated by Perl as | |
beb31b0b GS |
1733 | blessed objects. (This is handled automatically by C<h2xs -x>.) |
1734 | ||
1735 | If the same C type is used in several different contexts which require | |
1736 | different translations, C<typedef> several new types mapped to this C type, | |
1737 | and create separate F<typemap> entries for these new types. Use these | |
1738 | types in declarations of return type and parameters to XSUBs. | |
a0d0e21e | 1739 | |
a0d0e21e LW |
1740 | =head2 Perl Objects And C Structures |
1741 | ||
1742 | When dealing with C structures one should select either | |
1743 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are | |
1744 | designed to handle pointers to complex objects. The | |
1745 | T_PTRREF type will allow the Perl object to be unblessed | |
1746 | while the T_PTROBJ type requires that the object be blessed. | |
1747 | By using T_PTROBJ one can achieve a form of type-checking | |
d1b91892 | 1748 | because the XSUB will attempt to verify that the Perl object |
a0d0e21e LW |
1749 | is of the expected type. |
1750 | ||
1751 | The following XS code shows the getnetconfigent() function which is used | |
8e07c86e | 1752 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
a0d0e21e LW |
1753 | C structure and has the C prototype shown below. The example will |
1754 | demonstrate how the C pointer will become a Perl reference. Perl will | |
1755 | consider this reference to be a pointer to a blessed object and will | |
1756 | attempt to call a destructor for the object. A destructor will be | |
1757 | provided in the XS source to free the memory used by getnetconfigent(). | |
1758 | Destructors in XS can be created by specifying an XSUB function whose name | |
1759 | ends with the word B<DESTROY>. XS destructors can be used to free memory | |
1760 | which may have been malloc'd by another XSUB. | |
1761 | ||
1762 | struct netconfig *getnetconfigent(const char *netid); | |
1763 | ||
1764 | A C<typedef> will be created for C<struct netconfig>. The Perl | |
1765 | object will be blessed in a class matching the name of the C | |
1766 | type, with the tag C<Ptr> appended, and the name should not | |
1767 | have embedded spaces if it will be a Perl package name. The | |
1768 | destructor will be placed in a class corresponding to the | |
1769 | class of the object and the PREFIX keyword will be used to | |
1770 | trim the name to the word DESTROY as Perl will expect. | |
1771 | ||
1772 | typedef struct netconfig Netconfig; | |
1773 | ||
1774 | MODULE = RPC PACKAGE = RPC | |
1775 | ||
1776 | Netconfig * | |
1777 | getnetconfigent(netid) | |
8e07c86e | 1778 | char *netid |
a0d0e21e LW |
1779 | |
1780 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
1781 | ||
1782 | void | |
1783 | rpcb_DESTROY(netconf) | |
8e07c86e | 1784 | Netconfig *netconf |
beb31b0b | 1785 | CODE: |
a0d0e21e LW |
1786 | printf("Now in NetconfigPtr::DESTROY\n"); |
1787 | free( netconf ); | |
1788 | ||
1789 | This example requires the following typemap entry. Consult the typemap | |
1790 | section for more information about adding new typemaps for an extension. | |
1791 | ||
1792 | TYPEMAP | |
1793 | Netconfig * T_PTROBJ | |
1794 | ||
1795 | This example will be used with the following Perl statements. | |
1796 | ||
1797 | use RPC; | |
1798 | $netconf = getnetconfigent("udp"); | |
1799 | ||
1800 | When Perl destroys the object referenced by $netconf it will send the | |
1801 | object to the supplied XSUB DESTROY function. Perl cannot determine, and | |
1802 | does not care, that this object is a C struct and not a Perl object. In | |
1803 | this sense, there is no difference between the object created by the | |
1804 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. | |
1805 | ||
a0d0e21e LW |
1806 | =head2 The Typemap |
1807 | ||
1808 | The typemap is a collection of code fragments which are used by the B<xsubpp> | |
1809 | compiler to map C function parameters and values to Perl values. The | |
7817ba4d | 1810 | typemap file may consist of three sections labelled C<TYPEMAP>, C<INPUT>, and |
beb31b0b GS |
1811 | C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP> |
1812 | section. The INPUT section tells | |
7e9d670d | 1813 | the compiler how to translate Perl values |
a0d0e21e LW |
1814 | into variables of certain C types. The OUTPUT section tells the compiler |
1815 | how to translate the values from certain C types into values Perl can | |
1816 | understand. The TYPEMAP section tells the compiler which of the INPUT and | |
1817 | OUTPUT code fragments should be used to map a given C type to a Perl value. | |
7e9d670d GS |
1818 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
1819 | in the first column on a line by themselves, and must be in uppercase. | |
a0d0e21e | 1820 | |
c7af0b91 | 1821 | The default typemap in the F<lib/ExtUtils> directory of the Perl source |
dcd2ee75 YST |
1822 | contains many useful types which can be used by Perl extensions. Some |
1823 | extensions define additional typemaps which they keep in their own directory. | |
1824 | These additional typemaps may reference INPUT and OUTPUT maps in the main | |
a0d0e21e LW |
1825 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
1826 | override any mappings which are in the default typemap. | |
1827 | ||
1828 | Most extensions which require a custom typemap will need only the TYPEMAP | |
1829 | section of the typemap file. The custom typemap used in the | |
1830 | getnetconfigent() example shown earlier demonstrates what may be the typical | |
1831 | use of extension typemaps. That typemap is used to equate a C structure | |
1832 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown | |
1833 | here. Note that the C type is separated from the XS type with a tab and | |
1834 | that the C unary operator C<*> is considered to be a part of the C type name. | |
1835 | ||
beb31b0b GS |
1836 | TYPEMAP |
1837 | Netconfig *<tab>T_PTROBJ | |
a0d0e21e | 1838 | |
1748e8dd RS |
1839 | Here's a more complicated example: suppose that you wanted C<struct |
1840 | netconfig> to be blessed into the class C<Net::Config>. One way to do | |
1841 | this is to use underscores (_) to separate package names, as follows: | |
1842 | ||
1843 | typedef struct netconfig * Net_Config; | |
1844 | ||
1845 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to | |
1846 | double-colons (::), and declare C<Net_Config> to be of that type: | |
1847 | ||
1848 | ||
1849 | TYPEMAP | |
1850 | Net_Config T_PTROBJ_SPECIAL | |
1851 | ||
1852 | INPUT | |
1853 | T_PTROBJ_SPECIAL | |
1854 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { | |
1855 | IV tmp = SvIV((SV*)SvRV($arg)); | |
049cb411 | 1856 | $var = INT2PTR($type, tmp); |
1748e8dd RS |
1857 | } |
1858 | else | |
1859 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") | |
1860 | ||
1861 | OUTPUT | |
1862 | T_PTROBJ_SPECIAL | |
1863 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", | |
1864 | (void*)$var); | |
1865 | ||
1866 | The INPUT and OUTPUT sections substitute underscores for double-colons | |
1867 | on the fly, giving the desired effect. This example demonstrates some | |
1868 | of the power and versatility of the typemap facility. | |
1869 | ||
049cb411 RB |
1870 | The INT2PTR macro (defined in perl.h) casts an integer to a pointer, |
1871 | of a given type, taking care of the possible different size of integers | |
1872 | and pointers. There are also PTR2IV, PTR2UV, PTR2NV macros, | |
1873 | to map the other way, which may be useful in OUTPUT sections. | |
1874 | ||
662a0f8c JH |
1875 | =head2 Safely Storing Static Data in XS |
1876 | ||
1877 | Starting with Perl 5.8, a macro framework has been defined to allow | |
1878 | static data to be safely stored in XS modules that will be accessed from | |
1879 | a multi-threaded Perl. | |
1880 | ||
1881 | Although primarily designed for use with multi-threaded Perl, the macros | |
1882 | have been designed so that they will work with non-threaded Perl as well. | |
1883 | ||
1884 | It is therefore strongly recommended that these macros be used by all | |
1885 | XS modules that make use of static data. | |
1886 | ||
fe854a6f | 1887 | The easiest way to get a template set of macros to use is by specifying |
662a0f8c JH |
1888 | the C<-g> (C<--global>) option with h2xs (see L<h2xs>). |
1889 | ||
1890 | Below is an example module that makes use of the macros. | |
1891 | ||
1892 | #include "EXTERN.h" | |
1893 | #include "perl.h" | |
1894 | #include "XSUB.h" | |
7207e29d | 1895 | |
662a0f8c | 1896 | /* Global Data */ |
7207e29d | 1897 | |
662a0f8c | 1898 | #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION |
7207e29d | 1899 | |
662a0f8c JH |
1900 | typedef struct { |
1901 | int count; | |
1902 | char name[3][100]; | |
1903 | } my_cxt_t; | |
7207e29d | 1904 | |
662a0f8c | 1905 | START_MY_CXT |
7207e29d | 1906 | |
662a0f8c | 1907 | MODULE = BlindMice PACKAGE = BlindMice |
7207e29d | 1908 | |
662a0f8c JH |
1909 | BOOT: |
1910 | { | |
1911 | MY_CXT_INIT; | |
1912 | MY_CXT.count = 0; | |
1913 | strcpy(MY_CXT.name[0], "None"); | |
1914 | strcpy(MY_CXT.name[1], "None"); | |
1915 | strcpy(MY_CXT.name[2], "None"); | |
1916 | } | |
1917 | ||
1918 | int | |
1919 | newMouse(char * name) | |
1920 | char * name; | |
1921 | PREINIT: | |
1922 | dMY_CXT; | |
1923 | CODE: | |
1924 | if (MY_CXT.count >= 3) { | |
4358a253 | 1925 | warn("Already have 3 blind mice"); |
662a0f8c JH |
1926 | RETVAL = 0; |
1927 | } | |
1928 | else { | |
1929 | RETVAL = ++ MY_CXT.count; | |
1930 | strcpy(MY_CXT.name[MY_CXT.count - 1], name); | |
1931 | } | |
1932 | ||
1933 | char * | |
1934 | get_mouse_name(index) | |
1935 | int index | |
1936 | CODE: | |
1937 | dMY_CXT; | |
1938 | RETVAL = MY_CXT.lives ++; | |
1939 | if (index > MY_CXT.count) | |
1940 | croak("There are only 3 blind mice."); | |
1941 | else | |
1942 | RETVAL = newSVpv(MY_CXT.name[index - 1]); | |
1943 | ||
85ce96a1 DM |
1944 | void |
1945 | CLONE(...) | |
1946 | CODE: | |
1947 | MY_CXT_CLONE; | |
1948 | ||
662a0f8c JH |
1949 | B<REFERENCE> |
1950 | ||
1951 | =over 5 | |
1952 | ||
1953 | =item MY_CXT_KEY | |
1954 | ||
1955 | This macro is used to define a unique key to refer to the static data | |
1956 | for an XS module. The suggested naming scheme, as used by h2xs, is to | |
1957 | use a string that consists of the module name, the string "::_guts" | |
1958 | and the module version number. | |
1959 | ||
1960 | #define MY_CXT_KEY "MyModule::_guts" XS_VERSION | |
1961 | ||
1962 | =item typedef my_cxt_t | |
1963 | ||
ac036724 | 1964 | This struct typedef I<must> always be called C<my_cxt_t>. The other |
662a0f8c JH |
1965 | C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name. |
1966 | ||
1967 | Declare a typedef named C<my_cxt_t> that is a structure that contains | |
1968 | all the data that needs to be interpreter-local. | |
1969 | ||
1970 | typedef struct { | |
1971 | int some_value; | |
1972 | } my_cxt_t; | |
1973 | ||
1974 | =item START_MY_CXT | |
1975 | ||
1976 | Always place the START_MY_CXT macro directly after the declaration | |
1977 | of C<my_cxt_t>. | |
1978 | ||
1979 | =item MY_CXT_INIT | |
1980 | ||
1981 | The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct. | |
1982 | ||
ac036724 | 1983 | It I<must> be called exactly once, typically in a BOOT: section. If you |
85ce96a1 DM |
1984 | are maintaining multiple interpreters, it should be called once in each |
1985 | interpreter instance, except for interpreters cloned from existing ones. | |
c7af0b91 | 1986 | (But see L<MY_CXT_CLONE> below.) |
662a0f8c JH |
1987 | |
1988 | =item dMY_CXT | |
1989 | ||
1990 | Use the dMY_CXT macro (a declaration) in all the functions that access | |
1991 | MY_CXT. | |
1992 | ||
1993 | =item MY_CXT | |
1994 | ||
1995 | Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For | |
1996 | example, if C<my_cxt_t> is | |
1997 | ||
1998 | typedef struct { | |
1999 | int index; | |
2000 | } my_cxt_t; | |
2001 | ||
2002 | then use this to access the C<index> member | |
2003 | ||
2004 | dMY_CXT; | |
2005 | MY_CXT.index = 2; | |
2006 | ||
85ce96a1 DM |
2007 | =item aMY_CXT/pMY_CXT |
2008 | ||
2009 | C<dMY_CXT> may be quite expensive to calculate, and to avoid the overhead | |
2010 | of invoking it in each function it is possible to pass the declaration | |
2011 | onto other functions using the C<aMY_CXT>/C<pMY_CXT> macros, eg | |
2012 | ||
2013 | void sub1() { | |
2014 | dMY_CXT; | |
2015 | MY_CXT.index = 1; | |
2016 | sub2(aMY_CXT); | |
2017 | } | |
2018 | ||
2019 | void sub2(pMY_CXT) { | |
2020 | MY_CXT.index = 2; | |
2021 | } | |
2022 | ||
2023 | Analogously to C<pTHX>, there are equivalent forms for when the macro is the | |
2024 | first or last in multiple arguments, where an underscore represents a | |
2025 | comma, i.e. C<_aMY_CXT>, C<aMY_CXT_>, C<_pMY_CXT> and C<pMY_CXT_>. | |
2026 | ||
2027 | =item MY_CXT_CLONE | |
2028 | ||
2029 | By default, when a new interpreter is created as a copy of an existing one | |
0a3a8dc0 | 2030 | (eg via C<< threads->create() >>), both interpreters share the same physical |
85ce96a1 DM |
2031 | my_cxt_t structure. Calling C<MY_CXT_CLONE> (typically via the package's |
2032 | C<CLONE()> function), causes a byte-for-byte copy of the structure to be | |
2033 | taken, and any future dMY_CXT will cause the copy to be accessed instead. | |
2034 | ||
f16dd614 DM |
2035 | =item MY_CXT_INIT_INTERP(my_perl) |
2036 | ||
2037 | =item dMY_CXT_INTERP(my_perl) | |
2038 | ||
2039 | These are versions of the macros which take an explicit interpreter as an | |
2040 | argument. | |
2041 | ||
662a0f8c JH |
2042 | =back |
2043 | ||
f16dd614 DM |
2044 | Note that these macros will only work together within the I<same> source |
2045 | file; that is, a dMY_CTX in one source file will access a different structure | |
2046 | than a dMY_CTX in another source file. | |
2047 | ||
832a833b JH |
2048 | =head2 Thread-aware system interfaces |
2049 | ||
2050 | Starting from Perl 5.8, in C/C++ level Perl knows how to wrap | |
2051 | system/library interfaces that have thread-aware versions | |
2052 | (e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that | |
2053 | correctly handle the multithreaded interaction with the Perl | |
2054 | interpreter. This will happen transparently, the only thing | |
2055 | you need to do is to instantiate a Perl interpreter. | |
2056 | ||
2057 | This wrapping happens always when compiling Perl core source | |
2058 | (PERL_CORE is defined) or the Perl core extensions (PERL_EXT is | |
2059 | defined). When compiling XS code outside of Perl core the wrapping | |
2060 | does not take place. Note, however, that intermixing the _r-forms | |
2061 | (as Perl compiled for multithreaded operation will do) and the _r-less | |
2062 | forms is neither well-defined (inconsistent results, data corruption, | |
2063 | or even crashes become more likely), nor is it very portable. | |
2064 | ||
a0d0e21e LW |
2065 | =head1 EXAMPLES |
2066 | ||
2067 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. | |
2068 | ||
2069 | #include "EXTERN.h" | |
2070 | #include "perl.h" | |
2071 | #include "XSUB.h" | |
2072 | ||
2073 | #include <rpc/rpc.h> | |
2074 | ||
2075 | typedef struct netconfig Netconfig; | |
2076 | ||
2077 | MODULE = RPC PACKAGE = RPC | |
2078 | ||
e7ea3e70 | 2079 | SV * |
a0d0e21e | 2080 | rpcb_gettime(host="localhost") |
8e07c86e | 2081 | char *host |
beb31b0b | 2082 | PREINIT: |
a0d0e21e | 2083 | time_t timep; |
beb31b0b | 2084 | CODE: |
a0d0e21e LW |
2085 | ST(0) = sv_newmortal(); |
2086 | if( rpcb_gettime( host, &timep ) ) | |
2087 | sv_setnv( ST(0), (double)timep ); | |
a0d0e21e LW |
2088 | |
2089 | Netconfig * | |
2090 | getnetconfigent(netid="udp") | |
8e07c86e | 2091 | char *netid |
a0d0e21e LW |
2092 | |
2093 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ | |
2094 | ||
2095 | void | |
2096 | rpcb_DESTROY(netconf) | |
8e07c86e | 2097 | Netconfig *netconf |
beb31b0b | 2098 | CODE: |
a0d0e21e LW |
2099 | printf("NetconfigPtr::DESTROY\n"); |
2100 | free( netconf ); | |
2101 | ||
2102 | File C<typemap>: Custom typemap for RPC.xs. | |
2103 | ||
2104 | TYPEMAP | |
2105 | Netconfig * T_PTROBJ | |
2106 | ||
2107 | File C<RPC.pm>: Perl module for the RPC extension. | |
2108 | ||
2109 | package RPC; | |
2110 | ||
2111 | require Exporter; | |
2112 | require DynaLoader; | |
2113 | @ISA = qw(Exporter DynaLoader); | |
2114 | @EXPORT = qw(rpcb_gettime getnetconfigent); | |
2115 | ||
2116 | bootstrap RPC; | |
2117 | 1; | |
2118 | ||
2119 | File C<rpctest.pl>: Perl test program for the RPC extension. | |
2120 | ||
2121 | use RPC; | |
2122 | ||
2123 | $netconf = getnetconfigent(); | |
2124 | $a = rpcb_gettime(); | |
2125 | print "time = $a\n"; | |
2126 | print "netconf = $netconf\n"; | |
2127 | ||
2128 | $netconf = getnetconfigent("tcp"); | |
2129 | $a = rpcb_gettime("poplar"); | |
2130 | print "time = $a\n"; | |
2131 | print "netconf = $netconf\n"; | |
2132 | ||
2133 | ||
c07a80fd | 2134 | =head1 XS VERSION |
2135 | ||
f27cfbbe | 2136 | This document covers features supported by C<xsubpp> 1.935. |
c07a80fd | 2137 | |
a0d0e21e LW |
2138 | =head1 AUTHOR |
2139 | ||
beb31b0b GS |
2140 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
2141 | ||
7f2de2d2 | 2142 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |