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* newSVpvf(const char*, ...);
SV* newSVsv(SV*);
-To change the value of an *already-existing* SV, there are seven routines:
+If you require more complex initialisation you can create an empty SV with
+newSV(len). If C<len> 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* newSV(0); /* no storage allocated */
+ SV* newSV(10); /* 10 (+1) bytes of uninitialised storage allocated */
+
+To change the value of an *already-existing* SV, there are eight routines:
void sv_setiv(SV*, IV);
void sv_setuv(SV*, UV);
void sv_setpv(SV*, const char*);
void sv_setpvn(SV*, const char*, int)
void sv_setpvf(SV*, const char*, ...);
- void sv_setpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
+ void sv_vsetpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool *);
void sv_setsv(SV*, SV*);
Notice that you can choose to specify the length of the string to be
The arguments of C<sv_setpvf> are processed like C<sprintf>, and the
formatted output becomes the value.
-C<sv_setpvfn> is an analogue of C<vsprintf>, but it allows you to specify
+C<sv_vsetpvfn> is an analogue of C<vsprintf>, but it allows you to specify
either a pointer to a variable argument list or the address and length of
an array of SVs. The last argument points to a boolean; on return, if that
boolean is true, then locale-specific information has been used to format
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
+config.h) guaranteed to be large enough to represent the size of
any string that perl can handle.
The C<sv_set*()> functions are not generic enough to operate on values
void sv_catpv(SV*, const char*);
void sv_catpvn(SV*, const char*, STRLEN);
void sv_catpvf(SV*, const char*, ...);
- void sv_catpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
+ void sv_vcatpvfn(SV*, const char*, STRLEN, va_list *, SV **, I32, bool);
void sv_catsv(SV*, SV*);
The first function calculates the length of the string to be appended by
Perl provides the function C<sv_chop> to efficiently remove characters
from the beginning of a string; you give it an SV and a pointer to
-somewhere inside the the PV, and it discards everything before the
+somewhere inside the PV, and it discards everything before the
pointer. The efficiency comes by means of a little hack: instead of
actually removing the characters, C<sv_chop> sets the flag C<OOK>
(offset OK) to signal to other functions that the offset hack is in
effect, and it puts the number of bytes chopped off into the IV field
of the SV. It then moves the PV pointer (called C<SvPVX>) forward that
-many bytes, and adjusts C<SvCUR> and C<SvLEN>.
+many bytes, and adjusts C<SvCUR> and C<SvLEN>.
Hence, at this point, the start of the buffer that we allocated lives
at C<SvPVX(sv) - SvIV(sv)> in memory and the PV pointer is pointing
shown in parentheses, and the values of C<SvCUR> and C<SvLEN> reflect
the fake beginning, not the real one.
+Something similar to the offset hack is performed on AVs to enable
+efficient shifting and splicing off the beginning of the array; while
+C<AvARRAY> points to the first element in the array that is visible from
+Perl, C<AvALLOC> points to the real start of the C array. These are
+usually the same, but a C<shift> operation can be carried out by
+increasing C<AvARRAY> by one and decreasing C<AvFILL> and C<AvLEN>.
+Again, the location of the real start of the C array only comes into
+play when freeing the array. See C<av_shift> in F<av.c>.
+
=head2 What's Really Stored in an SV?
Recall that the usual method of determining the type of scalar you have is
These will tell you if you truly have an integer, double, or string pointer
stored in your SV. The "p" stands for private.
+The are various ways in which the private and public flags may differ.
+For example, a tied SV may have a valid underlying value in the IV slot
+(so SvIOKp is true), but the data should be accessed via the FETCH
+routine rather than directly, so SvIOK is false. Another is when
+numeric conversion has occured and precision has been lost: only the
+private flag is set on 'lossy' values. So when an NV is converted to an
+IV with loss, SvIOKp, SvNOKp and SvNOK will be set, while SvIOK wont be.
+
In general, though, it's best to use the C<Sv*V> macros.
=head2 Working with AVs
/* 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,
SV* newSVrv(SV* rv, const char* classname);
-Copies integer or double into an SV whose reference is C<rv>. SV is blessed
+Copies integer, unsigned integer or double into an SV whose reference is C<rv>. SV is blessed
if C<classname> 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<the address, not the string!>) into an SV whose
bool sv_derived_from(SV* sv, const char* name);
-To check if you've got an object derived from a specific class you have
+To check if you've got an object derived from a specific class you have
to write:
if (sv_isobject(sv) && sv_derived_from(sv, class)) { ... }
There are additional macros whose values may be bitwise OR'ed with the
C<TRUE> argument to enable certain extra features. Those bits are:
- GV_ADDMULTI Marks the variable as multiply defined, thus preventing the
- "Name <varname> used only once: possible typo" warning.
- GV_ADDWARN Issues the warning "Had to create <varname> 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 <varname> used only once: possible typo
+
+warning.
+
+=item GV_ADDWARN
+
+Issues the warning:
+
+ Had to create <varname> 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.
However, if you mortalize a variable twice, the reference count will
later be decremented twice.
-You should be careful about creating mortal variables. Strange things
-can happen if you make the same value mortal within multiple contexts,
-or if you make a variable mortal multiple times.
+"Mortal" SVs are mainly used for SVs that are placed on perl's stack.
+For example an SV which is created just to pass a number to a called sub
+is made mortal to have it cleaned up automatically when stack is popped.
+Similarly results returned by XSUBs (which go in the stack) are often
+made mortal.
To create a mortal variable, use the functions:
SV* sv_2mortal(SV*)
SV* sv_mortalcopy(SV*)
-The first call creates a mortal SV, the second converts an existing
+The first call creates a mortal SV (with no value), the second converts an existing
SV to a mortal SV (and thus defers a call to C<SvREFCNT_dec>), and the
third creates a mortal copy of an existing SV.
+Because C<sv_newmortal> gives the new SV no value,it must normally be given one
+via C<sv_setpv>, C<sv_setiv>, etc. :
+
+ SV *tmp = sv_newmortal();
+ sv_setiv(tmp, an_integer);
+
+As that is multiple C statements it is quite common so see this idiom instead:
+
+ SV *tmp = sv_2mortal(newSViv(an_integer));
+
+
+You should be careful about creating mortal variables. Strange things
+can happen if you make the same value mortal within multiple contexts,
+or if you make a variable mortal multiple times. Thinking of "Mortalization"
+as deferred C<SvREFCNT_dec> should help to minimize such problems.
+For example if you are passing an SV which you I<know> has high enough REFCNT
+to survive its use on the stack you need not do any mortalization.
+If you are not sure then doing an C<SvREFCNT_inc> and C<sv_2mortal>, or
+making a C<sv_mortalcopy> is safer.
The mortal routines are not just for SVs -- AVs and HVs can be
made mortal by passing their address (type-casted to C<SV*>) to the
feature.
If C<sv> is not already magical, Perl uses the C<SvUPGRADE> macro to
-set the C<SVt_PVMG> flag for the C<sv>. Perl then continues by adding
-it to the beginning of the linked list of magical features. Any prior
-entry of the same type of magic is deleted. Note that this can be
-overridden, and multiple instances of the same type of magic can be
-associated with an SV.
+convert C<sv> to type C<SVt_PVMG>. Perl then continues by adding new magic
+to the beginning of the linked list of magical features. Any prior entry
+of the same type of magic is deleted. Note that this can be overridden,
+and multiple instances of the same type of magic can be associated with an
+SV.
The C<name> and C<namlen> arguments are used to associate a string with
the magic, typically the name of a variable. C<namlen> is stored in the
-C<mg_len> field and if C<name> is non-null and C<namlen> >= 0 a malloc'd
+C<mg_len> field and if C<name> is non-null and C<namlen> E<gt>= 0 a malloc'd
copy of the name is stored in C<mg_ptr> field.
The sv_magic function uses C<how> to determine which, if any, predefined
"Magic Virtual Table" should be assigned to the C<mg_virtual> field.
See the "Magic Virtual Table" section below. The C<how> argument is also
-stored in the C<mg_type> field.
+stored in the C<mg_type> field. The value of C<how> should be chosen
+from the set of macros C<PERL_MAGIC_foo> found perl.h. Note that before
+these macros were added, Perl internals used to directly use character
+literals, so you may occasionally come across old code or documentation
+referring to 'U' magic rather than C<PERL_MAGIC_uvar> for example.
The C<obj> argument is stored in the C<mg_obj> field of the C<MAGIC>
structure. If it is not the same as the C<sv> argument, the reference
count of the C<obj> object is incremented. If it is the same, or if
-the C<how> argument is "#", or if it is a NULL pointer, then C<obj> is
-merely stored, without the reference count being incremented.
+the C<how> argument is C<PERL_MAGIC_arylen>, or if it is a NULL pointer,
+then C<obj> is merely stored, without the reference count being incremented.
There is also a function to add magic to an C<HV>:
=head2 Magic Virtual Tables
-The C<mg_virtual> field in the C<MAGIC> structure is a pointer to a
+The C<mg_virtual> field in the C<MAGIC> structure is a pointer to an
C<MGVTBL>, 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.
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_free Free any extra storage associated with the SV.
For instance, the MGVTBL structure called C<vtbl_sv> (which corresponds
-to an C<mg_type> of '\0') contains:
+to an C<mg_type> of C<PERL_MAGIC_sv>) contains:
{ magic_get, magic_set, magic_len, 0, 0 }
-Thus, when an SV is determined to be magical and of type '\0', if a get
-operation is being performed, the routine C<magic_get> is called. All
-the various routines for the various magical types begin with C<magic_>.
-NOTE: the magic routines are not considered part of the Perl API, and may
-not be exported by the Perl library.
+Thus, when an SV is determined to be magical and of type C<PERL_MAGIC_sv>,
+if a get operation is being performed, the routine C<magic_get> is
+called. All the various routines for the various magical types begin
+with C<magic_>. NOTE: the magic routines are not considered part of
+the Perl API, and may not be exported by the Perl library.
The current kinds of Magic Virtual Tables are:
- mg_type MGVTBL Type of magic
- ------- ------ ----------------------------
- \0 vtbl_sv Special scalar variable
- A vtbl_amagic %OVERLOAD hash
- a vtbl_amagicelem %OVERLOAD hash element
- c (none) Holds overload table (AMT) on stash
- B vtbl_bm Boyer-Moore (fast string search)
- D vtbl_regdata Regex match position data (@+ and @- vars)
- d vtbl_regdatum Regex match position data element
- E vtbl_env %ENV hash
- e vtbl_envelem %ENV hash element
- f vtbl_fm Formline ('compiled' format)
- g vtbl_mglob m//g target / study()ed string
- I vtbl_isa @ISA array
- i vtbl_isaelem @ISA array element
- k vtbl_nkeys scalar(keys()) lvalue
- L (none) Debugger %_<filename
- l vtbl_dbline Debugger %_<filename element
- o vtbl_collxfrm Locale transformation
- P vtbl_pack Tied array or hash
- p vtbl_packelem Tied array or hash element
- q vtbl_packelem Tied scalar or handle
- S vtbl_sig %SIG hash
- s vtbl_sigelem %SIG hash element
- t vtbl_taint Taintedness
- U vtbl_uvar Available for use by extensions
- v vtbl_vec vec() lvalue
- x vtbl_substr substr() lvalue
- y vtbl_defelem Shadow "foreach" iterator variable /
- smart parameter vivification
- * vtbl_glob GV (typeglob)
- # vtbl_arylen Array length ($#ary)
- . vtbl_pos pos() lvalue
- ~ (none) Available for use by extensions
+ mg_type
+ (old-style char and macro) MGVTBL Type of magic
+ -------------------------- ------ ----------------------------
+ \0 PERL_MAGIC_sv vtbl_sv Special scalar variable
+ A PERL_MAGIC_overload vtbl_amagic %OVERLOAD hash
+ a PERL_MAGIC_overload_elem vtbl_amagicelem %OVERLOAD hash element
+ c PERL_MAGIC_overload_table (none) Holds overload table (AMT)
+ on stash
+ B PERL_MAGIC_bm vtbl_bm Boyer-Moore (fast string search)
+ D PERL_MAGIC_regdata vtbl_regdata Regex match position data
+ (@+ and @- vars)
+ d PERL_MAGIC_regdatum vtbl_regdatum Regex match position data
+ element
+ E PERL_MAGIC_env vtbl_env %ENV hash
+ e PERL_MAGIC_envelem vtbl_envelem %ENV hash element
+ f PERL_MAGIC_fm vtbl_fm Formline ('compiled' format)
+ g PERL_MAGIC_regex_global vtbl_mglob m//g target / study()ed string
+ I PERL_MAGIC_isa vtbl_isa @ISA array
+ i PERL_MAGIC_isaelem vtbl_isaelem @ISA array element
+ k PERL_MAGIC_nkeys vtbl_nkeys scalar(keys()) lvalue
+ L PERL_MAGIC_dbfile (none) Debugger %_<filename
+ l PERL_MAGIC_dbline vtbl_dbline Debugger %_<filename element
+ m PERL_MAGIC_mutex vtbl_mutex ???
+ o PERL_MAGIC_collxfrm vtbl_collxfrm Locale collate transformation
+ P PERL_MAGIC_tied vtbl_pack Tied array or hash
+ p PERL_MAGIC_tiedelem vtbl_packelem Tied array or hash element
+ q PERL_MAGIC_tiedscalar vtbl_packelem Tied scalar or handle
+ r PERL_MAGIC_qr vtbl_qr precompiled qr// regex
+ S PERL_MAGIC_sig vtbl_sig %SIG hash
+ s PERL_MAGIC_sigelem vtbl_sigelem %SIG hash element
+ t PERL_MAGIC_taint vtbl_taint Taintedness
+ U PERL_MAGIC_uvar vtbl_uvar Available for use by extensions
+ v PERL_MAGIC_vec vtbl_vec vec() lvalue
+ x PERL_MAGIC_substr vtbl_substr substr() lvalue
+ y PERL_MAGIC_defelem vtbl_defelem Shadow "foreach" iterator
+ variable / smart parameter
+ vivification
+ * PERL_MAGIC_glob vtbl_glob GV (typeglob)
+ # PERL_MAGIC_arylen vtbl_arylen Array length ($#ary)
+ . PERL_MAGIC_pos vtbl_pos pos() lvalue
+ < PERL_MAGIC_backref vtbl_backref ???
+ ~ PERL_MAGIC_ext (none) Available for use by extensions
When an uppercase and lowercase letter both exist in the table, then the
uppercase letter is used to represent some kind of composite type (a list
or a hash), and the lowercase letter is used to represent an element of
-that composite type.
-
-The '~' and 'U' magic types are defined specifically for use by
-extensions and will not be used by perl itself. Extensions can use
-'~' magic to 'attach' private information to variables (typically
-objects). This is especially useful because there is no way for
-normal perl code to corrupt this private information (unlike using
-extra elements of a hash object).
-
-Similarly, 'U' magic can be used much like tie() to call a C function
-any time a scalar's value is used or changed. The C<MAGIC>'s
+that composite type. Some internals code makes use of this case
+relationship.
+
+The C<PERL_MAGIC_ext> and C<PERL_MAGIC_uvar> magic types are defined
+specifically for use by extensions and will not be used by perl itself.
+Extensions can use C<PERL_MAGIC_ext> magic to 'attach' private information
+to variables (typically objects). This is especially useful because
+there is no way for normal perl code to corrupt this private information
+(unlike using extra elements of a hash object).
+
+Similarly, C<PERL_MAGIC_uvar> magic can be used much like tie() to call a
+C function any time a scalar's value is used or changed. The C<MAGIC>'s
C<mg_ptr> field points to a C<ufuncs> structure:
struct ufuncs {
- I32 (*uf_val)(IV, SV*);
- I32 (*uf_set)(IV, SV*);
+ I32 (*uf_val)(pTHX_ IV, SV*);
+ I32 (*uf_set)(pTHX_ IV, SV*);
IV uf_index;
};
When the SV is read from or written to, the C<uf_val> or C<uf_set>
-function will be called with C<uf_index> as the first arg and a
-pointer to the SV as the second. A simple example of how to add 'U'
+function will be called with C<uf_index> as the first arg and a pointer to
+the SV as the second. A simple example of how to add C<PERL_MAGIC_uvar>
magic is shown below. Note that the ufuncs structure is copied by
sv_magic, so you can safely allocate it on the stack.
uf.uf_val = &my_get_fn;
uf.uf_set = &my_set_fn;
uf.uf_index = 0;
- sv_magic(sv, 0, 'U', (char*)&uf, sizeof(uf));
+ sv_magic(sv, 0, PERL_MAGIC_uvar, (char*)&uf, sizeof(uf));
-Note that because multiple extensions may be using '~' or 'U' magic,
-it is important for extensions to take extra care to avoid conflict.
-Typically only using the magic on objects blessed into the same class
-as the extension is sufficient. For '~' magic, it may also be
-appropriate to add an I32 'signature' at the top of the private data
-area and check that.
+Note that because multiple extensions may be using C<PERL_MAGIC_ext>
+or C<PERL_MAGIC_uvar> 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<PERL_MAGIC_ext> magic, it may also be appropriate to add an I32
+'signature' at the top of the private data area and check that.
Also note that the C<sv_set*()> and C<sv_cat*()> functions described
earlier do B<not> invoke 'set' magic on their targets. This must
=head2 Understanding the Magic of Tied Hashes and Arrays
-Tied hashes and arrays are magical beasts of the 'P' magic type.
+Tied hashes and arrays are magical beasts of the C<PERL_MAGIC_tied>
+magic type.
WARNING: As of the 5.004 release, proper usage of the array and hash
access functions requires understanding a few caveats. Some
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
tie = newRV_noinc((SV*)newHV());
stash = gv_stashpv("MyTie", TRUE);
sv_bless(tie, stash);
- hv_magic(hash, tie, 'P');
+ hv_magic(hash, (GV*)tie, PERL_MAGIC_tied);
RETVAL = newRV_noinc(hash);
OUTPUT:
RETVAL
The biggest difference is that the first construction would
reinstate the initial value of $var, irrespective of how control exits
-the block: C<goto>, C<return>, C<die>/C<eval> etc. It is a little bit
+the block: C<goto>, C<return>, C<die>/C<eval>, 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
=item C<SAVEFREESV(SV *sv)>
The refcount of C<sv> would be decremented at the end of
-I<pseudo-block>. This is similar to C<sv_2mortal>, which should (?) be
-used instead.
+I<pseudo-block>. This is similar to C<sv_2mortal> in that it is also a
+mechanism for doing a delayed C<SvREFCNT_dec>. However, while C<sv_2mortal>
+extends the lifetime of C<sv> until the beginning of the next statement,
+C<SAVEFREESV> extends it until the end of the enclosing scope. These
+lifetimes can be wildly different.
+
+Also compare C<SAVEMORTALIZESV>.
+
+=item C<SAVEMORTALIZESV(SV *sv)>
+
+Just like C<SAVEFREESV>, but mortalizes C<sv> at the end of the current
+scope instead of decrementing its reference count. This usually has the
+effect of keeping C<sv> alive until the statement that called the currently
+live scope has finished executing.
=item C<SAVEFREEOP(OP *op)>
The following API list contains functions, thus one needs to
provide pointers to the modifiable data explicitly (either C pointers,
-or Perlish C<GV *>s). Where the above macros take C<int>, a similar
+or Perlish C<GV *>s). Where the above macros take C<int>, a similar
function takes C<int *>.
=over 4
=item C<SV* save_svref(SV **sptr)>
-Similar to C<save_scalar>, but will reinstate a C<SV *>.
+Similar to C<save_scalar>, but will reinstate an C<SV *>.
=item C<void save_aptr(AV **aptr)>
where C<SP> is the macro that represents the local copy of the stack pointer,
and C<num> is the number of elements the stack should be extended by.
-Now that there is room on the stack, values can be pushed on it using the
-macros to push IVs, doubles, strings, and SV pointers respectively:
+Now that there is room on the stack, values can be pushed on it using C<PUSHs>
+macro. The values pushed will often need to be "mortal" (See L</Reference Counts and Mortality>).
- PUSHi(IV)
- PUSHn(double)
- PUSHp(char*, I32)
- PUSHs(SV*)
+ PUSHs(sv_2mortal(newSViv(an_integer)))
+ PUSHs(sv_2mortal(newSVpv("Some String",0)))
+ PUSHs(sv_2mortal(newSVnv(3.141592)))
And now the Perl program calling C<tzname>, the two values will be assigned
as in:
($standard_abbrev, $summer_abbrev) = POSIX::tzname;
An alternate (and possibly simpler) method to pushing values on the stack is
-to use the macros:
+to use the macro:
- XPUSHi(IV)
- XPUSHn(double)
- XPUSHp(char*, I32)
XPUSHs(SV*)
-These macros automatically adjust the stack for you, if needed. Thus, you
+This macro automatically adjust the stack for you, if needed. Thus, you
do not need to call C<EXTEND> to extend the stack.
+Despite their suggestions in earlier versions of this document the macros
+C<PUSHi>, C<PUSHn> and C<PUSHp> are I<not> suited to XSUBs which return
+multiple results, see L</Putting a C value on Perl stack>.
+
For more information, consult L<perlxs> and L<perlxstut>.
=head2 Calling Perl Routines from within C Programs
All four routines return the number of arguments that the subroutine returned
on the Perl stack.
-These routines used to be called C<perl_call_sv> etc., before Perl v5.6.0,
+These routines used to be called C<perl_call_sv>, etc., before Perl v5.6.0,
but those names are now deprecated; macros of the same name are provided for
compatibility.
instances of the size of the C<type> data structure (using the C<sizeof>
function).
-Here is a handy table of equivalents between ordinary C and Perl's
-memory abstraction layer:
-
- Instead Of: Use:
-
- malloc New
- calloc Newz
- realloc Renew
- memcopy Copy
- memmove Move
- free Safefree
- strdup savepv
- strndup savepvn (Hey, strndup doesn't exist!)
- memcpy/*(struct foo *) StructCopy
-
=head2 PerlIO
The most recent development releases of Perl has been experimenting with
directly used in some opcodes, as well as indirectly in zillions of
others, which use it via C<(X)PUSH[pni]>.
+Because the target is reused, you must be careful when pushing multiple
+values on the stack. The following code will not do what you think:
+
+ XPUSHi(10);
+ XPUSHi(20);
+
+This translates as "set C<TARG> to 10, push a pointer to C<TARG> onto
+the stack; set C<TARG> to 20, push a pointer to C<TARG> 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<TARG>, which we have set
+to 20. If you need to push multiple different values, use C<XPUSHs>,
+which bypasses C<TARG>.
+
+On a related note, if you do use C<(X)PUSH[npi]>, then you're going to
+need a C<dTARG> in your variable declarations so that the C<*PUSH*>
+macros can make use of the local variable C<TARG>.
+
=head2 Scratchpads
The question remains on when the SVs which are I<target>s for opcodes
(initially) one element, and this element is the scratchpad AV. Why do
we need an extra level of indirection?
-The answer is B<recursion>, and maybe (sometime soon) B<threads>. Both
+The answer is B<recursion>, and maybe B<threads>. 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
done in the subroutine peep(). Optimizations performed at this stage
are subject to the same restrictions as in the pass 2.
+=head2 Pluggable runops
+
+The compile tree is executed in a runops function. There are two runops
+functions in F<run.c>. C<Perl_runops_debug> is used with DEBUGGING and
+C<Perl_runops_standard> is used otherwise. For fine control over the
+execution of the compile tree it is possible to provide your own runops
+function.
+
+It's probably best to copy one of the existing runops functions and
+change it to suit your needs. Then, in the BOOT section of your XS
+file, add the line:
+
+ PL_runops = my_runops;
+
+This function should be as efficient as possible to keep your programs
+running as fast as possible.
+
=head1 Examining internal data structures with the C<dump> functions
To aid debugging, the source file F<dump.c> contains a number of
The most commonly used of these functions is C<Perl_sv_dump>; it's used
for dumping SVs, AVs, HVs, and CVs. The C<Devel::Peek> module calls
C<sv_dump> to produce debugging output from Perl-space, so users of that
-module should already be familiar with its format.
+module should already be familiar with its format.
C<Perl_op_dump> can be used to dump an C<OP> structure or any of its
-derivatives, and produces output simil
iar to C<perl -Dx>; in fact,
+derivatives, and produces output similar to C<perl -Dx>; in fact,
C<Perl_dump_eval> will dump the main root of the code being evaluated,
exactly like C<-Dx>.
for feeding it code or otherwise making it do things, but it also has
functions for its own use. This smells a lot like an object, and
there are ways for you to build Perl so that you can have multiple
-interpreters, with one interpreter represented either as a C++ object,
-a C structure, or inside a thread. The thread, the C structure, or
-the C++ object will contain all the context, the state of that
-interpreter.
-
-Three macros control the major Perl build flavors: MULTIPLICITY,
-USE_THREADS and PERL_OBJECT. The MULTIPLICITY build has a C structure
-that packages all the interpreter state, there is a similar thread-specific
-data structure under USE_THREADS, and the PERL_OBJECT build has a C++
-class to maintain interpreter state. In all three cases,
+interpreters, with one interpreter represented either as a C structure,
+or inside a thread-specific structure. These structures contain all
+the context, the state of that interpreter.
+
+Two macros control the major Perl build flavors: MULTIPLICITY and
+USE_5005THREADS. The MULTIPLICITY build has a C structure
+that packages all the interpreter state, and there is a similar thread-specific
+data structure under USE_5005THREADS. In both cases,
PERL_IMPLICIT_CONTEXT is also normally defined, and enables the
support for passing in a "hidden" first argument that represents all three
data structures.
All this obviously requires a way for the Perl internal functions to be
-C++ methods, subroutines taking some kind of structure as the first
+either subroutines taking some kind of structure as the first
argument, or subroutines taking nothing as the first argument. To
-enable these three very different ways of building the interpreter,
+enable these two very different ways of building the interpreter,
the Perl source (as it does in so many other situations) makes heavy
use of macros and subroutine naming conventions.
First problem: deciding which functions will be public API functions and
-which will be private. All functions whose names begin C<S_> are private
+which will be private. All functions whose names begin C<S_> are private
(think "S" for "secret" or "static"). All other functions begin with
"Perl_", but just because a function begins with "Perl_" does not mean it is
-part of the API. (See L</Internal Functions>.) The easiest way to be B<sure> a
-function is part of the API is to find its entry in L<perlapi>.
-If it exists in L<perlapi>, it's part of the API. If it doesn't, and you
-think it should be (i.e., you need it for your extension), send mail via
+part of the API. (See L</Internal Functions>.) The easiest way to be B<sure> a
+function is part of the API is to find its entry in L<perlapi>.
+If it exists in L<perlapi>, it's part of the API. If it doesn't, and you
+think it should be (i.e., you need it for your extension), send mail via
L<perlbug> explaining why you think it should be.
Second problem: there must be a syntax so that the same subroutine
STATIC void
S_incline(pTHX_ char *s)
-STATIC becomes "static" in C, and is #define'd to nothing in C++.
+STATIC becomes "static" in C, and may be #define'd to nothing in some
+configurations in future.
A public function (i.e. part of the internal API, but not necessarily
sanctioned for use in extensions) begins like this:
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<p>rototype, 'a' for B<a>rgument,
-or 'd' for B<d>eclaration.
+or 'd' for B<d>eclaration, so we have C<pTHX>, C<aTHX> and C<dTHX>, and
+their variants.
-When Perl is built without PERL_IMPLICIT_CONTEXT, there is no first
-argument containing the interpreter's context. The trailing underscore
+When Perl is built without options that set PERL_IMPLICIT_CONTEXT, there is no
+first argument containing the interpreter's context. The trailing underscore
in the pTHX_ macro indicates that the macro expansion needs a comma
after the context argument because other arguments follow it. If
PERL_IMPLICIT_CONTEXT is not defined, pTHX_ will be ignored, and the
explicit arguments.
When a core function calls another, it must pass the context. This
-is normally hidden via macros. Consider C<sv_setsv>. It expands
+is normally hidden via macros. Consider C<sv_setsv>. It expands into
something like this:
ifdef PERL_IMPLICIT_CONTEXT
- define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
+ define sv_setsv(a,b) Perl_sv_setsv(aTHX_ a, b)
/* can't do this for vararg functions, see below */
else
- define sv_setsv Perl_sv_setsv
+ define sv_setsv Perl_sv_setsv
endif
This works well, and means that XS authors can gleefully write:
and still have it work under all the modes Perl could have been
compiled with.
-Under PERL_OBJECT in the core, that will translate to either:
-
- CPerlObj::Perl_sv_setsv(foo,bar); # in CPerlObj functions,
- # C++ takes care of 'this'
- or
-
- pPerl->Perl_sv_setsv(foo,bar); # in truly static functions,
- # see objXSUB.h
-
-Under PERL_OBJECT in extensions (aka PERL_CAPI), or under
-MULTIPLICITY/USE_THREADS w/ PERL_IMPLICIT_CONTEXT in both core
-and extensions, it will be:
-
- Perl_sv_setsv(aTHX_ foo, bar); # the canonical Perl "API"
- # for all build flavors
-
This doesn't work so cleanly for varargs functions, though, as macros
imply that the number of arguments is known in advance. Instead we
either need to spell them out fully, passing C<aTHX_> as the first
compatibility at the expense of performance. (Passing an arg is
cheaper than grabbing it from thread-local storage.)
-You can ignore [pad]THX[xo] when browsing the Perl headers/sources.
+You can ignore [pad]THXx when browsing the Perl headers/sources.
Those are strictly for use within the core. Extensions and embedders
need only be aware of [pad]THX.
+=head2 So what happened to dTHR?
+
+C<dTHR> was introduced in perl 5.005 to support the older thread model.
+The older thread model now uses the C<THX> mechanism to pass context
+pointers around, so C<dTHR> is not useful any more. Perl 5.6.0 and
+later still have it for backward source compatibility, but it is defined
+to be a no-op.
+
=head2 How do I use all this in extensions?
When Perl is built with PERL_IMPLICIT_CONTEXT, extensions that call
The second, more efficient way is to use the following template for
your Foo.xs:
- #define PERL_NO_GET_CONTEXT /* we want efficiency */
- #include "EXTERN.h"
- #include "perl.h"
- #include "XSUB.h"
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
static my_private_function(int arg1, int arg2);
- static SV *
- my_private_function(int arg1, int arg2)
- {
- dTHX; /* fetch context */
- ... call many Perl API functions ...
- }
+ static SV *
+ my_private_function(int arg1, int arg2)
+ {
+ dTHX; /* fetch context */
+ ... call many Perl API functions ...
+ }
[... etc ...]
- MODULE = Foo PACKAGE = Foo
+ MODULE = Foo PACKAGE = Foo
- /* typical XSUB */
+ /* typical XSUB */
- void
- my_xsub(arg)
- int arg
- CODE:
- my_private_function(arg, 10);
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(arg, 10);
Note that the only two changes from the normal way of writing an
extension is the addition of a C<#define PERL_NO_GET_CONTEXT> before
the Perl guts:
- #define PERL_NO_GET_CONTEXT /* we want efficiency */
- #include "EXTERN.h"
- #include "perl.h"
- #include "XSUB.h"
+ #define PERL_NO_GET_CONTEXT /* we want efficiency */
+ #include "EXTERN.h"
+ #include "perl.h"
+ #include "XSUB.h"
/* pTHX_ only needed for functions that call Perl API */
static my_private_function(pTHX_ int arg1, int arg2);
- static SV *
- my_private_function(pTHX_ int arg1, int arg2)
- {
- /* dTHX; not needed here, because THX is an argument */
- ... call Perl API functions ...
- }
+ static SV *
+ my_private_function(pTHX_ int arg1, int arg2)
+ {
+ /* dTHX; not needed here, because THX is an argument */
+ ... call Perl API functions ...
+ }
[... etc ...]
- MODULE = Foo PACKAGE = Foo
+ MODULE = Foo PACKAGE = Foo
- /* typical XSUB */
+ /* typical XSUB */
- void
- my_xsub(arg)
- int arg
- CODE:
- my_private_function(aTHX_ arg, 10);
+ void
+ my_xsub(arg)
+ int arg
+ CODE:
+ my_private_function(aTHX_ arg, 10);
This implementation never has to fetch the context using a function
call, since it is always passed as an extra argument. Depending on
macro with the underscore for functions that take explicit arguments,
or the form without the argument for functions with no explicit arguments.
+=head2 Should I do anything special if I call perl from multiple threads?
+
+If you create interpreters in one thread and then proceed to call them in
+another, you need to make sure perl's own Thread Local Storage (TLS) slot is
+initialized correctly in each of those threads.
+
+The C<perl_alloc> and C<perl_clone> API functions will automatically set
+the TLS slot to the interpreter they created, so that there is no need to do
+anything special if the interpreter is always accessed in the same thread that
+created it, and that thread did not create or call any other interpreters
+afterwards. If that is not the case, you have to set the TLS slot of the
+thread before calling any functions in the Perl API on that particular
+interpreter. This is done by calling the C<PERL_SET_CONTEXT> macro in that
+thread as the first thing you do:
+
+ /* do this before doing anything else with some_perl */
+ PERL_SET_CONTEXT(some_perl);
+
+ ... other Perl API calls on some_perl go here ...
+
=head2 Future Plans and PERL_IMPLICIT_SYS
Just as PERL_IMPLICIT_CONTEXT provides a way to bundle up everything
that the interpreter knows about itself and pass it around, so too are
there plans to allow the interpreter to bundle up everything it knows
about the environment it's running on. This is enabled with the
-PERL_IMPLICIT_SYS macro. Currently it only works with PERL_OBJECT,
-but is mostly there for MULTIPLICITY and USE_THREADS (see inside
-iperlsys.h).
+PERL_IMPLICIT_SYS macro. Currently it only works with USE_ITHREADS
+and USE_5005THREADS on Windows (see inside iperlsys.h).
This allows the ability to provide an extra pointer (called the "host"
environment) for all the system calls. This makes it possible for
=item s
-This is a static function and is defined as C<S_whatever>.
+This is a static function and is defined as C<S_whatever>, and usually
+called within the sources as C<whatever(...)>.
=item n
Afprd |void |croak |const char* pat|...
-=item m
+=item M
-This function is part of the experimental development API, and may change
+This function is part of the experimental development API, and may change
or disappear without notice.
=item o
formatting codes like C<%d>, C<%ld>, C<%f>, you should use the
following macros for portability
- IVdf IV in decimal
- UVuf UV in decimal
- UVof UV in octal
- UVxf UV in hexadecimal
- NVef NV %e-like
- NVff NV %f-like
- NVgf NV %g-like
+ IVdf IV in decimal
+ UVuf UV in decimal
+ UVof UV in octal
+ UVxf UV in hexadecimal
+ NVef NV %e-like
+ NVff NV %f-like
+ NVgf NV %g-like
These will take care of 64-bit integers and long doubles.
For example:
- printf("IV is %"IVdf"\n", iv);
+ printf("IV is %"IVdf"\n", iv);
The IVdf will expand to whatever is the correct format for the IVs.
Because pointer size does not necessarily equal integer size,
use the follow macros to do it right.
- PTR2UV(pointer)
- PTR2IV(pointer)
- PTR2NV(pointer)
- INT2PTR(pointertotype, integer)
+ PTR2UV(pointer)
+ PTR2IV(pointer)
+ PTR2NV(pointer)
+ INT2PTR(pointertotype, integer)
For example:
- IV iv = ...;
- SV *sv = INT2PTR(SV*, iv);
+ IV iv = ...;
+ SV *sv = INT2PTR(SV*, iv);
and
- AV *av = ...;
- UV uv = PTR2UV(av);
+ AV *av = ...;
+ UV uv = PTR2UV(av);
=head2 Source Documentation
=back
+=head1 Custom Operators
+
+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<gvsv, gvsv, add>.)
+
+This feature is implemented as a new op type, C<OP_CUSTOM>. The Perl
+core does not "know" anything special about this op type, and so it will
+not be involved in any optimizations. This also means that you can
+define your custom ops to be any op structure - unary, binary, list and
+so on - you like.
+
+It's important to know what custom operators won't do for you. They
+won't let you add new syntax to Perl, directly. They won't even let you
+add new keywords, directly. In fact, they won't change the way Perl
+compiles a program at all. You have to do those changes yourself, after
+Perl has compiled the program. You do this either by manipulating the op
+tree using a C<CHECK> block and the C<B::Generate> module, or by adding
+a custom peephole optimizer with the C<optimize> module.
+
+When you do this, you replace ordinary Perl ops with custom ops by
+creating ops with the type C<OP_CUSTOM> and the C<pp_addr> of your own
+PP function. This should be defined in XS code, and should look like
+the PP ops in C<pp_*.c>. You are responsible for ensuring that your op
+takes the appropriate number of values from the stack, and you are
+responsible for adding stack marks if necessary.
+
+You should also "register" your op with the Perl interpreter so that it
+can produce sensible error and warning messages. Since it is possible to
+have multiple custom ops within the one "logical" op type C<OP_CUSTOM>,
+Perl uses the value of C<< o->op_ppaddr >> as a key into the
+C<PL_custom_op_descs> and C<PL_custom_op_names> hashes. This means you
+need to enter a name and description for your op at the appropriate
+place in the C<PL_custom_op_names> and C<PL_custom_op_descs> hashes.
+
+Forthcoming versions of C<B::Generate> (version 1.0 and above) should
+directly support the creation of custom ops by name; C<Opcodes::Custom>
+will provide functions which make it trivial to "register" custom ops to
+the Perl interpreter.
+
=head1 AUTHORS
Until May 1997, this document was maintained by Jeff Okamoto
-<okamoto@corp.hp.com>. It is now maintained as part of Perl itself
-by the Perl 5 Porters <perl5-porters@perl.org>.
+E<lt>okamoto@corp.hp.comE<gt>. It is now maintained as part of Perl
+itself by the Perl 5 Porters E<lt>perl5-porters@perl.orgE<gt>.
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 <roehrich@cray.com>.
+API Listing originally by Dean Roehrich E<lt>roehrich@cray.comE<gt>.
Modifications to autogenerate the API listing (L<perlapi>) by Benjamin
Stuhl.
https://perl5.git.perl.org / perl5.git / blobdiff