X-Git-Url: http://git.shadowcat.co.uk/gitweb/gitweb.cgi?a=blobdiff_plain;f=pod%2Fperlxs.pod;h=c09947d65c847a6a09393d2e3ed12f4e7227ca4d;hb=85b35914c9f3fc562f8a505e6508276be17f9d70;hp=78e3e7c97c5cb906052def10630c25bd7de96184;hpb=08ff138dc0c1cdf425c051c295eab8d1f59c736a;p=p5sagit%2Fp5-mst-13.2.git diff --git a/pod/perlxs.pod b/pod/perlxs.pod index 78e3e7c..c09947d 100644 --- a/pod/perlxs.pod +++ b/pod/perlxs.pod @@ -276,6 +276,63 @@ 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 C as return value.) +=head2 Returning SVs, AVs and HVs through RETVAL + +When you're using RETVAL to return an C, 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 L.) To make your life +easier, the typemap file automatically makes C mortal when +you're returning an C. Thus, the following two XSUBs are more +or less equivalent: + + 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 + +This is quite useful as it usually improves readability. While +this works fine for an C, it's unfortunately not as easy +to have C or C as a return value. You I be +able to write: + + AV * + array() + CODE: + RETVAL = newAV(); + /* do something with RETVAL */ + OUTPUT: + RETVAL + +But due to an unfixable bug (fixing it would break lots of existing +CPAN modules) in the typemap file, the reference count of the C +is not properly decremented. Thus, the above XSUB would leak memory +whenever it is being called. The same problem exists for C. + +When you're returning an C or a C, you have make sure +their reference count is decremented by making the AV or HV mortal: + + AV * + array() + CODE: + RETVAL = newAV(); + sv_2mortal((SV*)RETVAL); + /* do something with RETVAL */ + OUTPUT: + RETVAL + +And also remember that you don't have to do this for an C. + =head2 The MODULE Keyword The MODULE keyword is used to start the XS code and to specify the package @@ -310,6 +367,10 @@ keyword and must follow immediately after it when used. [ XS code in package RPC ] +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. + 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. @@ -1060,8 +1121,8 @@ then not push return values on the stack. Some people may be inclined to include an explicit C in the above XSUB, rather than letting control fall through to the end. In those situations C should be used, instead. This will ensure that -the XSUB stack is properly adjusted. Consult L for -other C macros. +the XSUB stack is properly adjusted. Consult L for other +C macros. Since C macros can be used with CODE blocks as well, one can rewrite this example as: @@ -1190,6 +1251,14 @@ prototypes. timep RETVAL +If the prototypes are enabled, you can disable it locally for a given +XSUB as in the following example: + + void + rpcb_gettime_noproto() + PROTOTYPE: DISABLE + ... + =head2 The ALIAS: Keyword The ALIAS: keyword allows an XSUB to have two or more unique Perl names @@ -1214,6 +1283,57 @@ C for this function. OUTPUT: timep +=head2 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 with three parameters (except +for the nomethod() function which needs four parameters). 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. + +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. + +To use the OVERLOAD: keyword, create an XS function which takes +three input parameters ( or use the c style '...' definition) like +this: + + SV * + cmp (lobj, robj, swap) + My_Module_obj lobj + My_Module_obj robj + IV swap + OVERLOAD: cmp <=> + { /* function defined here */} + +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, seperating +multiple overloads with whitespace. Note that "" (the stringify +overload) should be entered as \"\" (i.e. escaped). + +=head2 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: + + MODULE = RPC PACKAGE = RPC + + FALLBACK: TRUE + ... + +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 +L for more details. + =head2 The INTERFACE: Keyword This keyword declares the current XSUB as a keeper of the given