X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/4b19af017623bfa3bb72bb164598a517f586e0d3..c079d275c4f9c514ec0de3de1aef066d6f4595aa:/pod/perlguts.pod diff --git a/pod/perlguts.pod b/pod/perlguts.pod index f2b4b90..669ecf5 100644 --- a/pod/perlguts.pod +++ b/pod/perlguts.pod @@ -4,10 +4,10 @@ perlguts - Introduction to the Perl API =head1 DESCRIPTION -This document attempts to describe how to use the Perl API, as well as containing -some info on the basic workings of the Perl core. It is far from complete -and probably contains many errors. Please refer any questions or -comments to the author below. +This document attempts to describe how to use the Perl API, as well as +containing some info on the basic workings of the Perl core. It is far +from complete and probably contains many errors. Please refer any +questions or comments to the author below. =head1 Variables @@ -54,7 +54,7 @@ To change the value of an *already-existing* SV, there are seven routines: void sv_setpv(SV*, const char*); void sv_setpvn(SV*, const char*, int) void sv_setpvf(SV*, const char*, ...); - void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); + void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); void sv_setsv(SV*, SV*); Notice that you can choose to specify the length of the string to be @@ -67,7 +67,7 @@ string terminating with a NUL character. The arguments of C are processed like C, and the formatted output becomes the value. -C is an analogue of C, but it allows you to specify +C is an analogue of C, but it allows you to specify either a pointer to a variable argument list or the address and length of an array of SVs. The last argument points to a boolean; on return, if that boolean is true, then locale-specific information has been used to format @@ -76,6 +76,10 @@ L). This pointer may be NULL if that information is not important. Note that this function requires you to specify the length of the format. +STRLEN is an integer type (Size_t, usually defined as size_t in +config.h) guaranteed to be large enough to represent the size of +any string that perl can handle. + The C functions are not generic enough to operate on values that have "magic". See L later in this document. @@ -158,7 +162,7 @@ you can use the following functions: void sv_catpv(SV*, const char*); void sv_catpvn(SV*, const char*, STRLEN); void sv_catpvf(SV*, const char*, ...); - void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); + void sv_vcatpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); void sv_catsv(SV*, SV*); The first function calculates the length of the string to be appended by @@ -210,6 +214,48 @@ line and all will be well. To free an SV that you've created, call C. Normally this call is not necessary (see L). +=head2 Offsets + +Perl provides the function C to efficiently remove characters +from the beginning of a string; you give it an SV and a pointer to +somewhere inside the the PV, and it discards everything before the +pointer. The efficiency comes by means of a little hack: instead of +actually removing the characters, C sets the flag C +(offset OK) to signal to other functions that the offset hack is in +effect, and it puts the number of bytes chopped off into the IV field +of the SV. It then moves the PV pointer (called C) forward that +many bytes, and adjusts C and C. + +Hence, at this point, the start of the buffer that we allocated lives +at C in memory and the PV pointer is pointing +into the middle of this allocated storage. + +This is best demonstrated by example: + + % ./perl -Ilib -MDevel::Peek -le '$a="12345"; $a=~s/.//; Dump($a)' + SV = PVIV(0x8128450) at 0x81340f0 + REFCNT = 1 + FLAGS = (POK,OOK,pPOK) + IV = 1 (OFFSET) + PV = 0x8135781 ( "1" . ) "2345"\0 + CUR = 4 + LEN = 5 + +Here the number of bytes chopped off (1) is put into IV, and +C helpfully reminds us that this is an offset. The +portion of the string between the "real" and the "fake" beginnings is +shown in parentheses, and the values of C and C reflect +the fake beginning, not the real one. + +Something similar to the offset hack is perfomed on AVs to enable +efficient shifting and splicing off the beginning of the array; while +C points to the first element in the array that is visible from +Perl, C points to the real start of the C array. These are +usually the same, but a C operation can be carried out by +increasing C by one and decreasing C and C. +Again, the location of the real start of the C array only comes into +play when freeing the array. See C in F. + =head2 What's Really Stored in an SV? Recall that the usual method of determining the type of scalar you have is @@ -228,6 +274,14 @@ pointer in an SV, you can use the following three macros instead: These will tell you if you truly have an integer, double, or string pointer stored in your SV. The "p" stands for private. +The are various ways in which the private and public flags may differ. +For example, a tied SV may have a valid underlying value in the IV slot +(so SvIOKp is true), but the data should be accessed via the FETCH +routine rather than directly, so SvIOK is false. Another is when +numeric conversion has occured and precision has been lost: only the +private flag is set on 'lossy' values. So when an NV is converted to an +IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be. + In general, though, it's best to use the C macros. =head2 Working with AVs @@ -493,10 +547,11 @@ class. SV is returned. SV* newSVrv(SV* rv, const char* classname); -Copies integer or double into an SV whose reference is C. SV is blessed +Copies integer, unsigned integer or double into an SV whose reference is C. SV is blessed if C is non-null. SV* sv_setref_iv(SV* rv, const char* classname, IV iv); + SV* sv_setref_uv(SV* rv, const char* classname, UV uv); SV* sv_setref_nv(SV* rv, const char* classname, NV iv); Copies the pointer value (I) into an SV whose @@ -524,7 +579,7 @@ is the function implementing the C functionality. bool sv_derived_from(SV* sv, const char* name); -To check if you've got an object derived from a specific class you have +To check if you've got an object derived from a specific class you have to write: if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... } @@ -603,9 +658,11 @@ See L and L for more details on these macros. However, if you mortalize a variable twice, the reference count will later be decremented twice. -You should be careful about creating mortal variables. Strange things -can happen if you make the same value mortal within multiple contexts, -or if you make a variable mortal multiple times. +"Mortal" SVs are mainly used for SVs that are placed on perl's stack. +For example an SV which is created just to pass a number to a called sub +is made mortal to have it cleaned up automatically when stack is popped. +Similarly results returned by XSUBs (which go in the stack) are often +made mortal. To create a mortal variable, use the functions: @@ -613,9 +670,28 @@ To create a mortal variable, use the functions: SV* sv_2mortal(SV*) SV* sv_mortalcopy(SV*) -The first call creates a mortal SV, the second converts an existing +The first call creates a mortal SV (with no value), the second converts an existing SV to a mortal SV (and thus defers a call to C), and the third creates a mortal copy of an existing SV. +Because C gives the new SV no value,it must normally be given one +via C, C etc. : + + SV *tmp = sv_newmortal(); + sv_setiv(tmp, an_integer); + +As that is multiple C statements it is quite common so see this idiom instead: + + SV *tmp = sv_2mortal(newSViv(an_integer)); + + +You should be careful about creating mortal variables. Strange things +can happen if you make the same value mortal within multiple contexts, +or if you make a variable mortal multiple times. Thinking of "Mortalization" +as deferred C should help to minimize such problems. +For example if you are passing an SV which you I has high enough REFCNT +to survive its use on the stack you need not do any mortalization. +If you are not sure then doing an C and C, or +making a C is safer. The mortal routines are not just for SVs -- AVs and HVs can be made mortal by passing their address (type-casted to C) to the @@ -749,11 +825,11 @@ The C argument is a pointer to the SV that is to acquire a new magical feature. If C is not already magical, Perl uses the C macro to -set the C flag for the C. Perl then continues by adding -it to the beginning of the linked list of magical features. Any prior -entry of the same type of magic is deleted. Note that this can be -overridden, and multiple instances of the same type of magic can be -associated with an SV. +convert C to type C. Perl then continues by adding new magic +to the beginning of the linked list of magical features. Any prior entry +of the same type of magic is deleted. Note that this can be overridden, +and multiple instances of the same type of magic can be associated with an +SV. The C and C arguments are used to associate a string with the magic, typically the name of a variable. C is stored in the @@ -763,13 +839,17 @@ copy of the name is stored in C field. The sv_magic function uses C to determine which, if any, predefined "Magic Virtual Table" should be assigned to the C field. See the "Magic Virtual Table" section below. The C argument is also -stored in the C field. +stored in the C field. The value of C should be chosen +from the set of macros C found perl.h. Note that before +these macros were added, Perl internals used to directly use character +literals, so you may occasionally come across old code or documentation +referrring to 'U' magic rather than C for example. The C argument is stored in the C field of the C structure. If it is not the same as the C argument, the reference count of the C object is incremented. If it is the same, or if -the C argument is "#", or if it is a NULL pointer, then C is -merely stored, without the reference count being incremented. +the C argument is C, or if it is a NULL pointer, +then C is merely stored, without the reference count being incremented. There is also a function to add magic to an C: @@ -813,78 +893,87 @@ actions depending on which function is being called. svt_free Free any extra storage associated with the SV. For instance, the MGVTBL structure called C (which corresponds -to an C of '\0') contains: +to an C of C) contains: { magic_get, magic_set, magic_len, 0, 0 } -Thus, when an SV is determined to be magical and of type '\0', if a get -operation is being performed, the routine C is called. All -the various routines for the various magical types begin with C. -NOTE: the magic routines are not considered part of the Perl API, and may -not be exported by the Perl library. +Thus, when an SV is determined to be magical and of type C, +if a get operation is being performed, the routine C is +called. All the various routines for the various magical types begin +with C. NOTE: the magic routines are not considered part of +the Perl API, and may not be exported by the Perl library. The current kinds of Magic Virtual Tables are: - mg_type MGVTBL Type of magic - ------- ------ ---------------------------- - \0 vtbl_sv Special scalar variable - A vtbl_amagic %OVERLOAD hash - a vtbl_amagicelem %OVERLOAD hash element - c (none) Holds overload table (AMT) on stash - B vtbl_bm Boyer-Moore (fast string search) - D vtbl_regdata Regex match position data (@+ and @- vars) - d vtbl_regdatum Regex match position data element - E vtbl_env %ENV hash - e vtbl_envelem %ENV hash element - f vtbl_fm Formline ('compiled' format) - g vtbl_mglob m//g target / study()ed string - I vtbl_isa @ISA array - i vtbl_isaelem @ISA array element - k vtbl_nkeys scalar(keys()) lvalue - L (none) Debugger %_'s +that composite type. Some internals code makes use of this case +relationship. + +The C and C magic types are defined +specifically for use by extensions and will not be used by perl itself. +Extensions can use C magic to 'attach' private information +to variables (typically objects). This is especially useful because +there is no way for normal perl code to corrupt this private information +(unlike using extra elements of a hash object). + +Similarly, C magic can be used much like tie() to call a +C function any time a scalar's value is used or changed. The C's C field points to a C structure: struct ufuncs { - I32 (*uf_val)(IV, SV*); - I32 (*uf_set)(IV, SV*); + I32 (*uf_val)(pTHX_ IV, SV*); + I32 (*uf_set)(pTHX_ IV, SV*); IV uf_index; }; When the SV is read from or written to, the C or C -function will be called with C as the first arg and a -pointer to the SV as the second. A simple example of how to add 'U' +function will be called with C as the first arg and a pointer to +the SV as the second. A simple example of how to add C magic is shown below. Note that the ufuncs structure is copied by sv_magic, so you can safely allocate it on the stack. @@ -897,14 +986,14 @@ sv_magic, so you can safely allocate it on the stack. uf.uf_val = &my_get_fn; uf.uf_set = &my_set_fn; uf.uf_index = 0; - sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf)); + sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf)); -Note that because multiple extensions may be using '~' or 'U' magic, -it is important for extensions to take extra care to avoid conflict. -Typically only using the magic on objects blessed into the same class -as the extension is sufficient. For '~' magic, it may also be -appropriate to add an I32 'signature' at the top of the private data -area and check that. +Note that because multiple extensions may be using C +or C magic, it is important for extensions to take +extra care to avoid conflict. Typically only using the magic on +objects blessed into the same class as the extension is sufficient. +For C magic, it may also be appropriate to add an I32 +'signature' at the top of the private data area and check that. Also note that the C and C functions described earlier do B invoke 'set' magic on their targets. This must @@ -934,7 +1023,8 @@ the mg_type field is changed to be the lowercase letter. =head2 Understanding the Magic of Tied Hashes and Arrays -Tied hashes and arrays are magical beasts of the 'P' magic type. +Tied hashes and arrays are magical beasts of the C +magic type. WARNING: As of the 5.004 release, proper usage of the array and hash access functions requires understanding a few caveats. Some @@ -965,7 +1055,7 @@ to do this. tie = newRV_noinc((SV*)newHV()); stash = gv_stashpv("MyTie", TRUE); sv_bless(tie, stash); - hv_magic(hash, tie, 'P'); + hv_magic(hash, (GV*)tie, PERL_MAGIC_tied); RETVAL = newRV_noinc(hash); OUTPUT: RETVAL @@ -1055,7 +1145,7 @@ an C/C pair. Inside such a I the following service is available: -=over +=over 4 =item C @@ -1080,8 +1170,20 @@ and back. =item C The refcount of C would be decremented at the end of -I. This is similar to C, which should (?) be -used instead. +I. This is similar to C in that it is also a +mechanism for doing a delayed C. However, while C +extends the lifetime of C until the beginning of the next statement, +C extends it until the end of the enclosing scope. These +lifetimes can be wildly different. + +Also compare C. + +=item C + +Just like C, but mortalizes C at the end of the current +scope instead of decrementing its reference count. This usually has the +effect of keeping C alive until the statement that called the currently +live scope has finished executing. =item C @@ -1125,10 +1227,10 @@ at the end of I. The following API list contains functions, thus one needs to provide pointers to the modifiable data explicitly (either C pointers, -or Perlish Cs). Where the above macros take C, a similar +or Perlish Cs). Where the above macros take C, a similar function takes C. -=over +=over 4 =item C @@ -1194,13 +1296,12 @@ extended using the macro: where C is the macro that represents the local copy of the stack pointer, and C is the number of elements the stack should be extended by. -Now that there is room on the stack, values can be pushed on it using the -macros to push IVs, doubles, strings, and SV pointers respectively: +Now that there is room on the stack, values can be pushed on it using C +macro. The values pushed will often need to be "mortal" (See L). - PUSHi(IV) - PUSHn(double) - PUSHp(char*, I32) - PUSHs(SV*) + PUSHs(sv_2mortal(newSViv(an_integer))) + PUSHs(sv_2mortal(newSVpv("Some String",0))) + PUSHs(sv_2mortal(newSVnv(3.141592))) And now the Perl program calling C, the two values will be assigned as in: @@ -1208,16 +1309,17 @@ as in: ($standard_abbrev, $summer_abbrev) = POSIX::tzname; An alternate (and possibly simpler) method to pushing values on the stack is -to use the macros: +to use the macro: - XPUSHi(IV) - XPUSHn(double) - XPUSHp(char*, I32) XPUSHs(SV*) -These macros automatically adjust the stack for you, if needed. Thus, you +This macro automatically adjust the stack for you, if needed. Thus, you do not need to call C to extend the stack. +Despite their suggestions in earlier versions of this document the macros +C, C and C are I suited to XSUBs which return +multiple results, see L. + For more information, consult L and L. =head2 Calling Perl Routines from within C Programs @@ -1317,21 +1419,6 @@ destination starting points. Perl will move, copy, or zero out C instances of the size of the C data structure (using the C function). -Here is a handy table of equivalents between ordinary C and Perl's -memory abstraction layer: - - Instead Of: Use: - - malloc New - calloc Newz - realloc Renew - memcopy Copy - memmove Move - free Safefree - strdup savepv - strndup savepvn (Hey, strndup doesn't exist!) - memcpy/*(struct foo *) StructCopy - =head2 PerlIO The most recent development releases of Perl has been experimenting with @@ -1361,6 +1448,23 @@ The macro to put this target on stack is C, and it is directly used in some opcodes, as well as indirectly in zillions of others, which use it via C<(X)PUSH[pni]>. +Because the target is reused, you must be careful when pushing multiple +values on the stack. The following code will not do what you think: + + XPUSHi(10); + XPUSHi(20); + +This translates as "set C to 10, push a pointer to C onto +the stack; set C to 20, push a pointer to C onto the stack". +At the end of the operation, the stack does not contain the values 10 +and 20, but actually contains two pointers to C, which we have set +to 20. If you need to push multiple different values, use C, +which bypasses C. + +On a related note, if you do use C<(X)PUSH[npi]>, then you're going to +need a C in your variable declarations so that the C<*PUSH*> +macros can make use of the local variable C. + =head2 Scratchpads The question remains on when the SVs which are Is for opcodes @@ -1478,6 +1582,31 @@ The execution order is indicated by C<===E> marks, thus it is C<3 4 5 6> (node C<6> is not included into above listing), i.e., C. +Each of these nodes represents an op, a fundamental operation inside the +Perl core. The code which implements each operation can be found in the +F files; the function which implements the op with type C +is C, and so on. As the tree above shows, different ops have +different numbers of children: C is a binary operator, as one would +expect, and so has two children. To accommodate the various different +numbers of children, there are various types of op data structure, and +they link together in different ways. + +The simplest type of op structure is C: this has no children. Unary +operators, Cs, have one child, and this is pointed to by the +C field. Binary operators (Cs) have not only an +C field but also an C field. The most complex type of +op is a C, which has any number of children. In this case, the +first child is pointed to by C and the last child by +C. The children in between can be found by iteratively +following the C pointer from the first child to the last. + +There are also two other op types: a C holds a regular expression, +and has no children, and a C may or may not have children. If the +C field is non-zero, it behaves like a C. To +complicate matters, if a C is actually a C op after +optimization (see L) it will still +have children in accordance with its former type. + =head2 Compile pass 1: check routines The tree is created by the compiler while I code feeds it @@ -1538,6 +1667,58 @@ additional complications for conditionals). These optimizations are done in the subroutine peep(). Optimizations performed at this stage are subject to the same restrictions as in the pass 2. +=head2 Pluggable runops + +The compile tree is executed in a runops function. There are two runops +functions in F. C is used with DEBUGGING and +C is used otherwise. For fine control over the +execution of the compile tree it is possible to provide your own runops +function. + +It's probably best to copy one of the existing runops functions and +change it to suit your needs. Then, in the BOOT section of your XS +file, add the line: + + PL_runops = my_runops; + +This function should be as efficient as possible to keep your programs +running as fast as possible. + +=head1 Examining internal data structures with the C functions + +To aid debugging, the source file F contains a number of +functions which produce formatted output of internal data structures. + +The most commonly used of these functions is C; it's used +for dumping SVs, AVs, HVs, and CVs. The C module calls +C to produce debugging output from Perl-space, so users of that +module should already be familiar with its format. + +C can be used to dump an C structure or any of its +derivatives, and produces output similiar to C; in fact, +C will dump the main root of the code being evaluated, +exactly like C<-Dx>. + +Other useful functions are C, which turns a C into an +op tree, C which calls C on all the +subroutines in a package like so: (Thankfully, these are all xsubs, so +there is no op tree) + + (gdb) print Perl_dump_packsubs(PL_defstash) + + SUB attributes::bootstrap = (xsub 0x811fedc 0) + + SUB UNIVERSAL::can = (xsub 0x811f50c 0) + + SUB UNIVERSAL::isa = (xsub 0x811f304 0) + + SUB UNIVERSAL::VERSION = (xsub 0x811f7ac 0) + + SUB DynaLoader::boot_DynaLoader = (xsub 0x805b188 0) + +and C, which dumps all the subroutines in the stash and +the op tree of the main root. + =head1 How multiple interpreters and concurrency are supported =head2 Background and PERL_IMPLICIT_CONTEXT @@ -1546,35 +1727,33 @@ The Perl interpreter can be regarded as a closed box: it has an API for feeding it code or otherwise making it do things, but it also has functions for its own use. This smells a lot like an object, and there are ways for you to build Perl so that you can have multiple -interpreters, with one interpreter represented either as a C++ object, -a C structure, or inside a thread. The thread, the C structure, or -the C++ object will contain all the context, the state of that -interpreter. - -Three macros control the major Perl build flavors: MULTIPLICITY, -USE_THREADS and PERL_OBJECT. The MULTIPLICITY build has a C structure -that packages all the interpreter state, there is a similar thread-specific -data structure under USE_THREADS, and the PERL_OBJECT build has a C++ -class to maintain interpreter state. In all three cases, +interpreters, with one interpreter represented either as a C structure, +or inside a thread-specific structure. These structures contain all +the context, the state of that interpreter. + +Three macros control the major Perl build flavors: MULTIPLICITY, and +USE_5005THREADS. The MULTIPLICITY build has a C structure +that packages all the interpreter state, and there is a similar thread-specific +data structure under USE_5005THREADS. In both cases, PERL_IMPLICIT_CONTEXT is also normally defined, and enables the support for passing in a "hidden" first argument that represents all three data structures. All this obviously requires a way for the Perl internal functions to be -C++ methods, subroutines taking some kind of structure as the first +either subroutines taking some kind of structure as the first argument, or subroutines taking nothing as the first argument. To -enable these three very different ways of building the interpreter, +enable these two very different ways of building the interpreter, the Perl source (as it does in so many other situations) makes heavy use of macros and subroutine naming conventions. First problem: deciding which functions will be public API functions and -which will be private. All functions whose names begin C are private +which will be private. All functions whose names begin C are private (think "S" for "secret" or "static"). All other functions begin with "Perl_", but just because a function begins with "Perl_" does not mean it is -part of the API. (See L.) The easiest way to be B a -function is part of the API is to find its entry in L. -If it exists in L, it's part of the API. If it doesn't, and you -think it should be (i.e., you need it for your extension), send mail via +part of the API. (See L.) The easiest way to be B a +function is part of the API is to find its entry in L. +If it exists in L, it's part of the API. If it doesn't, and you +think it should be (i.e., you need it for your extension), send mail via L explaining why you think it should be. Second problem: there must be a syntax so that the same subroutine @@ -1586,7 +1765,8 @@ function used within the Perl guts: STATIC void S_incline(pTHX_ char *s) -STATIC becomes "static" in C, and is #define'd to nothing in C++. +STATIC becomes "static" in C, and may be #define'd to nothing in some +configurations in future. A public function (i.e. part of the internal API, but not necessarily sanctioned for use in extensions) begins like this: @@ -1598,10 +1778,11 @@ C is one of a number of macros (in perl.h) that hide the details of the interpreter's context. THX stands for "thread", "this", or "thingy", as the case may be. (And no, George Lucas is not involved. :-) The first character could be 'p' for a B

rototype, 'a' for Brgument, -or 'd' for Beclaration. +or 'd' for Beclaration, so we have C, C and C, and +their variants. -When Perl is built without PERL_IMPLICIT_CONTEXT, there is no first -argument containing the interpreter's context. The trailing underscore +When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no +first argument containing the interpreter's context. The trailing underscore in the pTHX_ macro indicates that the macro expansion needs a comma after the context argument because other arguments follow it. If PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the @@ -1610,14 +1791,14 @@ macro without the trailing underscore is used when there are no additional explicit arguments. When a core function calls another, it must pass the context. This -is normally hidden via macros. Consider C. It expands +is normally hidden via macros. Consider C. It expands into something like this: ifdef PERL_IMPLICIT_CONTEXT - define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b) + define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b) /* can't do this for vararg functions, see below */ else - define sv_setsv Perl_sv_setsv + define sv_setsv Perl_sv_setsv endif This works well, and means that XS authors can gleefully write: @@ -1627,22 +1808,6 @@ This works well, and means that XS authors can gleefully write: and still have it work under all the modes Perl could have been compiled with. -Under PERL_OBJECT in the core, that will translate to either: - - CPerlObj::Perl_sv_setsv(foo,bar); # in CPerlObj functions, - # C++ takes care of 'this' - or - - pPerl->Perl_sv_setsv(foo,bar); # in truly static functions, - # see objXSUB.h - -Under PERL_OBJECT in extensions (aka PERL_CAPI), or under -MULTIPLICITY/USE_THREADS w/ PERL_IMPLICIT_CONTEXT in both core -and extensions, it will be: - - Perl_sv_setsv(aTHX_ foo, bar); # the canonical Perl "API" - # for all build flavors - This doesn't work so cleanly for varargs functions, though, as macros imply that the number of arguments is known in advance. Instead we either need to spell them out fully, passing C as the first @@ -1656,10 +1821,18 @@ C<#define warner Perl_warner_nocontext> so that extensions get source compatibility at the expense of performance. (Passing an arg is cheaper than grabbing it from thread-local storage.) -You can ignore [pad]THX[xo] when browsing the Perl headers/sources. +You can ignore [pad]THXx when browsing the Perl headers/sources. Those are strictly for use within the core. Extensions and embedders need only be aware of [pad]THX. +=head2 So what happened to dTHR? + +C was introduced in perl 5.005 to support the older thread model. +The older thread model now uses the C mechanism to pass context +pointers around, so C is not useful any more. Perl 5.6.0 and +later still have it for backward source compatibility, but it is defined +to be a no-op. + =head2 How do I use all this in extensions? When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call @@ -1692,31 +1865,31 @@ work. The second, more efficient way is to use the following template for your Foo.xs: - #define PERL_NO_GET_CONTEXT /* we want efficiency */ - #include "EXTERN.h" - #include "perl.h" - #include "XSUB.h" + #define PERL_NO_GET_CONTEXT /* we want efficiency */ + #include "EXTERN.h" + #include "perl.h" + #include "XSUB.h" static my_private_function(int arg1, int arg2); - static SV * - my_private_function(int arg1, int arg2) - { - dTHX; /* fetch context */ - ... call many Perl API functions ... - } + static SV * + my_private_function(int arg1, int arg2) + { + dTHX; /* fetch context */ + ... call many Perl API functions ... + } [... etc ...] - MODULE = Foo PACKAGE = Foo + MODULE = Foo PACKAGE = Foo - /* typical XSUB */ + /* typical XSUB */ - void - my_xsub(arg) - int arg - CODE: - my_private_function(arg, 10); + void + my_xsub(arg) + int arg + CODE: + my_private_function(arg, 10); Note that the only two changes from the normal way of writing an extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before @@ -1731,32 +1904,32 @@ The third, even more efficient way is to ape how it is done within the Perl guts: - #define PERL_NO_GET_CONTEXT /* we want efficiency */ - #include "EXTERN.h" - #include "perl.h" - #include "XSUB.h" + #define PERL_NO_GET_CONTEXT /* we want efficiency */ + #include "EXTERN.h" + #include "perl.h" + #include "XSUB.h" /* pTHX_ only needed for functions that call Perl API */ static my_private_function(pTHX_ int arg1, int arg2); - static SV * - my_private_function(pTHX_ int arg1, int arg2) - { - /* dTHX; not needed here, because THX is an argument */ - ... call Perl API functions ... - } + static SV * + my_private_function(pTHX_ int arg1, int arg2) + { + /* dTHX; not needed here, because THX is an argument */ + ... call Perl API functions ... + } [... etc ...] - MODULE = Foo PACKAGE = Foo + MODULE = Foo PACKAGE = Foo - /* typical XSUB */ + /* typical XSUB */ - void - my_xsub(arg) - int arg - CODE: - my_private_function(aTHX_ arg, 10); + void + my_xsub(arg) + int arg + CODE: + my_private_function(aTHX_ arg, 10); This implementation never has to fetch the context using a function call, since it is always passed as an extra argument. Depending on @@ -1767,15 +1940,34 @@ Never add a comma after C yourself--always use the form of the macro with the underscore for functions that take explicit arguments, or the form without the argument for functions with no explicit arguments. +=head2 Should I do anything special if I call perl from multiple threads? + +If you create interpreters in one thread and then proceed to call them in +another, you need to make sure perl's own Thread Local Storage (TLS) slot is +initialized correctly in each of those threads. + +The C and C API functions will automatically set +the TLS slot to the interpreter they created, so that there is no need to do +anything special if the interpreter is always accessed in the same thread that +created it, and that thread did not create or call any other interpreters +afterwards. If that is not the case, you have to set the TLS slot of the +thread before calling any functions in the Perl API on that particular +interpreter. This is done by calling the C macro in that +thread as the first thing you do: + + /* do this before doing anything else with some_perl */ + PERL_SET_CONTEXT(some_perl); + + ... other Perl API calls on some_perl go here ... + =head2 Future Plans and PERL_IMPLICIT_SYS Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything that the interpreter knows about itself and pass it around, so too are there plans to allow the interpreter to bundle up everything it knows about the environment it's running on. This is enabled with the -PERL_IMPLICIT_SYS macro. Currently it only works with PERL_OBJECT, -but is mostly there for MULTIPLICITY and USE_THREADS (see inside -iperlsys.h). +PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS +and USE_5005THREADS on Windows (see inside iperlsys.h). This allows the ability to provide an extra pointer (called the "host" environment) for all the system calls. This makes it possible for @@ -1835,7 +2027,8 @@ Other available flags are: =item s -This is a static function and is defined as C. +This is a static function and is defined as C, and usually +called within the sources as C. =item n @@ -1853,9 +2046,9 @@ The argument list should end with C<...>, like this: Afprd |void |croak |const char* pat|... -=item m +=item M -This function is part of the experimental development API, and may change +This function is part of the experimental development API, and may change or disappear without notice. =item o @@ -1877,18 +2070,49 @@ This function isn't exported out of the Perl core. If you edit F, you will need to run C to force a rebuild of F and other auto-generated files. -=head2 Formatted Printing of IVs and UVs +=head2 Formatted Printing of IVs, UVs, and NVs + +If you are printing IVs, UVs, or NVS instead of the stdio(3) style +formatting codes like C<%d>, C<%ld>, C<%f>, you should use the +following macros for portability + + IVdf IV in decimal + UVuf UV in decimal + UVof UV in octal + UVxf UV in hexadecimal + NVef NV %e-like + NVff NV %f-like + NVgf NV %g-like + +These will take care of 64-bit integers and long doubles. +For example: -If you are printing IVs or UVs instead of the stdio(3) style formatting -codes like C<%d> you should use the following macros for portability + printf("IV is %"IVdf"\n", iv); - IVdf IV in decimal - UVuf UV in decimal - UVof UV in octal - UVxf UV in hexadecimal +The IVdf will expand to whatever is the correct format for the IVs. -For example: printf("IV is %"IVdf"\n", iv); That will expand -to whatever is the correct format for the IVs. +If you are printing addresses of pointers, use UVxf combined +with PTR2UV(), do not use %lx or %p. + +=head2 Pointer-To-Integer and Integer-To-Pointer + +Because pointer size does not necessarily equal integer size, +use the follow macros to do it right. + + PTR2UV(pointer) + PTR2IV(pointer) + PTR2NV(pointer) + INT2PTR(pointertotype, integer) + +For example: + + IV iv = ...; + SV *sv = INT2PTR(SV*, iv); + +and + + AV *av = ...; + UV uv = PTR2UV(av); =head2 Source Documentation @@ -1941,8 +2165,7 @@ produced a new character set containing all the characters you can possibly think of and more. There are several ways of representing these characters, and the one Perl uses is called UTF8. UTF8 uses a variable number of bytes to represent a character, instead of just -one. You can learn more about Unicode at -L +one. You can learn more about Unicode at http://www.unicode.org/ =head2 How can I recognise a UTF8 string? @@ -1963,7 +2186,7 @@ whether the current character in a string is valid UTF8. As mentioned above, UTF8 uses a variable number of bytes to store a character. Characters with values 1...128 are stored in one byte, just like good ol' ASCII. Character 129 is stored as C; this -contines up to character 191, which is C. Now we've run out of +continues up to character 191, which is C. Now we've run out of bits (191 is binary C<10111111>) so we move on; 192 is C. And so it goes on, moving to three bytes at character 2048. @@ -2075,12 +2298,12 @@ However, you must not do this, for example: sv_utf8_upgrade(left); If you do this in a binary operator, you will actually change one of the -strings that came into the operator, and, while it shouldn't be noticable +strings that came into the operator, and, while it shouldn't be noticeable by the end user, it can cause problems. Instead, C will give you a UTF8-encoded B of its string argument. This is useful for having the data available for -comparisons and so on, without harming the orginal SV. There's also +comparisons and so on, without harming the original SV. There's also C to go the other way, but naturally, this will fail if the string contains any characters above 255 that can't be represented in a single byte. @@ -2117,6 +2340,49 @@ high character - C is one of those. =back +=head1 Custom Operators + +Custom operator support is a new experimental feature that allows you do +define your own ops. This is primarily to allow the building of +interpreters for other languages in the Perl core, but it also allows +optimizations through the creation of "macro-ops" (ops which perform the +functions of multiple ops which are usually executed together, such as +C.) + +This feature is implemented as a new op type, C. The Perl +core does not "know" anything special about this op type, and so it will +not be involved in any optimizations. This also means that you can +define your custom ops to be any op structure - unary, binary, list and +so on - you like. + +It's important to know what custom operators won't do for you. They +won't let you add new syntax to Perl, directly. They won't even let you +add new keywords, directly. In fact, they won't change the way Perl +compiles a program at all. You have to do those changes yourself, after +Perl has compiled the program. You do this either by manipulating the op +tree using a C block and the C module, or by adding +a custom peephole optimizer with the C module. + +When you do this, you replace ordinary Perl ops with custom ops by +creating ops with the type C and the C of your own +PP function. This should be defined in XS code, and should look like +the PP ops in C. You are responsible for ensuring that your op +takes the appropriate number of values from the stack, and you are +responsible for adding stack marks if necessary. + +You should also "register" your op with the Perl interpreter so that it +can produce sensible error and warning messages. Since it is possible to +have multiple custom ops within the one "logical" op type C, +Perl uses the value of C<< o->op_ppaddr >> as a key into the +C and C hashes. This means you +need to enter a name and description for your op at the appropriate +place in the C and C hashes. + +Forthcoming versions of C (version 1.0 and above) should +directly support the creation of custom ops by name; C +will provide functions which make it trivial to "register" custom ops to +the Perl interpreter. + =head1 AUTHORS Until May 1997, this document was maintained by Jeff Okamoto