X-Git-Url: https://perl5.git.perl.org/perl5.git/blobdiff_plain/da75cd15705fec9f427a4cc8a647f3b6919c6e04..0177730e7e0c099d1250571eb39367a76e2d91eb:/pod/perlguts.pod diff --git a/pod/perlguts.pod b/pod/perlguts.pod index 8ccdde8..d8f0527 100644 --- a/pod/perlguts.pod +++ b/pod/perlguts.pod @@ -5,7 +5,7 @@ perlguts - Introduction to the Perl API =head1 DESCRIPTION This document attempts to describe how to use the Perl API, as well as -containing some info on the basic workings of the Perl core. It is far +to provide some info on the basic workings of the Perl core. It is far from complete and probably contains many errors. Please refer any questions or comments to the author below. @@ -29,32 +29,47 @@ Additionally, there is the UV, which is simply an unsigned IV. Perl also uses two special typedefs, I32 and I16, which will always be at least 32-bits and 16-bits long, respectively. (Again, there are U32 and U16, -as well.) +as well.) They will usually be exactly 32 and 16 bits long, but on Crays +they will both be 64 bits. =head2 Working with SVs -An SV can be created and loaded with one command. There are four types of -values that can be loaded: an integer value (IV), a double (NV), -a string (PV), and another scalar (SV). +An SV can be created and loaded with one command. There are five types of +values that can be loaded: an integer value (IV), an unsigned integer +value (UV), a double (NV), a string (PV), and another scalar (SV). -The six routines are: +The seven routines are: SV* newSViv(IV); + SV* newSVuv(UV); SV* newSVnv(double); - SV* newSVpv(const char*, int); - SV* newSVpvn(const char*, int); + SV* newSVpv(const char*, STRLEN); + SV* newSVpvn(const char*, STRLEN); SV* newSVpvf(const char*, ...); SV* newSVsv(SV*); -To change the value of an *already-existing* SV, there are seven routines: +C is an integer type (Size_t, usually defined as size_t in +F) guaranteed to be large enough to represent the size of +any string that perl can handle. + +In the unlikely case of a SV requiring more complex initialisation, you +can create an empty SV with newSV(len). If C is 0 an empty SV of +type NULL is returned, else an SV of type PV is returned with len + 1 (for +the NUL) bytes of storage allocated, accessible via SvPVX. In both cases +the SV has value undef. + + SV *sv = newSV(0); /* no storage allocated */ + SV *sv = newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */ + +To change the value of an I SV, there are eight routines: void sv_setiv(SV*, IV); void sv_setuv(SV*, UV); void sv_setnv(SV*, double); void sv_setpv(SV*, const char*); - void sv_setpvn(SV*, const char*, int) + void sv_setpvn(SV*, const char*, STRLEN) void sv_setpvf(SV*, const char*, ...); - void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool); + void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *); void sv_setsv(SV*, SV*); Notice that you can choose to specify the length of the string to be @@ -76,10 +91,6 @@ L). This pointer may be NULL if that information is not important. Note that this function requires you to specify the length of the format. -STRLEN is an integer type (Size_t, usually defined as size_t in -config.h) guaranteed to be large enough to represent the size of -any string that perl can handle. - The C functions are not generic enough to operate on values that have "magic". See L later in this document. @@ -115,11 +126,11 @@ Also remember that C doesn't allow you to safely say C. It might work with your compiler, but it won't work for everyone. Break this sort of statement up into separate assignments: - SV *s; - STRLEN len; - char * ptr; - ptr = SvPV(s, len); - foo(ptr, len); + SV *s; + STRLEN len; + char * ptr; + ptr = SvPV(s, len); + foo(ptr, len); If you want to know if the scalar value is TRUE, you can use: @@ -180,7 +191,7 @@ have "magic". See L later in this document. If you know the name of a scalar variable, you can get a pointer to its SV by using the following: - SV* get_sv("package::varname", FALSE); + SV* get_sv("package::varname", 0); This returns NULL if the variable does not exist. @@ -189,12 +200,27 @@ you can call: SvOK(SV*) -The scalar C value is stored in an SV instance called C. Its -address can be used whenever an C is needed. +The scalar C value is stored in an SV instance called C. + +Its address can be used whenever an C is needed. Make sure that +you don't try to compare a random sv with C<&PL_sv_undef>. For example +when interfacing Perl code, it'll work correctly for: + + foo(undef); + +But won't work when called as: -There are also the two values C and C, which contain Boolean -TRUE and FALSE values, respectively. Like C, their addresses can -be used whenever an C is needed. + $x = undef; + foo($x); + +So to repeat always use SvOK() to check whether an sv is defined. + +Also you have to be careful when using C<&PL_sv_undef> as a value in +AVs or HVs (see L). + +There are also the two values C and C, which contain +boolean TRUE and FALSE values, respectively. Like C, their +addresses can be used whenever an C is needed. Do not be fooled into thinking that C<(SV *) 0> is the same as C<&PL_sv_undef>. Take this code: @@ -208,8 +234,8 @@ Take this code: This code tries to return a new SV (which contains the value 42) if it should return a real value, or undef otherwise. Instead it has returned a NULL pointer which, somewhere down the line, will cause a segmentation violation, -bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the first -line and all will be well. +bus error, or just weird results. Change the zero to C<&PL_sv_undef> in the +first line and all will be well. To free an SV that you've created, call C. Normally this call is not necessary (see L). @@ -247,12 +273,12 @@ portion of the string between the "real" and the "fake" beginnings is shown in parentheses, and the values of C and C reflect the fake beginning, not the real one. -Something similar to the offset hack is perfomed on AVs to enable +Something similar to the offset hack is performed on AVs to enable efficient shifting and splicing off the beginning of the array; while C points to the first element in the array that is visible from Perl, C points to the real start of the C array. These are usually the same, but a C operation can be carried out by -increasing C by one and decreasing C and C. +increasing C by one and decreasing C and C. Again, the location of the real start of the C array only comes into play when freeing the array. See C in F. @@ -278,7 +304,7 @@ The are various ways in which the private and public flags may differ. For example, a tied SV may have a valid underlying value in the IV slot (so SvIOKp is true), but the data should be accessed via the FETCH routine rather than directly, so SvIOK is false. Another is when -numeric conversion has occured and precision has been lost: only the +numeric conversion has occurred and precision has been lost: only the private flag is set on 'lossy' values. So when an NV is converted to an IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be. @@ -341,7 +367,7 @@ then nothing is done. If you know the name of an array variable, you can get a pointer to its AV by using the following: - AV* get_av("package::varname", FALSE); + AV* get_av("package::varname", 0); This returns NULL if the variable does not exist. @@ -405,7 +431,7 @@ specified below. /* Get the key from an HE structure and also return the length of the key string */ SV* hv_iterval(HV*, HE* entry); - /* Return a SV pointer to the value of the HE + /* Return an SV pointer to the value of the HE structure */ SV* hv_iternextsv(HV*, char** key, I32* retlen); /* This convenience routine combines hv_iternext, @@ -416,7 +442,7 @@ specified below. If you know the name of a hash variable, you can get a pointer to its HV by using the following: - HV* get_hv("package::varname", FALSE); + HV* get_hv("package::varname", 0); This returns NULL if the variable does not exist. @@ -478,6 +504,58 @@ reference count of the stored C, which is the caller's responsibility. If these functions return a NULL value, the caller will usually have to decrement the reference count of C to avoid a memory leak. +=head2 AVs, HVs and undefined values + +Sometimes you have to store undefined values in AVs or HVs. Although +this may be a rare case, it can be tricky. That's because you're +used to using C<&PL_sv_undef> if you need an undefined SV. + +For example, intuition tells you that this XS code: + + AV *av = newAV(); + av_store( av, 0, &PL_sv_undef ); + +is equivalent to this Perl code: + + my @av; + $av[0] = undef; + +Unfortunately, this isn't true. AVs use C<&PL_sv_undef> as a marker +for indicating that an array element has not yet been initialized. +Thus, C would be true for the above Perl code, but +false for the array generated by the XS code. + +Other problems can occur when storing C<&PL_sv_undef> in HVs: + + hv_store( hv, "key", 3, &PL_sv_undef, 0 ); + +This will indeed make the value C, but if you try to modify +the value of C, you'll get the following error: + + Modification of non-creatable hash value attempted + +In perl 5.8.0, C<&PL_sv_undef> was also used to mark placeholders +in restricted hashes. This caused such hash entries not to appear +when iterating over the hash or when checking for the keys +with the C function. + +You can run into similar problems when you store C<&PL_sv_yes> or +C<&PL_sv_no> into AVs or HVs. Trying to modify such elements +will give you the following error: + + Modification of a read-only value attempted + +To make a long story short, you can use the special variables +C<&PL_sv_undef>, C<&PL_sv_yes> and C<&PL_sv_no> with AVs and +HVs, but you have to make sure you know what you're doing. + +Generally, if you want to store an undefined value in an AV +or HV, you should not use C<&PL_sv_undef>, but rather create a +new undefined value using the C function, for example: + + av_store( av, 42, newSV(0) ); + hv_store( hv, "foo", 3, newSV(0), 0 ); + =head2 References References are a special type of scalar that point to other data types @@ -522,11 +600,11 @@ The most useful types that will be returned are: SVt_PVGV Glob (possible a file handle) SVt_PVMG Blessed or Magical Scalar - See the sv.h header file for more details. +See the F header file for more details. =head2 Blessed References and Class Objects -References are also used to support object-oriented programming. In the +References are also used to support object-oriented programming. In perl's OO lexicon, an object is simply a reference that has been blessed into a package (or class). Once blessed, the programmer may now use the reference to access the various methods in the class. @@ -535,47 +613,51 @@ A reference can be blessed into a package with the following function: SV* sv_bless(SV* sv, HV* stash); -The C argument must be a reference. The C argument specifies -which class the reference will belong to. See +The C argument must be a reference value. The C argument +specifies which class the reference will belong to. See L for information on converting class names into stashes. /* Still under construction */ -Upgrades rv to reference if not already one. Creates new SV for rv to -point to. If C is non-null, the SV is blessed into the specified -class. SV is returned. +The following function upgrades rv to reference if not already one. +Creates a new SV for rv to point to. If C is non-null, the SV +is blessed into the specified class. SV is returned. SV* newSVrv(SV* rv, const char* classname); -Copies integer, unsigned integer or double into an SV whose reference is C. SV is blessed -if C is non-null. +The following three functions copy integer, unsigned integer or double +into an SV whose reference is C. SV is blessed if C is +non-null. SV* sv_setref_iv(SV* rv, const char* classname, IV iv); SV* sv_setref_uv(SV* rv, const char* classname, UV uv); SV* sv_setref_nv(SV* rv, const char* classname, NV iv); -Copies the pointer value (I) into an SV whose -reference is rv. SV is blessed if C is non-null. +The following function copies the pointer value (I) into an SV whose reference is rv. SV is blessed if C +is non-null. - SV* sv_setref_pv(SV* rv, const char* classname, PV iv); + SV* sv_setref_pv(SV* rv, const char* classname, void* pv); -Copies string into an SV whose reference is C. Set length to 0 to let -Perl calculate the string length. SV is blessed if C is non-null. +The following function copies string into an SV whose reference is C. +Set length to 0 to let Perl calculate the string length. SV is blessed if +C is non-null. - SV* sv_setref_pvn(SV* rv, const char* classname, PV iv, STRLEN length); + SV* sv_setref_pvn(SV* rv, const char* classname, char* pv, STRLEN length); -Tests whether the SV is blessed into the specified class. It does not -check inheritance relationships. +The following function tests whether the SV is blessed into the specified +class. It does not check inheritance relationships. int sv_isa(SV* sv, const char* name); -Tests whether the SV is a reference to a blessed object. +The following function tests whether the SV is a reference to a blessed object. int sv_isobject(SV* sv); -Tests whether the SV is derived from the specified class. SV can be either -a reference to a blessed object or a string containing a class name. This -is the function implementing the C functionality. +The following function tests whether the SV is derived from the specified +class. SV can be either a reference to a blessed object or a string +containing a class name. This is the function implementing the +C functionality. bool sv_derived_from(SV* sv, const char* name); @@ -589,27 +671,42 @@ to write: To create a new Perl variable with an undef value which can be accessed from your Perl script, use the following routines, depending on the variable type. - SV* get_sv("package::varname", TRUE); - AV* get_av("package::varname", TRUE); - HV* get_hv("package::varname", TRUE); + SV* get_sv("package::varname", GV_ADD); + AV* get_av("package::varname", GV_ADD); + HV* get_hv("package::varname", GV_ADD); -Notice the use of TRUE as the second parameter. The new variable can now +Notice the use of GV_ADD as the second parameter. The new variable can now be set, using the routines appropriate to the data type. There are additional macros whose values may be bitwise OR'ed with the -C argument to enable certain extra features. Those bits are: +C argument to enable certain extra features. Those bits are: - GV_ADDMULTI Marks the variable as multiply defined, thus preventing the - "Name used only once: possible typo" warning. - GV_ADDWARN Issues the warning "Had to create unexpectedly" if - the variable did not exist before the function was called. +=over + +=item GV_ADDMULTI + +Marks the variable as multiply defined, thus preventing the: + + Name used only once: possible typo + +warning. + +=item GV_ADDWARN + +Issues the warning: + + Had to create unexpectedly + +if the variable did not exist before the function was called. + +=back If you do not specify a package name, the variable is created in the current package. =head2 Reference Counts and Mortality -Perl uses an reference count-driven garbage collection mechanism. SVs, +Perl uses a reference count-driven garbage collection mechanism. SVs, AVs, or HVs (xV for short in the following) start their life with a reference count of 1. If the reference count of an xV ever drops to 0, then it will be destroyed and its memory made available for reuse. @@ -660,9 +757,9 @@ later be decremented twice. "Mortal" SVs are mainly used for SVs that are placed on perl's stack. For example an SV which is created just to pass a number to a called sub -is made mortal to have it cleaned up automatically when stack is popped. -Similarly results returned by XSUBs (which go in the stack) are often -made mortal. +is made mortal to have it cleaned up automatically when it's popped off +the stack. Similarly, results returned by XSUBs (which are pushed on the +stack) are often made mortal. To create a mortal variable, use the functions: @@ -674,7 +771,7 @@ The first call creates a mortal SV (with no value), the second converts an exist SV to a mortal SV (and thus defers a call to C), and the third creates a mortal copy of an existing SV. Because C gives the new SV no value,it must normally be given one -via C, C etc. : +via C, C, etc. : SV *tmp = sv_newmortal(); sv_setiv(tmp, an_integer); @@ -693,14 +790,14 @@ to survive its use on the stack you need not do any mortalization. If you are not sure then doing an C and C, or making a C is safer. -The mortal routines are not just for SVs -- AVs and HVs can be +The mortal routines are not just for SVs; AVs and HVs can be made mortal by passing their address (type-casted to C) to the C or C routines. =head2 Stashes and Globs -A "stash" is a hash that contains all of the different objects that -are contained within a package. Each key of the stash is a symbol +A B is a hash that contains all variables that are defined +within a package. Each key of the stash is a symbol name (shared by all the different types of objects that have the same name), and each value in the hash table is a GV (Glob Value). This GV in turn contains references to the various objects of that name, @@ -713,20 +810,20 @@ including (but not limited to) the following: Format Subroutine -There is a single stash called "PL_defstash" that holds the items that exist -in the "main" package. To get at the items in other packages, append the -string "::" to the package name. The items in the "Foo" package are in -the stash "Foo::" in PL_defstash. The items in the "Bar::Baz" package are -in the stash "Baz::" in "Bar::"'s stash. +There is a single stash called C that holds the items that exist +in the C
package. To get at the items in other packages, append the +string "::" to the package name. The items in the C package are in +the stash C in PL_defstash. The items in the C package are +in the stash C in C's stash. To get the stash pointer for a particular package, use the function: - HV* gv_stashpv(const char* name, I32 create) - HV* gv_stashsv(SV*, I32 create) + HV* gv_stashpv(const char* name, I32 flags) + HV* gv_stashsv(SV*, I32 flags) The first function takes a literal string, the second uses the string stored in the SV. Remember that a stash is just a hash table, so you get back an -C. The C flag will create a new package if it is set. +C. The C flag will create a new package if it is set to GV_ADD. The name that C wants is the name of the package whose symbol table you want. The default package is called C
. If you have multiply nested @@ -785,7 +882,7 @@ following code: extern int dberror; extern char *dberror_list; - SV* sv = get_sv("dberror", TRUE); + SV* sv = get_sv("dberror", GV_ADD); sv_setiv(sv, (IV) dberror); sv_setpv(sv, dberror_list[dberror]); SvIOK_on(sv); @@ -808,9 +905,9 @@ linked list of C's, typedef'ed to C. U16 mg_private; char mg_type; U8 mg_flags; + I32 mg_len; SV* mg_obj; char* mg_ptr; - I32 mg_len; }; Note this is current as of patchlevel 0, and could change at any time. @@ -833,17 +930,20 @@ SV. The C and C arguments are used to associate a string with the magic, typically the name of a variable. C is stored in the -C field and if C is non-null and C >= 0 a malloc'd -copy of the name is stored in C field. +C field and if C is non-null then either a C copy of +C or C itself is stored in the C field, depending on +whether C is greater than zero or equal to zero respectively. As a +special case, if C<(name && namlen == HEf_SVKEY)> then C is assumed +to contain an C and is stored as-is with its REFCNT incremented. The sv_magic function uses C to determine which, if any, predefined "Magic Virtual Table" should be assigned to the C field. -See the "Magic Virtual Table" section below. The C argument is also +See the L section below. The C argument is also stored in the C field. The value of C should be chosen -from the set of macros C found perl.h. Note that before +from the set of macros C found in F. Note that before these macros were added, Perl internals used to directly use character literals, so you may occasionally come across old code or documentation -referrring to 'U' magic rather than C for example. +referring to 'U' magic rather than C for example. The C argument is stored in the C field of the C structure. If it is not the same as the C argument, the reference @@ -851,6 +951,9 @@ count of the C object is incremented. If it is the same, or if the C argument is C, or if it is a NULL pointer, then C is merely stored, without the reference count being incremented. +See also C in L for a more flexible way to add magic +to an SV. + There is also a function to add magic to an C: void hv_magic(HV *hv, GV *gv, int how); @@ -859,19 +962,26 @@ This simply calls C and coerces the C argument into an C. To remove the magic from an SV, call the function sv_unmagic: - void sv_unmagic(SV *sv, int type); + int sv_unmagic(SV *sv, int type); The C argument should be equal to the C value when the C was initially made magical. +However, note that C removes all magic of a certain C from the +C. If you want to remove only certain magic of a C based on the magic +virtual table, use C instead: + + int sv_unmagicext(SV *sv, int type, MGVTBL *vtbl); + =head2 Magic Virtual Tables -The C field in the C structure is a pointer to a +The C field in the C structure is a pointer to an C, which is a structure of function pointers and stands for "Magic Virtual Table" to handle the various operations that might be applied to that variable. -The C has five pointers to the following routine types: +The C has five (or sometimes eight) pointers to the following +routine types: int (*svt_get)(SV* sv, MAGIC* mg); int (*svt_set)(SV* sv, MAGIC* mg); @@ -879,19 +989,28 @@ The C has five pointers to the following routine types: int (*svt_clear)(SV* sv, MAGIC* mg); int (*svt_free)(SV* sv, MAGIC* mg); -This MGVTBL structure is set at compile-time in C and there are -currently 19 types (or 21 with overloading turned on). These different -structures contain pointers to various routines that perform additional -actions depending on which function is being called. + int (*svt_copy)(SV *sv, MAGIC* mg, SV *nsv, const char *name, I32 namlen); + int (*svt_dup)(MAGIC *mg, CLONE_PARAMS *param); + int (*svt_local)(SV *nsv, MAGIC *mg); + + +This MGVTBL structure is set at compile-time in F and there are +currently 32 types. These different structures contain pointers to various +routines that perform additional actions depending on which function is +being called. Function pointer Action taken ---------------- ------------ - svt_get Do something after the value of the SV is retrieved. + svt_get Do something before the value of the SV is retrieved. svt_set Do something after the SV is assigned a value. svt_len Report on the SV's length. - svt_clear Clear something the SV represents. + svt_clear Clear something the SV represents. svt_free Free any extra storage associated with the SV. + svt_copy copy tied variable magic to a tied element + svt_dup duplicate a magic structure during thread cloning + svt_local copy magic to local value during 'local' + For instance, the MGVTBL structure called C (which corresponds to an C of C) contains: @@ -903,56 +1022,77 @@ called. All the various routines for the various magical types begin with C. NOTE: the magic routines are not considered part of the Perl API, and may not be exported by the Perl library. +The last three slots are a recent addition, and for source code +compatibility they are only checked for if one of the three flags +MGf_COPY, MGf_DUP or MGf_LOCAL is set in mg_flags. This means that most +code can continue declaring a vtable as a 5-element value. These three are +currently used exclusively by the threading code, and are highly subject +to change. + The current kinds of Magic Virtual Tables are: mg_type - (old-style char and macro) MGVTBL Type of magic - -------------------------- ------ ---------------------------- - \0 PERL_MAGIC_sv vtbl_sv Special scalar variable - A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash + (old-style char and macro) MGVTBL Type of magic + -------------------------- ------ ------------- + \0 PERL_MAGIC_sv vtbl_sv Special scalar variable + # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary) + % PERL_MAGIC_rhash (none) extra data for restricted + hashes + . PERL_MAGIC_pos vtbl_pos pos() lvalue + : PERL_MAGIC_symtab (none) extra data for symbol tables + < PERL_MAGIC_backref vtbl_backref for weak ref data + @ PERL_MAGIC_arylen_p (none) to move arylen out of XPVAV + A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element - c PERL_MAGIC_overload_table (none) Holds overload table (AMT) - on stash - B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search) - D PERL_MAGIC_regdata vtbl_regdata Regex match position data - (@+ and @- vars) - d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data - element - E PERL_MAGIC_env vtbl_env %ENV hash - e PERL_MAGIC_envelem vtbl_envelem %ENV hash element - f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format) - g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string - I PERL_MAGIC_isa vtbl_isa @ISA array - i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element - k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue - L PERL_MAGIC_dbfile (none) Debugger %_ and C magic types are defined specifically for use by extensions and will not be used by perl itself. @@ -988,12 +1128,35 @@ sv_magic, so you can safely allocate it on the stack. uf.uf_index = 0; sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf)); +Attaching C to arrays is permissible but has no effect. + +For hashes there is a specialized hook that gives control over hash +keys (but not values). This hook calls C 'get' magic +if the "set" function in the C structure is NULL. The hook +is activated whenever the hash is accessed with a key specified as +an C through the functions C, C, +C, and C. Accessing the key as a string +through the functions without the C<..._ent> suffix circumvents the +hook. See L for a detailed description. + Note that because multiple extensions may be using C or C magic, it is important for extensions to take extra care to avoid conflict. Typically only using the magic on objects blessed into the same class as the extension is sufficient. -For C magic, it may also be appropriate to add an I32 -'signature' at the top of the private data area and check that. +For C magic, it is usually a good idea to define an +C, even if all its fields will be C<0>, so that individual +C pointers can be identified as a particular kind of magic +using their magic virtual table. C provides an easy way +to do that: + + STATIC MGVTBL my_vtbl = { 0, 0, 0, 0, 0, 0, 0, 0 }; + + MAGIC *mg; + if ((mg = mg_findext(sv, PERL_MAGIC_ext, &my_vtbl))) { + /* this is really ours, not another module's PERL_MAGIC_ext */ + my_priv_data_t *priv = (my_priv_data_t *)mg->mg_ptr; + ... + } Also note that the C and C functions described earlier do B invoke 'set' magic on their targets. This must @@ -1009,11 +1172,18 @@ since their implementation handles 'get' magic. =head2 Finding Magic - MAGIC* mg_find(SV*, int type); /* Finds the magic pointer of that type */ + MAGIC *mg_find(SV *sv, int type); /* Finds the magic pointer of that type */ + +This routine returns a pointer to a C structure stored in the SV. +If the SV does not have that magical feature, C is returned. If the +SV has multiple instances of that magical feature, the first one will be +returned. C can be used to find a C structure of an SV +based on both it's magic type and it's magic virtual table: + + MAGIC *mg_findext(SV *sv, int type, MGVTBL *vtbl); -This routine returns a pointer to the C structure stored in the SV. -If the SV does not have that magical feature, C is returned. Also, -if the SV is not of type SVt_PVMG, Perl may core dump. +Also, if the SV passed to C or C is not of type +SVt_PVMG, Perl may core dump. int mg_copy(SV* sv, SV* nsv, const char* key, STRLEN klen); @@ -1034,7 +1204,7 @@ you find yourself actually applying such information in this section, be aware that the behavior may change in the future, umm, without warning. The perl tie function associates a variable with an object that implements -the various GET, SET etc methods. To perform the equivalent of the perl +the various GET, SET, etc methods. To perform the equivalent of the perl tie function from an XSUB, you must mimic this behaviour. The code below carries out the necessary steps - firstly it creates a new hash, and then creates a second hash which it blesses into the class which will implement @@ -1053,7 +1223,7 @@ to do this. CODE: hash = newHV(); tie = newRV_noinc((SV*)newHV()); - stash = gv_stashpv("MyTie", TRUE); + stash = gv_stashpv("MyTie", GV_ADD); sv_bless(tie, stash); hv_magic(hash, (GV*)tie, PERL_MAGIC_tied); RETVAL = newRV_noinc(hash); @@ -1128,7 +1298,7 @@ This construction is I equivalent to The biggest difference is that the first construction would reinstate the initial value of $var, irrespective of how control exits -the block: C, C, C/C etc. It is a little bit +the block: C, C, C/C, etc. It is a little bit more efficient as well. There is a way to achieve a similar task from C via Perl API: create a @@ -1246,7 +1416,8 @@ Similar to C, but localize C<@gv> and C<%gv>. Duplicates the current value of C, on the exit from the current C/C I will restore the value of C -using the stored value. +using the stored value. It doesn't handle magic. Use C if +magic is affected. =item C @@ -1255,7 +1426,7 @@ C of C of length C. =item C -Similar to C, but will reinstate a C. +Similar to C, but will reinstate an C. =item C @@ -1297,11 +1468,15 @@ where C is the macro that represents the local copy of the stack pointer, and C is the number of elements the stack should be extended by. Now that there is room on the stack, values can be pushed on it using C -macro. The values pushed will often need to be "mortal" (See L). +macro. The pushed values will often need to be "mortal" (See +L): PUSHs(sv_2mortal(newSViv(an_integer))) + PUSHs(sv_2mortal(newSVuv(an_unsigned_integer))) + PUSHs(sv_2mortal(newSVnv(a_double))) PUSHs(sv_2mortal(newSVpv("Some String",0))) - PUSHs(sv_2mortal(newSVnv(3.141592))) + /* Although the last example is better written as the more efficient: */ + PUSHs(newSVpvs_flags("Some String", SVs_TEMP)) And now the Perl program calling C, the two values will be assigned as in: @@ -1317,8 +1492,9 @@ This macro automatically adjust the stack for you, if needed. Thus, you do not need to call C to extend the stack. Despite their suggestions in earlier versions of this document the macros -C, C and C are I suited to XSUBs which return -multiple results, see L. +C<(X)PUSH[iunp]> are I suited to XSUBs which return multiple results. +For that, either stick to the C<(X)PUSHs> macros shown above, or use the new +C macros instead; see L. For more information, consult L and L. @@ -1342,7 +1518,7 @@ trapped, and how to treat return values. All four routines return the number of arguments that the subroutine returned on the Perl stack. -These routines used to be called C etc., before Perl v5.6.0, +These routines used to be called C, etc., before Perl v5.6.0, but those names are now deprecated; macros of the same name are provided for compatibility. @@ -1367,6 +1543,8 @@ consult L. =head2 Memory Allocation +=head3 Allocation + All memory meant to be used with the Perl API functions should be manipulated using the macros described in this section. The macros provide the necessary transparency between differences in the actual malloc implementation that is @@ -1377,29 +1555,26 @@ with Perl. It keeps pools of various sizes of unallocated memory in order to satisfy allocation requests more quickly. However, on some platforms, it may cause spurious malloc or free errors. - New(x, pointer, number, type); - Newc(x, pointer, number, type, cast); - Newz(x, pointer, number, type); - -These three macros are used to initially allocate memory. +The following three macros are used to initially allocate memory : -The first argument C was a "magic cookie" that was used to keep track -of who called the macro, to help when debugging memory problems. However, -the current code makes no use of this feature (most Perl developers now -use run-time memory checkers), so this argument can be any number. + Newx(pointer, number, type); + Newxc(pointer, number, type, cast); + Newxz(pointer, number, type); -The second argument C should be the name of a variable that will +The first argument C should be the name of a variable that will point to the newly allocated memory. -The third and fourth arguments C and C specify how many of +The second and third arguments C and C specify how many of the specified type of data structure should be allocated. The argument -C is passed to C. The final argument to C, C, +C is passed to C. The final argument to C, C, should be used if the C argument is different from the C argument. -Unlike the C and C macros, the C macro calls C +Unlike the C and C macros, the C macro calls C to zero out all the newly allocated memory. +=head3 Reallocation + Renew(pointer, number, type); Renewc(pointer, number, type, cast); Safefree(pointer) @@ -1409,6 +1584,8 @@ piece of memory no longer needed. The arguments to C and C match those of C and C with the exception of not needing the "magic cookie" argument. +=head3 Moving + Move(source, dest, number, type); Copy(source, dest, number, type); Zero(dest, number, type); @@ -1446,7 +1623,7 @@ corresponding parts of its I and puts the I on stack. The macro to put this target on stack is C, and it is directly used in some opcodes, as well as indirectly in zillions of -others, which use it via C<(X)PUSH[pni]>. +others, which use it via C<(X)PUSH[iunp]>. Because the target is reused, you must be careful when pushing multiple values on the stack. The following code will not do what you think: @@ -1458,21 +1635,38 @@ This translates as "set C to 10, push a pointer to C onto the stack; set C to 20, push a pointer to C onto the stack". At the end of the operation, the stack does not contain the values 10 and 20, but actually contains two pointers to C, which we have set -to 20. If you need to push multiple different values, use C, -which bypasses C. +to 20. + +If you need to push multiple different values then you should either use +the C<(X)PUSHs> macros, or else use the new C macros, +none of which make use of C. The C<(X)PUSHs> macros simply push an +SV* on the stack, which, as noted under L, +will often need to be "mortal". The new C macros make +this a little easier to achieve by creating a new mortal for you (via +C<(X)PUSHmortal>), pushing that onto the stack (extending it if necessary +in the case of the C macros), and then setting its value. +Thus, instead of writing this to "fix" the example above: -On a related note, if you do use C<(X)PUSH[npi]>, then you're going to + XPUSHs(sv_2mortal(newSViv(10))) + XPUSHs(sv_2mortal(newSViv(20))) + +you can simply write: + + mXPUSHi(10) + mXPUSHi(20) + +On a related note, if you do use C<(X)PUSH[iunp]>, then you're going to need a C in your variable declarations so that the C<*PUSH*> -macros can make use of the local variable C. +macros can make use of the local variable C. See also C +and C. =head2 Scratchpads The question remains on when the SVs which are Is for opcodes -are created. The answer is that they are created when the current unit -- -a subroutine or a file (for opcodes for statements outside of -subroutines) -- is compiled. During this time a special anonymous Perl -array is created, which is called a scratchpad for the current -unit. +are created. The answer is that they are created when the current +unit--a subroutine or a file (for opcodes for statements outside of +subroutines)--is compiled. During this time a special anonymous Perl +array is created, which is called a scratchpad for the current unit. A scratchpad keeps SVs which are lexicals for the current unit and are targets for opcodes. One can deduce that an SV lives on a scratchpad @@ -1490,7 +1684,7 @@ the scratchpad AV. In fact it contains a pointer to an AV of (initially) one element, and this element is the scratchpad AV. Why do we need an extra level of indirection? -The answer is B, and maybe (sometime soon) B. Both +The answer is B, and maybe B. Both these can create several execution pointers going into the same subroutine. For the subroutine-child not write over the temporaries for the subroutine-parent (lifespan of which covers the call to the @@ -1537,8 +1731,8 @@ is the same as in our example. =head2 Examining the tree -If you have your perl compiled for debugging (usually done with C<-D -optimize=-g> on C command line), you may examine the +If you have your perl compiled for debugging (usually done with +C<-DDEBUGGING> on the C command line), you may examine the compiled tree by specifying C<-Dx> on the Perl command line. The output takes several lines per node, and for C<$b+$c> it looks like this: @@ -1607,6 +1801,9 @@ complicate matters, if a C is actually a C op after optimization (see L) it will still have children in accordance with its former type. +Another way to examine the tree is to use a compiler back-end module, such +as L. + =head2 Compile pass 1: check routines The tree is created by the compiler while I code feeds it @@ -1663,17 +1860,49 @@ of free()ing (i.e. their type is changed to OP_NULL). After the compile tree for a subroutine (or for an C or a file) is created, an additional pass over the code is performed. This pass is neither top-down or bottom-up, but in the execution order (with -additional complications for conditionals). These optimizations are -done in the subroutine peep(). Optimizations performed at this stage -are subject to the same restrictions as in the pass 2. +additional complications for conditionals). Optimizations performed +at this stage are subject to the same restrictions as in the pass 2. + +Peephole optimizations are done by calling the function pointed to +by the global variable C. By default, C just +calls the function pointed to by the global variable C. +By default, that performs some basic op fixups and optimisations along +the execution-order op chain, and recursively calls C for +each side chain of ops (resulting from conditionals). Extensions may +provide additional optimisations or fixups, hooking into either the +per-subroutine or recursive stage, like this: + + static peep_t prev_peepp; + static void my_peep(pTHX_ OP *o) + { + /* custom per-subroutine optimisation goes here */ + prev_peepp(o); + /* custom per-subroutine optimisation may also go here */ + } + BOOT: + prev_peepp = PL_peepp; + PL_peepp = my_peep; + + static peep_t prev_rpeepp; + static void my_rpeep(pTHX_ OP *o) + { + OP *orig_o = o; + for(; o; o = o->op_next) { + /* custom per-op optimisation goes here */ + } + prev_rpeepp(orig_o); + } + BOOT: + prev_rpeepp = PL_rpeepp; + PL_rpeepp = my_rpeep; =head2 Pluggable runops The compile tree is executed in a runops function. There are two runops -functions in F. C is used with DEBUGGING and -C is used otherwise. For fine control over the -execution of the compile tree it is possible to provide your own runops -function. +functions, in F and in F. C is used +with DEBUGGING and C is used otherwise. For fine +control over the execution of the compile tree it is possible to provide +your own runops function. It's probably best to copy one of the existing runops functions and change it to suit your needs. Then, in the BOOT section of your XS @@ -1684,6 +1913,76 @@ file, add the line: This function should be as efficient as possible to keep your programs running as fast as possible. +=head2 Compile-time scope hooks + +As of perl 5.14 it is possible to hook into the compile-time lexical +scope mechanism using C. This is used like +this: + + STATIC void my_start_hook(pTHX_ int full); + STATIC BHK my_hooks; + + BOOT: + BhkENTRY_set(&my_hooks, bhk_start, my_start_hook); + Perl_blockhook_register(aTHX_ &my_hooks); + +This will arrange to have C called at the start of +compiling every lexical scope. The available hooks are: + +=over 4 + +=item C + +This is called just after starting a new lexical scope. Note that Perl +code like + + if ($x) { ... } + +creates two scopes: the first starts at the C<(> and has C, +the second starts at the C<{> and has C. Both end at the +C<}>, so calls to C and C
 will match. Anything
+pushed onto the save stack by this hook will be popped just before the
+scope ends (between the C and C hooks, in fact).
+
+=item C
+
+This is called at the end of a lexical scope, just before unwinding the
+stack. I is the root of the optree representing the scope; it is a
+double pointer so you can replace the OP if you need to.
+
+=item C
+
+This is called at the end of a lexical scope, just after unwinding the
+stack. I is as above. Note that it is possible for calls to C
+and C to nest, if there is something on the save stack that
+calls string eval.
+
+=item C
+
+This is called just before starting to compile an C, C, C or C, after the eval has been set up. I is the
+OP that requested the eval, and will normally be an C,
+C or C.
+
+=back
+
+Once you have your hook functions, you need a C structure to put
+them in. It's best to allocate it statically, since there is no way to
+free it once it's registered. The function pointers should be inserted
+into this structure using the C macro, which will also set
+flags indicating which entries are valid. If you do need to allocate
+your C dynamically for some reason, be sure to zero it before you
+start.
+
+Once registered, there is no mechanism to switch these hooks off, so if
+that is necessary you will need to do this yourself. An entry in C<%^H>
+is probably the best way, so the effect is lexically scoped; however it
+is also possible to use the C and C macros to
+temporarily switch entries on and off. You should also be aware that
+generally speaking at least one scope will have opened before your
+extension is loaded, so you will see some C
 pairs that
+didn't have a matching C.
+
 =head1 Examining internal data structures with the C functions
 
 To aid debugging, the source file F contains a number of
@@ -1695,7 +1994,7 @@ C to produce debugging output from Perl-space, so users of that
 module should already be familiar with its format.
 
 C can be used to dump an C structure or any of its
-derivatives, and produces output similiar to C; in fact,
+derivatives, and produces output similar to C; in fact,
 C will dump the main root of the code being evaluated,
 exactly like C<-Dx>.
 
@@ -1731,13 +2030,39 @@ interpreters, with one interpreter represented either as a C structure,
 or inside a thread-specific structure.  These structures contain all
 the context, the state of that interpreter.
 
-Three macros control the major Perl build flavors: MULTIPLICITY, and
-USE_5005THREADS.  The MULTIPLICITY build has a C structure
-that packages all the interpreter state, and there is a similar thread-specific
-data structure under USE_5005THREADS.  In both cases,
-PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
-support for passing in a "hidden" first argument that represents all three
-data structures.
+One macro controls the major Perl build flavor: MULTIPLICITY. The
+MULTIPLICITY build has a C structure that packages all the interpreter
+state. With multiplicity-enabled perls, PERL_IMPLICIT_CONTEXT is also
+normally defined, and enables the support for passing in a "hidden" first
+argument that represents all three data structures. MULTIPLICITY makes
+multi-threaded perls possible (with the ithreads threading model, related
+to the macro USE_ITHREADS.)
+
+Two other "encapsulation" macros are the PERL_GLOBAL_STRUCT and
+PERL_GLOBAL_STRUCT_PRIVATE (the latter turns on the former, and the
+former turns on MULTIPLICITY.)  The PERL_GLOBAL_STRUCT causes all the
+internal variables of Perl to be wrapped inside a single global struct,
+struct perl_vars, accessible as (globals) &PL_Vars or PL_VarsPtr or
+the function  Perl_GetVars().  The PERL_GLOBAL_STRUCT_PRIVATE goes
+one step further, there is still a single struct (allocated in main()
+either from heap or from stack) but there are no global data symbols
+pointing to it.  In either case the global struct should be initialised
+as the very first thing in main() using Perl_init_global_struct() and
+correspondingly tear it down after perl_free() using Perl_free_global_struct(),
+please see F for usage details.  You may also need
+to use C in your coding to "declare the global variables"
+when you are using them.  dTHX does this for you automatically.
+
+To see whether you have non-const data you can use a BSD-compatible C:
+
+  nm libperl.a | grep -v ' [TURtr] '
+
+If this displays any C or C symbols, you have non-const data.
+
+For backward compatibility reasons defining just PERL_GLOBAL_STRUCT
+doesn't actually hide all symbols inside a big global struct: some
+PerlIO_xxx vtables are left visible.  The PERL_GLOBAL_STRUCT_PRIVATE
+then hides everything (see how the PERLIO_FUNCS_DECL is used).
 
 All this obviously requires a way for the Perl internal functions to be
 either subroutines taking some kind of structure as the first
@@ -1772,9 +2097,9 @@ A public function (i.e. part of the internal API, but not necessarily
 sanctioned for use in extensions) begins like this:
 
   void
-  Perl_sv_setsv(pTHX_ SV* dsv, SV* ssv)
+  Perl_sv_setiv(pTHX_ SV* dsv, IV num)
 
-C is one of a number of macros (in perl.h) that hide the
+C is one of a number of macros (in F) that hide the
 details of the interpreter's context.  THX stands for "thread", "this",
 or "thingy", as the case may be.  (And no, George Lucas is not involved. :-)
 The first character could be 'p' for a B
rototype, 'a' for Brgument,
@@ -1791,19 +2116,19 @@ macro without the trailing underscore is used when there are no additional
 explicit arguments.
 
 When a core function calls another, it must pass the context.  This
-is normally hidden via macros.  Consider C.  It expands into
+is normally hidden via macros.  Consider C.  It expands into
 something like this:
 
-    ifdef PERL_IMPLICIT_CONTEXT
-      define sv_setsv(a,b)      Perl_sv_setsv(aTHX_ a, b)
+    #ifdef PERL_IMPLICIT_CONTEXT
+      #define sv_setiv(a,b)      Perl_sv_setiv(aTHX_ a, b)
       /* can't do this for vararg functions, see below */
-    else
-      define sv_setsv           Perl_sv_setsv
-    endif
+    #else
+      #define sv_setiv           Perl_sv_setiv
+    #endif
 
 This works well, and means that XS authors can gleefully write:
 
-    sv_setsv(foo, bar);
+    sv_setiv(foo, bar);
 
 and still have it work under all the modes Perl could have been
 compiled with.
@@ -1843,20 +2168,20 @@ built with PERL_IMPLICIT_CONTEXT enabled.
 
 There are three ways to do this.  First, the easy but inefficient way,
 which is also the default, in order to maintain source compatibility
-with extensions: whenever XSUB.h is #included, it redefines the aTHX
+with extensions: whenever F is #included, it redefines the aTHX
 and aTHX_ macros to call a function that will return the context.
 Thus, something like:
 
-        sv_setsv(asv, bsv);
+        sv_setiv(sv, num);
 
 in your extension will translate to this when PERL_IMPLICIT_CONTEXT is
 in effect:
 
-        Perl_sv_setsv(Perl_get_context(), asv, bsv);
+        Perl_sv_setiv(Perl_get_context(), sv, num);
 
 or to this otherwise:
 
-        Perl_sv_setsv(asv, bsv);
+        Perl_sv_setiv(sv, num);
 
 You have to do nothing new in your extension to get this; since
 the Perl library provides Perl_get_context(), it will all just
@@ -1870,9 +2195,9 @@ your Foo.xs:
         #include "perl.h"
         #include "XSUB.h"
 
-        static my_private_function(int arg1, int arg2);
+        STATIC void my_private_function(int arg1, int arg2);
 
-        static SV *
+        STATIC void
         my_private_function(int arg1, int arg2)
         {
             dTHX;       /* fetch context */
@@ -1910,9 +2235,9 @@ the Perl guts:
         #include "XSUB.h"
 
         /* pTHX_ only needed for functions that call Perl API */
-        static my_private_function(pTHX_ int arg1, int arg2);
+        STATIC void my_private_function(pTHX_ int arg1, int arg2);
 
-        static SV *
+        STATIC void
         my_private_function(pTHX_ int arg1, int arg2)
         {
             /* dTHX; not needed here, because THX is an argument */
@@ -1940,6 +2265,13 @@ Never add a comma after C yourself--always use the form of the
 macro with the underscore for functions that take explicit arguments,
 or the form without the argument for functions with no explicit arguments.
 
+If one is compiling Perl with the C<-DPERL_GLOBAL_STRUCT> the C
+definition is needed if the Perl global variables (see F
+or F) are accessed in the function and C is not
+used (the C includes the C if necessary).  One notices
+the need for C only with the said compile-time define, because
+otherwise the Perl global variables are visible as-is.
+
 =head2 Should I do anything special if I call perl from multiple threads?
 
 If you create interpreters in one thread and then proceed to call them in
@@ -1966,14 +2298,14 @@ Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
 that the interpreter knows about itself and pass it around, so too are
 there plans to allow the interpreter to bundle up everything it knows
 about the environment it's running on.  This is enabled with the
-PERL_IMPLICIT_SYS macro.  Currently it only works with USE_ITHREADS
-and USE_5005THREADS on Windows (see inside iperlsys.h).
+PERL_IMPLICIT_SYS macro.  Currently it only works with USE_ITHREADS on
+Windows.
 
 This allows the ability to provide an extra pointer (called the "host"
 environment) for all the system calls.  This makes it possible for
 all the system stuff to maintain their own state, broken down into
 seven C structures.  These are thin wrappers around the usual system
-calls (see win32/perllib.c) for the default perl executable, but for a
+calls (see F) for the default perl executable, but for a
 more ambitious host (like the one that would do fork() emulation) all
 the extra work needed to pretend that different interpreters are
 actually different "processes", would be done here.
@@ -1985,19 +2317,24 @@ more "hosts", with free association between them.
 =head1 Internal Functions
 
 All of Perl's internal functions which will be exposed to the outside
-world are be prefixed by C so that they will not conflict with XS
+world are prefixed by C so that they will not conflict with XS
 functions or functions used in a program in which Perl is embedded.
 Similarly, all global variables begin with C. (By convention,
-static functions start with C)
-
-Inside the Perl core, you can get at the functions either with or
-without the C prefix, thanks to a bunch of defines that live in
-F. This header file is generated automatically from
-F. F also creates the prototyping header files for
-the internal functions, generates the documentation and a lot of other
-bits and pieces. It's important that when you add a new function to the
-core or change an existing one, you change the data in the table at the
-end of F as well. Here's a sample entry from that table:
+static functions start with C.)
+
+Inside the Perl core (C defined), you can get at the functions
+either with or without the C prefix, thanks to a bunch of defines
+that live in F. Note that extension code should I set
+C; this exposes the full perl internals, and is likely to cause
+breakage of the XS in each new perl release.
+
+The file F is generated automatically from
+F and F. F also creates the prototyping
+header files for the internal functions, generates the documentation
+and a lot of other bits and pieces. It's important that when you add
+a new function to the core or change an existing one, you change the
+data in the table in F as well. Here's a sample entry from
+that table:
 
     Apd |SV**   |av_fetch   |AV* ar|I32 key|I32 lval
 
@@ -2008,16 +2345,18 @@ after that are the arguments. The first column is a set of flags:
 
 =item A
 
-This function is a part of the public API.
+This function is a part of the public API. All such functions should also
+have 'd', very few do not.
 
 =item p
 
-This function has a C prefix; ie, it is defined as C
+This function has a C prefix; i.e. it is defined as
+C.
 
 =item d
 
 This function has documentation using the C feature which we'll
-look at in a second.
+look at in a second.  Some functions have 'd' but not 'A'; docs are good.
 
 =back
 
@@ -2027,13 +2366,14 @@ Other available flags are:
 
 =item s
 
-This is a static function and is defined as C, and usually
-called within the sources as C.
+This is a static function and is defined as C, and
+usually called within the sources as C.
 
 =item n
 
-This does not use C and C to pass interpreter context. (See
-L.)
+This does not need a interpreter context, so the definition has no
+C, and it follows that callers don't use C.  (See
+L.)
 
 =item r
 
@@ -2056,19 +2396,36 @@ or disappear without notice.
 This function should not have a compatibility macro to define, say,
 C to C. It must be called as C.
 
-=item j
-
-This function is not a member of C. If you don't know
-what this means, don't use it.
-
 =item x
 
 This function isn't exported out of the Perl core.
 
+=item m
+
+This is implemented as a macro.
+
+=item X
+
+This function is explicitly exported.
+
+=item E
+
+This function is visible to extensions included in the Perl core.
+
+=item b
+
+Binary backward compatibility; this function is a macro but also has
+a C implementation (which is exported).
+
+=item others
+
+See the comments at the top of C for others.
+
 =back
 
-If you edit F, you will need to run C to
-force a rebuild of F and other auto-generated files.
+If you edit F or F, you will need to run
+C to force a rebuild of F and other
+auto-generated files.
 
 =head2 Formatted Printing of IVs, UVs, and NVs
 
@@ -2114,6 +2471,39 @@ and
         AV *av = ...;
         UV  uv = PTR2UV(av);
 
+=head2 Exception Handling
+
+There are a couple of macros to do very basic exception handling in XS
+modules. You have to define C before including F to
+be able to use these macros:
+
+        #define NO_XSLOCKS
+        #include "XSUB.h"
+
+You can use these macros if you call code that may croak, but you need
+to do some cleanup before giving control back to Perl. For example:
+
+        dXCPT;    /* set up necessary variables */
+
+        XCPT_TRY_START {
+          code_that_may_croak();
+        } XCPT_TRY_END
+
+        XCPT_CATCH
+        {
+          /* do cleanup here */
+          XCPT_RETHROW;
+        }
+
+Note that you always have to rethrow an exception that has been
+caught. Using these macros, it is not possible to just catch the
+exception and ignore it. If you have to ignore the exception, you
+have to use the C function.
+
+The advantage of using the above macros is that you don't have
+to setup an extra function for C, and that using these
+macros is faster than using C.
+
 =head2 Source Documentation
 
 There's an effort going on to document the internal functions and
@@ -2137,6 +2527,26 @@ source, like this:
 Please try and supply some documentation if you add functions to the
 Perl core.
 
+=head2 Backwards compatibility
+
+The Perl API changes over time. New functions are added or the interfaces
+of existing functions are changed. The C module tries to
+provide compatibility code for some of these changes, so XS writers don't
+have to code it themselves when supporting multiple versions of Perl.
+
+C generates a C header file F that can also
+be run as a Perl script. To generate F, run:
+
+    perl -MDevel::PPPort -eDevel::PPPort::WriteFile
+
+Besides checking existing XS code, the script can also be used to retrieve
+compatibility information for various API calls using the C<--api-info>
+command line switch. For example:
+
+  % perl ppport.h --api-info=sv_magicext
+
+For details, see C.
+
 =head1 Unicode Support
 
 Perl 5.6.0 introduced Unicode support. It's important for porters and XS
@@ -2163,34 +2573,35 @@ to one character.
 To fix this, some people formed Unicode, Inc. and
 produced a new character set containing all the characters you can
 possibly think of and more. There are several ways of representing these
-characters, and the one Perl uses is called UTF8. UTF8 uses
-a variable number of bytes to represent a character, instead of just
-one. You can learn more about Unicode at http://www.unicode.org/
+characters, and the one Perl uses is called UTF-8. UTF-8 uses
+a variable number of bytes to represent a character. You can learn more
+about Unicode and Perl's Unicode model in L.
 
-=head2 How can I recognise a UTF8 string?
+=head2 How can I recognise a UTF-8 string?
 
-You can't. This is because UTF8 data is stored in bytes just like
-non-UTF8 data. The Unicode character 200, (C<0xC8> for you hex types)
+You can't. This is because UTF-8 data is stored in bytes just like
+non-UTF-8 data. The Unicode character 200, (C<0xC8> for you hex types)
 capital E with a grave accent, is represented by the two bytes
 C. Unfortunately, the non-Unicode string C
 has that byte sequence as well. So you can't tell just by looking - this
 is what makes Unicode input an interesting problem.
 
-The API function C can help; it'll tell you if a string
-contains only valid UTF8 characters. However, it can't do the work for
-you. On a character-by-character basis, C will tell you
-whether the current character in a string is valid UTF8.
+In general, you either have to know what you're dealing with, or you
+have to guess.  The API function C can help; it'll tell
+you if a string contains only valid UTF-8 characters. However, it can't
+do the work for you. On a character-by-character basis, C
+will tell you whether the current character in a string is valid UTF-8. 
 
-=head2 How does UTF8 represent Unicode characters?
+=head2 How does UTF-8 represent Unicode characters?
 
-As mentioned above, UTF8 uses a variable number of bytes to store a
-character. Characters with values 1...128 are stored in one byte, just
-like good ol' ASCII. Character 129 is stored as C; this
+As mentioned above, UTF-8 uses a variable number of bytes to store a
+character. Characters with values 0...127 are stored in one byte, just
+like good ol' ASCII. Character 128 is stored as C; this
 continues up to character 191, which is C. Now we've run out of
 bits (191 is binary C<10111111>) so we move on; 192 is C. And
 so it goes on, moving to three bytes at character 2048.
 
-Assuming you know you're dealing with a UTF8 string, you can find out
+Assuming you know you're dealing with a UTF-8 string, you can find out
 how long the first character in it is with the C macro:
 
     char *utf = "\305\233\340\240\201";
@@ -2200,19 +2611,21 @@ how long the first character in it is with the C macro:
     utf += len;
     len = UTF8SKIP(utf); /* len is 3 here */
 
-Another way to skip over characters in a UTF8 string is to use
+Another way to skip over characters in a UTF-8 string is to use
 C, which takes a string and a number of characters to skip
 over. You're on your own about bounds checking, though, so don't use it
 lightly.
 
-All bytes in a multi-byte UTF8 character will have the high bit set, so
-you can test if you need to do something special with this character
-like this:
+All bytes in a multi-byte UTF-8 character will have the high bit set,
+so you can test if you need to do something special with this
+character like this (the UTF8_IS_INVARIANT() is a macro that tests
+whether the byte can be encoded as a single byte even in UTF-8):
 
-    UV uv;
+    U8 *utf;
+    UV uv;	/* Note: a UV, not a U8, not a char */
 
-    if (utf & 0x80)
-        /* Must treat this as UTF8 */
+    if (!UTF8_IS_INVARIANT(*utf))
+        /* Must treat this as UTF-8 */
         uv = utf8_to_uv(utf);
     else
         /* OK to treat this character as a byte */
@@ -2220,9 +2633,9 @@ like this:
 
 You can also see in that example that we use C to get the
 value of the character; the inverse function C is available
-for putting a UV into UTF8:
+for putting a UV into UTF-8:
 
-    if (uv > 0x80)
+    if (!UTF8_IS_INVARIANT(uv))
         /* Must treat this as UTF8 */
         utf8 = uv_to_utf8(utf8, uv);
     else
@@ -2230,19 +2643,22 @@ for putting a UV into UTF8:
         *utf8++ = uv;
 
 You B convert characters to UVs using the above functions if
-you're ever in a situation where you have to match UTF8 and non-UTF8
-characters. You may not skip over UTF8 characters in this case. If you
-do this, you'll lose the ability to match hi-bit non-UTF8 characters;
-for instance, if your UTF8 string contains C, and you skip
-that character, you can never match a C in a non-UTF8 string.
+you're ever in a situation where you have to match UTF-8 and non-UTF-8
+characters. You may not skip over UTF-8 characters in this case. If you
+do this, you'll lose the ability to match hi-bit non-UTF-8 characters;
+for instance, if your UTF-8 string contains C, and you skip
+that character, you can never match a C in a non-UTF-8 string.
 So don't do that!
 
-=head2 How does Perl store UTF8 strings?
+=head2 How does Perl store UTF-8 strings?
 
 Currently, Perl deals with Unicode strings and non-Unicode strings
-slightly differently. If a string has been identified as being UTF-8
-encoded, Perl will set a flag in the SV, C. You can check and
-manipulate this flag with the following macros:
+slightly differently. A flag in the SV, C, indicates that the
+string is internally encoded as UTF-8. Without it, the byte value is the
+codepoint number and vice versa (in other words, the string is encoded
+as iso-8859-1, but C is needed to get iso-8859-1
+semantics). You can check and manipulate this flag with the
+following macros:
 
     SvUTF8(sv)
     SvUTF8_on(sv)
@@ -2254,8 +2670,8 @@ C, C and other string handling operations will have
 undesirable results.
 
 The problem comes when you have, for instance, a string that isn't
-flagged is UTF8, and contains a byte sequence that could be UTF8 -
-especially when combining non-UTF8 and UTF8 strings.
+flagged as UTF-8, and contains a byte sequence that could be UTF-8 -
+especially when combining non-UTF-8 and UTF-8 strings.
 
 Never forget that the C flag is separate to the PV value; you
 need be sure you don't accidentally knock it off while you're
@@ -2281,14 +2697,18 @@ old SV has the UTF8 flag set, and act accordingly:
         SvUTF8_on(nsv);
 
 In fact, your C function should be made aware of whether or
-not it's dealing with UTF8 data, so that it can handle the string
+not it's dealing with UTF-8 data, so that it can handle the string
 appropriately.
 
-=head2 How do I convert a string to UTF8?
+Since just passing an SV to an XS function and copying the data of
+the SV is not enough to copy the UTF8 flags, even less right is just
+passing a C to an XS function.
+
+=head2 How do I convert a string to UTF-8?
 
-If you're mixing UTF8 and non-UTF8 strings, you might find it necessary
-to upgrade one of the strings to UTF8. If you've got an SV, the easiest
-way to do this is:
+If you're mixing UTF-8 and non-UTF-8 strings, it is necessary to upgrade
+one of the strings to UTF-8. If you've got an SV, the easiest way to do
+this is:
 
     sv_utf8_upgrade(sv);
 
@@ -2299,9 +2719,9 @@ However, you must not do this, for example:
 
 If you do this in a binary operator, you will actually change one of the
 strings that came into the operator, and, while it shouldn't be noticeable
-by the end user, it can cause problems.
+by the end user, it can cause problems in deficient code.
 
-Instead, C will give you a UTF8-encoded B of its
+Instead, C will give you a UTF-8-encoded B of its
 string argument. This is useful for having the data available for
 comparisons and so on, without harming the original SV. There's also
 C to go the other way, but naturally, this will fail if
@@ -2316,38 +2736,37 @@ Not really. Just remember these things:
 
 =item *
 
-There's no way to tell if a string is UTF8 or not. You can tell if an SV
-is UTF8 by looking at is C flag. Don't forget to set the flag if
-something should be UTF8. Treat the flag as part of the PV, even though
+There's no way to tell if a string is UTF-8 or not. You can tell if an SV
+is UTF-8 by looking at is C flag. Don't forget to set the flag if
+something should be UTF-8. Treat the flag as part of the PV, even though
 it's not - if you pass on the PV to somewhere, pass on the flag too.
 
 =item *
 
-If a string is UTF8, B use C to get at the value,
-unless C in which case you can use C<*s>.
+If a string is UTF-8, B use C to get at the value,
+unless C in which case you can use C<*s>.
 
 =item *
 
-When writing to a UTF8 string, B use C, unless
-C in which case you can use C<*s = uv>.
+When writing a character C to a UTF-8 string, B use
+C, unless C in which case
+you can use C<*s = uv>.
 
 =item *
 
-Mixing UTF8 and non-UTF8 strings is tricky. Use C to get
-a new string which is UTF8 encoded. There are tricks you can use to
-delay deciding whether you need to use a UTF8 string until you get to a
-high character - C is one of those.
+Mixing UTF-8 and non-UTF-8 strings is tricky. Use C to get
+a new string which is UTF-8 encoded, and then combine them.
 
 =back
 
 =head1 Custom Operators
 
-Custom operator support is a new experimental feature that allows you do
+Custom operator support is a new experimental feature that allows you to
 define your own ops. This is primarily to allow the building of
 interpreters for other languages in the Perl core, but it also allows
 optimizations through the creation of "macro-ops" (ops which perform the
 functions of multiple ops which are usually executed together, such as
-C.) 
+C.)
 
 This feature is implemented as a new op type, C. The Perl
 core does not "know" anything special about this op type, and so it will
@@ -2373,32 +2792,93 @@ responsible for adding stack marks if necessary.
 You should also "register" your op with the Perl interpreter so that it
 can produce sensible error and warning messages. Since it is possible to
 have multiple custom ops within the one "logical" op type C,
-Perl uses the value of C<< o->op_ppaddr >> as a key into the
-C and C hashes. This means you
-need to enter a name and description for your op at the appropriate
-place in the C and C hashes.
+Perl uses the value of C<< o->op_ppaddr >> to determine which custom op
+it is dealing with. You should create an C structure for each
+ppaddr you use, set the properties of the custom op with
+C, and register the structure against the ppaddr using
+C. A trivial example might look like:
+
+    static XOP my_xop;
+    static OP *my_pp(pTHX);
+
+    BOOT:
+        XopENTRY_set(&my_xop, xop_name, "myxop");
+        XopENTRY_set(&my_xop, xop_desc, "Useless custom op");
+        Perl_custom_op_register(aTHX_ my_pp, &my_xop);
+
+The available fields in the structure are:
+
+=over 4
+
+=item xop_name
+
+A short name for your op. This will be included in some error messages,
+and will also be returned as C<< $op->name >> by the L module, so
+it will appear in the output of module like L.
+
+=item xop_desc
+
+A short description of the function of the op.
+
+=item xop_class
+
+Which of the various C<*OP> structures this op uses. This should be one of
+the C constants from F, namely
+
+=over 4
+
+=item OA_BASEOP
+
+=item OA_UNOP
 
-Forthcoming versions of C (version 1.0 and above) should
-directly support the creation of custom ops by name; C 
-will provide functions which make it trivial to "register" custom ops to
-the Perl interpreter.
+=item OA_BINOP
+
+=item OA_LOGOP
+
+=item OA_LISTOP
+
+=item OA_PMOP
+
+=item OA_SVOP
+
+=item OA_PADOP
+
+=item OA_PVOP_OR_SVOP
+
+This should be interpreted as 'C' only. The C<_OR_SVOP> is because
+the only core C, C, can sometimes be a C instead.
+
+=item OA_LOOP
+
+=item OA_COP
+
+=back
+
+The other C constants should not be used.
+
+=item xop_peep
+
+This member is of type C, which expands to C. If it is set, this function
+will be called from C when ops of this type are encountered
+by the peephole optimizer. I is the OP that needs optimizing;
+I is the previous OP optimized, whose C points to I.
+
+=back
+
+C directly supports the creation of custom ops by name.
 
 =head1 AUTHORS
 
 Until May 1997, this document was maintained by Jeff Okamoto
-.  It is now maintained as part of Perl itself
-by the Perl 5 Porters .
+Eokamoto@corp.hp.comE.  It is now maintained as part of Perl
+itself by the Perl 5 Porters Eperl5-porters@perl.orgE.
 
 With lots of help and suggestions from Dean Roehrich, Malcolm Beattie,
 Andreas Koenig, Paul Hudson, Ilya Zakharevich, Paul Marquess, Neil
 Bowers, Matthew Green, Tim Bunce, Spider Boardman, Ulrich Pfeifer,
 Stephen McCamant, and Gurusamy Sarathy.
 
-API Listing originally by Dean Roehrich .
-
-Modifications to autogenerate the API listing (L) by Benjamin
-Stuhl.
-
 =head1 SEE ALSO
 
-perlapi(1), perlintern(1), perlxs(1), perlembed(1)
+L, L, L, L