| 1 | =head1 NAME |
| 2 | |
| 3 | perlxs - XS language reference manual |
| 4 | |
| 5 | =head1 DESCRIPTION |
| 6 | |
| 7 | =head2 Introduction |
| 8 | |
| 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 |
| 60 | uses B<typemaps> to determine how to map C function parameters |
| 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 |
| 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. |
| 72 | |
| 73 | See L<perlxstut> for a tutorial on the whole extension creation process. |
| 74 | |
| 75 | Note: For some extensions, Dave Beazley's SWIG system may provide a |
| 76 | significantly more convenient mechanism for creating the extension |
| 77 | glue code. See L<http://www.swig.org/> for more information. |
| 78 | |
| 79 | =head2 On The Road |
| 80 | |
| 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. |
| 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) |
| 123 | char *host |
| 124 | time_t &timep |
| 125 | OUTPUT: |
| 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 | |
| 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 | |
| 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. |
| 166 | |
| 167 | double |
| 168 | sin(x) |
| 169 | double x |
| 170 | |
| 171 | Optionally, one can merge the description of types and the list of |
| 172 | argument names, rewriting this as |
| 173 | |
| 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 |
| 185 | |
| 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: |
| 191 | |
| 192 | char * s |
| 193 | char &c |
| 194 | |
| 195 | Both these XS declarations correspond to the C<char*> C type, but they have |
| 196 | different semantics, see L<"The & Unary Operator">. |
| 197 | |
| 198 | It is convenient to think that the indirection operator |
| 199 | C<*> should be considered as a part of the type and the address operator C<&> |
| 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. |
| 202 | |
| 203 | The function name and the return type must be placed on |
| 204 | separate lines and should be flush left-adjusted. |
| 205 | |
| 206 | INCORRECT CORRECT |
| 207 | |
| 208 | double sin(x) double |
| 209 | double x sin(x) |
| 210 | double x |
| 211 | |
| 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. |
| 215 | |
| 216 | CORRECT |
| 217 | |
| 218 | double |
| 219 | sin(x) |
| 220 | double x |
| 221 | |
| 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 | |
| 232 | =head2 The Argument Stack |
| 233 | |
| 234 | The Perl argument stack is used to store the values which are |
| 235 | sent as parameters to the XSUB and to store the XSUB's |
| 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 |
| 239 | first position on that stack which belongs to the active |
| 240 | function will be referred to as position 0 for that function. |
| 241 | |
| 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 |
| 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 | |
| 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. |
| 260 | |
| 261 | If the XSUB has a return type of C<void> then the compiler will |
| 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. |
| 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: |
| 268 | directive is used which sets ST(0) explicitly. |
| 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 |
| 272 | segfaults in cases when XSUB was I<truly> C<void>. This practice is |
| 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 |
| 275 | some heuristic code which tries to disambiguate between "truly-void" |
| 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.) |
| 278 | |
| 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); |
| 296 | |
| 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 | C<CV *>, and C<SVREF> (which indicates a scalar reference, not |
| 322 | a general C<SV *>). |
| 323 | In XS code on perls starting with perl 5.16, you can override the |
| 324 | typemaps for any of these types with a version that has proper |
| 325 | handling of refcounts. In your C<TYPEMAP> section, do |
| 326 | |
| 327 | AV* T_AVREF_REFCOUNT_FIXED |
| 328 | |
| 329 | to get the repaired variant. For backward compatibility with older |
| 330 | versions of perl, you can instead decrement the reference count |
| 331 | manually when you're returning one of the aforementioned |
| 332 | types using C<sv_2mortal>: |
| 333 | |
| 334 | AV * |
| 335 | array() |
| 336 | CODE: |
| 337 | RETVAL = newAV(); |
| 338 | sv_2mortal((SV*)RETVAL); |
| 339 | /* do something with RETVAL */ |
| 340 | OUTPUT: |
| 341 | RETVAL |
| 342 | |
| 343 | Remember that you don't have to do this for an C<SV *>. |
| 344 | |
| 345 | =head2 The MODULE Keyword |
| 346 | |
| 347 | The MODULE keyword is used to start the XS code and to specify the package |
| 348 | of the functions which are being defined. All text preceding the first |
| 349 | MODULE keyword is considered C code and is passed through to the output with |
| 350 | POD stripped, but otherwise untouched. Every XS module will have a |
| 351 | bootstrap function which is used to hook the XSUBs into Perl. The package |
| 352 | name of this bootstrap function will match the value of the last MODULE |
| 353 | statement in the XS source files. The value of MODULE should always remain |
| 354 | constant within the same XS file, though this is not required. |
| 355 | |
| 356 | The following example will start the XS code and will place |
| 357 | all functions in a package named RPC. |
| 358 | |
| 359 | MODULE = RPC |
| 360 | |
| 361 | =head2 The PACKAGE Keyword |
| 362 | |
| 363 | When functions within an XS source file must be separated into packages |
| 364 | the PACKAGE keyword should be used. This keyword is used with the MODULE |
| 365 | keyword and must follow immediately after it when used. |
| 366 | |
| 367 | MODULE = RPC PACKAGE = RPC |
| 368 | |
| 369 | [ XS code in package RPC ] |
| 370 | |
| 371 | MODULE = RPC PACKAGE = RPCB |
| 372 | |
| 373 | [ XS code in package RPCB ] |
| 374 | |
| 375 | MODULE = RPC PACKAGE = RPC |
| 376 | |
| 377 | [ XS code in package RPC ] |
| 378 | |
| 379 | The same package name can be used more than once, allowing for |
| 380 | non-contiguous code. This is useful if you have a stronger ordering |
| 381 | principle than package names. |
| 382 | |
| 383 | Although this keyword is optional and in some cases provides redundant |
| 384 | information it should always be used. This keyword will ensure that the |
| 385 | XSUBs appear in the desired package. |
| 386 | |
| 387 | =head2 The PREFIX Keyword |
| 388 | |
| 389 | The PREFIX keyword designates prefixes which should be |
| 390 | removed from the Perl function names. If the C function is |
| 391 | C<rpcb_gettime()> and the PREFIX value is C<rpcb_> then Perl will |
| 392 | see this function as C<gettime()>. |
| 393 | |
| 394 | This keyword should follow the PACKAGE keyword when used. |
| 395 | If PACKAGE is not used then PREFIX should follow the MODULE |
| 396 | keyword. |
| 397 | |
| 398 | MODULE = RPC PREFIX = rpc_ |
| 399 | |
| 400 | MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ |
| 401 | |
| 402 | =head2 The OUTPUT: Keyword |
| 403 | |
| 404 | The OUTPUT: keyword indicates that certain function parameters should be |
| 405 | updated (new values made visible to Perl) when the XSUB terminates or that |
| 406 | certain values should be returned to the calling Perl function. For |
| 407 | simple functions which have no CODE: or PPCODE: section, |
| 408 | such as the sin() function above, the RETVAL variable is |
| 409 | automatically designated as an output value. For more complex functions |
| 410 | the B<xsubpp> compiler will need help to determine which variables are output |
| 411 | variables. |
| 412 | |
| 413 | This keyword will normally be used to complement the CODE: keyword. |
| 414 | The RETVAL variable is not recognized as an output variable when the |
| 415 | CODE: keyword is present. The OUTPUT: keyword is used in this |
| 416 | situation to tell the compiler that RETVAL really is an output |
| 417 | variable. |
| 418 | |
| 419 | The OUTPUT: keyword can also be used to indicate that function parameters |
| 420 | are output variables. This may be necessary when a parameter has been |
| 421 | modified within the function and the programmer would like the update to |
| 422 | be seen by Perl. |
| 423 | |
| 424 | bool_t |
| 425 | rpcb_gettime(host,timep) |
| 426 | char *host |
| 427 | time_t &timep |
| 428 | OUTPUT: |
| 429 | timep |
| 430 | |
| 431 | The OUTPUT: keyword will also allow an output parameter to |
| 432 | be mapped to a matching piece of code rather than to a |
| 433 | typemap. |
| 434 | |
| 435 | bool_t |
| 436 | rpcb_gettime(host,timep) |
| 437 | char *host |
| 438 | time_t &timep |
| 439 | OUTPUT: |
| 440 | timep sv_setnv(ST(1), (double)timep); |
| 441 | |
| 442 | B<xsubpp> emits an automatic C<SvSETMAGIC()> for all parameters in the |
| 443 | OUTPUT section of the XSUB, except RETVAL. This is the usually desired |
| 444 | behavior, as it takes care of properly invoking 'set' magic on output |
| 445 | parameters (needed for hash or array element parameters that must be |
| 446 | created if they didn't exist). If for some reason, this behavior is |
| 447 | not desired, the OUTPUT section may contain a C<SETMAGIC: DISABLE> line |
| 448 | to disable it for the remainder of the parameters in the OUTPUT section. |
| 449 | Likewise, C<SETMAGIC: ENABLE> can be used to reenable it for the |
| 450 | remainder of the OUTPUT section. See L<perlguts> for more details |
| 451 | about 'set' magic. |
| 452 | |
| 453 | =head2 The NO_OUTPUT Keyword |
| 454 | |
| 455 | The NO_OUTPUT can be placed as the first token of the XSUB. This keyword |
| 456 | indicates that while the C subroutine we provide an interface to has |
| 457 | a non-C<void> return type, the return value of this C subroutine should not |
| 458 | be returned from the generated Perl subroutine. |
| 459 | |
| 460 | With this keyword present L<The RETVAL Variable> is created, and in the |
| 461 | generated call to the subroutine this variable is assigned to, but the value |
| 462 | of this variable is not going to be used in the auto-generated code. |
| 463 | |
| 464 | This keyword makes sense only if C<RETVAL> is going to be accessed by the |
| 465 | user-supplied code. It is especially useful to make a function interface |
| 466 | more Perl-like, especially when the C return value is just an error condition |
| 467 | indicator. For example, |
| 468 | |
| 469 | NO_OUTPUT int |
| 470 | delete_file(char *name) |
| 471 | POSTCALL: |
| 472 | if (RETVAL != 0) |
| 473 | croak("Error %d while deleting file '%s'", RETVAL, name); |
| 474 | |
| 475 | Here the generated XS function returns nothing on success, and will die() |
| 476 | with a meaningful error message on error. |
| 477 | |
| 478 | =head2 The CODE: Keyword |
| 479 | |
| 480 | This keyword is used in more complicated XSUBs which require |
| 481 | special handling for the C function. The RETVAL variable is |
| 482 | still declared, but it will not be returned unless it is specified |
| 483 | in the OUTPUT: section. |
| 484 | |
| 485 | The following XSUB is for a C function which requires special handling of |
| 486 | its parameters. The Perl usage is given first. |
| 487 | |
| 488 | $status = rpcb_gettime( "localhost", $timep ); |
| 489 | |
| 490 | The XSUB follows. |
| 491 | |
| 492 | bool_t |
| 493 | rpcb_gettime(host,timep) |
| 494 | char *host |
| 495 | time_t timep |
| 496 | CODE: |
| 497 | RETVAL = rpcb_gettime( host, &timep ); |
| 498 | OUTPUT: |
| 499 | timep |
| 500 | RETVAL |
| 501 | |
| 502 | =head2 The INIT: Keyword |
| 503 | |
| 504 | The INIT: keyword allows initialization to be inserted into the XSUB before |
| 505 | the compiler generates the call to the C function. Unlike the CODE: keyword |
| 506 | above, this keyword does not affect the way the compiler handles RETVAL. |
| 507 | |
| 508 | bool_t |
| 509 | rpcb_gettime(host,timep) |
| 510 | char *host |
| 511 | time_t &timep |
| 512 | INIT: |
| 513 | printf("# Host is %s\n", host ); |
| 514 | OUTPUT: |
| 515 | timep |
| 516 | |
| 517 | Another use for the INIT: section is to check for preconditions before |
| 518 | making a call to the C function: |
| 519 | |
| 520 | long long |
| 521 | lldiv(a,b) |
| 522 | long long a |
| 523 | long long b |
| 524 | INIT: |
| 525 | if (a == 0 && b == 0) |
| 526 | XSRETURN_UNDEF; |
| 527 | if (b == 0) |
| 528 | croak("lldiv: cannot divide by 0"); |
| 529 | |
| 530 | =head2 The NO_INIT Keyword |
| 531 | |
| 532 | The NO_INIT keyword is used to indicate that a function |
| 533 | parameter is being used only as an output value. The B<xsubpp> |
| 534 | compiler will normally generate code to read the values of |
| 535 | all function parameters from the argument stack and assign |
| 536 | them to C variables upon entry to the function. NO_INIT |
| 537 | will tell the compiler that some parameters will be used for |
| 538 | output rather than for input and that they will be handled |
| 539 | before the function terminates. |
| 540 | |
| 541 | The following example shows a variation of the rpcb_gettime() function. |
| 542 | This function uses the timep variable only as an output variable and does |
| 543 | not care about its initial contents. |
| 544 | |
| 545 | bool_t |
| 546 | rpcb_gettime(host,timep) |
| 547 | char *host |
| 548 | time_t &timep = NO_INIT |
| 549 | OUTPUT: |
| 550 | timep |
| 551 | |
| 552 | =head2 The TYPEMAP: Keyword |
| 553 | |
| 554 | Starting with Perl 5.16, you can embed typemaps into your XS code |
| 555 | instead of or in addition to typemaps in a separate file. Multiple |
| 556 | such embedded typemaps will be processed in order of appearance in |
| 557 | the XS code and like local typemap files take precendence over the |
| 558 | default typemap, the embedded typemaps may overwrite previous |
| 559 | definitions of TYPEMAP, INPUT, and OUTPUT stanzas. The syntax for |
| 560 | embedded typemaps is |
| 561 | |
| 562 | TYPEMAP: <<HERE |
| 563 | ... your typemap code here ... |
| 564 | HERE |
| 565 | |
| 566 | where the C<TYPEMAP> keyword must appear in the first column of a |
| 567 | new line. |
| 568 | |
| 569 | Refer to the section on L<The Typemap> for details on writing typemaps. |
| 570 | |
| 571 | =head2 Initializing Function Parameters |
| 572 | |
| 573 | C function parameters are normally initialized with their values from |
| 574 | the argument stack (which in turn contains the parameters that were |
| 575 | passed to the XSUB from Perl). The typemaps contain the |
| 576 | code segments which are used to translate the Perl values to |
| 577 | the C parameters. The programmer, however, is allowed to |
| 578 | override the typemaps and supply alternate (or additional) |
| 579 | initialization code. Initialization code starts with the first |
| 580 | C<=>, C<;> or C<+> on a line in the INPUT: section. The only |
| 581 | exception happens if this C<;> terminates the line, then this C<;> |
| 582 | is quietly ignored. |
| 583 | |
| 584 | The following code demonstrates how to supply initialization code for |
| 585 | function parameters. The initialization code is eval'ed within double |
| 586 | quotes by the compiler before it is added to the output so anything |
| 587 | which should be interpreted literally [mainly C<$>, C<@>, or C<\\>] |
| 588 | must be protected with backslashes. The variables $var, $arg, |
| 589 | and $type can be used as in typemaps. |
| 590 | |
| 591 | bool_t |
| 592 | rpcb_gettime(host,timep) |
| 593 | char *host = (char *)SvPV_nolen($arg); |
| 594 | time_t &timep = 0; |
| 595 | OUTPUT: |
| 596 | timep |
| 597 | |
| 598 | This should not be used to supply default values for parameters. One |
| 599 | would normally use this when a function parameter must be processed by |
| 600 | another library function before it can be used. Default parameters are |
| 601 | covered in the next section. |
| 602 | |
| 603 | If the initialization begins with C<=>, then it is output in |
| 604 | the declaration for the input variable, replacing the initialization |
| 605 | supplied by the typemap. If the initialization |
| 606 | begins with C<;> or C<+>, then it is performed after |
| 607 | all of the input variables have been declared. In the C<;> |
| 608 | case the initialization normally supplied by the typemap is not performed. |
| 609 | For the C<+> case, the declaration for the variable will include the |
| 610 | initialization from the typemap. A global |
| 611 | variable, C<%v>, is available for the truly rare case where |
| 612 | information from one initialization is needed in another |
| 613 | initialization. |
| 614 | |
| 615 | Here's a truly obscure example: |
| 616 | |
| 617 | bool_t |
| 618 | rpcb_gettime(host,timep) |
| 619 | time_t &timep; /* \$v{timep}=@{[$v{timep}=$arg]} */ |
| 620 | char *host + SvOK($v{timep}) ? SvPV_nolen($arg) : NULL; |
| 621 | OUTPUT: |
| 622 | timep |
| 623 | |
| 624 | The construct C<\$v{timep}=@{[$v{timep}=$arg]}> used in the above |
| 625 | example has a two-fold purpose: first, when this line is processed by |
| 626 | B<xsubpp>, the Perl snippet C<$v{timep}=$arg> is evaluated. Second, |
| 627 | the text of the evaluated snippet is output into the generated C file |
| 628 | (inside a C comment)! During the processing of C<char *host> line, |
| 629 | $arg will evaluate to C<ST(0)>, and C<$v{timep}> will evaluate to |
| 630 | C<ST(1)>. |
| 631 | |
| 632 | =head2 Default Parameter Values |
| 633 | |
| 634 | Default values for XSUB arguments can be specified by placing an |
| 635 | assignment statement in the parameter list. The default value may |
| 636 | be a number, a string or the special string C<NO_INIT>. Defaults should |
| 637 | always be used on the right-most parameters only. |
| 638 | |
| 639 | To allow the XSUB for rpcb_gettime() to have a default host |
| 640 | value the parameters to the XSUB could be rearranged. The |
| 641 | XSUB will then call the real rpcb_gettime() function with |
| 642 | the parameters in the correct order. This XSUB can be called |
| 643 | from Perl with either of the following statements: |
| 644 | |
| 645 | $status = rpcb_gettime( $timep, $host ); |
| 646 | |
| 647 | $status = rpcb_gettime( $timep ); |
| 648 | |
| 649 | The XSUB will look like the code which follows. A CODE: |
| 650 | block is used to call the real rpcb_gettime() function with |
| 651 | the parameters in the correct order for that function. |
| 652 | |
| 653 | bool_t |
| 654 | rpcb_gettime(timep,host="localhost") |
| 655 | char *host |
| 656 | time_t timep = NO_INIT |
| 657 | CODE: |
| 658 | RETVAL = rpcb_gettime( host, &timep ); |
| 659 | OUTPUT: |
| 660 | timep |
| 661 | RETVAL |
| 662 | |
| 663 | =head2 The PREINIT: Keyword |
| 664 | |
| 665 | The PREINIT: keyword allows extra variables to be declared immediately |
| 666 | before or after the declarations of the parameters from the INPUT: section |
| 667 | are emitted. |
| 668 | |
| 669 | If a variable is declared inside a CODE: section it will follow any typemap |
| 670 | code that is emitted for the input parameters. This may result in the |
| 671 | declaration ending up after C code, which is C syntax error. Similar |
| 672 | errors may happen with an explicit C<;>-type or C<+>-type initialization of |
| 673 | parameters is used (see L<"Initializing Function Parameters">). Declaring |
| 674 | these variables in an INIT: section will not help. |
| 675 | |
| 676 | In such cases, to force an additional variable to be declared together |
| 677 | with declarations of other variables, place the declaration into a |
| 678 | PREINIT: section. The PREINIT: keyword may be used one or more times |
| 679 | within an XSUB. |
| 680 | |
| 681 | The following examples are equivalent, but if the code is using complex |
| 682 | typemaps then the first example is safer. |
| 683 | |
| 684 | bool_t |
| 685 | rpcb_gettime(timep) |
| 686 | time_t timep = NO_INIT |
| 687 | PREINIT: |
| 688 | char *host = "localhost"; |
| 689 | CODE: |
| 690 | RETVAL = rpcb_gettime( host, &timep ); |
| 691 | OUTPUT: |
| 692 | timep |
| 693 | RETVAL |
| 694 | |
| 695 | For this particular case an INIT: keyword would generate the |
| 696 | same C code as the PREINIT: keyword. Another correct, but error-prone example: |
| 697 | |
| 698 | bool_t |
| 699 | rpcb_gettime(timep) |
| 700 | time_t timep = NO_INIT |
| 701 | CODE: |
| 702 | char *host = "localhost"; |
| 703 | RETVAL = rpcb_gettime( host, &timep ); |
| 704 | OUTPUT: |
| 705 | timep |
| 706 | RETVAL |
| 707 | |
| 708 | Another way to declare C<host> is to use a C block in the CODE: section: |
| 709 | |
| 710 | bool_t |
| 711 | rpcb_gettime(timep) |
| 712 | time_t timep = NO_INIT |
| 713 | CODE: |
| 714 | { |
| 715 | char *host = "localhost"; |
| 716 | RETVAL = rpcb_gettime( host, &timep ); |
| 717 | } |
| 718 | OUTPUT: |
| 719 | timep |
| 720 | RETVAL |
| 721 | |
| 722 | The ability to put additional declarations before the typemap entries are |
| 723 | processed is very handy in the cases when typemap conversions manipulate |
| 724 | some global state: |
| 725 | |
| 726 | MyObject |
| 727 | mutate(o) |
| 728 | PREINIT: |
| 729 | MyState st = global_state; |
| 730 | INPUT: |
| 731 | MyObject o; |
| 732 | CLEANUP: |
| 733 | reset_to(global_state, st); |
| 734 | |
| 735 | Here we suppose that conversion to C<MyObject> in the INPUT: section and from |
| 736 | MyObject when processing RETVAL will modify a global variable C<global_state>. |
| 737 | After these conversions are performed, we restore the old value of |
| 738 | C<global_state> (to avoid memory leaks, for example). |
| 739 | |
| 740 | There is another way to trade clarity for compactness: INPUT sections allow |
| 741 | declaration of C variables which do not appear in the parameter list of |
| 742 | a subroutine. Thus the above code for mutate() can be rewritten as |
| 743 | |
| 744 | MyObject |
| 745 | mutate(o) |
| 746 | MyState st = global_state; |
| 747 | MyObject o; |
| 748 | CLEANUP: |
| 749 | reset_to(global_state, st); |
| 750 | |
| 751 | and the code for rpcb_gettime() can be rewritten as |
| 752 | |
| 753 | bool_t |
| 754 | rpcb_gettime(timep) |
| 755 | time_t timep = NO_INIT |
| 756 | char *host = "localhost"; |
| 757 | C_ARGS: |
| 758 | host, &timep |
| 759 | OUTPUT: |
| 760 | timep |
| 761 | RETVAL |
| 762 | |
| 763 | =head2 The SCOPE: Keyword |
| 764 | |
| 765 | The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If |
| 766 | enabled, the XSUB will invoke ENTER and LEAVE automatically. |
| 767 | |
| 768 | To support potentially complex type mappings, if a typemap entry used |
| 769 | by an XSUB contains a comment like C</*scope*/> then scoping will |
| 770 | be automatically enabled for that XSUB. |
| 771 | |
| 772 | To enable scoping: |
| 773 | |
| 774 | SCOPE: ENABLE |
| 775 | |
| 776 | To disable scoping: |
| 777 | |
| 778 | SCOPE: DISABLE |
| 779 | |
| 780 | =head2 The INPUT: Keyword |
| 781 | |
| 782 | The XSUB's parameters are usually evaluated immediately after entering the |
| 783 | XSUB. The INPUT: keyword can be used to force those parameters to be |
| 784 | evaluated a little later. The INPUT: keyword can be used multiple times |
| 785 | within an XSUB and can be used to list one or more input variables. This |
| 786 | keyword is used with the PREINIT: keyword. |
| 787 | |
| 788 | The following example shows how the input parameter C<timep> can be |
| 789 | evaluated late, after a PREINIT. |
| 790 | |
| 791 | bool_t |
| 792 | rpcb_gettime(host,timep) |
| 793 | char *host |
| 794 | PREINIT: |
| 795 | time_t tt; |
| 796 | INPUT: |
| 797 | time_t timep |
| 798 | CODE: |
| 799 | RETVAL = rpcb_gettime( host, &tt ); |
| 800 | timep = tt; |
| 801 | OUTPUT: |
| 802 | timep |
| 803 | RETVAL |
| 804 | |
| 805 | The next example shows each input parameter evaluated late. |
| 806 | |
| 807 | bool_t |
| 808 | rpcb_gettime(host,timep) |
| 809 | PREINIT: |
| 810 | time_t tt; |
| 811 | INPUT: |
| 812 | char *host |
| 813 | PREINIT: |
| 814 | char *h; |
| 815 | INPUT: |
| 816 | time_t timep |
| 817 | CODE: |
| 818 | h = host; |
| 819 | RETVAL = rpcb_gettime( h, &tt ); |
| 820 | timep = tt; |
| 821 | OUTPUT: |
| 822 | timep |
| 823 | RETVAL |
| 824 | |
| 825 | Since INPUT sections allow declaration of C variables which do not appear |
| 826 | in the parameter list of a subroutine, this may be shortened to: |
| 827 | |
| 828 | bool_t |
| 829 | rpcb_gettime(host,timep) |
| 830 | time_t tt; |
| 831 | char *host; |
| 832 | char *h = host; |
| 833 | time_t timep; |
| 834 | CODE: |
| 835 | RETVAL = rpcb_gettime( h, &tt ); |
| 836 | timep = tt; |
| 837 | OUTPUT: |
| 838 | timep |
| 839 | RETVAL |
| 840 | |
| 841 | (We used our knowledge that input conversion for C<char *> is a "simple" one, |
| 842 | thus C<host> is initialized on the declaration line, and our assignment |
| 843 | C<h = host> is not performed too early. Otherwise one would need to have the |
| 844 | assignment C<h = host> in a CODE: or INIT: section.) |
| 845 | |
| 846 | =head2 The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords |
| 847 | |
| 848 | In the list of parameters for an XSUB, one can precede parameter names |
| 849 | by the C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> keywords. |
| 850 | C<IN> keyword is the default, the other keywords indicate how the Perl |
| 851 | interface should differ from the C interface. |
| 852 | |
| 853 | Parameters preceded by C<OUTLIST>/C<IN_OUTLIST>/C<OUT>/C<IN_OUT> |
| 854 | keywords are considered to be used by the C subroutine I<via |
| 855 | pointers>. C<OUTLIST>/C<OUT> keywords indicate that the C subroutine |
| 856 | does not inspect the memory pointed by this parameter, but will write |
| 857 | through this pointer to provide additional return values. |
| 858 | |
| 859 | Parameters preceded by C<OUTLIST> keyword do not appear in the usage |
| 860 | signature of the generated Perl function. |
| 861 | |
| 862 | Parameters preceded by C<IN_OUTLIST>/C<IN_OUT>/C<OUT> I<do> appear as |
| 863 | parameters to the Perl function. With the exception of |
| 864 | C<OUT>-parameters, these parameters are converted to the corresponding |
| 865 | C type, then pointers to these data are given as arguments to the C |
| 866 | function. It is expected that the C function will write through these |
| 867 | pointers. |
| 868 | |
| 869 | The return list of the generated Perl function consists of the C return value |
| 870 | from the function (unless the XSUB is of C<void> return type or |
| 871 | C<The NO_OUTPUT Keyword> was used) followed by all the C<OUTLIST> |
| 872 | and C<IN_OUTLIST> parameters (in the order of appearance). On the |
| 873 | return from the XSUB the C<IN_OUT>/C<OUT> Perl parameter will be |
| 874 | modified to have the values written by the C function. |
| 875 | |
| 876 | For example, an XSUB |
| 877 | |
| 878 | void |
| 879 | day_month(OUTLIST day, IN unix_time, OUTLIST month) |
| 880 | int day |
| 881 | int unix_time |
| 882 | int month |
| 883 | |
| 884 | should be used from Perl as |
| 885 | |
| 886 | my ($day, $month) = day_month(time); |
| 887 | |
| 888 | The C signature of the corresponding function should be |
| 889 | |
| 890 | void day_month(int *day, int unix_time, int *month); |
| 891 | |
| 892 | The C<IN>/C<OUTLIST>/C<IN_OUTLIST>/C<IN_OUT>/C<OUT> keywords can be |
| 893 | mixed with ANSI-style declarations, as in |
| 894 | |
| 895 | void |
| 896 | day_month(OUTLIST int day, int unix_time, OUTLIST int month) |
| 897 | |
| 898 | (here the optional C<IN> keyword is omitted). |
| 899 | |
| 900 | The C<IN_OUT> parameters are identical with parameters introduced with |
| 901 | L<The & Unary Operator> and put into the C<OUTPUT:> section (see |
| 902 | L<The OUTPUT: Keyword>). The C<IN_OUTLIST> parameters are very similar, |
| 903 | the only difference being that the value C function writes through the |
| 904 | pointer would not modify the Perl parameter, but is put in the output |
| 905 | list. |
| 906 | |
| 907 | The C<OUTLIST>/C<OUT> parameter differ from C<IN_OUTLIST>/C<IN_OUT> |
| 908 | parameters only by the initial value of the Perl parameter not |
| 909 | being read (and not being given to the C function - which gets some |
| 910 | garbage instead). For example, the same C function as above can be |
| 911 | interfaced with as |
| 912 | |
| 913 | void day_month(OUT int day, int unix_time, OUT int month); |
| 914 | |
| 915 | or |
| 916 | |
| 917 | void |
| 918 | day_month(day, unix_time, month) |
| 919 | int &day = NO_INIT |
| 920 | int unix_time |
| 921 | int &month = NO_INIT |
| 922 | OUTPUT: |
| 923 | day |
| 924 | month |
| 925 | |
| 926 | However, the generated Perl function is called in very C-ish style: |
| 927 | |
| 928 | my ($day, $month); |
| 929 | day_month($day, time, $month); |
| 930 | |
| 931 | =head2 The C<length(NAME)> Keyword |
| 932 | |
| 933 | If one of the input arguments to the C function is the length of a string |
| 934 | argument C<NAME>, one can substitute the name of the length-argument by |
| 935 | C<length(NAME)> in the XSUB declaration. This argument must be omitted when |
| 936 | the generated Perl function is called. E.g., |
| 937 | |
| 938 | void |
| 939 | dump_chars(char *s, short l) |
| 940 | { |
| 941 | short n = 0; |
| 942 | while (n < l) { |
| 943 | printf("s[%d] = \"\\%#03o\"\n", n, (int)s[n]); |
| 944 | n++; |
| 945 | } |
| 946 | } |
| 947 | |
| 948 | MODULE = x PACKAGE = x |
| 949 | |
| 950 | void dump_chars(char *s, short length(s)) |
| 951 | |
| 952 | should be called as C<dump_chars($string)>. |
| 953 | |
| 954 | This directive is supported with ANSI-type function declarations only. |
| 955 | |
| 956 | =head2 Variable-length Parameter Lists |
| 957 | |
| 958 | XSUBs can have variable-length parameter lists by specifying an ellipsis |
| 959 | C<(...)> in the parameter list. This use of the ellipsis is similar to that |
| 960 | found in ANSI C. The programmer is able to determine the number of |
| 961 | arguments passed to the XSUB by examining the C<items> variable which the |
| 962 | B<xsubpp> compiler supplies for all XSUBs. By using this mechanism one can |
| 963 | create an XSUB which accepts a list of parameters of unknown length. |
| 964 | |
| 965 | The I<host> parameter for the rpcb_gettime() XSUB can be |
| 966 | optional so the ellipsis can be used to indicate that the |
| 967 | XSUB will take a variable number of parameters. Perl should |
| 968 | be able to call this XSUB with either of the following statements. |
| 969 | |
| 970 | $status = rpcb_gettime( $timep, $host ); |
| 971 | |
| 972 | $status = rpcb_gettime( $timep ); |
| 973 | |
| 974 | The XS code, with ellipsis, follows. |
| 975 | |
| 976 | bool_t |
| 977 | rpcb_gettime(timep, ...) |
| 978 | time_t timep = NO_INIT |
| 979 | PREINIT: |
| 980 | char *host = "localhost"; |
| 981 | CODE: |
| 982 | if( items > 1 ) |
| 983 | host = (char *)SvPV_nolen(ST(1)); |
| 984 | RETVAL = rpcb_gettime( host, &timep ); |
| 985 | OUTPUT: |
| 986 | timep |
| 987 | RETVAL |
| 988 | |
| 989 | =head2 The C_ARGS: Keyword |
| 990 | |
| 991 | The C_ARGS: keyword allows creating of XSUBS which have different |
| 992 | calling sequence from Perl than from C, without a need to write |
| 993 | CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is |
| 994 | put as the argument to the called C function without any change. |
| 995 | |
| 996 | For example, suppose that a C function is declared as |
| 997 | |
| 998 | symbolic nth_derivative(int n, symbolic function, int flags); |
| 999 | |
| 1000 | and that the default flags are kept in a global C variable |
| 1001 | C<default_flags>. Suppose that you want to create an interface which |
| 1002 | is called as |
| 1003 | |
| 1004 | $second_deriv = $function->nth_derivative(2); |
| 1005 | |
| 1006 | To do this, declare the XSUB as |
| 1007 | |
| 1008 | symbolic |
| 1009 | nth_derivative(function, n) |
| 1010 | symbolic function |
| 1011 | int n |
| 1012 | C_ARGS: |
| 1013 | n, function, default_flags |
| 1014 | |
| 1015 | =head2 The PPCODE: Keyword |
| 1016 | |
| 1017 | The PPCODE: keyword is an alternate form of the CODE: keyword and is used |
| 1018 | to tell the B<xsubpp> compiler that the programmer is supplying the code to |
| 1019 | control the argument stack for the XSUBs return values. Occasionally one |
| 1020 | will want an XSUB to return a list of values rather than a single value. |
| 1021 | In these cases one must use PPCODE: and then explicitly push the list of |
| 1022 | values on the stack. The PPCODE: and CODE: keywords should not be used |
| 1023 | together within the same XSUB. |
| 1024 | |
| 1025 | The actual difference between PPCODE: and CODE: sections is in the |
| 1026 | initialization of C<SP> macro (which stands for the I<current> Perl |
| 1027 | stack pointer), and in the handling of data on the stack when returning |
| 1028 | from an XSUB. In CODE: sections SP preserves the value which was on |
| 1029 | entry to the XSUB: SP is on the function pointer (which follows the |
| 1030 | last parameter). In PPCODE: sections SP is moved backward to the |
| 1031 | beginning of the parameter list, which allows C<PUSH*()> macros |
| 1032 | to place output values in the place Perl expects them to be when |
| 1033 | the XSUB returns back to Perl. |
| 1034 | |
| 1035 | The generated trailer for a CODE: section ensures that the number of return |
| 1036 | values Perl will see is either 0 or 1 (depending on the C<void>ness of the |
| 1037 | return value of the C function, and heuristics mentioned in |
| 1038 | L<"The RETVAL Variable">). The trailer generated for a PPCODE: section |
| 1039 | is based on the number of return values and on the number of times |
| 1040 | C<SP> was updated by C<[X]PUSH*()> macros. |
| 1041 | |
| 1042 | Note that macros C<ST(i)>, C<XST_m*()> and C<XSRETURN*()> work equally |
| 1043 | well in CODE: sections and PPCODE: sections. |
| 1044 | |
| 1045 | The following XSUB will call the C rpcb_gettime() function |
| 1046 | and will return its two output values, timep and status, to |
| 1047 | Perl as a single list. |
| 1048 | |
| 1049 | void |
| 1050 | rpcb_gettime(host) |
| 1051 | char *host |
| 1052 | PREINIT: |
| 1053 | time_t timep; |
| 1054 | bool_t status; |
| 1055 | PPCODE: |
| 1056 | status = rpcb_gettime( host, &timep ); |
| 1057 | EXTEND(SP, 2); |
| 1058 | PUSHs(sv_2mortal(newSViv(status))); |
| 1059 | PUSHs(sv_2mortal(newSViv(timep))); |
| 1060 | |
| 1061 | Notice that the programmer must supply the C code necessary |
| 1062 | to have the real rpcb_gettime() function called and to have |
| 1063 | the return values properly placed on the argument stack. |
| 1064 | |
| 1065 | The C<void> return type for this function tells the B<xsubpp> compiler that |
| 1066 | the RETVAL variable is not needed or used and that it should not be created. |
| 1067 | In most scenarios the void return type should be used with the PPCODE: |
| 1068 | directive. |
| 1069 | |
| 1070 | The EXTEND() macro is used to make room on the argument |
| 1071 | stack for 2 return values. The PPCODE: directive causes the |
| 1072 | B<xsubpp> compiler to create a stack pointer available as C<SP>, and it |
| 1073 | is this pointer which is being used in the EXTEND() macro. |
| 1074 | The values are then pushed onto the stack with the PUSHs() |
| 1075 | macro. |
| 1076 | |
| 1077 | Now the rpcb_gettime() function can be used from Perl with |
| 1078 | the following statement. |
| 1079 | |
| 1080 | ($status, $timep) = rpcb_gettime("localhost"); |
| 1081 | |
| 1082 | When handling output parameters with a PPCODE section, be sure to handle |
| 1083 | 'set' magic properly. See L<perlguts> for details about 'set' magic. |
| 1084 | |
| 1085 | =head2 Returning Undef And Empty Lists |
| 1086 | |
| 1087 | Occasionally the programmer will want to return simply |
| 1088 | C<undef> or an empty list if a function fails rather than a |
| 1089 | separate status value. The rpcb_gettime() function offers |
| 1090 | just this situation. If the function succeeds we would like |
| 1091 | to have it return the time and if it fails we would like to |
| 1092 | have undef returned. In the following Perl code the value |
| 1093 | of $timep will either be undef or it will be a valid time. |
| 1094 | |
| 1095 | $timep = rpcb_gettime( "localhost" ); |
| 1096 | |
| 1097 | The following XSUB uses the C<SV *> return type as a mnemonic only, |
| 1098 | and uses a CODE: block to indicate to the compiler |
| 1099 | that the programmer has supplied all the necessary code. The |
| 1100 | sv_newmortal() call will initialize the return value to undef, making that |
| 1101 | the default return value. |
| 1102 | |
| 1103 | SV * |
| 1104 | rpcb_gettime(host) |
| 1105 | char * host |
| 1106 | PREINIT: |
| 1107 | time_t timep; |
| 1108 | bool_t x; |
| 1109 | CODE: |
| 1110 | ST(0) = sv_newmortal(); |
| 1111 | if( rpcb_gettime( host, &timep ) ) |
| 1112 | sv_setnv( ST(0), (double)timep); |
| 1113 | |
| 1114 | The next example demonstrates how one would place an explicit undef in the |
| 1115 | return value, should the need arise. |
| 1116 | |
| 1117 | SV * |
| 1118 | rpcb_gettime(host) |
| 1119 | char * host |
| 1120 | PREINIT: |
| 1121 | time_t timep; |
| 1122 | bool_t x; |
| 1123 | CODE: |
| 1124 | if( rpcb_gettime( host, &timep ) ){ |
| 1125 | ST(0) = sv_newmortal(); |
| 1126 | sv_setnv( ST(0), (double)timep); |
| 1127 | } |
| 1128 | else{ |
| 1129 | ST(0) = &PL_sv_undef; |
| 1130 | } |
| 1131 | |
| 1132 | To return an empty list one must use a PPCODE: block and |
| 1133 | then not push return values on the stack. |
| 1134 | |
| 1135 | void |
| 1136 | rpcb_gettime(host) |
| 1137 | char *host |
| 1138 | PREINIT: |
| 1139 | time_t timep; |
| 1140 | PPCODE: |
| 1141 | if( rpcb_gettime( host, &timep ) ) |
| 1142 | PUSHs(sv_2mortal(newSViv(timep))); |
| 1143 | else{ |
| 1144 | /* Nothing pushed on stack, so an empty |
| 1145 | * list is implicitly returned. */ |
| 1146 | } |
| 1147 | |
| 1148 | Some people may be inclined to include an explicit C<return> in the above |
| 1149 | XSUB, rather than letting control fall through to the end. In those |
| 1150 | situations C<XSRETURN_EMPTY> should be used, instead. This will ensure that |
| 1151 | the XSUB stack is properly adjusted. Consult L<perlapi> for other |
| 1152 | C<XSRETURN> macros. |
| 1153 | |
| 1154 | Since C<XSRETURN_*> macros can be used with CODE blocks as well, one can |
| 1155 | rewrite this example as: |
| 1156 | |
| 1157 | int |
| 1158 | rpcb_gettime(host) |
| 1159 | char *host |
| 1160 | PREINIT: |
| 1161 | time_t timep; |
| 1162 | CODE: |
| 1163 | RETVAL = rpcb_gettime( host, &timep ); |
| 1164 | if (RETVAL == 0) |
| 1165 | XSRETURN_UNDEF; |
| 1166 | OUTPUT: |
| 1167 | RETVAL |
| 1168 | |
| 1169 | In fact, one can put this check into a POSTCALL: section as well. Together |
| 1170 | with PREINIT: simplifications, this leads to: |
| 1171 | |
| 1172 | int |
| 1173 | rpcb_gettime(host) |
| 1174 | char *host |
| 1175 | time_t timep; |
| 1176 | POSTCALL: |
| 1177 | if (RETVAL == 0) |
| 1178 | XSRETURN_UNDEF; |
| 1179 | |
| 1180 | =head2 The REQUIRE: Keyword |
| 1181 | |
| 1182 | The REQUIRE: keyword is used to indicate the minimum version of the |
| 1183 | B<xsubpp> compiler needed to compile the XS module. An XS module which |
| 1184 | contains the following statement will compile with only B<xsubpp> version |
| 1185 | 1.922 or greater: |
| 1186 | |
| 1187 | REQUIRE: 1.922 |
| 1188 | |
| 1189 | =head2 The CLEANUP: Keyword |
| 1190 | |
| 1191 | This keyword can be used when an XSUB requires special cleanup procedures |
| 1192 | before it terminates. When the CLEANUP: keyword is used it must follow |
| 1193 | any CODE:, PPCODE:, or OUTPUT: blocks which are present in the XSUB. The |
| 1194 | code specified for the cleanup block will be added as the last statements |
| 1195 | in the XSUB. |
| 1196 | |
| 1197 | =head2 The POSTCALL: Keyword |
| 1198 | |
| 1199 | This keyword can be used when an XSUB requires special procedures |
| 1200 | executed after the C subroutine call is performed. When the POSTCALL: |
| 1201 | keyword is used it must precede OUTPUT: and CLEANUP: blocks which are |
| 1202 | present in the XSUB. |
| 1203 | |
| 1204 | See examples in L<"The NO_OUTPUT Keyword"> and L<"Returning Undef And Empty Lists">. |
| 1205 | |
| 1206 | The POSTCALL: block does not make a lot of sense when the C subroutine |
| 1207 | call is supplied by user by providing either CODE: or PPCODE: section. |
| 1208 | |
| 1209 | =head2 The BOOT: Keyword |
| 1210 | |
| 1211 | The BOOT: keyword is used to add code to the extension's bootstrap |
| 1212 | function. The bootstrap function is generated by the B<xsubpp> compiler and |
| 1213 | normally holds the statements necessary to register any XSUBs with Perl. |
| 1214 | With the BOOT: keyword the programmer can tell the compiler to add extra |
| 1215 | statements to the bootstrap function. |
| 1216 | |
| 1217 | This keyword may be used any time after the first MODULE keyword and should |
| 1218 | appear on a line by itself. The first blank line after the keyword will |
| 1219 | terminate the code block. |
| 1220 | |
| 1221 | BOOT: |
| 1222 | # The following message will be printed when the |
| 1223 | # bootstrap function executes. |
| 1224 | printf("Hello from the bootstrap!\n"); |
| 1225 | |
| 1226 | =head2 The VERSIONCHECK: Keyword |
| 1227 | |
| 1228 | The VERSIONCHECK: keyword corresponds to B<xsubpp>'s C<-versioncheck> and |
| 1229 | C<-noversioncheck> options. This keyword overrides the command line |
| 1230 | options. Version checking is enabled by default. When version checking is |
| 1231 | enabled the XS module will attempt to verify that its version matches the |
| 1232 | version of the PM module. |
| 1233 | |
| 1234 | To enable version checking: |
| 1235 | |
| 1236 | VERSIONCHECK: ENABLE |
| 1237 | |
| 1238 | To disable version checking: |
| 1239 | |
| 1240 | VERSIONCHECK: DISABLE |
| 1241 | |
| 1242 | Note that if the version of the PM module is an NV (a floating point |
| 1243 | number), it will be stringified with a possible loss of precision |
| 1244 | (currently chopping to nine decimal places) so that it may not match |
| 1245 | the version of the XS module anymore. Quoting the $VERSION declaration |
| 1246 | to make it a string is recommended if long version numbers are used. |
| 1247 | |
| 1248 | =head2 The PROTOTYPES: Keyword |
| 1249 | |
| 1250 | The PROTOTYPES: keyword corresponds to B<xsubpp>'s C<-prototypes> and |
| 1251 | C<-noprototypes> options. This keyword overrides the command line options. |
| 1252 | Prototypes are enabled by default. When prototypes are enabled XSUBs will |
| 1253 | be given Perl prototypes. This keyword may be used multiple times in an XS |
| 1254 | module to enable and disable prototypes for different parts of the module. |
| 1255 | |
| 1256 | To enable prototypes: |
| 1257 | |
| 1258 | PROTOTYPES: ENABLE |
| 1259 | |
| 1260 | To disable prototypes: |
| 1261 | |
| 1262 | PROTOTYPES: DISABLE |
| 1263 | |
| 1264 | =head2 The PROTOTYPE: Keyword |
| 1265 | |
| 1266 | This keyword is similar to the PROTOTYPES: keyword above but can be used to |
| 1267 | force B<xsubpp> to use a specific prototype for the XSUB. This keyword |
| 1268 | overrides all other prototype options and keywords but affects only the |
| 1269 | current XSUB. Consult L<perlsub/Prototypes> for information about Perl |
| 1270 | prototypes. |
| 1271 | |
| 1272 | bool_t |
| 1273 | rpcb_gettime(timep, ...) |
| 1274 | time_t timep = NO_INIT |
| 1275 | PROTOTYPE: $;$ |
| 1276 | PREINIT: |
| 1277 | char *host = "localhost"; |
| 1278 | CODE: |
| 1279 | if( items > 1 ) |
| 1280 | host = (char *)SvPV_nolen(ST(1)); |
| 1281 | RETVAL = rpcb_gettime( host, &timep ); |
| 1282 | OUTPUT: |
| 1283 | timep |
| 1284 | RETVAL |
| 1285 | |
| 1286 | If the prototypes are enabled, you can disable it locally for a given |
| 1287 | XSUB as in the following example: |
| 1288 | |
| 1289 | void |
| 1290 | rpcb_gettime_noproto() |
| 1291 | PROTOTYPE: DISABLE |
| 1292 | ... |
| 1293 | |
| 1294 | =head2 The ALIAS: Keyword |
| 1295 | |
| 1296 | The ALIAS: keyword allows an XSUB to have two or more unique Perl names |
| 1297 | and to know which of those names was used when it was invoked. The Perl |
| 1298 | names may be fully-qualified with package names. Each alias is given an |
| 1299 | index. The compiler will setup a variable called C<ix> which contain the |
| 1300 | index of the alias which was used. When the XSUB is called with its |
| 1301 | declared name C<ix> will be 0. |
| 1302 | |
| 1303 | The following example will create aliases C<FOO::gettime()> and |
| 1304 | C<BAR::getit()> for this function. |
| 1305 | |
| 1306 | bool_t |
| 1307 | rpcb_gettime(host,timep) |
| 1308 | char *host |
| 1309 | time_t &timep |
| 1310 | ALIAS: |
| 1311 | FOO::gettime = 1 |
| 1312 | BAR::getit = 2 |
| 1313 | INIT: |
| 1314 | printf("# ix = %d\n", ix ); |
| 1315 | OUTPUT: |
| 1316 | timep |
| 1317 | |
| 1318 | =head2 The OVERLOAD: Keyword |
| 1319 | |
| 1320 | Instead of writing an overloaded interface using pure Perl, you |
| 1321 | can also use the OVERLOAD keyword to define additional Perl names |
| 1322 | for your functions (like the ALIAS: keyword above). However, the |
| 1323 | overloaded functions must be defined with three parameters (except |
| 1324 | for the nomethod() function which needs four parameters). If any |
| 1325 | function has the OVERLOAD: keyword, several additional lines |
| 1326 | will be defined in the c file generated by xsubpp in order to |
| 1327 | register with the overload magic. |
| 1328 | |
| 1329 | Since blessed objects are actually stored as RV's, it is useful |
| 1330 | to use the typemap features to preprocess parameters and extract |
| 1331 | the actual SV stored within the blessed RV. See the sample for |
| 1332 | T_PTROBJ_SPECIAL below. |
| 1333 | |
| 1334 | To use the OVERLOAD: keyword, create an XS function which takes |
| 1335 | three input parameters ( or use the c style '...' definition) like |
| 1336 | this: |
| 1337 | |
| 1338 | SV * |
| 1339 | cmp (lobj, robj, swap) |
| 1340 | My_Module_obj lobj |
| 1341 | My_Module_obj robj |
| 1342 | IV swap |
| 1343 | OVERLOAD: cmp <=> |
| 1344 | { /* function defined here */} |
| 1345 | |
| 1346 | In this case, the function will overload both of the three way |
| 1347 | comparison operators. For all overload operations using non-alpha |
| 1348 | characters, you must type the parameter without quoting, separating |
| 1349 | multiple overloads with whitespace. Note that "" (the stringify |
| 1350 | overload) should be entered as \"\" (i.e. escaped). |
| 1351 | |
| 1352 | =head2 The FALLBACK: Keyword |
| 1353 | |
| 1354 | In addition to the OVERLOAD keyword, if you need to control how |
| 1355 | Perl autogenerates missing overloaded operators, you can set the |
| 1356 | FALLBACK keyword in the module header section, like this: |
| 1357 | |
| 1358 | MODULE = RPC PACKAGE = RPC |
| 1359 | |
| 1360 | FALLBACK: TRUE |
| 1361 | ... |
| 1362 | |
| 1363 | where FALLBACK can take any of the three values TRUE, FALSE, or |
| 1364 | UNDEF. If you do not set any FALLBACK value when using OVERLOAD, |
| 1365 | it defaults to UNDEF. FALLBACK is not used except when one or |
| 1366 | more functions using OVERLOAD have been defined. Please see |
| 1367 | L<overload/fallback> for more details. |
| 1368 | |
| 1369 | =head2 The INTERFACE: Keyword |
| 1370 | |
| 1371 | This keyword declares the current XSUB as a keeper of the given |
| 1372 | calling signature. If some text follows this keyword, it is |
| 1373 | considered as a list of functions which have this signature, and |
| 1374 | should be attached to the current XSUB. |
| 1375 | |
| 1376 | For example, if you have 4 C functions multiply(), divide(), add(), |
| 1377 | subtract() all having the signature: |
| 1378 | |
| 1379 | symbolic f(symbolic, symbolic); |
| 1380 | |
| 1381 | you can make them all to use the same XSUB using this: |
| 1382 | |
| 1383 | symbolic |
| 1384 | interface_s_ss(arg1, arg2) |
| 1385 | symbolic arg1 |
| 1386 | symbolic arg2 |
| 1387 | INTERFACE: |
| 1388 | multiply divide |
| 1389 | add subtract |
| 1390 | |
| 1391 | (This is the complete XSUB code for 4 Perl functions!) Four generated |
| 1392 | Perl function share names with corresponding C functions. |
| 1393 | |
| 1394 | The advantage of this approach comparing to ALIAS: keyword is that there |
| 1395 | is no need to code a switch statement, each Perl function (which shares |
| 1396 | the same XSUB) knows which C function it should call. Additionally, one |
| 1397 | can attach an extra function remainder() at runtime by using |
| 1398 | |
| 1399 | CV *mycv = newXSproto("Symbolic::remainder", |
| 1400 | XS_Symbolic_interface_s_ss, __FILE__, "$$"); |
| 1401 | XSINTERFACE_FUNC_SET(mycv, remainder); |
| 1402 | |
| 1403 | say, from another XSUB. (This example supposes that there was no |
| 1404 | INTERFACE_MACRO: section, otherwise one needs to use something else instead of |
| 1405 | C<XSINTERFACE_FUNC_SET>, see the next section.) |
| 1406 | |
| 1407 | =head2 The INTERFACE_MACRO: Keyword |
| 1408 | |
| 1409 | This keyword allows one to define an INTERFACE using a different way |
| 1410 | to extract a function pointer from an XSUB. The text which follows |
| 1411 | this keyword should give the name of macros which would extract/set a |
| 1412 | function pointer. The extractor macro is given return type, C<CV*>, |
| 1413 | and C<XSANY.any_dptr> for this C<CV*>. The setter macro is given cv, |
| 1414 | and the function pointer. |
| 1415 | |
| 1416 | The default value is C<XSINTERFACE_FUNC> and C<XSINTERFACE_FUNC_SET>. |
| 1417 | An INTERFACE keyword with an empty list of functions can be omitted if |
| 1418 | INTERFACE_MACRO keyword is used. |
| 1419 | |
| 1420 | Suppose that in the previous example functions pointers for |
| 1421 | multiply(), divide(), add(), subtract() are kept in a global C array |
| 1422 | C<fp[]> with offsets being C<multiply_off>, C<divide_off>, C<add_off>, |
| 1423 | C<subtract_off>. Then one can use |
| 1424 | |
| 1425 | #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \ |
| 1426 | ((XSINTERFACE_CVT_ANON(ret))fp[CvXSUBANY(cv).any_i32]) |
| 1427 | #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \ |
| 1428 | CvXSUBANY(cv).any_i32 = CAT2( f, _off ) |
| 1429 | |
| 1430 | in C section, |
| 1431 | |
| 1432 | symbolic |
| 1433 | interface_s_ss(arg1, arg2) |
| 1434 | symbolic arg1 |
| 1435 | symbolic arg2 |
| 1436 | INTERFACE_MACRO: |
| 1437 | XSINTERFACE_FUNC_BYOFFSET |
| 1438 | XSINTERFACE_FUNC_BYOFFSET_set |
| 1439 | INTERFACE: |
| 1440 | multiply divide |
| 1441 | add subtract |
| 1442 | |
| 1443 | in XSUB section. |
| 1444 | |
| 1445 | =head2 The INCLUDE: Keyword |
| 1446 | |
| 1447 | This keyword can be used to pull other files into the XS module. The other |
| 1448 | files may have XS code. INCLUDE: can also be used to run a command to |
| 1449 | generate the XS code to be pulled into the module. |
| 1450 | |
| 1451 | The file F<Rpcb1.xsh> contains our C<rpcb_gettime()> function: |
| 1452 | |
| 1453 | bool_t |
| 1454 | rpcb_gettime(host,timep) |
| 1455 | char *host |
| 1456 | time_t &timep |
| 1457 | OUTPUT: |
| 1458 | timep |
| 1459 | |
| 1460 | The XS module can use INCLUDE: to pull that file into it. |
| 1461 | |
| 1462 | INCLUDE: Rpcb1.xsh |
| 1463 | |
| 1464 | If the parameters to the INCLUDE: keyword are followed by a pipe (C<|>) then |
| 1465 | the compiler will interpret the parameters as a command. This feature is |
| 1466 | mildly deprecated in favour of the C<INCLUDE_COMMAND:> directive, as documented |
| 1467 | below. |
| 1468 | |
| 1469 | INCLUDE: cat Rpcb1.xsh | |
| 1470 | |
| 1471 | Do not use this to run perl: C<INCLUDE: perl |> will run the perl that |
| 1472 | happens to be the first in your path and not necessarily the same perl that is |
| 1473 | used to run C<xsubpp>. See L<"The INCLUDE_COMMAND: Keyword">. |
| 1474 | |
| 1475 | =head2 The INCLUDE_COMMAND: Keyword |
| 1476 | |
| 1477 | Runs the supplied command and includes its output into the current XS |
| 1478 | document. C<INCLUDE_COMMAND> assigns special meaning to the C<$^X> token |
| 1479 | in that it runs the same perl interpreter that is running C<xsubpp>: |
| 1480 | |
| 1481 | INCLUDE_COMMAND: cat Rpcb1.xsh |
| 1482 | |
| 1483 | INCLUDE_COMMAND: $^X -e ... |
| 1484 | |
| 1485 | =head2 The CASE: Keyword |
| 1486 | |
| 1487 | The CASE: keyword allows an XSUB to have multiple distinct parts with each |
| 1488 | part acting as a virtual XSUB. CASE: is greedy and if it is used then all |
| 1489 | other XS keywords must be contained within a CASE:. This means nothing may |
| 1490 | precede the first CASE: in the XSUB and anything following the last CASE: is |
| 1491 | included in that case. |
| 1492 | |
| 1493 | A CASE: might switch via a parameter of the XSUB, via the C<ix> ALIAS: |
| 1494 | variable (see L<"The ALIAS: Keyword">), or maybe via the C<items> variable |
| 1495 | (see L<"Variable-length Parameter Lists">). The last CASE: becomes the |
| 1496 | B<default> case if it is not associated with a conditional. The following |
| 1497 | example shows CASE switched via C<ix> with a function C<rpcb_gettime()> |
| 1498 | having an alias C<x_gettime()>. When the function is called as |
| 1499 | C<rpcb_gettime()> its parameters are the usual C<(char *host, time_t *timep)>, |
| 1500 | but when the function is called as C<x_gettime()> its parameters are |
| 1501 | reversed, C<(time_t *timep, char *host)>. |
| 1502 | |
| 1503 | long |
| 1504 | rpcb_gettime(a,b) |
| 1505 | CASE: ix == 1 |
| 1506 | ALIAS: |
| 1507 | x_gettime = 1 |
| 1508 | INPUT: |
| 1509 | # 'a' is timep, 'b' is host |
| 1510 | char *b |
| 1511 | time_t a = NO_INIT |
| 1512 | CODE: |
| 1513 | RETVAL = rpcb_gettime( b, &a ); |
| 1514 | OUTPUT: |
| 1515 | a |
| 1516 | RETVAL |
| 1517 | CASE: |
| 1518 | # 'a' is host, 'b' is timep |
| 1519 | char *a |
| 1520 | time_t &b = NO_INIT |
| 1521 | OUTPUT: |
| 1522 | b |
| 1523 | RETVAL |
| 1524 | |
| 1525 | That function can be called with either of the following statements. Note |
| 1526 | the different argument lists. |
| 1527 | |
| 1528 | $status = rpcb_gettime( $host, $timep ); |
| 1529 | |
| 1530 | $status = x_gettime( $timep, $host ); |
| 1531 | |
| 1532 | =head2 The EXPORT_XSUB_SYMBOLS: Keyword |
| 1533 | |
| 1534 | The EXPORT_XSUB_SYMBOLS: keyword is likely something you will never need. |
| 1535 | In perl versions earlier than 5.16.0, this keyword does nothing. Starting |
| 1536 | with 5.16, XSUB symbols are no longer exported by default. That is, they |
| 1537 | are C<static> functions. If you include |
| 1538 | |
| 1539 | EXPORT_XSUB_SYMBOLS: ENABLE |
| 1540 | |
| 1541 | in your XS code, the XSUBs following this line will not be declared C<static>. |
| 1542 | You can later disable this with |
| 1543 | |
| 1544 | EXPORT_XSUB_SYMBOLS: DISABLE |
| 1545 | |
| 1546 | which, again, is the default that you should probably never change. |
| 1547 | You cannot use this keyword on versions of perl before 5.16 to make |
| 1548 | XSUBs C<static>. |
| 1549 | |
| 1550 | =head2 The & Unary Operator |
| 1551 | |
| 1552 | The C<&> unary operator in the INPUT: section is used to tell B<xsubpp> |
| 1553 | that it should convert a Perl value to/from C using the C type to the left |
| 1554 | of C<&>, but provide a pointer to this value when the C function is called. |
| 1555 | |
| 1556 | This is useful to avoid a CODE: block for a C function which takes a parameter |
| 1557 | by reference. Typically, the parameter should be not a pointer type (an |
| 1558 | C<int> or C<long> but not an C<int*> or C<long*>). |
| 1559 | |
| 1560 | The following XSUB will generate incorrect C code. The B<xsubpp> compiler will |
| 1561 | turn this into code which calls C<rpcb_gettime()> with parameters C<(char |
| 1562 | *host, time_t timep)>, but the real C<rpcb_gettime()> wants the C<timep> |
| 1563 | parameter to be of type C<time_t*> rather than C<time_t>. |
| 1564 | |
| 1565 | bool_t |
| 1566 | rpcb_gettime(host,timep) |
| 1567 | char *host |
| 1568 | time_t timep |
| 1569 | OUTPUT: |
| 1570 | timep |
| 1571 | |
| 1572 | That problem is corrected by using the C<&> operator. The B<xsubpp> compiler |
| 1573 | will now turn this into code which calls C<rpcb_gettime()> correctly with |
| 1574 | parameters C<(char *host, time_t *timep)>. It does this by carrying the |
| 1575 | C<&> through, so the function call looks like C<rpcb_gettime(host, &timep)>. |
| 1576 | |
| 1577 | bool_t |
| 1578 | rpcb_gettime(host,timep) |
| 1579 | char *host |
| 1580 | time_t &timep |
| 1581 | OUTPUT: |
| 1582 | timep |
| 1583 | |
| 1584 | =head2 Inserting POD, Comments and C Preprocessor Directives |
| 1585 | |
| 1586 | C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:, |
| 1587 | PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions. |
| 1588 | Comments are allowed anywhere after the MODULE keyword. The compiler will |
| 1589 | pass the preprocessor directives through untouched and will remove the |
| 1590 | commented lines. POD documentation is allowed at any point, both in the |
| 1591 | C and XS language sections. POD must be terminated with a C<=cut> command; |
| 1592 | C<xsubpp> will exit with an error if it does not. It is very unlikely that |
| 1593 | human generated C code will be mistaken for POD, as most indenting styles |
| 1594 | result in whitespace in front of any line starting with C<=>. Machine |
| 1595 | generated XS files may fall into this trap unless care is taken to |
| 1596 | ensure that a space breaks the sequence "\n=". |
| 1597 | |
| 1598 | Comments can be added to XSUBs by placing a C<#> as the first |
| 1599 | non-whitespace of a line. Care should be taken to avoid making the |
| 1600 | comment look like a C preprocessor directive, lest it be interpreted as |
| 1601 | such. The simplest way to prevent this is to put whitespace in front of |
| 1602 | the C<#>. |
| 1603 | |
| 1604 | If you use preprocessor directives to choose one of two |
| 1605 | versions of a function, use |
| 1606 | |
| 1607 | #if ... version1 |
| 1608 | #else /* ... version2 */ |
| 1609 | #endif |
| 1610 | |
| 1611 | and not |
| 1612 | |
| 1613 | #if ... version1 |
| 1614 | #endif |
| 1615 | #if ... version2 |
| 1616 | #endif |
| 1617 | |
| 1618 | because otherwise B<xsubpp> will believe that you made a duplicate |
| 1619 | definition of the function. Also, put a blank line before the |
| 1620 | #else/#endif so it will not be seen as part of the function body. |
| 1621 | |
| 1622 | =head2 Using XS With C++ |
| 1623 | |
| 1624 | If an XSUB name contains C<::>, it is considered to be a C++ method. |
| 1625 | The generated Perl function will assume that |
| 1626 | its first argument is an object pointer. The object pointer |
| 1627 | will be stored in a variable called THIS. The object should |
| 1628 | have been created by C++ with the new() function and should |
| 1629 | be blessed by Perl with the sv_setref_pv() macro. The |
| 1630 | blessing of the object by Perl can be handled by a typemap. An example |
| 1631 | typemap is shown at the end of this section. |
| 1632 | |
| 1633 | If the return type of the XSUB includes C<static>, the method is considered |
| 1634 | to be a static method. It will call the C++ |
| 1635 | function using the class::method() syntax. If the method is not static |
| 1636 | the function will be called using the THIS-E<gt>method() syntax. |
| 1637 | |
| 1638 | The next examples will use the following C++ class. |
| 1639 | |
| 1640 | class color { |
| 1641 | public: |
| 1642 | color(); |
| 1643 | ~color(); |
| 1644 | int blue(); |
| 1645 | void set_blue( int ); |
| 1646 | |
| 1647 | private: |
| 1648 | int c_blue; |
| 1649 | }; |
| 1650 | |
| 1651 | The XSUBs for the blue() and set_blue() methods are defined with the class |
| 1652 | name but the parameter for the object (THIS, or "self") is implicit and is |
| 1653 | not listed. |
| 1654 | |
| 1655 | int |
| 1656 | color::blue() |
| 1657 | |
| 1658 | void |
| 1659 | color::set_blue( val ) |
| 1660 | int val |
| 1661 | |
| 1662 | Both Perl functions will expect an object as the first parameter. In the |
| 1663 | generated C++ code the object is called C<THIS>, and the method call will |
| 1664 | be performed on this object. So in the C++ code the blue() and set_blue() |
| 1665 | methods will be called as this: |
| 1666 | |
| 1667 | RETVAL = THIS->blue(); |
| 1668 | |
| 1669 | THIS->set_blue( val ); |
| 1670 | |
| 1671 | You could also write a single get/set method using an optional argument: |
| 1672 | |
| 1673 | int |
| 1674 | color::blue( val = NO_INIT ) |
| 1675 | int val |
| 1676 | PROTOTYPE $;$ |
| 1677 | CODE: |
| 1678 | if (items > 1) |
| 1679 | THIS->set_blue( val ); |
| 1680 | RETVAL = THIS->blue(); |
| 1681 | OUTPUT: |
| 1682 | RETVAL |
| 1683 | |
| 1684 | If the function's name is B<DESTROY> then the C++ C<delete> function will be |
| 1685 | called and C<THIS> will be given as its parameter. The generated C++ code for |
| 1686 | |
| 1687 | void |
| 1688 | color::DESTROY() |
| 1689 | |
| 1690 | will look like this: |
| 1691 | |
| 1692 | color *THIS = ...; // Initialized as in typemap |
| 1693 | |
| 1694 | delete THIS; |
| 1695 | |
| 1696 | If the function's name is B<new> then the C++ C<new> function will be called |
| 1697 | to create a dynamic C++ object. The XSUB will expect the class name, which |
| 1698 | will be kept in a variable called C<CLASS>, to be given as the first |
| 1699 | argument. |
| 1700 | |
| 1701 | color * |
| 1702 | color::new() |
| 1703 | |
| 1704 | The generated C++ code will call C<new>. |
| 1705 | |
| 1706 | RETVAL = new color(); |
| 1707 | |
| 1708 | The following is an example of a typemap that could be used for this C++ |
| 1709 | example. |
| 1710 | |
| 1711 | TYPEMAP |
| 1712 | color * O_OBJECT |
| 1713 | |
| 1714 | OUTPUT |
| 1715 | # The Perl object is blessed into 'CLASS', which should be a |
| 1716 | # char* having the name of the package for the blessing. |
| 1717 | O_OBJECT |
| 1718 | sv_setref_pv( $arg, CLASS, (void*)$var ); |
| 1719 | |
| 1720 | INPUT |
| 1721 | O_OBJECT |
| 1722 | if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) |
| 1723 | $var = ($type)SvIV((SV*)SvRV( $arg )); |
| 1724 | else{ |
| 1725 | warn( \"${Package}::$func_name() -- $var is not a blessed SV reference\" ); |
| 1726 | XSRETURN_UNDEF; |
| 1727 | } |
| 1728 | |
| 1729 | =head2 Interface Strategy |
| 1730 | |
| 1731 | When designing an interface between Perl and a C library a straight |
| 1732 | translation from C to XS (such as created by C<h2xs -x>) is often sufficient. |
| 1733 | However, sometimes the interface will look |
| 1734 | very C-like and occasionally nonintuitive, especially when the C function |
| 1735 | modifies one of its parameters, or returns failure inband (as in "negative |
| 1736 | return values mean failure"). In cases where the programmer wishes to |
| 1737 | create a more Perl-like interface the following strategy may help to |
| 1738 | identify the more critical parts of the interface. |
| 1739 | |
| 1740 | Identify the C functions with input/output or output parameters. The XSUBs for |
| 1741 | these functions may be able to return lists to Perl. |
| 1742 | |
| 1743 | Identify the C functions which use some inband info as an indication |
| 1744 | of failure. They may be |
| 1745 | candidates to return undef or an empty list in case of failure. If the |
| 1746 | failure may be detected without a call to the C function, you may want to use |
| 1747 | an INIT: section to report the failure. For failures detectable after the C |
| 1748 | function returns one may want to use a POSTCALL: section to process the |
| 1749 | failure. In more complicated cases use CODE: or PPCODE: sections. |
| 1750 | |
| 1751 | If many functions use the same failure indication based on the return value, |
| 1752 | you may want to create a special typedef to handle this situation. Put |
| 1753 | |
| 1754 | typedef int negative_is_failure; |
| 1755 | |
| 1756 | near the beginning of XS file, and create an OUTPUT typemap entry |
| 1757 | for C<negative_is_failure> which converts negative values to C<undef>, or |
| 1758 | maybe croak()s. After this the return value of type C<negative_is_failure> |
| 1759 | will create more Perl-like interface. |
| 1760 | |
| 1761 | Identify which values are used by only the C and XSUB functions |
| 1762 | themselves, say, when a parameter to a function should be a contents of a |
| 1763 | global variable. If Perl does not need to access the contents of the value |
| 1764 | then it may not be necessary to provide a translation for that value |
| 1765 | from C to Perl. |
| 1766 | |
| 1767 | Identify the pointers in the C function parameter lists and return |
| 1768 | values. Some pointers may be used to implement input/output or |
| 1769 | output parameters, they can be handled in XS with the C<&> unary operator, |
| 1770 | and, possibly, using the NO_INIT keyword. |
| 1771 | Some others will require handling of types like C<int *>, and one needs |
| 1772 | to decide what a useful Perl translation will do in such a case. When |
| 1773 | the semantic is clear, it is advisable to put the translation into a typemap |
| 1774 | file. |
| 1775 | |
| 1776 | Identify the structures used by the C functions. In many |
| 1777 | cases it may be helpful to use the T_PTROBJ typemap for |
| 1778 | these structures so they can be manipulated by Perl as |
| 1779 | blessed objects. (This is handled automatically by C<h2xs -x>.) |
| 1780 | |
| 1781 | If the same C type is used in several different contexts which require |
| 1782 | different translations, C<typedef> several new types mapped to this C type, |
| 1783 | and create separate F<typemap> entries for these new types. Use these |
| 1784 | types in declarations of return type and parameters to XSUBs. |
| 1785 | |
| 1786 | =head2 Perl Objects And C Structures |
| 1787 | |
| 1788 | When dealing with C structures one should select either |
| 1789 | B<T_PTROBJ> or B<T_PTRREF> for the XS type. Both types are |
| 1790 | designed to handle pointers to complex objects. The |
| 1791 | T_PTRREF type will allow the Perl object to be unblessed |
| 1792 | while the T_PTROBJ type requires that the object be blessed. |
| 1793 | By using T_PTROBJ one can achieve a form of type-checking |
| 1794 | because the XSUB will attempt to verify that the Perl object |
| 1795 | is of the expected type. |
| 1796 | |
| 1797 | The following XS code shows the getnetconfigent() function which is used |
| 1798 | with ONC+ TIRPC. The getnetconfigent() function will return a pointer to a |
| 1799 | C structure and has the C prototype shown below. The example will |
| 1800 | demonstrate how the C pointer will become a Perl reference. Perl will |
| 1801 | consider this reference to be a pointer to a blessed object and will |
| 1802 | attempt to call a destructor for the object. A destructor will be |
| 1803 | provided in the XS source to free the memory used by getnetconfigent(). |
| 1804 | Destructors in XS can be created by specifying an XSUB function whose name |
| 1805 | ends with the word B<DESTROY>. XS destructors can be used to free memory |
| 1806 | which may have been malloc'd by another XSUB. |
| 1807 | |
| 1808 | struct netconfig *getnetconfigent(const char *netid); |
| 1809 | |
| 1810 | A C<typedef> will be created for C<struct netconfig>. The Perl |
| 1811 | object will be blessed in a class matching the name of the C |
| 1812 | type, with the tag C<Ptr> appended, and the name should not |
| 1813 | have embedded spaces if it will be a Perl package name. The |
| 1814 | destructor will be placed in a class corresponding to the |
| 1815 | class of the object and the PREFIX keyword will be used to |
| 1816 | trim the name to the word DESTROY as Perl will expect. |
| 1817 | |
| 1818 | typedef struct netconfig Netconfig; |
| 1819 | |
| 1820 | MODULE = RPC PACKAGE = RPC |
| 1821 | |
| 1822 | Netconfig * |
| 1823 | getnetconfigent(netid) |
| 1824 | char *netid |
| 1825 | |
| 1826 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
| 1827 | |
| 1828 | void |
| 1829 | rpcb_DESTROY(netconf) |
| 1830 | Netconfig *netconf |
| 1831 | CODE: |
| 1832 | printf("Now in NetconfigPtr::DESTROY\n"); |
| 1833 | free( netconf ); |
| 1834 | |
| 1835 | This example requires the following typemap entry. Consult the typemap |
| 1836 | section for more information about adding new typemaps for an extension. |
| 1837 | |
| 1838 | TYPEMAP |
| 1839 | Netconfig * T_PTROBJ |
| 1840 | |
| 1841 | This example will be used with the following Perl statements. |
| 1842 | |
| 1843 | use RPC; |
| 1844 | $netconf = getnetconfigent("udp"); |
| 1845 | |
| 1846 | When Perl destroys the object referenced by $netconf it will send the |
| 1847 | object to the supplied XSUB DESTROY function. Perl cannot determine, and |
| 1848 | does not care, that this object is a C struct and not a Perl object. In |
| 1849 | this sense, there is no difference between the object created by the |
| 1850 | getnetconfigent() XSUB and an object created by a normal Perl subroutine. |
| 1851 | |
| 1852 | =head2 The Typemap |
| 1853 | |
| 1854 | The typemap is a collection of code fragments which are used by the B<xsubpp> |
| 1855 | compiler to map C function parameters and values to Perl values. The |
| 1856 | typemap file may consist of three sections labelled C<TYPEMAP>, C<INPUT>, and |
| 1857 | C<OUTPUT>. An unlabelled initial section is assumed to be a C<TYPEMAP> |
| 1858 | section. The INPUT section tells |
| 1859 | the compiler how to translate Perl values |
| 1860 | into variables of certain C types. The OUTPUT section tells the compiler |
| 1861 | how to translate the values from certain C types into values Perl can |
| 1862 | understand. The TYPEMAP section tells the compiler which of the INPUT and |
| 1863 | OUTPUT code fragments should be used to map a given C type to a Perl value. |
| 1864 | The section labels C<TYPEMAP>, C<INPUT>, or C<OUTPUT> must begin |
| 1865 | in the first column on a line by themselves, and must be in uppercase. |
| 1866 | |
| 1867 | The default typemap in the F<lib/ExtUtils> directory of the Perl source |
| 1868 | contains many useful types which can be used by Perl extensions. Some |
| 1869 | extensions define additional typemaps which they keep in their own directory. |
| 1870 | These additional typemaps may reference INPUT and OUTPUT maps in the main |
| 1871 | typemap. The B<xsubpp> compiler will allow the extension's own typemap to |
| 1872 | override any mappings which are in the default typemap. Instead of using |
| 1873 | an additional F<typemap> file, typemaps may be embedded verbatim in XS |
| 1874 | with a heredoc-like syntax. See the documentation on the C<TYPEMAP:> XS |
| 1875 | keyword. |
| 1876 | |
| 1877 | Most extensions which require a custom typemap will need only the TYPEMAP |
| 1878 | section of the typemap file. The custom typemap used in the |
| 1879 | getnetconfigent() example shown earlier demonstrates what may be the typical |
| 1880 | use of extension typemaps. That typemap is used to equate a C structure |
| 1881 | with the T_PTROBJ typemap. The typemap used by getnetconfigent() is shown |
| 1882 | here. Note that the C type is separated from the XS type with a tab and |
| 1883 | that the C unary operator C<*> is considered to be a part of the C type name. |
| 1884 | |
| 1885 | TYPEMAP |
| 1886 | Netconfig *<tab>T_PTROBJ |
| 1887 | |
| 1888 | Here's a more complicated example: suppose that you wanted C<struct |
| 1889 | netconfig> to be blessed into the class C<Net::Config>. One way to do |
| 1890 | this is to use underscores (_) to separate package names, as follows: |
| 1891 | |
| 1892 | typedef struct netconfig * Net_Config; |
| 1893 | |
| 1894 | And then provide a typemap entry C<T_PTROBJ_SPECIAL> that maps underscores to |
| 1895 | double-colons (::), and declare C<Net_Config> to be of that type: |
| 1896 | |
| 1897 | |
| 1898 | TYPEMAP |
| 1899 | Net_Config T_PTROBJ_SPECIAL |
| 1900 | |
| 1901 | INPUT |
| 1902 | T_PTROBJ_SPECIAL |
| 1903 | if (sv_derived_from($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\")) { |
| 1904 | IV tmp = SvIV((SV*)SvRV($arg)); |
| 1905 | $var = INT2PTR($type, tmp); |
| 1906 | } |
| 1907 | else |
| 1908 | croak(\"$var is not of type ${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\") |
| 1909 | |
| 1910 | OUTPUT |
| 1911 | T_PTROBJ_SPECIAL |
| 1912 | sv_setref_pv($arg, \"${(my $ntt=$ntype)=~s/_/::/g;\$ntt}\", |
| 1913 | (void*)$var); |
| 1914 | |
| 1915 | The INPUT and OUTPUT sections substitute underscores for double-colons |
| 1916 | on the fly, giving the desired effect. This example demonstrates some |
| 1917 | of the power and versatility of the typemap facility. |
| 1918 | |
| 1919 | The INT2PTR macro (defined in perl.h) casts an integer to a pointer, |
| 1920 | of a given type, taking care of the possible different size of integers |
| 1921 | and pointers. There are also PTR2IV, PTR2UV, PTR2NV macros, |
| 1922 | to map the other way, which may be useful in OUTPUT sections. |
| 1923 | |
| 1924 | =head2 Safely Storing Static Data in XS |
| 1925 | |
| 1926 | Starting with Perl 5.8, a macro framework has been defined to allow |
| 1927 | static data to be safely stored in XS modules that will be accessed from |
| 1928 | a multi-threaded Perl. |
| 1929 | |
| 1930 | Although primarily designed for use with multi-threaded Perl, the macros |
| 1931 | have been designed so that they will work with non-threaded Perl as well. |
| 1932 | |
| 1933 | It is therefore strongly recommended that these macros be used by all |
| 1934 | XS modules that make use of static data. |
| 1935 | |
| 1936 | The easiest way to get a template set of macros to use is by specifying |
| 1937 | the C<-g> (C<--global>) option with h2xs (see L<h2xs>). |
| 1938 | |
| 1939 | Below is an example module that makes use of the macros. |
| 1940 | |
| 1941 | #include "EXTERN.h" |
| 1942 | #include "perl.h" |
| 1943 | #include "XSUB.h" |
| 1944 | |
| 1945 | /* Global Data */ |
| 1946 | |
| 1947 | #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION |
| 1948 | |
| 1949 | typedef struct { |
| 1950 | int count; |
| 1951 | char name[3][100]; |
| 1952 | } my_cxt_t; |
| 1953 | |
| 1954 | START_MY_CXT |
| 1955 | |
| 1956 | MODULE = BlindMice PACKAGE = BlindMice |
| 1957 | |
| 1958 | BOOT: |
| 1959 | { |
| 1960 | MY_CXT_INIT; |
| 1961 | MY_CXT.count = 0; |
| 1962 | strcpy(MY_CXT.name[0], "None"); |
| 1963 | strcpy(MY_CXT.name[1], "None"); |
| 1964 | strcpy(MY_CXT.name[2], "None"); |
| 1965 | } |
| 1966 | |
| 1967 | int |
| 1968 | newMouse(char * name) |
| 1969 | char * name; |
| 1970 | PREINIT: |
| 1971 | dMY_CXT; |
| 1972 | CODE: |
| 1973 | if (MY_CXT.count >= 3) { |
| 1974 | warn("Already have 3 blind mice"); |
| 1975 | RETVAL = 0; |
| 1976 | } |
| 1977 | else { |
| 1978 | RETVAL = ++ MY_CXT.count; |
| 1979 | strcpy(MY_CXT.name[MY_CXT.count - 1], name); |
| 1980 | } |
| 1981 | |
| 1982 | char * |
| 1983 | get_mouse_name(index) |
| 1984 | int index |
| 1985 | CODE: |
| 1986 | dMY_CXT; |
| 1987 | RETVAL = MY_CXT.lives ++; |
| 1988 | if (index > MY_CXT.count) |
| 1989 | croak("There are only 3 blind mice."); |
| 1990 | else |
| 1991 | RETVAL = newSVpv(MY_CXT.name[index - 1]); |
| 1992 | |
| 1993 | void |
| 1994 | CLONE(...) |
| 1995 | CODE: |
| 1996 | MY_CXT_CLONE; |
| 1997 | |
| 1998 | B<REFERENCE> |
| 1999 | |
| 2000 | =over 5 |
| 2001 | |
| 2002 | =item MY_CXT_KEY |
| 2003 | |
| 2004 | This macro is used to define a unique key to refer to the static data |
| 2005 | for an XS module. The suggested naming scheme, as used by h2xs, is to |
| 2006 | use a string that consists of the module name, the string "::_guts" |
| 2007 | and the module version number. |
| 2008 | |
| 2009 | #define MY_CXT_KEY "MyModule::_guts" XS_VERSION |
| 2010 | |
| 2011 | =item typedef my_cxt_t |
| 2012 | |
| 2013 | This struct typedef I<must> always be called C<my_cxt_t>. The other |
| 2014 | C<CXT*> macros assume the existence of the C<my_cxt_t> typedef name. |
| 2015 | |
| 2016 | Declare a typedef named C<my_cxt_t> that is a structure that contains |
| 2017 | all the data that needs to be interpreter-local. |
| 2018 | |
| 2019 | typedef struct { |
| 2020 | int some_value; |
| 2021 | } my_cxt_t; |
| 2022 | |
| 2023 | =item START_MY_CXT |
| 2024 | |
| 2025 | Always place the START_MY_CXT macro directly after the declaration |
| 2026 | of C<my_cxt_t>. |
| 2027 | |
| 2028 | =item MY_CXT_INIT |
| 2029 | |
| 2030 | The MY_CXT_INIT macro initialises storage for the C<my_cxt_t> struct. |
| 2031 | |
| 2032 | It I<must> be called exactly once, typically in a BOOT: section. If you |
| 2033 | are maintaining multiple interpreters, it should be called once in each |
| 2034 | interpreter instance, except for interpreters cloned from existing ones. |
| 2035 | (But see L</MY_CXT_CLONE> below.) |
| 2036 | |
| 2037 | =item dMY_CXT |
| 2038 | |
| 2039 | Use the dMY_CXT macro (a declaration) in all the functions that access |
| 2040 | MY_CXT. |
| 2041 | |
| 2042 | =item MY_CXT |
| 2043 | |
| 2044 | Use the MY_CXT macro to access members of the C<my_cxt_t> struct. For |
| 2045 | example, if C<my_cxt_t> is |
| 2046 | |
| 2047 | typedef struct { |
| 2048 | int index; |
| 2049 | } my_cxt_t; |
| 2050 | |
| 2051 | then use this to access the C<index> member |
| 2052 | |
| 2053 | dMY_CXT; |
| 2054 | MY_CXT.index = 2; |
| 2055 | |
| 2056 | =item aMY_CXT/pMY_CXT |
| 2057 | |
| 2058 | C<dMY_CXT> may be quite expensive to calculate, and to avoid the overhead |
| 2059 | of invoking it in each function it is possible to pass the declaration |
| 2060 | onto other functions using the C<aMY_CXT>/C<pMY_CXT> macros, eg |
| 2061 | |
| 2062 | void sub1() { |
| 2063 | dMY_CXT; |
| 2064 | MY_CXT.index = 1; |
| 2065 | sub2(aMY_CXT); |
| 2066 | } |
| 2067 | |
| 2068 | void sub2(pMY_CXT) { |
| 2069 | MY_CXT.index = 2; |
| 2070 | } |
| 2071 | |
| 2072 | Analogously to C<pTHX>, there are equivalent forms for when the macro is the |
| 2073 | first or last in multiple arguments, where an underscore represents a |
| 2074 | comma, i.e. C<_aMY_CXT>, C<aMY_CXT_>, C<_pMY_CXT> and C<pMY_CXT_>. |
| 2075 | |
| 2076 | =item MY_CXT_CLONE |
| 2077 | |
| 2078 | By default, when a new interpreter is created as a copy of an existing one |
| 2079 | (eg via C<< threads->create() >>), both interpreters share the same physical |
| 2080 | my_cxt_t structure. Calling C<MY_CXT_CLONE> (typically via the package's |
| 2081 | C<CLONE()> function), causes a byte-for-byte copy of the structure to be |
| 2082 | taken, and any future dMY_CXT will cause the copy to be accessed instead. |
| 2083 | |
| 2084 | =item MY_CXT_INIT_INTERP(my_perl) |
| 2085 | |
| 2086 | =item dMY_CXT_INTERP(my_perl) |
| 2087 | |
| 2088 | These are versions of the macros which take an explicit interpreter as an |
| 2089 | argument. |
| 2090 | |
| 2091 | =back |
| 2092 | |
| 2093 | Note that these macros will only work together within the I<same> source |
| 2094 | file; that is, a dMY_CTX in one source file will access a different structure |
| 2095 | than a dMY_CTX in another source file. |
| 2096 | |
| 2097 | =head2 Thread-aware system interfaces |
| 2098 | |
| 2099 | Starting from Perl 5.8, in C/C++ level Perl knows how to wrap |
| 2100 | system/library interfaces that have thread-aware versions |
| 2101 | (e.g. getpwent_r()) into frontend macros (e.g. getpwent()) that |
| 2102 | correctly handle the multithreaded interaction with the Perl |
| 2103 | interpreter. This will happen transparently, the only thing |
| 2104 | you need to do is to instantiate a Perl interpreter. |
| 2105 | |
| 2106 | This wrapping happens always when compiling Perl core source |
| 2107 | (PERL_CORE is defined) or the Perl core extensions (PERL_EXT is |
| 2108 | defined). When compiling XS code outside of Perl core the wrapping |
| 2109 | does not take place. Note, however, that intermixing the _r-forms |
| 2110 | (as Perl compiled for multithreaded operation will do) and the _r-less |
| 2111 | forms is neither well-defined (inconsistent results, data corruption, |
| 2112 | or even crashes become more likely), nor is it very portable. |
| 2113 | |
| 2114 | =head1 EXAMPLES |
| 2115 | |
| 2116 | File C<RPC.xs>: Interface to some ONC+ RPC bind library functions. |
| 2117 | |
| 2118 | #include "EXTERN.h" |
| 2119 | #include "perl.h" |
| 2120 | #include "XSUB.h" |
| 2121 | |
| 2122 | #include <rpc/rpc.h> |
| 2123 | |
| 2124 | typedef struct netconfig Netconfig; |
| 2125 | |
| 2126 | MODULE = RPC PACKAGE = RPC |
| 2127 | |
| 2128 | SV * |
| 2129 | rpcb_gettime(host="localhost") |
| 2130 | char *host |
| 2131 | PREINIT: |
| 2132 | time_t timep; |
| 2133 | CODE: |
| 2134 | ST(0) = sv_newmortal(); |
| 2135 | if( rpcb_gettime( host, &timep ) ) |
| 2136 | sv_setnv( ST(0), (double)timep ); |
| 2137 | |
| 2138 | Netconfig * |
| 2139 | getnetconfigent(netid="udp") |
| 2140 | char *netid |
| 2141 | |
| 2142 | MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ |
| 2143 | |
| 2144 | void |
| 2145 | rpcb_DESTROY(netconf) |
| 2146 | Netconfig *netconf |
| 2147 | CODE: |
| 2148 | printf("NetconfigPtr::DESTROY\n"); |
| 2149 | free( netconf ); |
| 2150 | |
| 2151 | File C<typemap>: Custom typemap for RPC.xs. |
| 2152 | |
| 2153 | TYPEMAP |
| 2154 | Netconfig * T_PTROBJ |
| 2155 | |
| 2156 | File C<RPC.pm>: Perl module for the RPC extension. |
| 2157 | |
| 2158 | package RPC; |
| 2159 | |
| 2160 | require Exporter; |
| 2161 | require DynaLoader; |
| 2162 | @ISA = qw(Exporter DynaLoader); |
| 2163 | @EXPORT = qw(rpcb_gettime getnetconfigent); |
| 2164 | |
| 2165 | bootstrap RPC; |
| 2166 | 1; |
| 2167 | |
| 2168 | File C<rpctest.pl>: Perl test program for the RPC extension. |
| 2169 | |
| 2170 | use RPC; |
| 2171 | |
| 2172 | $netconf = getnetconfigent(); |
| 2173 | $a = rpcb_gettime(); |
| 2174 | print "time = $a\n"; |
| 2175 | print "netconf = $netconf\n"; |
| 2176 | |
| 2177 | $netconf = getnetconfigent("tcp"); |
| 2178 | $a = rpcb_gettime("poplar"); |
| 2179 | print "time = $a\n"; |
| 2180 | print "netconf = $netconf\n"; |
| 2181 | |
| 2182 | |
| 2183 | =head1 XS VERSION |
| 2184 | |
| 2185 | This document covers features supported by C<xsubpp> 1.935. |
| 2186 | |
| 2187 | =head1 AUTHOR |
| 2188 | |
| 2189 | Originally written by Dean Roehrich <F<roehrich@cray.com>>. |
| 2190 | |
| 2191 | Maintained since 1996 by The Perl Porters <F<perlbug@perl.org>>. |