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diff --git a/upstream/mageia-cauldron/man1/perlxs.1 b/upstream/mageia-cauldron/man1/perlxs.1 new file mode 100644 index 00000000..4445c22a --- /dev/null +++ b/upstream/mageia-cauldron/man1/perlxs.1 @@ -0,0 +1,2656 @@ +.\" -*- mode: troff; coding: utf-8 -*- +.\" Automatically generated by Pod::Man 5.01 (Pod::Simple 3.43) +.\" +.\" Standard preamble: +.\" ======================================================================== +.de Sp \" Vertical space (when we can't use .PP) +.if t .sp .5v +.if n .sp +.. +.de Vb \" Begin verbatim text +.ft CW +.nf +.ne \\$1 +.. +.de Ve \" End verbatim text +.ft R +.fi +.. +.\" \*(C` and \*(C' are quotes in nroff, nothing in troff, for use with C<>. +.ie n \{\ +. ds C` "" +. ds C' "" +'br\} +.el\{\ +. ds C` +. ds C' +'br\} +.\" +.\" Escape single quotes in literal strings from groff's Unicode transform. +.ie \n(.g .ds Aq \(aq +.el .ds Aq ' +.\" +.\" If the F register is >0, we'll generate index entries on stderr for +.\" titles (.TH), headers (.SH), subsections (.SS), items (.Ip), and index +.\" entries marked with X<> in POD. Of course, you'll have to process the +.\" output yourself in some meaningful fashion. +.\" +.\" Avoid warning from groff about undefined register 'F'. +.de IX +.. +.nr rF 0 +.if \n(.g .if rF .nr rF 1 +.if (\n(rF:(\n(.g==0)) \{\ +. if \nF \{\ +. de IX +. tm Index:\\$1\t\\n%\t"\\$2" +.. +. if !\nF==2 \{\ +. nr % 0 +. nr F 2 +. \} +. \} +.\} +.rr rF +.\" ======================================================================== +.\" +.IX Title "PERLXS 1" +.TH PERLXS 1 2023-11-28 "perl v5.38.2" "Perl Programmers Reference Guide" +.\" For nroff, turn off justification. Always turn off hyphenation; it makes +.\" way too many mistakes in technical documents. +.if n .ad l +.nh +.SH NAME +perlxs \- XS language reference manual +.SH DESCRIPTION +.IX Header "DESCRIPTION" +.SS Introduction +.IX Subsection "Introduction" +XS is an interface description file format used to create an extension +interface between Perl and C code (or a C library) which one wishes +to use with Perl. The XS interface is combined with the library to +create a new library which can then be either dynamically loaded +or statically linked into perl. The XS interface description is +written in the XS language and is the core component of the Perl +extension interface. +.PP +Before writing XS, read the "CAVEATS" section below. +.PP +An \fBXSUB\fR forms the basic unit of the XS interface. After compilation +by the \fBxsubpp\fR compiler, each XSUB amounts to a C function definition +which will provide the glue between Perl calling conventions and C +calling conventions. +.PP +The glue code pulls the arguments from the Perl stack, converts these +Perl values to the formats expected by a C function, calls this C function, +and then transfers the return values of the C function back to Perl. +Return values here may be a conventional C return value or any C +function arguments that may serve as output parameters. These return +values may be passed back to Perl either by putting them on the +Perl stack, or by modifying the arguments supplied from the Perl side. +.PP +The above is a somewhat simplified view of what really happens. Since +Perl allows more flexible calling conventions than C, XSUBs may do much +more in practice, such as checking input parameters for validity, +throwing exceptions (or returning undef/empty list) if the return value +from the C function indicates failure, calling different C functions +based on numbers and types of the arguments, providing an object-oriented +interface, etc. +.PP +Of course, one could write such glue code directly in C. However, this +would be a tedious task, especially if one needs to write glue for +multiple C functions, and/or one is not familiar enough with the Perl +stack discipline and other such arcana. XS comes to the rescue here: +instead of writing this glue C code in long-hand, one can write +a more concise short-hand \fIdescription\fR of what should be done by +the glue, and let the XS compiler \fBxsubpp\fR handle the rest. +.PP +The XS language allows one to describe the mapping between how the C +routine is used, and how the corresponding Perl routine is used. It +also allows creation of Perl routines which are directly translated to +C code and which are not related to a pre-existing C function. In cases +when the C interface coincides with the Perl interface, the XSUB +declaration is almost identical to a declaration of a C function (in K&R +style). In such circumstances, there is another tool called \f(CW\*(C`h2xs\*(C'\fR +that is able to translate an entire C header file into a corresponding +XS file that will provide glue to the functions/macros described in +the header file. +.PP +The XS compiler is called \fBxsubpp\fR. This compiler creates +the constructs necessary to let an XSUB manipulate Perl values, and +creates the glue necessary to let Perl call the XSUB. The compiler +uses \fBtypemaps\fR to determine how to map C function parameters +and output values to Perl values and back. The default typemap +(which comes with Perl) handles many common C types. A supplementary +typemap may also be needed to handle any special structures and types +for the library being linked. For more information on typemaps, +see perlxstypemap. +.PP +A file in XS format starts with a C language section which goes until the +first \f(CW\*(C`MODULE =\*(C'\fR directive. Other XS directives and XSUB definitions +may follow this line. The "language" used in this part of the file +is usually referred to as the XS language. \fBxsubpp\fR recognizes and +skips POD (see perlpod) in both the C and XS language sections, which +allows the XS file to contain embedded documentation. +.PP +See perlxstut for a tutorial on the whole extension creation process. +.PP +Note: For some extensions, Dave Beazley's SWIG system may provide a +significantly more convenient mechanism for creating the extension +glue code. See <http://www.swig.org/> for more information. +.PP +For simple bindings to C libraries as well as other machine code libraries, +consider instead using the much simpler +libffi <http://sourceware.org/libffi/> interface via CPAN modules like +FFI::Platypus or FFI::Raw. +.SS "On The Road" +.IX Subsection "On The Road" +Many of the examples which follow will concentrate on creating an interface +between Perl and the ONC+ RPC bind library functions. The \fBrpcb_gettime()\fR +function is used to demonstrate many features of the XS language. This +function has two parameters; the first is an input parameter and the second +is an output parameter. The function also returns a status value. +.PP +.Vb 1 +\& bool_t rpcb_gettime(const char *host, time_t *timep); +.Ve +.PP +From C this function will be called with the following +statements. +.PP +.Vb 4 +\& #include <rpc/rpc.h> +\& bool_t status; +\& time_t timep; +\& status = rpcb_gettime( "localhost", &timep ); +.Ve +.PP +If an XSUB is created to offer a direct translation between this function +and Perl, then this XSUB will be used from Perl with the following code. +The \f(CW$status\fR and \f(CW$timep\fR variables will contain the output of the function. +.PP +.Vb 2 +\& use RPC; +\& $status = rpcb_gettime( "localhost", $timep ); +.Ve +.PP +The following XS file shows an XS subroutine, or XSUB, which +demonstrates one possible interface to the \fBrpcb_gettime()\fR +function. This XSUB represents a direct translation between +C and Perl and so preserves the interface even from Perl. +This XSUB will be invoked from Perl with the usage shown +above. Note that the first three #include statements, for +\&\f(CW\*(C`EXTERN.h\*(C'\fR, \f(CW\*(C`perl.h\*(C'\fR, and \f(CW\*(C`XSUB.h\*(C'\fR, will always be present at the +beginning of an XS file. This approach and others will be +expanded later in this document. A #define for \f(CW\*(C`PERL_NO_GET_CONTEXT\*(C'\fR +should be present to fetch the interpreter context more efficiently, +see perlguts for details. +.PP +.Vb 5 +\& #define PERL_NO_GET_CONTEXT +\& #include "EXTERN.h" +\& #include "perl.h" +\& #include "XSUB.h" +\& #include <rpc/rpc.h> +\& +\& MODULE = RPC PACKAGE = RPC +\& +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& OUTPUT: +\& timep +.Ve +.PP +Any extension to Perl, including those containing XSUBs, +should have a Perl module to serve as the bootstrap which +pulls the extension into Perl. This module will export the +extension's functions and variables to the Perl program and +will cause the extension's XSUBs to be linked into Perl. +The following module will be used for most of the examples +in this document and should be used from Perl with the \f(CW\*(C`use\*(C'\fR +command as shown earlier. Perl modules are explained in +more detail later in this document. +.PP +.Vb 1 +\& package RPC; +\& +\& require Exporter; +\& require DynaLoader; +\& @ISA = qw(Exporter DynaLoader); +\& @EXPORT = qw( rpcb_gettime ); +\& +\& bootstrap RPC; +\& 1; +.Ve +.PP +Throughout this document a variety of interfaces to the \fBrpcb_gettime()\fR +XSUB will be explored. The XSUBs will take their parameters in different +orders or will take different numbers of parameters. In each case the +XSUB is an abstraction between Perl and the real C \fBrpcb_gettime()\fR +function, and the XSUB must always ensure that the real \fBrpcb_gettime()\fR +function is called with the correct parameters. This abstraction will +allow the programmer to create a more Perl-like interface to the C +function. +.SS "The Anatomy of an XSUB" +.IX Subsection "The Anatomy of an XSUB" +The simplest XSUBs consist of 3 parts: a description of the return +value, the name of the XSUB routine and the names of its arguments, +and a description of types or formats of the arguments. +.PP +The following XSUB allows a Perl program to access a C library function +called \fBsin()\fR. The XSUB will imitate the C function which takes a single +argument and returns a single value. +.PP +.Vb 3 +\& double +\& sin(x) +\& double x +.Ve +.PP +Optionally, one can merge the description of types and the list of +argument names, rewriting this as +.PP +.Vb 2 +\& double +\& sin(double x) +.Ve +.PP +This makes this XSUB look similar to an ANSI C declaration. An optional +semicolon is allowed after the argument list, as in +.PP +.Vb 2 +\& double +\& sin(double x); +.Ve +.PP +Parameters with C pointer types can have different semantic: C functions +with similar declarations +.PP +.Vb 2 +\& bool string_looks_as_a_number(char *s); +\& bool make_char_uppercase(char *c); +.Ve +.PP +are used in absolutely incompatible manner. Parameters to these functions +could be described to \fBxsubpp\fR like this: +.PP +.Vb 2 +\& char * s +\& char &c +.Ve +.PP +Both these XS declarations correspond to the \f(CW\*(C`char*\*(C'\fR C type, but they have +different semantics, see "The & Unary Operator". +.PP +It is convenient to think that the indirection operator +\&\f(CW\*(C`*\*(C'\fR should be considered as a part of the type and the address operator \f(CW\*(C`&\*(C'\fR +should be considered part of the variable. See perlxstypemap +for more info about handling qualifiers and unary operators in C types. +.PP +The function name and the return type must be placed on +separate lines and should be flush left-adjusted. +.PP +.Vb 1 +\& INCORRECT CORRECT +\& +\& double sin(x) double +\& double x sin(x) +\& double x +.Ve +.PP +The rest of the function description may be indented or left-adjusted. The +following example shows a function with its body left-adjusted. Most +examples in this document will indent the body for better readability. +.PP +.Vb 1 +\& CORRECT +\& +\& double +\& sin(x) +\& double x +.Ve +.PP +More complicated XSUBs may contain many other sections. Each section of +an XSUB starts with the corresponding keyword, such as INIT: or CLEANUP:. +However, the first two lines of an XSUB always contain the same data: +descriptions of the return type and the names of the function and its +parameters. Whatever immediately follows these is considered to be +an INPUT: section unless explicitly marked with another keyword. +(See "The INPUT: Keyword".) +.PP +An XSUB section continues until another section-start keyword is found. +.SS "The Argument Stack" +.IX Subsection "The Argument Stack" +The Perl argument stack is used to store the values which are +sent as parameters to the XSUB and to store the XSUB's +return value(s). In reality all Perl functions (including non-XSUB +ones) keep their values on this stack all the same time, each limited +to its own range of positions on the stack. In this document the +first position on that stack which belongs to the active +function will be referred to as position 0 for that function. +.PP +XSUBs refer to their stack arguments with the macro \fBST(x)\fR, where \fIx\fR +refers to a position in this XSUB's part of the stack. Position 0 for that +function would be known to the XSUB as \fBST\fR\|(0). The XSUB's incoming +parameters and outgoing return values always begin at \fBST\fR\|(0). For many +simple cases the \fBxsubpp\fR compiler will generate the code necessary to +handle the argument stack by embedding code fragments found in the +typemaps. In more complex cases the programmer must supply the code. +.SS "The RETVAL Variable" +.IX Subsection "The RETVAL Variable" +The RETVAL variable is a special C variable that is declared automatically +for you. The C type of RETVAL matches the return type of the C library +function. The \fBxsubpp\fR compiler will declare this variable in each XSUB +with non\-\f(CW\*(C`void\*(C'\fR return type. By default the generated C function +will use RETVAL to hold the return value of the C library function being +called. In simple cases the value of RETVAL will be placed in \fBST\fR\|(0) of +the argument stack where it can be received by Perl as the return value +of the XSUB. +.PP +If the XSUB has a return type of \f(CW\*(C`void\*(C'\fR then the compiler will +not declare a RETVAL variable for that function. When using +a PPCODE: section no manipulation of the RETVAL variable is required, the +section may use direct stack manipulation to place output values on the stack. +.PP +If PPCODE: directive is not used, \f(CW\*(C`void\*(C'\fR return value should be used +only for subroutines which do not return a value, \fIeven if\fR CODE: +directive is used which sets \fBST\fR\|(0) explicitly. +.PP +Older versions of this document recommended to use \f(CW\*(C`void\*(C'\fR return +value in such cases. It was discovered that this could lead to +segfaults in cases when XSUB was \fItruly\fR \f(CW\*(C`void\*(C'\fR. This practice is +now deprecated, and may be not supported at some future version. Use +the return value \f(CW\*(C`SV *\*(C'\fR in such cases. (Currently \f(CW\*(C`xsubpp\*(C'\fR contains +some heuristic code which tries to disambiguate between "truly-void" +and "old-practice-declared-as-void" functions. Hence your code is at +mercy of this heuristics unless you use \f(CW\*(C`SV *\*(C'\fR as return value.) +.SS "Returning SVs, AVs and HVs through RETVAL" +.IX Subsection "Returning SVs, AVs and HVs through RETVAL" +When you're using RETVAL to return an \f(CW\*(C`SV *\*(C'\fR, there's some magic +going on behind the scenes that should be mentioned. When you're +manipulating the argument stack using the ST(x) macro, for example, +you usually have to pay special attention to reference counts. (For +more about reference counts, see perlguts.) To make your life +easier, the typemap file automatically makes \f(CW\*(C`RETVAL\*(C'\fR mortal when +you're returning an \f(CW\*(C`SV *\*(C'\fR. Thus, the following two XSUBs are more +or less equivalent: +.PP +.Vb 6 +\& void +\& alpha() +\& PPCODE: +\& ST(0) = newSVpv("Hello World",0); +\& sv_2mortal(ST(0)); +\& XSRETURN(1); +\& +\& SV * +\& beta() +\& CODE: +\& RETVAL = newSVpv("Hello World",0); +\& OUTPUT: +\& RETVAL +.Ve +.PP +This is quite useful as it usually improves readability. While +this works fine for an \f(CW\*(C`SV *\*(C'\fR, it's unfortunately not as easy +to have \f(CW\*(C`AV *\*(C'\fR or \f(CW\*(C`HV *\*(C'\fR as a return value. You \fIshould\fR be +able to write: +.PP +.Vb 7 +\& AV * +\& array() +\& CODE: +\& RETVAL = newAV(); +\& /* do something with RETVAL */ +\& OUTPUT: +\& RETVAL +.Ve +.PP +But due to an unfixable bug (fixing it would break lots of existing +CPAN modules) in the typemap file, the reference count of the \f(CW\*(C`AV *\*(C'\fR +is not properly decremented. Thus, the above XSUB would leak memory +whenever it is being called. The same problem exists for \f(CW\*(C`HV *\*(C'\fR, +\&\f(CW\*(C`CV *\*(C'\fR, and \f(CW\*(C`SVREF\*(C'\fR (which indicates a scalar reference, not +a general \f(CW\*(C`SV *\*(C'\fR). +In XS code on perls starting with perl 5.16, you can override the +typemaps for any of these types with a version that has proper +handling of refcounts. In your \f(CW\*(C`TYPEMAP\*(C'\fR section, do +.PP +.Vb 1 +\& AV* T_AVREF_REFCOUNT_FIXED +.Ve +.PP +to get the repaired variant. For backward compatibility with older +versions of perl, you can instead decrement the reference count +manually when you're returning one of the aforementioned +types using \f(CW\*(C`sv_2mortal\*(C'\fR: +.PP +.Vb 8 +\& AV * +\& array() +\& CODE: +\& RETVAL = newAV(); +\& sv_2mortal((SV*)RETVAL); +\& /* do something with RETVAL */ +\& OUTPUT: +\& RETVAL +.Ve +.PP +Remember that you don't have to do this for an \f(CW\*(C`SV *\*(C'\fR. The reference +documentation for all core typemaps can be found in perlxstypemap. +.SS "The MODULE Keyword" +.IX Subsection "The MODULE Keyword" +The MODULE keyword is used to start the XS code and to specify the package +of the functions which are being defined. All text preceding the first +MODULE keyword is considered C code and is passed through to the output with +POD stripped, but otherwise untouched. Every XS module will have a +bootstrap function which is used to hook the XSUBs into Perl. The package +name of this bootstrap function will match the value of the last MODULE +statement in the XS source files. The value of MODULE should always remain +constant within the same XS file, though this is not required. +.PP +The following example will start the XS code and will place +all functions in a package named RPC. +.PP +.Vb 1 +\& MODULE = RPC +.Ve +.SS "The PACKAGE Keyword" +.IX Subsection "The PACKAGE Keyword" +When functions within an XS source file must be separated into packages +the PACKAGE keyword should be used. This keyword is used with the MODULE +keyword and must follow immediately after it when used. +.PP +.Vb 1 +\& MODULE = RPC PACKAGE = RPC +\& +\& [ XS code in package RPC ] +\& +\& MODULE = RPC PACKAGE = RPCB +\& +\& [ XS code in package RPCB ] +\& +\& MODULE = RPC PACKAGE = RPC +\& +\& [ XS code in package RPC ] +.Ve +.PP +The same package name can be used more than once, allowing for +non-contiguous code. This is useful if you have a stronger ordering +principle than package names. +.PP +Although this keyword is optional and in some cases provides redundant +information it should always be used. This keyword will ensure that the +XSUBs appear in the desired package. +.SS "The PREFIX Keyword" +.IX Subsection "The PREFIX Keyword" +The PREFIX keyword designates prefixes which should be +removed from the Perl function names. If the C function is +\&\f(CWrpcb_gettime()\fR and the PREFIX value is \f(CW\*(C`rpcb_\*(C'\fR then Perl will +see this function as \f(CWgettime()\fR. +.PP +This keyword should follow the PACKAGE keyword when used. +If PACKAGE is not used then PREFIX should follow the MODULE +keyword. +.PP +.Vb 1 +\& MODULE = RPC PREFIX = rpc_ +\& +\& MODULE = RPC PACKAGE = RPCB PREFIX = rpcb_ +.Ve +.SS "The OUTPUT: Keyword" +.IX Subsection "The OUTPUT: Keyword" +The OUTPUT: keyword indicates that certain function parameters should be +updated (new values made visible to Perl) when the XSUB terminates or that +certain values should be returned to the calling Perl function. For +simple functions which have no CODE: or PPCODE: section, +such as the \fBsin()\fR function above, the RETVAL variable is +automatically designated as an output value. For more complex functions +the \fBxsubpp\fR compiler will need help to determine which variables are output +variables. +.PP +This keyword will normally be used to complement the CODE: keyword. +The RETVAL variable is not recognized as an output variable when the +CODE: keyword is present. The OUTPUT: keyword is used in this +situation to tell the compiler that RETVAL really is an output +variable. +.PP +The OUTPUT: keyword can also be used to indicate that function parameters +are output variables. This may be necessary when a parameter has been +modified within the function and the programmer would like the update to +be seen by Perl. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& OUTPUT: +\& timep +.Ve +.PP +The OUTPUT: keyword will also allow an output parameter to +be mapped to a matching piece of code rather than to a +typemap. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& OUTPUT: +\& timep sv_setnv(ST(1), (double)timep); +.Ve +.PP +\&\fBxsubpp\fR emits an automatic \f(CWSvSETMAGIC()\fR for all parameters in the +OUTPUT section of the XSUB, except RETVAL. This is the usually desired +behavior, as it takes care of properly invoking 'set' magic on output +parameters (needed for hash or array element parameters that must be +created if they didn't exist). If for some reason, this behavior is +not desired, the OUTPUT section may contain a \f(CW\*(C`SETMAGIC: DISABLE\*(C'\fR line +to disable it for the remainder of the parameters in the OUTPUT section. +Likewise, \f(CW\*(C`SETMAGIC: ENABLE\*(C'\fR can be used to reenable it for the +remainder of the OUTPUT section. See perlguts for more details +about 'set' magic. +.SS "The NO_OUTPUT Keyword" +.IX Subsection "The NO_OUTPUT Keyword" +The NO_OUTPUT can be placed as the first token of the XSUB. This keyword +indicates that while the C subroutine we provide an interface to has +a non\-\f(CW\*(C`void\*(C'\fR return type, the return value of this C subroutine should not +be returned from the generated Perl subroutine. +.PP +With this keyword present "The RETVAL Variable" is created, and in the +generated call to the subroutine this variable is assigned to, but the value +of this variable is not going to be used in the auto-generated code. +.PP +This keyword makes sense only if \f(CW\*(C`RETVAL\*(C'\fR is going to be accessed by the +user-supplied code. It is especially useful to make a function interface +more Perl-like, especially when the C return value is just an error condition +indicator. For example, +.PP +.Vb 5 +\& NO_OUTPUT int +\& delete_file(char *name) +\& POSTCALL: +\& if (RETVAL != 0) +\& croak("Error %d while deleting file \*(Aq%s\*(Aq", RETVAL, name); +.Ve +.PP +Here the generated XS function returns nothing on success, and will \fBdie()\fR +with a meaningful error message on error. +.SS "The CODE: Keyword" +.IX Subsection "The CODE: Keyword" +This keyword is used in more complicated XSUBs which require +special handling for the C function. The RETVAL variable is +still declared, but it will not be returned unless it is specified +in the OUTPUT: section. +.PP +The following XSUB is for a C function which requires special handling of +its parameters. The Perl usage is given first. +.PP +.Vb 1 +\& $status = rpcb_gettime( "localhost", $timep ); +.Ve +.PP +The XSUB follows. +.PP +.Vb 9 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t timep +\& CODE: +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.SS "The INIT: Keyword" +.IX Subsection "The INIT: Keyword" +The INIT: keyword allows initialization to be inserted into the XSUB before +the compiler generates the call to the C function. Unlike the CODE: keyword +above, this keyword does not affect the way the compiler handles RETVAL. +.PP +.Vb 8 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& INIT: +\& printf("# Host is %s\en", host ); +\& OUTPUT: +\& timep +.Ve +.PP +Another use for the INIT: section is to check for preconditions before +making a call to the C function: +.PP +.Vb 9 +\& long long +\& lldiv(a,b) +\& long long a +\& long long b +\& INIT: +\& if (a == 0 && b == 0) +\& XSRETURN_UNDEF; +\& if (b == 0) +\& croak("lldiv: cannot divide by 0"); +.Ve +.SS "The NO_INIT Keyword" +.IX Subsection "The NO_INIT Keyword" +The NO_INIT keyword is used to indicate that a function +parameter is being used only as an output value. The \fBxsubpp\fR +compiler will normally generate code to read the values of +all function parameters from the argument stack and assign +them to C variables upon entry to the function. NO_INIT +will tell the compiler that some parameters will be used for +output rather than for input and that they will be handled +before the function terminates. +.PP +The following example shows a variation of the \fBrpcb_gettime()\fR function. +This function uses the timep variable only as an output variable and does +not care about its initial contents. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep = NO_INIT +\& OUTPUT: +\& timep +.Ve +.SS "The TYPEMAP: Keyword" +.IX Subsection "The TYPEMAP: Keyword" +Starting with Perl 5.16, you can embed typemaps into your XS code +instead of or in addition to typemaps in a separate file. Multiple +such embedded typemaps will be processed in order of appearance in +the XS code and like local typemap files take precedence over the +default typemap, the embedded typemaps may overwrite previous +definitions of TYPEMAP, INPUT, and OUTPUT stanzas. The syntax for +embedded typemaps is +.PP +.Vb 3 +\& TYPEMAP: <<HERE +\& ... your typemap code here ... +\& HERE +.Ve +.PP +where the \f(CW\*(C`TYPEMAP\*(C'\fR keyword must appear in the first column of a +new line. +.PP +Refer to perlxstypemap for details on writing typemaps. +.SS "Initializing Function Parameters" +.IX Subsection "Initializing Function Parameters" +C function parameters are normally initialized with their values from +the argument stack (which in turn contains the parameters that were +passed to the XSUB from Perl). The typemaps contain the +code segments which are used to translate the Perl values to +the C parameters. The programmer, however, is allowed to +override the typemaps and supply alternate (or additional) +initialization code. Initialization code starts with the first +\&\f(CW\*(C`=\*(C'\fR, \f(CW\*(C`;\*(C'\fR or \f(CW\*(C`+\*(C'\fR on a line in the INPUT: section. The only +exception happens if this \f(CW\*(C`;\*(C'\fR terminates the line, then this \f(CW\*(C`;\*(C'\fR +is quietly ignored. +.PP +The following code demonstrates how to supply initialization code for +function parameters. The initialization code is eval'ed within double +quotes by the compiler before it is added to the output so anything +which should be interpreted literally [mainly \f(CW\*(C`$\*(C'\fR, \f(CW\*(C`@\*(C'\fR, or \f(CW\*(C`\e\e\*(C'\fR] +must be protected with backslashes. The variables \f(CW$var\fR, \f(CW$arg\fR, +and \f(CW$type\fR can be used as in typemaps. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host = (char *)SvPVbyte_nolen($arg); +\& time_t &timep = 0; +\& OUTPUT: +\& timep +.Ve +.PP +This should not be used to supply default values for parameters. One +would normally use this when a function parameter must be processed by +another library function before it can be used. Default parameters are +covered in the next section. +.PP +If the initialization begins with \f(CW\*(C`=\*(C'\fR, then it is output in +the declaration for the input variable, replacing the initialization +supplied by the typemap. If the initialization +begins with \f(CW\*(C`;\*(C'\fR or \f(CW\*(C`+\*(C'\fR, then it is performed after +all of the input variables have been declared. In the \f(CW\*(C`;\*(C'\fR +case the initialization normally supplied by the typemap is not performed. +For the \f(CW\*(C`+\*(C'\fR case, the declaration for the variable will include the +initialization from the typemap. A global +variable, \f(CW%v\fR, is available for the truly rare case where +information from one initialization is needed in another +initialization. +.PP +Here's a truly obscure example: +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& time_t &timep; /* \e$v{timep}=@{[$v{timep}=$arg]} */ +\& char *host + SvOK($v{timep}) ? SvPVbyte_nolen($arg) : NULL; +\& OUTPUT: +\& timep +.Ve +.PP +The construct \f(CW\*(C`\e$v{timep}=@{[$v{timep}=$arg]}\*(C'\fR used in the above +example has a two-fold purpose: first, when this line is processed by +\&\fBxsubpp\fR, the Perl snippet \f(CW\*(C`$v{timep}=$arg\*(C'\fR is evaluated. Second, +the text of the evaluated snippet is output into the generated C file +(inside a C comment)! During the processing of \f(CW\*(C`char *host\*(C'\fR line, +\&\f(CW$arg\fR will evaluate to \f(CWST(0)\fR, and \f(CW$v{timep}\fR will evaluate to +\&\f(CWST(1)\fR. +.SS "Default Parameter Values" +.IX Subsection "Default Parameter Values" +Default values for XSUB arguments can be specified by placing an +assignment statement in the parameter list. The default value may +be a number, a string or the special string \f(CW\*(C`NO_INIT\*(C'\fR. Defaults should +always be used on the right-most parameters only. +.PP +To allow the XSUB for \fBrpcb_gettime()\fR to have a default host +value the parameters to the XSUB could be rearranged. The +XSUB will then call the real \fBrpcb_gettime()\fR function with +the parameters in the correct order. This XSUB can be called +from Perl with either of the following statements: +.PP +.Vb 1 +\& $status = rpcb_gettime( $timep, $host ); +\& +\& $status = rpcb_gettime( $timep ); +.Ve +.PP +The XSUB will look like the code which follows. A CODE: +block is used to call the real \fBrpcb_gettime()\fR function with +the parameters in the correct order for that function. +.PP +.Vb 9 +\& bool_t +\& rpcb_gettime(timep,host="localhost") +\& char *host +\& time_t timep = NO_INIT +\& CODE: +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.SS "The PREINIT: Keyword" +.IX Subsection "The PREINIT: Keyword" +The PREINIT: keyword allows extra variables to be declared immediately +before or after the declarations of the parameters from the INPUT: section +are emitted. +.PP +If a variable is declared inside a CODE: section it will follow any typemap +code that is emitted for the input parameters. This may result in the +declaration ending up after C code, which is C syntax error. Similar +errors may happen with an explicit \f(CW\*(C`;\*(C'\fR\-type or \f(CW\*(C`+\*(C'\fR\-type initialization of +parameters is used (see "Initializing Function Parameters"). Declaring +these variables in an INIT: section will not help. +.PP +In such cases, to force an additional variable to be declared together +with declarations of other variables, place the declaration into a +PREINIT: section. The PREINIT: keyword may be used one or more times +within an XSUB. +.PP +The following examples are equivalent, but if the code is using complex +typemaps then the first example is safer. +.PP +.Vb 10 +\& bool_t +\& rpcb_gettime(timep) +\& time_t timep = NO_INIT +\& PREINIT: +\& char *host = "localhost"; +\& CODE: +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +For this particular case an INIT: keyword would generate the +same C code as the PREINIT: keyword. Another correct, but error-prone example: +.PP +.Vb 9 +\& bool_t +\& rpcb_gettime(timep) +\& time_t timep = NO_INIT +\& CODE: +\& char *host = "localhost"; +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +Another way to declare \f(CW\*(C`host\*(C'\fR is to use a C block in the CODE: section: +.PP +.Vb 11 +\& bool_t +\& rpcb_gettime(timep) +\& time_t timep = NO_INIT +\& CODE: +\& { +\& char *host = "localhost"; +\& RETVAL = rpcb_gettime( host, &timep ); +\& } +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +The ability to put additional declarations before the typemap entries are +processed is very handy in the cases when typemap conversions manipulate +some global state: +.PP +.Vb 8 +\& MyObject +\& mutate(o) +\& PREINIT: +\& MyState st = global_state; +\& INPUT: +\& MyObject o; +\& CLEANUP: +\& reset_to(global_state, st); +.Ve +.PP +Here we suppose that conversion to \f(CW\*(C`MyObject\*(C'\fR in the INPUT: section and from +MyObject when processing RETVAL will modify a global variable \f(CW\*(C`global_state\*(C'\fR. +After these conversions are performed, we restore the old value of +\&\f(CW\*(C`global_state\*(C'\fR (to avoid memory leaks, for example). +.PP +There is another way to trade clarity for compactness: INPUT sections allow +declaration of C variables which do not appear in the parameter list of +a subroutine. Thus the above code for \fBmutate()\fR can be rewritten as +.PP +.Vb 6 +\& MyObject +\& mutate(o) +\& MyState st = global_state; +\& MyObject o; +\& CLEANUP: +\& reset_to(global_state, st); +.Ve +.PP +and the code for \fBrpcb_gettime()\fR can be rewritten as +.PP +.Vb 9 +\& bool_t +\& rpcb_gettime(timep) +\& time_t timep = NO_INIT +\& char *host = "localhost"; +\& C_ARGS: +\& host, &timep +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.SS "The SCOPE: Keyword" +.IX Subsection "The SCOPE: Keyword" +The SCOPE: keyword allows scoping to be enabled for a particular XSUB. If +enabled, the XSUB will invoke ENTER and LEAVE automatically. +.PP +To support potentially complex type mappings, if a typemap entry used +by an XSUB contains a comment like \f(CW\*(C`/*scope*/\*(C'\fR then scoping will +be automatically enabled for that XSUB. +.PP +To enable scoping: +.PP +.Vb 1 +\& SCOPE: ENABLE +.Ve +.PP +To disable scoping: +.PP +.Vb 1 +\& SCOPE: DISABLE +.Ve +.SS "The INPUT: Keyword" +.IX Subsection "The INPUT: Keyword" +The XSUB's parameters are usually evaluated immediately after entering the +XSUB. The INPUT: keyword can be used to force those parameters to be +evaluated a little later. The INPUT: keyword can be used multiple times +within an XSUB and can be used to list one or more input variables. This +keyword is used with the PREINIT: keyword. +.PP +The following example shows how the input parameter \f(CW\*(C`timep\*(C'\fR can be +evaluated late, after a PREINIT. +.PP +.Vb 10 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& PREINIT: +\& time_t tt; +\& INPUT: +\& time_t timep +\& CODE: +\& RETVAL = rpcb_gettime( host, &tt ); +\& timep = tt; +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +The next example shows each input parameter evaluated late. +.PP +.Vb 10 +\& bool_t +\& rpcb_gettime(host,timep) +\& PREINIT: +\& time_t tt; +\& INPUT: +\& char *host +\& PREINIT: +\& char *h; +\& INPUT: +\& time_t timep +\& CODE: +\& h = host; +\& RETVAL = rpcb_gettime( h, &tt ); +\& timep = tt; +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +Since INPUT sections allow declaration of C variables which do not appear +in the parameter list of a subroutine, this may be shortened to: +.PP +.Vb 12 +\& bool_t +\& rpcb_gettime(host,timep) +\& time_t tt; +\& char *host; +\& char *h = host; +\& time_t timep; +\& CODE: +\& RETVAL = rpcb_gettime( h, &tt ); +\& timep = tt; +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +(We used our knowledge that input conversion for \f(CW\*(C`char *\*(C'\fR is a "simple" one, +thus \f(CW\*(C`host\*(C'\fR is initialized on the declaration line, and our assignment +\&\f(CW\*(C`h = host\*(C'\fR is not performed too early. Otherwise one would need to have the +assignment \f(CW\*(C`h = host\*(C'\fR in a CODE: or INIT: section.) +.SS "The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords" +.IX Subsection "The IN/OUTLIST/IN_OUTLIST/OUT/IN_OUT Keywords" +In the list of parameters for an XSUB, one can precede parameter names +by the \f(CW\*(C`IN\*(C'\fR/\f(CW\*(C`OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUTLIST\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR/\f(CW\*(C`IN_OUT\*(C'\fR keywords. +\&\f(CW\*(C`IN\*(C'\fR keyword is the default, the other keywords indicate how the Perl +interface should differ from the C interface. +.PP +Parameters preceded by \f(CW\*(C`OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUTLIST\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR/\f(CW\*(C`IN_OUT\*(C'\fR +keywords are considered to be used by the C subroutine \fIvia +pointers\fR. \f(CW\*(C`OUTLIST\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR keywords indicate that the C subroutine +does not inspect the memory pointed by this parameter, but will write +through this pointer to provide additional return values. +.PP +Parameters preceded by \f(CW\*(C`OUTLIST\*(C'\fR keyword do not appear in the usage +signature of the generated Perl function. +.PP +Parameters preceded by \f(CW\*(C`IN_OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUT\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR \fIdo\fR appear as +parameters to the Perl function. With the exception of +\&\f(CW\*(C`OUT\*(C'\fR\-parameters, these parameters are converted to the corresponding +C type, then pointers to these data are given as arguments to the C +function. It is expected that the C function will write through these +pointers. +.PP +The return list of the generated Perl function consists of the C return value +from the function (unless the XSUB is of \f(CW\*(C`void\*(C'\fR return type or +\&\f(CW\*(C`The NO_OUTPUT Keyword\*(C'\fR was used) followed by all the \f(CW\*(C`OUTLIST\*(C'\fR +and \f(CW\*(C`IN_OUTLIST\*(C'\fR parameters (in the order of appearance). On the +return from the XSUB the \f(CW\*(C`IN_OUT\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR Perl parameter will be +modified to have the values written by the C function. +.PP +For example, an XSUB +.PP +.Vb 5 +\& void +\& day_month(OUTLIST day, IN unix_time, OUTLIST month) +\& int day +\& int unix_time +\& int month +.Ve +.PP +should be used from Perl as +.PP +.Vb 1 +\& my ($day, $month) = day_month(time); +.Ve +.PP +The C signature of the corresponding function should be +.PP +.Vb 1 +\& void day_month(int *day, int unix_time, int *month); +.Ve +.PP +The \f(CW\*(C`IN\*(C'\fR/\f(CW\*(C`OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUT\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR keywords can be +mixed with ANSI-style declarations, as in +.PP +.Vb 2 +\& void +\& day_month(OUTLIST int day, int unix_time, OUTLIST int month) +.Ve +.PP +(here the optional \f(CW\*(C`IN\*(C'\fR keyword is omitted). +.PP +The \f(CW\*(C`IN_OUT\*(C'\fR parameters are identical with parameters introduced with +"The & Unary Operator" and put into the \f(CW\*(C`OUTPUT:\*(C'\fR section (see +"The OUTPUT: Keyword"). The \f(CW\*(C`IN_OUTLIST\*(C'\fR parameters are very similar, +the only difference being that the value C function writes through the +pointer would not modify the Perl parameter, but is put in the output +list. +.PP +The \f(CW\*(C`OUTLIST\*(C'\fR/\f(CW\*(C`OUT\*(C'\fR parameter differ from \f(CW\*(C`IN_OUTLIST\*(C'\fR/\f(CW\*(C`IN_OUT\*(C'\fR +parameters only by the initial value of the Perl parameter not +being read (and not being given to the C function \- which gets some +garbage instead). For example, the same C function as above can be +interfaced with as +.PP +.Vb 1 +\& void day_month(OUT int day, int unix_time, OUT int month); +.Ve +.PP +or +.PP +.Vb 8 +\& void +\& day_month(day, unix_time, month) +\& int &day = NO_INIT +\& int unix_time +\& int &month = NO_INIT +\& OUTPUT: +\& day +\& month +.Ve +.PP +However, the generated Perl function is called in very C\-ish style: +.PP +.Vb 2 +\& my ($day, $month); +\& day_month($day, time, $month); +.Ve +.ie n .SS "The length(NAME) Keyword" +.el .SS "The \f(CWlength(NAME)\fP Keyword" +.IX Subsection "The length(NAME) Keyword" +If one of the input arguments to the C function is the length of a string +argument \f(CW\*(C`NAME\*(C'\fR, one can substitute the name of the length-argument by +\&\f(CWlength(NAME)\fR in the XSUB declaration. This argument must be omitted when +the generated Perl function is called. E.g., +.PP +.Vb 9 +\& void +\& dump_chars(char *s, short l) +\& { +\& short n = 0; +\& while (n < l) { +\& printf("s[%d] = \e"\e\e%#03o\e"\en", n, (int)s[n]); +\& n++; +\& } +\& } +\& +\& MODULE = x PACKAGE = x +\& +\& void dump_chars(char *s, short length(s)) +.Ve +.PP +should be called as \f(CWdump_chars($string)\fR. +.PP +This directive is supported with ANSI-type function declarations only. +.SS "Variable-length Parameter Lists" +.IX Subsection "Variable-length Parameter Lists" +XSUBs can have variable-length parameter lists by specifying an ellipsis +\&\f(CW\*(C`(...)\*(C'\fR in the parameter list. This use of the ellipsis is similar to that +found in ANSI C. The programmer is able to determine the number of +arguments passed to the XSUB by examining the \f(CW\*(C`items\*(C'\fR variable which the +\&\fBxsubpp\fR compiler supplies for all XSUBs. By using this mechanism one can +create an XSUB which accepts a list of parameters of unknown length. +.PP +The \fIhost\fR parameter for the \fBrpcb_gettime()\fR XSUB can be +optional so the ellipsis can be used to indicate that the +XSUB will take a variable number of parameters. Perl should +be able to call this XSUB with either of the following statements. +.PP +.Vb 1 +\& $status = rpcb_gettime( $timep, $host ); +\& +\& $status = rpcb_gettime( $timep ); +.Ve +.PP +The XS code, with ellipsis, follows. +.PP +.Vb 12 +\& bool_t +\& rpcb_gettime(timep, ...) +\& time_t timep = NO_INIT +\& PREINIT: +\& char *host = "localhost"; +\& CODE: +\& if( items > 1 ) +\& host = (char *)SvPVbyte_nolen(ST(1)); +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.SS "The C_ARGS: Keyword" +.IX Subsection "The C_ARGS: Keyword" +The C_ARGS: keyword allows creating of XSUBS which have different +calling sequence from Perl than from C, without a need to write +CODE: or PPCODE: section. The contents of the C_ARGS: paragraph is +put as the argument to the called C function without any change. +.PP +For example, suppose that a C function is declared as +.PP +.Vb 1 +\& symbolic nth_derivative(int n, symbolic function, int flags); +.Ve +.PP +and that the default flags are kept in a global C variable +\&\f(CW\*(C`default_flags\*(C'\fR. Suppose that you want to create an interface which +is called as +.PP +.Vb 1 +\& $second_deriv = $function\->nth_derivative(2); +.Ve +.PP +To do this, declare the XSUB as +.PP +.Vb 6 +\& symbolic +\& nth_derivative(function, n) +\& symbolic function +\& int n +\& C_ARGS: +\& n, function, default_flags +.Ve +.SS "The PPCODE: Keyword" +.IX Subsection "The PPCODE: Keyword" +The PPCODE: keyword is an alternate form of the CODE: keyword and is used +to tell the \fBxsubpp\fR compiler that the programmer is supplying the code to +control the argument stack for the XSUBs return values. Occasionally one +will want an XSUB to return a list of values rather than a single value. +In these cases one must use PPCODE: and then explicitly push the list of +values on the stack. The PPCODE: and CODE: keywords should not be used +together within the same XSUB. +.PP +The actual difference between PPCODE: and CODE: sections is in the +initialization of \f(CW\*(C`SP\*(C'\fR macro (which stands for the \fIcurrent\fR Perl +stack pointer), and in the handling of data on the stack when returning +from an XSUB. In CODE: sections SP preserves the value which was on +entry to the XSUB: SP is on the function pointer (which follows the +last parameter). In PPCODE: sections SP is moved backward to the +beginning of the parameter list, which allows \f(CW\*(C`PUSH*()\*(C'\fR macros +to place output values in the place Perl expects them to be when +the XSUB returns back to Perl. +.PP +The generated trailer for a CODE: section ensures that the number of return +values Perl will see is either 0 or 1 (depending on the \f(CW\*(C`void\*(C'\fRness of the +return value of the C function, and heuristics mentioned in +"The RETVAL Variable"). The trailer generated for a PPCODE: section +is based on the number of return values and on the number of times +\&\f(CW\*(C`SP\*(C'\fR was updated by \f(CW\*(C`[X]PUSH*()\*(C'\fR macros. +.PP +Note that macros \f(CWST(i)\fR, \f(CW\*(C`XST_m*()\*(C'\fR and \f(CW\*(C`XSRETURN*()\*(C'\fR work equally +well in CODE: sections and PPCODE: sections. +.PP +The following XSUB will call the C \fBrpcb_gettime()\fR function +and will return its two output values, timep and status, to +Perl as a single list. +.PP +.Vb 11 +\& void +\& rpcb_gettime(host) +\& char *host +\& PREINIT: +\& time_t timep; +\& bool_t status; +\& PPCODE: +\& status = rpcb_gettime( host, &timep ); +\& EXTEND(SP, 2); +\& PUSHs(sv_2mortal(newSViv(status))); +\& PUSHs(sv_2mortal(newSViv(timep))); +.Ve +.PP +Notice that the programmer must supply the C code necessary +to have the real \fBrpcb_gettime()\fR function called and to have +the return values properly placed on the argument stack. +.PP +The \f(CW\*(C`void\*(C'\fR return type for this function tells the \fBxsubpp\fR compiler that +the RETVAL variable is not needed or used and that it should not be created. +In most scenarios the void return type should be used with the PPCODE: +directive. +.PP +The \fBEXTEND()\fR macro is used to make room on the argument +stack for 2 return values. The PPCODE: directive causes the +\&\fBxsubpp\fR compiler to create a stack pointer available as \f(CW\*(C`SP\*(C'\fR, and it +is this pointer which is being used in the \fBEXTEND()\fR macro. +The values are then pushed onto the stack with the \fBPUSHs()\fR +macro. +.PP +Now the \fBrpcb_gettime()\fR function can be used from Perl with +the following statement. +.PP +.Vb 1 +\& ($status, $timep) = rpcb_gettime("localhost"); +.Ve +.PP +When handling output parameters with a PPCODE section, be sure to handle +\&'set' magic properly. See perlguts for details about 'set' magic. +.SS "Returning Undef And Empty Lists" +.IX Subsection "Returning Undef And Empty Lists" +Occasionally the programmer will want to return simply +\&\f(CW\*(C`undef\*(C'\fR or an empty list if a function fails rather than a +separate status value. The \fBrpcb_gettime()\fR function offers +just this situation. If the function succeeds we would like +to have it return the time and if it fails we would like to +have undef returned. In the following Perl code the value +of \f(CW$timep\fR will either be undef or it will be a valid time. +.PP +.Vb 1 +\& $timep = rpcb_gettime( "localhost" ); +.Ve +.PP +The following XSUB uses the \f(CW\*(C`SV *\*(C'\fR return type as a mnemonic only, +and uses a CODE: block to indicate to the compiler +that the programmer has supplied all the necessary code. The +\&\fBsv_newmortal()\fR call will initialize the return value to undef, making that +the default return value. +.PP +.Vb 10 +\& SV * +\& rpcb_gettime(host) +\& char * host +\& PREINIT: +\& time_t timep; +\& bool_t x; +\& CODE: +\& ST(0) = sv_newmortal(); +\& if( rpcb_gettime( host, &timep ) ) +\& sv_setnv( ST(0), (double)timep); +.Ve +.PP +The next example demonstrates how one would place an explicit undef in the +return value, should the need arise. +.PP +.Vb 10 +\& SV * +\& rpcb_gettime(host) +\& char * host +\& PREINIT: +\& time_t timep; +\& bool_t x; +\& CODE: +\& if( rpcb_gettime( host, &timep ) ){ +\& ST(0) = sv_newmortal(); +\& sv_setnv( ST(0), (double)timep); +\& } +\& else{ +\& ST(0) = &PL_sv_undef; +\& } +.Ve +.PP +To return an empty list one must use a PPCODE: block and +then not push return values on the stack. +.PP +.Vb 12 +\& void +\& rpcb_gettime(host) +\& char *host +\& PREINIT: +\& time_t timep; +\& PPCODE: +\& if( rpcb_gettime( host, &timep ) ) +\& PUSHs(sv_2mortal(newSViv(timep))); +\& else{ +\& /* Nothing pushed on stack, so an empty +\& * list is implicitly returned. */ +\& } +.Ve +.PP +Some people may be inclined to include an explicit \f(CW\*(C`return\*(C'\fR in the above +XSUB, rather than letting control fall through to the end. In those +situations \f(CW\*(C`XSRETURN_EMPTY\*(C'\fR should be used, instead. This will ensure that +the XSUB stack is properly adjusted. Consult perlapi for other +\&\f(CW\*(C`XSRETURN\*(C'\fR macros. +.PP +Since \f(CW\*(C`XSRETURN_*\*(C'\fR macros can be used with CODE blocks as well, one can +rewrite this example as: +.PP +.Vb 11 +\& int +\& rpcb_gettime(host) +\& char *host +\& PREINIT: +\& time_t timep; +\& CODE: +\& RETVAL = rpcb_gettime( host, &timep ); +\& if (RETVAL == 0) +\& XSRETURN_UNDEF; +\& OUTPUT: +\& RETVAL +.Ve +.PP +In fact, one can put this check into a POSTCALL: section as well. Together +with PREINIT: simplifications, this leads to: +.PP +.Vb 7 +\& int +\& rpcb_gettime(host) +\& char *host +\& time_t timep; +\& POSTCALL: +\& if (RETVAL == 0) +\& XSRETURN_UNDEF; +.Ve +.SS "The REQUIRE: Keyword" +.IX Subsection "The REQUIRE: Keyword" +The REQUIRE: keyword is used to indicate the minimum version of the +\&\fBxsubpp\fR compiler needed to compile the XS module. An XS module which +contains the following statement will compile with only \fBxsubpp\fR version +1.922 or greater: +.PP +.Vb 1 +\& REQUIRE: 1.922 +.Ve +.SS "The CLEANUP: Keyword" +.IX Subsection "The CLEANUP: Keyword" +This keyword can be used when an XSUB requires special cleanup procedures +before it terminates. When the CLEANUP: keyword is used it must follow +any CODE:, or OUTPUT: blocks which are present in the XSUB. The code +specified for the cleanup block will be added as the last statements in +the XSUB. +.SS "The POSTCALL: Keyword" +.IX Subsection "The POSTCALL: Keyword" +This keyword can be used when an XSUB requires special procedures +executed after the C subroutine call is performed. When the POSTCALL: +keyword is used it must precede OUTPUT: and CLEANUP: blocks which are +present in the XSUB. +.PP +See examples in "The NO_OUTPUT Keyword" and "Returning Undef And Empty Lists". +.PP +The POSTCALL: block does not make a lot of sense when the C subroutine +call is supplied by user by providing either CODE: or PPCODE: section. +.SS "The BOOT: Keyword" +.IX Subsection "The BOOT: Keyword" +The BOOT: keyword is used to add code to the extension's bootstrap +function. The bootstrap function is generated by the \fBxsubpp\fR compiler and +normally holds the statements necessary to register any XSUBs with Perl. +With the BOOT: keyword the programmer can tell the compiler to add extra +statements to the bootstrap function. +.PP +This keyword may be used any time after the first MODULE keyword and should +appear on a line by itself. The first blank line after the keyword will +terminate the code block. +.PP +.Vb 4 +\& BOOT: +\& # The following message will be printed when the +\& # bootstrap function executes. +\& printf("Hello from the bootstrap!\en"); +.Ve +.SS "The VERSIONCHECK: Keyword" +.IX Subsection "The VERSIONCHECK: Keyword" +The VERSIONCHECK: keyword corresponds to \fBxsubpp\fR's \f(CW\*(C`\-versioncheck\*(C'\fR and +\&\f(CW\*(C`\-noversioncheck\*(C'\fR options. This keyword overrides the command line +options. Version checking is enabled by default. When version checking is +enabled the XS module will attempt to verify that its version matches the +version of the PM module. +.PP +To enable version checking: +.PP +.Vb 1 +\& VERSIONCHECK: ENABLE +.Ve +.PP +To disable version checking: +.PP +.Vb 1 +\& VERSIONCHECK: DISABLE +.Ve +.PP +Note that if the version of the PM module is an NV (a floating point +number), it will be stringified with a possible loss of precision +(currently chopping to nine decimal places) so that it may not match +the version of the XS module anymore. Quoting the \f(CW$VERSION\fR declaration +to make it a string is recommended if long version numbers are used. +.SS "The PROTOTYPES: Keyword" +.IX Subsection "The PROTOTYPES: Keyword" +The PROTOTYPES: keyword corresponds to \fBxsubpp\fR's \f(CW\*(C`\-prototypes\*(C'\fR and +\&\f(CW\*(C`\-noprototypes\*(C'\fR options. This keyword overrides the command line options. +Prototypes are disabled by default. When prototypes are enabled, XSUBs will +be given Perl prototypes. This keyword may be used multiple times in an XS +module to enable and disable prototypes for different parts of the module. +Note that \fBxsubpp\fR will nag you if you don't explicitly enable or disable +prototypes, with: +.PP +.Vb 1 +\& Please specify prototyping behavior for Foo.xs (see perlxs manual) +.Ve +.PP +To enable prototypes: +.PP +.Vb 1 +\& PROTOTYPES: ENABLE +.Ve +.PP +To disable prototypes: +.PP +.Vb 1 +\& PROTOTYPES: DISABLE +.Ve +.SS "The PROTOTYPE: Keyword" +.IX Subsection "The PROTOTYPE: Keyword" +This keyword is similar to the PROTOTYPES: keyword above but can be used to +force \fBxsubpp\fR to use a specific prototype for the XSUB. This keyword +overrides all other prototype options and keywords but affects only the +current XSUB. Consult "Prototypes" in perlsub for information about Perl +prototypes. +.PP +.Vb 10 +\& bool_t +\& rpcb_gettime(timep, ...) +\& time_t timep = NO_INIT +\& PROTOTYPE: $;$ +\& PREINIT: +\& char *host = "localhost"; +\& CODE: +\& if( items > 1 ) +\& host = (char *)SvPVbyte_nolen(ST(1)); +\& RETVAL = rpcb_gettime( host, &timep ); +\& OUTPUT: +\& timep +\& RETVAL +.Ve +.PP +If the prototypes are enabled, you can disable it locally for a given +XSUB as in the following example: +.PP +.Vb 4 +\& void +\& rpcb_gettime_noproto() +\& PROTOTYPE: DISABLE +\& ... +.Ve +.SS "The ALIAS: Keyword" +.IX Subsection "The ALIAS: Keyword" +The ALIAS: keyword allows an XSUB to have two or more unique Perl names +and to know which of those names was used when it was invoked. The Perl +names may be fully-qualified with package names. Each alias is given an +index. The compiler will setup a variable called \f(CW\*(C`ix\*(C'\fR which contain the +index of the alias which was used. When the XSUB is called with its +declared name \f(CW\*(C`ix\*(C'\fR will be 0. +.PP +The following example will create aliases \f(CWFOO::gettime()\fR and +\&\f(CWBAR::getit()\fR for this function. +.PP +.Vb 11 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& ALIAS: +\& FOO::gettime = 1 +\& BAR::getit = 2 +\& INIT: +\& printf("# ix = %d\en", ix ); +\& OUTPUT: +\& timep +.Ve +.PP +A warning will be produced when you create more than one alias to the same +value. This may be worked around in a backwards compatible way by creating +multiple defines which resolve to the same value, or with a modern version +of ExtUtils::ParseXS you can use a symbolic alias, which are denoted with +a \f(CW\*(C`=>\*(C'\fR instead of a \f(CW\*(C`=\*(C'\fR. For instance you could change the above +so that the alias section looked like this: +.PP +.Vb 4 +\& ALIAS: +\& FOO::gettime = 1 +\& BAR::getit = 2 +\& BAZ::gettime => FOO::gettime +.Ve +.PP +this would have the same effect as this: +.PP +.Vb 4 +\& ALIAS: +\& FOO::gettime = 1 +\& BAR::getit = 2 +\& BAZ::gettime = 1 +.Ve +.PP +except that the latter will produce warnings during the build process. A +mechanism that would work in a backwards compatible way with older +versions of our tool chain would be to do this: +.PP +.Vb 3 +\& #define FOO_GETTIME 1 +\& #define BAR_GETIT 2 +\& #define BAZ_GETTIME 1 +\& +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& ALIAS: +\& FOO::gettime = FOO_GETTIME +\& BAR::getit = BAR_GETIT +\& BAZ::gettime = BAZ_GETTIME +\& INIT: +\& printf("# ix = %d\en", ix ); +\& OUTPUT: +\& timep +.Ve +.SS "The OVERLOAD: Keyword" +.IX Subsection "The OVERLOAD: Keyword" +Instead of writing an overloaded interface using pure Perl, you +can also use the OVERLOAD keyword to define additional Perl names +for your functions (like the ALIAS: keyword above). However, the +overloaded functions must be defined in such a way as to accept the number +of parameters supplied by perl's overload system. For most overload +methods, it will be three parameters; for the \f(CW\*(C`nomethod\*(C'\fR function it will +be four. However, the bitwise operators \f(CW\*(C`&\*(C'\fR, \f(CW\*(C`|\*(C'\fR, \f(CW\*(C`^\*(C'\fR, and \f(CW\*(C`~\*(C'\fR may be +called with three \fIor\fR five arguments (see overload). +.PP +If any +function has the OVERLOAD: keyword, several additional lines +will be defined in the c file generated by xsubpp in order to +register with the overload magic. +.PP +Since blessed objects are actually stored as RV's, it is useful +to use the typemap features to preprocess parameters and extract +the actual SV stored within the blessed RV. See the sample for +T_PTROBJ_SPECIAL below. +.PP +To use the OVERLOAD: keyword, create an XS function which takes +three input parameters (or use the C\-style '...' definition) like +this: +.PP +.Vb 7 +\& SV * +\& cmp (lobj, robj, swap) +\& My_Module_obj lobj +\& My_Module_obj robj +\& IV swap +\& OVERLOAD: cmp <=> +\& { /* function defined here */} +.Ve +.PP +In this case, the function will overload both of the three way +comparison operators. For all overload operations using non-alpha +characters, you must type the parameter without quoting, separating +multiple overloads with whitespace. Note that "" (the stringify +overload) should be entered as \e"\e" (i.e. escaped). +.PP +Since, as mentioned above, bitwise operators may take extra arguments, you +may want to use something like \f(CW\*(C`(lobj, robj, swap, ...)\*(C'\fR (with +literal \f(CW\*(C`...\*(C'\fR) as your parameter list. +.SS "The FALLBACK: Keyword" +.IX Subsection "The FALLBACK: Keyword" +In addition to the OVERLOAD keyword, if you need to control how +Perl autogenerates missing overloaded operators, you can set the +FALLBACK keyword in the module header section, like this: +.PP +.Vb 1 +\& MODULE = RPC PACKAGE = RPC +\& +\& FALLBACK: TRUE +\& ... +.Ve +.PP +where FALLBACK can take any of the three values TRUE, FALSE, or +UNDEF. If you do not set any FALLBACK value when using OVERLOAD, +it defaults to UNDEF. FALLBACK is not used except when one or +more functions using OVERLOAD have been defined. Please see +"fallback" in overload for more details. +.SS "The INTERFACE: Keyword" +.IX Subsection "The INTERFACE: Keyword" +This keyword declares the current XSUB as a keeper of the given +calling signature. If some text follows this keyword, it is +considered as a list of functions which have this signature, and +should be attached to the current XSUB. +.PP +For example, if you have 4 C functions \fBmultiply()\fR, \fBdivide()\fR, \fBadd()\fR, +\&\fBsubtract()\fR all having the signature: +.PP +.Vb 1 +\& symbolic f(symbolic, symbolic); +.Ve +.PP +you can make them all to use the same XSUB using this: +.PP +.Vb 7 +\& symbolic +\& interface_s_ss(arg1, arg2) +\& symbolic arg1 +\& symbolic arg2 +\& INTERFACE: +\& multiply divide +\& add subtract +.Ve +.PP +(This is the complete XSUB code for 4 Perl functions!) Four generated +Perl function share names with corresponding C functions. +.PP +The advantage of this approach comparing to ALIAS: keyword is that there +is no need to code a switch statement, each Perl function (which shares +the same XSUB) knows which C function it should call. Additionally, one +can attach an extra function \fBremainder()\fR at runtime by using +.PP +.Vb 3 +\& CV *mycv = newXSproto("Symbolic::remainder", +\& XS_Symbolic_interface_s_ss, _\|_FILE_\|_, "$$"); +\& XSINTERFACE_FUNC_SET(mycv, remainder); +.Ve +.PP +say, from another XSUB. (This example supposes that there was no +INTERFACE_MACRO: section, otherwise one needs to use something else instead of +\&\f(CW\*(C`XSINTERFACE_FUNC_SET\*(C'\fR, see the next section.) +.SS "The INTERFACE_MACRO: Keyword" +.IX Subsection "The INTERFACE_MACRO: Keyword" +This keyword allows one to define an INTERFACE using a different way +to extract a function pointer from an XSUB. The text which follows +this keyword should give the name of macros which would extract/set a +function pointer. The extractor macro is given return type, \f(CW\*(C`CV*\*(C'\fR, +and \f(CW\*(C`XSANY.any_dptr\*(C'\fR for this \f(CW\*(C`CV*\*(C'\fR. The setter macro is given cv, +and the function pointer. +.PP +The default value is \f(CW\*(C`XSINTERFACE_FUNC\*(C'\fR and \f(CW\*(C`XSINTERFACE_FUNC_SET\*(C'\fR. +An INTERFACE keyword with an empty list of functions can be omitted if +INTERFACE_MACRO keyword is used. +.PP +Suppose that in the previous example functions pointers for +\&\fBmultiply()\fR, \fBdivide()\fR, \fBadd()\fR, \fBsubtract()\fR are kept in a global C array +\&\f(CW\*(C`fp[]\*(C'\fR with offsets being \f(CW\*(C`multiply_off\*(C'\fR, \f(CW\*(C`divide_off\*(C'\fR, \f(CW\*(C`add_off\*(C'\fR, +\&\f(CW\*(C`subtract_off\*(C'\fR. Then one can use +.PP +.Vb 4 +\& #define XSINTERFACE_FUNC_BYOFFSET(ret,cv,f) \e +\& ((XSINTERFACE_CVT_ANON(ret))fp[CvXSUBANY(cv).any_i32]) +\& #define XSINTERFACE_FUNC_BYOFFSET_set(cv,f) \e +\& CvXSUBANY(cv).any_i32 = CAT2( f, _off ) +.Ve +.PP +in C section, +.PP +.Vb 10 +\& symbolic +\& interface_s_ss(arg1, arg2) +\& symbolic arg1 +\& symbolic arg2 +\& INTERFACE_MACRO: +\& XSINTERFACE_FUNC_BYOFFSET +\& XSINTERFACE_FUNC_BYOFFSET_set +\& INTERFACE: +\& multiply divide +\& add subtract +.Ve +.PP +in XSUB section. +.SS "The INCLUDE: Keyword" +.IX Subsection "The INCLUDE: Keyword" +This keyword can be used to pull other files into the XS module. The other +files may have XS code. INCLUDE: can also be used to run a command to +generate the XS code to be pulled into the module. +.PP +The file \fIRpcb1.xsh\fR contains our \f(CWrpcb_gettime()\fR function: +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& OUTPUT: +\& timep +.Ve +.PP +The XS module can use INCLUDE: to pull that file into it. +.PP +.Vb 1 +\& INCLUDE: Rpcb1.xsh +.Ve +.PP +If the parameters to the INCLUDE: keyword are followed by a pipe (\f(CW\*(C`|\*(C'\fR) then +the compiler will interpret the parameters as a command. This feature is +mildly deprecated in favour of the \f(CW\*(C`INCLUDE_COMMAND:\*(C'\fR directive, as documented +below. +.PP +.Vb 1 +\& INCLUDE: cat Rpcb1.xsh | +.Ve +.PP +Do not use this to run perl: \f(CW\*(C`INCLUDE: perl |\*(C'\fR will run the perl that +happens to be the first in your path and not necessarily the same perl that is +used to run \f(CW\*(C`xsubpp\*(C'\fR. See "The INCLUDE_COMMAND: Keyword". +.SS "The INCLUDE_COMMAND: Keyword" +.IX Subsection "The INCLUDE_COMMAND: Keyword" +Runs the supplied command and includes its output into the current XS +document. \f(CW\*(C`INCLUDE_COMMAND\*(C'\fR assigns special meaning to the \f(CW$^X\fR token +in that it runs the same perl interpreter that is running \f(CW\*(C`xsubpp\*(C'\fR: +.PP +.Vb 1 +\& INCLUDE_COMMAND: cat Rpcb1.xsh +\& +\& INCLUDE_COMMAND: $^X \-e ... +.Ve +.SS "The CASE: Keyword" +.IX Subsection "The CASE: Keyword" +The CASE: keyword allows an XSUB to have multiple distinct parts with each +part acting as a virtual XSUB. CASE: is greedy and if it is used then all +other XS keywords must be contained within a CASE:. This means nothing may +precede the first CASE: in the XSUB and anything following the last CASE: is +included in that case. +.PP +A CASE: might switch via a parameter of the XSUB, via the \f(CW\*(C`ix\*(C'\fR ALIAS: +variable (see "The ALIAS: Keyword"), or maybe via the \f(CW\*(C`items\*(C'\fR variable +(see "Variable-length Parameter Lists"). The last CASE: becomes the +\&\fBdefault\fR case if it is not associated with a conditional. The following +example shows CASE switched via \f(CW\*(C`ix\*(C'\fR with a function \f(CWrpcb_gettime()\fR +having an alias \f(CWx_gettime()\fR. When the function is called as +\&\f(CWrpcb_gettime()\fR its parameters are the usual \f(CW\*(C`(char *host, time_t *timep)\*(C'\fR, +but when the function is called as \f(CWx_gettime()\fR its parameters are +reversed, \f(CW\*(C`(time_t *timep, char *host)\*(C'\fR. +.PP +.Vb 10 +\& long +\& rpcb_gettime(a,b) +\& CASE: ix == 1 +\& ALIAS: +\& x_gettime = 1 +\& INPUT: +\& # \*(Aqa\*(Aq is timep, \*(Aqb\*(Aq is host +\& char *b +\& time_t a = NO_INIT +\& CODE: +\& RETVAL = rpcb_gettime( b, &a ); +\& OUTPUT: +\& a +\& RETVAL +\& CASE: +\& # \*(Aqa\*(Aq is host, \*(Aqb\*(Aq is timep +\& char *a +\& time_t &b = NO_INIT +\& OUTPUT: +\& b +\& RETVAL +.Ve +.PP +That function can be called with either of the following statements. Note +the different argument lists. +.PP +.Vb 1 +\& $status = rpcb_gettime( $host, $timep ); +\& +\& $status = x_gettime( $timep, $host ); +.Ve +.SS "The EXPORT_XSUB_SYMBOLS: Keyword" +.IX Subsection "The EXPORT_XSUB_SYMBOLS: Keyword" +The EXPORT_XSUB_SYMBOLS: keyword is likely something you will never need. +In perl versions earlier than 5.16.0, this keyword does nothing. Starting +with 5.16, XSUB symbols are no longer exported by default. That is, they +are \f(CW\*(C`static\*(C'\fR functions. If you include +.PP +.Vb 1 +\& EXPORT_XSUB_SYMBOLS: ENABLE +.Ve +.PP +in your XS code, the XSUBs following this line will not be declared \f(CW\*(C`static\*(C'\fR. +You can later disable this with +.PP +.Vb 1 +\& EXPORT_XSUB_SYMBOLS: DISABLE +.Ve +.PP +which, again, is the default that you should probably never change. +You cannot use this keyword on versions of perl before 5.16 to make +XSUBs \f(CW\*(C`static\*(C'\fR. +.SS "The & Unary Operator" +.IX Subsection "The & Unary Operator" +The \f(CW\*(C`&\*(C'\fR unary operator in the INPUT: section is used to tell \fBxsubpp\fR +that it should convert a Perl value to/from C using the C type to the left +of \f(CW\*(C`&\*(C'\fR, but provide a pointer to this value when the C function is called. +.PP +This is useful to avoid a CODE: block for a C function which takes a parameter +by reference. Typically, the parameter should be not a pointer type (an +\&\f(CW\*(C`int\*(C'\fR or \f(CW\*(C`long\*(C'\fR but not an \f(CW\*(C`int*\*(C'\fR or \f(CW\*(C`long*\*(C'\fR). +.PP +The following XSUB will generate incorrect C code. The \fBxsubpp\fR compiler will +turn this into code which calls \f(CWrpcb_gettime()\fR with parameters \f(CW\*(C`(char +*host, time_t timep)\*(C'\fR, but the real \f(CWrpcb_gettime()\fR wants the \f(CW\*(C`timep\*(C'\fR +parameter to be of type \f(CW\*(C`time_t*\*(C'\fR rather than \f(CW\*(C`time_t\*(C'\fR. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t timep +\& OUTPUT: +\& timep +.Ve +.PP +That problem is corrected by using the \f(CW\*(C`&\*(C'\fR operator. The \fBxsubpp\fR compiler +will now turn this into code which calls \f(CWrpcb_gettime()\fR correctly with +parameters \f(CW\*(C`(char *host, time_t *timep)\*(C'\fR. It does this by carrying the +\&\f(CW\*(C`&\*(C'\fR through, so the function call looks like \f(CW\*(C`rpcb_gettime(host, &timep)\*(C'\fR. +.PP +.Vb 6 +\& bool_t +\& rpcb_gettime(host,timep) +\& char *host +\& time_t &timep +\& OUTPUT: +\& timep +.Ve +.SS "Inserting POD, Comments and C Preprocessor Directives" +.IX Subsection "Inserting POD, Comments and C Preprocessor Directives" +C preprocessor directives are allowed within BOOT:, PREINIT: INIT:, CODE:, +PPCODE:, POSTCALL:, and CLEANUP: blocks, as well as outside the functions. +Comments are allowed anywhere after the MODULE keyword. The compiler will +pass the preprocessor directives through untouched and will remove the +commented lines. POD documentation is allowed at any point, both in the +C and XS language sections. POD must be terminated with a \f(CW\*(C`=cut\*(C'\fR command; +\&\f(CW\*(C`xsubpp\*(C'\fR will exit with an error if it does not. It is very unlikely that +human generated C code will be mistaken for POD, as most indenting styles +result in whitespace in front of any line starting with \f(CW\*(C`=\*(C'\fR. Machine +generated XS files may fall into this trap unless care is taken to +ensure that a space breaks the sequence "\en=". +.PP +Comments can be added to XSUBs by placing a \f(CW\*(C`#\*(C'\fR as the first +non-whitespace of a line. Care should be taken to avoid making the +comment look like a C preprocessor directive, lest it be interpreted as +such. The simplest way to prevent this is to put whitespace in front of +the \f(CW\*(C`#\*(C'\fR. +.PP +If you use preprocessor directives to choose one of two +versions of a function, use +.PP +.Vb 3 +\& #if ... version1 +\& #else /* ... version2 */ +\& #endif +.Ve +.PP +and not +.PP +.Vb 4 +\& #if ... version1 +\& #endif +\& #if ... version2 +\& #endif +.Ve +.PP +because otherwise \fBxsubpp\fR will believe that you made a duplicate +definition of the function. Also, put a blank line before the +#else/#endif so it will not be seen as part of the function body. +.SS "Using XS With C++" +.IX Subsection "Using XS With C++" +If an XSUB name contains \f(CW\*(C`::\*(C'\fR, it is considered to be a C++ method. +The generated Perl function will assume that +its first argument is an object pointer. The object pointer +will be stored in a variable called THIS. The object should +have been created by C++ with the \fBnew()\fR function and should +be blessed by Perl with the \fBsv_setref_pv()\fR macro. The +blessing of the object by Perl can be handled by a typemap. An example +typemap is shown at the end of this section. +.PP +If the return type of the XSUB includes \f(CW\*(C`static\*(C'\fR, the method is considered +to be a static method. It will call the C++ +function using the \fBclass::method()\fR syntax. If the method is not static +the function will be called using the THIS\->\fBmethod()\fR syntax. +.PP +The next examples will use the following C++ class. +.PP +.Vb 6 +\& class color { +\& public: +\& color(); +\& ~color(); +\& int blue(); +\& void set_blue( int ); +\& +\& private: +\& int c_blue; +\& }; +.Ve +.PP +The XSUBs for the \fBblue()\fR and \fBset_blue()\fR methods are defined with the class +name but the parameter for the object (THIS, or "self") is implicit and is +not listed. +.PP +.Vb 2 +\& int +\& color::blue() +\& +\& void +\& color::set_blue( val ) +\& int val +.Ve +.PP +Both Perl functions will expect an object as the first parameter. In the +generated C++ code the object is called \f(CW\*(C`THIS\*(C'\fR, and the method call will +be performed on this object. So in the C++ code the \fBblue()\fR and \fBset_blue()\fR +methods will be called as this: +.PP +.Vb 1 +\& RETVAL = THIS\->blue(); +\& +\& THIS\->set_blue( val ); +.Ve +.PP +You could also write a single get/set method using an optional argument: +.PP +.Vb 10 +\& int +\& color::blue( val = NO_INIT ) +\& int val +\& PROTOTYPE $;$ +\& CODE: +\& if (items > 1) +\& THIS\->set_blue( val ); +\& RETVAL = THIS\->blue(); +\& OUTPUT: +\& RETVAL +.Ve +.PP +If the function's name is \fBDESTROY\fR then the C++ \f(CW\*(C`delete\*(C'\fR function will be +called and \f(CW\*(C`THIS\*(C'\fR will be given as its parameter. The generated C++ code for +.PP +.Vb 2 +\& void +\& color::DESTROY() +.Ve +.PP +will look like this: +.PP +.Vb 1 +\& color *THIS = ...; // Initialized as in typemap +\& +\& delete THIS; +.Ve +.PP +If the function's name is \fBnew\fR then the C++ \f(CW\*(C`new\*(C'\fR function will be called +to create a dynamic C++ object. The XSUB will expect the class name, which +will be kept in a variable called \f(CW\*(C`CLASS\*(C'\fR, to be given as the first +argument. +.PP +.Vb 2 +\& color * +\& color::new() +.Ve +.PP +The generated C++ code will call \f(CW\*(C`new\*(C'\fR. +.PP +.Vb 1 +\& RETVAL = new color(); +.Ve +.PP +The following is an example of a typemap that could be used for this C++ +example. +.PP +.Vb 2 +\& TYPEMAP +\& color * O_OBJECT +\& +\& OUTPUT +\& # The Perl object is blessed into \*(AqCLASS\*(Aq, which should be a +\& # char* having the name of the package for the blessing. +\& O_OBJECT +\& sv_setref_pv( $arg, CLASS, (void*)$var ); +\& +\& INPUT +\& O_OBJECT +\& if( sv_isobject($arg) && (SvTYPE(SvRV($arg)) == SVt_PVMG) ) +\& $var = ($type)SvIV((SV*)SvRV( $arg )); +\& else{ +\& warn(\e"${Package}::$func_name() \-\- \e" +\& \e"$var is not a blessed SV reference\e"); +\& XSRETURN_UNDEF; +\& } +.Ve +.SS "Interface Strategy" +.IX Subsection "Interface Strategy" +When designing an interface between Perl and a C library a straight +translation from C to XS (such as created by \f(CW\*(C`h2xs \-x\*(C'\fR) is often sufficient. +However, sometimes the interface will look +very C\-like and occasionally nonintuitive, especially when the C function +modifies one of its parameters, or returns failure inband (as in "negative +return values mean failure"). In cases where the programmer wishes to +create a more Perl-like interface the following strategy may help to +identify the more critical parts of the interface. +.PP +Identify the C functions with input/output or output parameters. The XSUBs for +these functions may be able to return lists to Perl. +.PP +Identify the C functions which use some inband info as an indication +of failure. They may be +candidates to return undef or an empty list in case of failure. If the +failure may be detected without a call to the C function, you may want to use +an INIT: section to report the failure. For failures detectable after the C +function returns one may want to use a POSTCALL: section to process the +failure. In more complicated cases use CODE: or PPCODE: sections. +.PP +If many functions use the same failure indication based on the return value, +you may want to create a special typedef to handle this situation. Put +.PP +.Vb 1 +\& typedef int negative_is_failure; +.Ve +.PP +near the beginning of XS file, and create an OUTPUT typemap entry +for \f(CW\*(C`negative_is_failure\*(C'\fR which converts negative values to \f(CW\*(C`undef\*(C'\fR, or +maybe \fBcroak()\fRs. After this the return value of type \f(CW\*(C`negative_is_failure\*(C'\fR +will create more Perl-like interface. +.PP +Identify which values are used by only the C and XSUB functions +themselves, say, when a parameter to a function should be a contents of a +global variable. If Perl does not need to access the contents of the value +then it may not be necessary to provide a translation for that value +from C to Perl. +.PP +Identify the pointers in the C function parameter lists and return +values. Some pointers may be used to implement input/output or +output parameters, they can be handled in XS with the \f(CW\*(C`&\*(C'\fR unary operator, +and, possibly, using the NO_INIT keyword. +Some others will require handling of types like \f(CW\*(C`int *\*(C'\fR, and one needs +to decide what a useful Perl translation will do in such a case. When +the semantic is clear, it is advisable to put the translation into a typemap +file. +.PP +Identify the structures used by the C functions. In many +cases it may be helpful to use the T_PTROBJ typemap for +these structures so they can be manipulated by Perl as +blessed objects. (This is handled automatically by \f(CW\*(C`h2xs \-x\*(C'\fR.) +.PP +If the same C type is used in several different contexts which require +different translations, \f(CW\*(C`typedef\*(C'\fR several new types mapped to this C type, +and create separate \fItypemap\fR entries for these new types. Use these +types in declarations of return type and parameters to XSUBs. +.SS "Perl Objects And C Structures" +.IX Subsection "Perl Objects And C Structures" +When dealing with C structures one should select either +\&\fBT_PTROBJ\fR or \fBT_PTRREF\fR for the XS type. Both types are +designed to handle pointers to complex objects. The +T_PTRREF type will allow the Perl object to be unblessed +while the T_PTROBJ type requires that the object be blessed. +By using T_PTROBJ one can achieve a form of type-checking +because the XSUB will attempt to verify that the Perl object +is of the expected type. +.PP +The following XS code shows the \fBgetnetconfigent()\fR function which is used +with ONC+ TIRPC. The \fBgetnetconfigent()\fR function will return a pointer to a +C structure and has the C prototype shown below. The example will +demonstrate how the C pointer will become a Perl reference. Perl will +consider this reference to be a pointer to a blessed object and will +attempt to call a destructor for the object. A destructor will be +provided in the XS source to free the memory used by \fBgetnetconfigent()\fR. +Destructors in XS can be created by specifying an XSUB function whose name +ends with the word \fBDESTROY\fR. XS destructors can be used to free memory +which may have been malloc'd by another XSUB. +.PP +.Vb 1 +\& struct netconfig *getnetconfigent(const char *netid); +.Ve +.PP +A \f(CW\*(C`typedef\*(C'\fR will be created for \f(CW\*(C`struct netconfig\*(C'\fR. The Perl +object will be blessed in a class matching the name of the C +type, with the tag \f(CW\*(C`Ptr\*(C'\fR appended, and the name should not +have embedded spaces if it will be a Perl package name. The +destructor will be placed in a class corresponding to the +class of the object and the PREFIX keyword will be used to +trim the name to the word DESTROY as Perl will expect. +.PP +.Vb 1 +\& typedef struct netconfig Netconfig; +\& +\& MODULE = RPC PACKAGE = RPC +\& +\& Netconfig * +\& getnetconfigent(netid) +\& char *netid +\& +\& MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ +\& +\& void +\& rpcb_DESTROY(netconf) +\& Netconfig *netconf +\& CODE: +\& printf("Now in NetconfigPtr::DESTROY\en"); +\& free( netconf ); +.Ve +.PP +This example requires the following typemap entry. Consult +perlxstypemap for more information about adding new typemaps +for an extension. +.PP +.Vb 2 +\& TYPEMAP +\& Netconfig * T_PTROBJ +.Ve +.PP +This example will be used with the following Perl statements. +.PP +.Vb 2 +\& use RPC; +\& $netconf = getnetconfigent("udp"); +.Ve +.PP +When Perl destroys the object referenced by \f(CW$netconf\fR it will send the +object to the supplied XSUB DESTROY function. Perl cannot determine, and +does not care, that this object is a C struct and not a Perl object. In +this sense, there is no difference between the object created by the +\&\fBgetnetconfigent()\fR XSUB and an object created by a normal Perl subroutine. +.SS "Safely Storing Static Data in XS" +.IX Subsection "Safely Storing Static Data in XS" +Starting with Perl 5.8, a macro framework has been defined to allow +static data to be safely stored in XS modules that will be accessed from +a multi-threaded Perl. +.PP +Although primarily designed for use with multi-threaded Perl, the macros +have been designed so that they will work with non-threaded Perl as well. +.PP +It is therefore strongly recommended that these macros be used by all +XS modules that make use of static data. +.PP +The easiest way to get a template set of macros to use is by specifying +the \f(CW\*(C`\-g\*(C'\fR (\f(CW\*(C`\-\-global\*(C'\fR) option with h2xs (see h2xs). +.PP +Below is an example module that makes use of the macros. +.PP +.Vb 4 +\& #define PERL_NO_GET_CONTEXT +\& #include "EXTERN.h" +\& #include "perl.h" +\& #include "XSUB.h" +\& +\& /* Global Data */ +\& +\& #define MY_CXT_KEY "BlindMice::_guts" XS_VERSION +\& +\& typedef struct { +\& int count; +\& char name[3][100]; +\& } my_cxt_t; +\& +\& START_MY_CXT +\& +\& MODULE = BlindMice PACKAGE = BlindMice +\& +\& BOOT: +\& { +\& MY_CXT_INIT; +\& MY_CXT.count = 0; +\& strcpy(MY_CXT.name[0], "None"); +\& strcpy(MY_CXT.name[1], "None"); +\& strcpy(MY_CXT.name[2], "None"); +\& } +\& +\& int +\& newMouse(char * name) +\& PREINIT: +\& dMY_CXT; +\& CODE: +\& if (MY_CXT.count >= 3) { +\& warn("Already have 3 blind mice"); +\& RETVAL = 0; +\& } +\& else { +\& RETVAL = ++ MY_CXT.count; +\& strcpy(MY_CXT.name[MY_CXT.count \- 1], name); +\& } +\& OUTPUT: +\& RETVAL +\& +\& char * +\& get_mouse_name(index) +\& int index +\& PREINIT: +\& dMY_CXT; +\& CODE: +\& if (index > MY_CXT.count) +\& croak("There are only 3 blind mice."); +\& else +\& RETVAL = MY_CXT.name[index \- 1]; +\& OUTPUT: +\& RETVAL +\& +\& void +\& CLONE(...) +\& CODE: +\& MY_CXT_CLONE; +.Ve +.PP +\fIMY_CXT REFERENCE\fR +.IX Subsection "MY_CXT REFERENCE" +.IP MY_CXT_KEY 5 +.IX Item "MY_CXT_KEY" +This macro is used to define a unique key to refer to the static data +for an XS module. The suggested naming scheme, as used by h2xs, is to +use a string that consists of the module name, the string "::_guts" +and the module version number. +.Sp +.Vb 1 +\& #define MY_CXT_KEY "MyModule::_guts" XS_VERSION +.Ve +.IP "typedef my_cxt_t" 5 +.IX Item "typedef my_cxt_t" +This struct typedef \fImust\fR always be called \f(CW\*(C`my_cxt_t\*(C'\fR. The other +\&\f(CW\*(C`CXT*\*(C'\fR macros assume the existence of the \f(CW\*(C`my_cxt_t\*(C'\fR typedef name. +.Sp +Declare a typedef named \f(CW\*(C`my_cxt_t\*(C'\fR that is a structure that contains +all the data that needs to be interpreter-local. +.Sp +.Vb 3 +\& typedef struct { +\& int some_value; +\& } my_cxt_t; +.Ve +.IP START_MY_CXT 5 +.IX Item "START_MY_CXT" +Always place the START_MY_CXT macro directly after the declaration +of \f(CW\*(C`my_cxt_t\*(C'\fR. +.IP MY_CXT_INIT 5 +.IX Item "MY_CXT_INIT" +The MY_CXT_INIT macro initializes storage for the \f(CW\*(C`my_cxt_t\*(C'\fR struct. +.Sp +It \fImust\fR be called exactly once, typically in a BOOT: section. If you +are maintaining multiple interpreters, it should be called once in each +interpreter instance, except for interpreters cloned from existing ones. +(But see "MY_CXT_CLONE" below.) +.IP dMY_CXT 5 +.IX Item "dMY_CXT" +Use the dMY_CXT macro (a declaration) in all the functions that access +MY_CXT. +.IP MY_CXT 5 +.IX Item "MY_CXT" +Use the MY_CXT macro to access members of the \f(CW\*(C`my_cxt_t\*(C'\fR struct. For +example, if \f(CW\*(C`my_cxt_t\*(C'\fR is +.Sp +.Vb 3 +\& typedef struct { +\& int index; +\& } my_cxt_t; +.Ve +.Sp +then use this to access the \f(CW\*(C`index\*(C'\fR member +.Sp +.Vb 2 +\& dMY_CXT; +\& MY_CXT.index = 2; +.Ve +.IP aMY_CXT/pMY_CXT 5 +.IX Item "aMY_CXT/pMY_CXT" +\&\f(CW\*(C`dMY_CXT\*(C'\fR may be quite expensive to calculate, and to avoid the overhead +of invoking it in each function it is possible to pass the declaration +onto other functions using the \f(CW\*(C`aMY_CXT\*(C'\fR/\f(CW\*(C`pMY_CXT\*(C'\fR macros, eg +.Sp +.Vb 5 +\& void sub1() { +\& dMY_CXT; +\& MY_CXT.index = 1; +\& sub2(aMY_CXT); +\& } +\& +\& void sub2(pMY_CXT) { +\& MY_CXT.index = 2; +\& } +.Ve +.Sp +Analogously to \f(CW\*(C`pTHX\*(C'\fR, there are equivalent forms for when the macro is the +first or last in multiple arguments, where an underscore represents a +comma, i.e. \f(CW\*(C`_aMY_CXT\*(C'\fR, \f(CW\*(C`aMY_CXT_\*(C'\fR, \f(CW\*(C`_pMY_CXT\*(C'\fR and \f(CW\*(C`pMY_CXT_\*(C'\fR. +.IP MY_CXT_CLONE 5 +.IX Item "MY_CXT_CLONE" +By default, when a new interpreter is created as a copy of an existing one +(eg via \f(CW\*(C`threads\->create()\*(C'\fR), both interpreters share the same physical +my_cxt_t structure. Calling \f(CW\*(C`MY_CXT_CLONE\*(C'\fR (typically via the package's +\&\f(CWCLONE()\fR function), causes a byte-for-byte copy of the structure to be +taken, and any future dMY_CXT will cause the copy to be accessed instead. +.IP MY_CXT_INIT_INTERP(my_perl) 5 +.IX Item "MY_CXT_INIT_INTERP(my_perl)" +.PD 0 +.IP dMY_CXT_INTERP(my_perl) 5 +.IX Item "dMY_CXT_INTERP(my_perl)" +.PD +These are versions of the macros which take an explicit interpreter as an +argument. +.PP +Note that these macros will only work together within the \fIsame\fR source +file; that is, a dMY_CTX in one source file will access a different structure +than a dMY_CTX in another source file. +.SS "Thread-aware system interfaces" +.IX Subsection "Thread-aware system interfaces" +Starting from Perl 5.8, in C/C++ level Perl knows how to wrap +system/library interfaces that have thread-aware versions +(e.g. \fBgetpwent_r()\fR) into frontend macros (e.g. \fBgetpwent()\fR) that +correctly handle the multithreaded interaction with the Perl +interpreter. This will happen transparently, the only thing +you need to do is to instantiate a Perl interpreter. +.PP +This wrapping happens always when compiling Perl core source +(PERL_CORE is defined) or the Perl core extensions (PERL_EXT is +defined). When compiling XS code outside of the Perl core, the wrapping +does not take place before Perl 5.28. Starting in that release you can +.PP +.Vb 1 +\& #define PERL_REENTRANT +.Ve +.PP +in your code to enable the wrapping. It is advisable to do so if you +are using such functions, as intermixing the \f(CW\*(C`_r\*(C'\fR\-forms (as Perl compiled +for multithreaded operation will do) and the \f(CW\*(C`_r\*(C'\fR\-less forms is neither +well-defined (inconsistent results, data corruption, or even crashes +become more likely), nor is it very portable. Unfortunately, not all +systems have all the \f(CW\*(C`_r\*(C'\fR forms, but using this \f(CW\*(C`#define\*(C'\fR gives you +whatever protection that Perl is aware is available on each system. +.SH EXAMPLES +.IX Header "EXAMPLES" +File \f(CW\*(C`RPC.xs\*(C'\fR: Interface to some ONC+ RPC bind library functions. +.PP +.Vb 4 +\& #define PERL_NO_GET_CONTEXT +\& #include "EXTERN.h" +\& #include "perl.h" +\& #include "XSUB.h" +\& +\& /* Note: On glibc 2.13 and earlier, this needs be <rpc/rpc.h> */ +\& #include <tirpc/rpc.h> +\& +\& typedef struct netconfig Netconfig; +\& +\& MODULE = RPC PACKAGE = RPC +\& +\& SV * +\& rpcb_gettime(host="localhost") +\& char *host +\& PREINIT: +\& time_t timep; +\& CODE: +\& ST(0) = sv_newmortal(); +\& if( rpcb_gettime( host, &timep ) ) +\& sv_setnv( ST(0), (double)timep ); +\& +\& Netconfig * +\& getnetconfigent(netid="udp") +\& char *netid +\& +\& MODULE = RPC PACKAGE = NetconfigPtr PREFIX = rpcb_ +\& +\& void +\& rpcb_DESTROY(netconf) +\& Netconfig *netconf +\& CODE: +\& printf("NetconfigPtr::DESTROY\en"); +\& free( netconf ); +.Ve +.PP +File \f(CW\*(C`typemap\*(C'\fR: Custom typemap for RPC.xs. (cf. perlxstypemap) +.PP +.Vb 2 +\& TYPEMAP +\& Netconfig * T_PTROBJ +.Ve +.PP +File \f(CW\*(C`RPC.pm\*(C'\fR: Perl module for the RPC extension. +.PP +.Vb 1 +\& package RPC; +\& +\& require Exporter; +\& require DynaLoader; +\& @ISA = qw(Exporter DynaLoader); +\& @EXPORT = qw(rpcb_gettime getnetconfigent); +\& +\& bootstrap RPC; +\& 1; +.Ve +.PP +File \f(CW\*(C`rpctest.pl\*(C'\fR: Perl test program for the RPC extension. +.PP +.Vb 1 +\& use RPC; +\& +\& $netconf = getnetconfigent(); +\& $a = rpcb_gettime(); +\& print "time = $a\en"; +\& print "netconf = $netconf\en"; +\& +\& $netconf = getnetconfigent("tcp"); +\& $a = rpcb_gettime("poplar"); +\& print "time = $a\en"; +\& print "netconf = $netconf\en"; +.Ve +.PP +In Makefile.PL add \-ltirpc and \-I/usr/include/tirpc. +.SH CAVEATS +.IX Header "CAVEATS" +XS code has full access to system calls including C library functions. +It thus has the capability of interfering with things that the Perl core +or other modules have set up, such as signal handlers or file handles. +It could mess with the memory, or any number of harmful things. Don't. +.PP +Some modules have an event loop, waiting for user-input. It is highly +unlikely that two such modules would work adequately together in a +single Perl application. +.PP +In general, the perl interpreter views itself as the center of the +universe as far as the Perl program goes. XS code is viewed as a +help-mate, to accomplish things that perl doesn't do, or doesn't do fast +enough, but always subservient to perl. The closer XS code adheres to +this model, the less likely conflicts will occur. +.PP +One area where there has been conflict is in regards to C locales. (See +perllocale.) perl, with one exception and unless told otherwise, +sets up the underlying locale the program is running in to the locale +passed +into it from the environment. This is an important difference from a +generic C language program, where the underlying locale is the "C" +locale unless the program changes it. As of v5.20, this underlying +locale is completely hidden from pure Perl code outside the lexical +scope of \f(CW\*(C`use\ locale\*(C'\fR except for a couple of function calls in the +POSIX module which of necessity use it. But the underlying locale, with +that +one exception is exposed to XS code, affecting all C library routines +whose behavior is locale-dependent. Your XS code better not assume that +the underlying locale is "C". The exception is the +\&\f(CW\*(C`LC_NUMERIC\*(C'\fR +locale category, and the reason it is an exception is that experience +has shown that it can be problematic for XS code, whereas we have not +had reports of problems with the +other locale categories. And the reason +for this one category being problematic is that the character used as a +decimal point can vary. Many European languages use a comma, whereas +English, and hence Perl are expecting a dot (U+002E: FULL STOP). Many +modules can handle only the radix character being a dot, and so perl +attempts to make it so. Up through Perl v5.20, the attempt was merely +to set \f(CW\*(C`LC_NUMERIC\*(C'\fR upon startup to the \f(CW"C"\fR locale. Any +\&\fBsetlocale()\fR otherwise would change +it; this caused some failures. Therefore, starting in v5.22, perl tries +to keep \f(CW\*(C`LC_NUMERIC\*(C'\fR always set to \f(CW"C"\fR for XS code. +.PP +To summarize, here's what to expect and how to handle locales in XS code: +.IP "Non-locale-aware XS code" 4 +.IX Item "Non-locale-aware XS code" +Keep in mind that even if you think your code is not locale-aware, it +may call a library function that is. Hopefully the man page for such +a function will indicate that dependency, but the documentation is +imperfect. +.Sp +The current locale is exposed to XS code except possibly \f(CW\*(C`LC_NUMERIC\*(C'\fR +(explained in the next paragraph). +There have not been reports of problems with the other categories. +Perl initializes things on start-up so that the current locale is the +one which is indicated by the user's environment in effect at that time. +See "ENVIRONMENT" in perllocale. +.Sp +However, up through v5.20, Perl initialized things on start-up so that +\&\f(CW\*(C`LC_NUMERIC\*(C'\fR was set to the "C" locale. But if any code anywhere +changed it, it would stay changed. This means that your module can't +count on \f(CW\*(C`LC_NUMERIC\*(C'\fR being something in particular, and you can't +expect floating point numbers (including version strings) to have dots +in them. If you don't allow for a non-dot, your code could break if +anyone anywhere changed the locale. For this reason, v5.22 changed +the behavior so that Perl tries to keep \f(CW\*(C`LC_NUMERIC\*(C'\fR in the "C" locale +except around the operations internally where it should be something +else. Misbehaving XS code will always be able to change the locale +anyway, but the most common instance of this is checked for and +handled. +.IP "Locale-aware XS code" 4 +.IX Item "Locale-aware XS code" +If the locale from the user's environment is desired, there should be no +need for XS code to set the locale except for \f(CW\*(C`LC_NUMERIC\*(C'\fR, as perl has +already set the others up. XS code should avoid changing the locale, as +it can adversely affect other, unrelated, code and may not be +thread-safe. To minimize problems, the macros +"STORE_LC_NUMERIC_SET_TO_NEEDED" in perlapi, +"STORE_LC_NUMERIC_FORCE_TO_UNDERLYING" in perlapi, and +"RESTORE_LC_NUMERIC" in perlapi should be used to affect any needed +change. +.Sp +But, starting with Perl v5.28, locales are thread-safe on platforms that +support this functionality. Windows has this starting with Visual +Studio 2005. Many other modern platforms support the thread-safe POSIX +2008 functions. The C \f(CW\*(C`#define\*(C'\fR \f(CW\*(C`USE_THREAD_SAFE_LOCALE\*(C'\fR will be +defined iff this build is using these. From Perl-space, the read-only +variable \f(CW\*(C`${SAFE_LOCALES}\*(C'\fR is 1 if either the build is not threaded, or +if \f(CW\*(C`USE_THREAD_SAFE_LOCALE\*(C'\fR is defined; otherwise it is 0. +.Sp +The way this works under-the-hood is that every thread has a choice of +using a locale specific to it (this is the Windows and POSIX 2008 +functionality), or the global locale that is accessible to all threads +(this is the functionality that has always been there). The +implementations for Windows and POSIX are completely different. On +Windows, the runtime can be set up so that the standard +\&\f(CWsetlocale(3)\fR function either only knows about the global locale or +the locale for this thread. On POSIX, \f(CW\*(C`setlocale\*(C'\fR always deals with +the global locale, and other functions have been created to handle +per-thread locales. Perl makes this transparent to perl-space code. It +continues to use \f(CWPOSIX::setlocale()\fR, and the interpreter translates +that into the per-thread functions. +.Sp +All other locale-sensitive functions automatically use the per-thread +locale, if that is turned on, and failing that, the global locale. Thus +calls to \f(CW\*(C`setlocale\*(C'\fR are ineffective on POSIX systems for the current +thread if that thread is using a per-thread locale. If perl is compiled +for single-thread operation, it does not use the per-thread functions, +so \f(CW\*(C`setlocale\*(C'\fR does work as expected. +.Sp +If you have loaded the \f(CW\*(C`POSIX\*(C'\fR module you can use the methods given +in perlcall to call \f(CW\*(C`POSIX::setlocale\*(C'\fR to safely +change or query the locale (on systems where it is safe to do so), or +you can use the new 5.28 function "Perl_setlocale" in perlapi instead, +which is a drop-in replacement for the system \f(CWsetlocale(3)\fR, and +handles single-threaded and multi-threaded applications transparently. +.Sp +There are some locale-related library calls that still aren't +thread-safe because they return data in a buffer global to all threads. +In the past, these didn't matter as locales weren't thread-safe at all. +But now you have to be aware of them in case your module is called in a +multi-threaded application. The known ones are +.Sp +.Vb 8 +\& asctime() +\& ctime() +\& gcvt() [POSIX.1\-2001 only (function removed in POSIX.1\-2008)] +\& getdate() +\& wcrtomb() if its final argument is NULL +\& wcsrtombs() if its final argument is NULL +\& wcstombs() +\& wctomb() +.Ve +.Sp +Some of these shouldn't really be called in a Perl application, and for +others there are thread-safe versions of these already implemented: +.Sp +.Vb 3 +\& asctime_r() +\& ctime_r() +\& Perl_langinfo() +.Ve +.Sp +The \f(CW\*(C`_r\*(C'\fR forms are automatically used, starting in Perl 5.28, if you +compile your code, with +.Sp +.Vb 1 +\& #define PERL_REENTRANT +.Ve +.Sp +See also "Perl_langinfo" in perlapi. +You can use the methods given in perlcall, to get the best available +locale-safe versions of these +.Sp +.Vb 3 +\& POSIX::localeconv() +\& POSIX::wcstombs() +\& POSIX::wctomb() +.Ve +.Sp +And note, that some items returned by \f(CW\*(C`Localeconv\*(C'\fR are available +through "Perl_langinfo" in perlapi. +.Sp +The others shouldn't be used in a threaded application. +.Sp +Some modules may call a non-perl library that is locale-aware. This is +fine as long as it doesn't try to query or change the locale using the +system \f(CW\*(C`setlocale\*(C'\fR. But if these do call the system \f(CW\*(C`setlocale\*(C'\fR, +those calls may be ineffective. Instead, +\&\f(CW\*(C`Perl_setlocale\*(C'\fR works in all circumstances. +Plain setlocale is ineffective on multi-threaded POSIX 2008 systems. It +operates only on the global locale, whereas each thread has its own +locale, paying no attention to the global one. Since converting +these non-Perl libraries to \f(CW\*(C`Perl_setlocale\*(C'\fR is out of the question, +there is a new function in v5.28 +\&\f(CW\*(C`switch_to_global_locale\*(C'\fR that will +switch the thread it is called from so that any system \f(CW\*(C`setlocale\*(C'\fR +calls will have their desired effect. The function +\&\f(CW\*(C`sync_locale\*(C'\fR must be called before returning to +perl. +.Sp +This thread can change the locale all it wants and it won't affect any +other thread, except any that also have been switched to the global +locale. This means that a multi-threaded application can have a single +thread using an alien library without a problem; but no more than a +single thread can be so-occupied. Bad results likely will happen. +.Sp +In perls without multi-thread locale support, some alien libraries, +such as \f(CW\*(C`Gtk\*(C'\fR change locales. This can cause problems for the Perl +core and other modules. For these, before control is returned to +perl, starting in v5.20.1, calling the function +\&\fBsync_locale()\fR from XS should be sufficient to +avoid most of these problems. Prior to this, you need a pure Perl +statement that does this: +.Sp +.Vb 1 +\& POSIX::setlocale(LC_ALL, POSIX::setlocale(LC_ALL)); +.Ve +.Sp +or use the methods given in perlcall. +.SH "XS VERSION" +.IX Header "XS VERSION" +This document covers features supported by \f(CW\*(C`ExtUtils::ParseXS\*(C'\fR +(also known as \f(CW\*(C`xsubpp\*(C'\fR) 3.51 +.SH "AUTHOR DIAGNOSTICS" +.IX Header "AUTHOR DIAGNOSTICS" +As of version 3.49 certain warnings are disabled by default. While developing +you can set \f(CW$ENV{AUTHOR_WARNINGS}\fR to true in your environment or in your +Makefile.PL, or set \f(CW$ExtUtils::ParseXS::AUTHOR_WARNINGS\fR to true via code, or +pass \f(CW\*(C`author_warnings=>1\*(C'\fR into \fBprocess_file()\fR explicitly. Currently this will +enable stricter alias checking but more warnings might be added in the future. +The kind of warnings this will enable are only helpful to the author of the XS +file, and the diagnostics produced will not include installation specific +details so they are only useful to the maintainer of the XS code itself. +.SH AUTHOR +.IX Header "AUTHOR" +Originally written by Dean Roehrich <\fIroehrich@cray.com\fR>. +.PP +Maintained since 1996 by The Perl Porters <\fIperl5\-porters@perl.org\fR>. |