Страницы справочника OS X

Эта страница руководства для  версии 10.9 Mac OS X

Читать страницы руководства

Devel::Peek(3pm)                      Perl Programmers Reference Guide                      Devel::Peek(3pm)



NAME
       Devel::Peek - A data debugging tool for the XS programmer

SYNOPSIS
               use Devel::Peek;
               Dump( $a );
               Dump( $a, 5 );
               DumpArray( 5, $a, $b, ... );
               mstat "Point 5";

               use Devel::Peek ':opd=st';

DESCRIPTION
       Devel::Peek contains functions which allows raw Perl datatypes to be manipulated from a Perl script.
       This is used by those who do XS programming to check that the data they are sending from C to Perl
       looks as they think it should look.  The trick, then, is to know what the raw datatype is supposed to
       look like when it gets to Perl.  This document offers some tips and hints to describe good and bad
       raw data.

       It is very possible that this document will fall far short of being useful to the casual reader.  The
       reader is expected to understand the material in the first few sections of perlguts.

       Devel::Peek supplies a "Dump()" function which can dump a raw Perl datatype, and "mstat("marker")"
       function to report on memory usage (if perl is compiled with corresponding option).  The function
       DeadCode() provides statistics on the data "frozen" into inactive "CV".  Devel::Peek also supplies
       "SvREFCNT()", "SvREFCNT_inc()", and "SvREFCNT_dec()" which can query, increment, and decrement
       reference counts on SVs.  This document will take a passive, and safe, approach to data debugging and
       for that it will describe only the "Dump()" function.

       Function "DumpArray()" allows dumping of multiple values (useful when you need to analyze returns of
       functions).

       The global variable $Devel::Peek::pv_limit can be set to limit the number of character printed in
       various string values.  Setting it to 0 means no limit.

       If "use Devel::Peek" directive has a ":opd=FLAGS" argument, this switches on debugging of opcode
       dispatch.  "FLAGS" should be a combination of "s", "t", and "P" (see -D flags in perlrun).  ":opd" is
       a shortcut for ":opd=st".

   Runtime debugging
       "CvGV($cv)" return one of the globs associated to a subroutine reference $cv.

       debug_flags() returns a string representation of $^D (similar to what is allowed for -D flag).  When
       called with a numeric argument, sets $^D to the corresponding value.  When called with an argument of
       the form "flags-flags", set on/off bits of $^D corresponding to letters before/after "-".  (The
       returned value is for $^D before the modification.)

       runops_debug() returns true if the current opcode dispatcher is the debugging one.  When called with
       an argument, switches to debugging or non-debugging dispatcher depending on the argument (active for
       newly-entered subs/etc only).  (The returned value is for the dispatcher before the modification.)

   Memory footprint debugging
       When perl is compiled with support for memory footprint debugging (default with Perl's malloc()),
       Devel::Peek provides an access to this API.

       Use mstat() function to emit a memory state statistic to the terminal.  For more information on the
       format of output of mstat() see "Using $ENV{PERL_DEBUG_MSTATS}" in perldebguts.

       Three additional functions allow access to this statistic from Perl.  First, use
       "mstats_fillhash(%hash)" to get the information contained in the output of mstat() into %hash. The
       field of this hash are

         minbucket nbuckets sbrk_good sbrk_slack sbrked_remains sbrks start_slack
         topbucket topbucket_ev topbucket_odd total total_chain total_sbrk totfree

       Two additional fields "free", "used" contain array references which provide per-bucket count of free
       and used chunks.  Two other fields "mem_size", "available_size" contain array references which
       provide the information about the allocated size and usable size of chunks in each bucket.  Again,
       see "Using $ENV{PERL_DEBUG_MSTATS}" in perldebguts for details.

       Keep in mind that only the first several "odd-numbered" buckets are used, so the information on size
       of the "odd-numbered" buckets which are not used is probably meaningless.

       The information in

        mem_size available_size minbucket nbuckets

       is the property of a particular build of perl, and does not depend on the current process.  If you do
       not provide the optional argument to the functions mstats_fillhash(), fill_mstats(), mstats2hash(),
       then the information in fields "mem_size", "available_size" is not updated.

       "fill_mstats($buf)" is a much cheaper call (both speedwise and memory-wise) which collects the
       statistic into $buf in machine-readable form.  At a later moment you may need to call
       "mstats2hash($buf, %hash)" to use this information to fill %hash.

       All three APIs "fill_mstats($buf)", "mstats_fillhash(%hash)", and "mstats2hash($buf, %hash)" are
       designed to allocate no memory if used the second time on the same $buf and/or %hash.

       So, if you want to collect memory info in a cycle, you may call

         $#buf = 999;
         fill_mstats($_) for @buf;
         mstats_fillhash(%report, 1);          # Static info too

         foreach (@buf) {
           # Do something...
           fill_mstats $_;                     # Collect statistic
         }
         foreach (@buf) {
           mstats2hash($_, %report);           # Preserve static info
           # Do something with %report
         }

EXAMPLES
       The following examples don't attempt to show everything as that would be a monumental task, and,
       frankly, we don't want this manpage to be an internals document for Perl.  The examples do
       demonstrate some basics of the raw Perl datatypes, and should suffice to get most determined people
       on their way.  There are no guidewires or safety nets, nor blazed trails, so be prepared to travel
       alone from this point and on and, if at all possible, don't fall into the quicksand (it's bad for
       business).

       Oh, one final bit of advice: take perlguts with you.  When you return we expect to see it well-thumbed. wellthumbed.
       thumbed.

   A simple scalar string
       Let's begin by looking a simple scalar which is holding a string.

               use Devel::Peek;
               $a = 42; $a = "hello";
               Dump $a;

       The output:

               SV = PVIV(0xbc288) at 0xbe9a8
                 REFCNT = 1
                 FLAGS = (POK,pPOK)
                 IV = 42
                 PV = 0xb2048 "hello"\0
                 CUR = 5
                 LEN = 8

       This says $a is an SV, a scalar.  The scalar type is a PVIV, which is capable of holding an integer
       (IV) and/or a string (PV) value. The scalar's head is allocated at address 0xbe9a8, while the body is
       at 0xbc288.  Its reference count is 1.  It has the "POK" flag set, meaning its current PV field is
       valid.  Because POK is set we look at the PV item to see what is in the scalar.  The \0 at the end
       indicate that this PV is properly NUL-terminated.  Note that the IV field still contains its old
       numeric value, but because FLAGS doesn't have IOK set, we must ignore the IV item.  CUR indicates the
       number of characters in the PV.  LEN indicates the number of bytes allocated for the PV (at least one
       more than CUR, because LEN includes an extra byte for the end-of-string marker, then usually rounded
       up to some efficient allocation unit).

   A simple scalar number
       If the scalar contains a number the raw SV will be leaner.

               use Devel::Peek;
               $a = 42;
               Dump $a;

       The output:

               SV = IV(0xbc818) at 0xbe9a8
                 REFCNT = 1
                 FLAGS = (IOK,pIOK)
                 IV = 42

       This says $a is an SV, a scalar.  The scalar is an IV, a number.  Its reference count is 1.  It has
       the "IOK" flag set, meaning it is currently being evaluated as a number.  Because IOK is set we look
       at the IV item to see what is in the scalar.

   A simple scalar with an extra reference
       If the scalar from the previous example had an extra reference:

               use Devel::Peek;
               $a = 42;
               $b = \$a;
               Dump $a;

       The output:

               SV = IV(0xbe860) at 0xbe9a8
                 REFCNT = 2
                 FLAGS = (IOK,pIOK)
                 IV = 42

       Notice that this example differs from the previous example only in its reference count.  Compare this
       to the next example, where we dump $b instead of $a.

   A reference to a simple scalar
       This shows what a reference looks like when it references a simple scalar.

               use Devel::Peek;
               $a = 42;
               $b = \$a;
               Dump $b;

       The output:

               SV = IV(0xf041c) at 0xbe9a0
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0xbab08
                 SV = IV(0xbe860) at 0xbe9a8
                   REFCNT = 2
                   FLAGS = (IOK,pIOK)
                   IV = 42

       Starting from the top, this says $b is an SV.  The scalar is an IV, which is capable of holding an
       integer or reference value.  It has the "ROK" flag set, meaning it is a reference (rather than an
       integer or string).  Notice that Dump follows the reference and shows us what $b was referencing.  We
       see the same $a that we found in the previous example.

       Note that the value of "RV" coincides with the numbers we see when we stringify $b. The addresses
       inside IV() are addresses of "X***" structures which hold the current state of an "SV". This address
       may change during lifetime of an SV.

   A reference to an array
       This shows what a reference to an array looks like.

               use Devel::Peek;
               $a = [42];
               Dump $a;

       The output:

               SV = IV(0xc85998) at 0xc859a8
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0xc70de8
                 SV = PVAV(0xc71e10) at 0xc70de8
                   REFCNT = 1
                   FLAGS = ()
                   ARRAY = 0xc7e820
                   FILL = 0
                   MAX = 0
                   ARYLEN = 0x0
                   FLAGS = (REAL)
                   Elt No. 0
                   SV = IV(0xc70f88) at 0xc70f98
                     REFCNT = 1
                     FLAGS = (IOK,pIOK)
                     IV = 42

       This says $a is a reference (ROK), which points to another SV which is a PVAV, an array.  The array
       has one element, element zero, which is another SV. The field "FILL" above indicates the last element
       in the array, similar to "$#$a".

       If $a pointed to an array of two elements then we would see the following.

               use Devel::Peek 'Dump';
               $a = [42,24];
               Dump $a;

       The output:

               SV = IV(0x158c998) at 0x158c9a8
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0x1577de8
                 SV = PVAV(0x1578e10) at 0x1577de8
                   REFCNT = 1
                   FLAGS = ()
                   ARRAY = 0x1585820
                   FILL = 1
                   MAX = 1
                   ARYLEN = 0x0
                   FLAGS = (REAL)
                   Elt No. 0
                   SV = IV(0x1577f88) at 0x1577f98
                     REFCNT = 1
                     FLAGS = (IOK,pIOK)
                     IV = 42
                   Elt No. 1
                   SV = IV(0x158be88) at 0x158be98
                     REFCNT = 1
                     FLAGS = (IOK,pIOK)
                     IV = 24

       Note that "Dump" will not report all the elements in the array, only several first (depending on how
       deep it already went into the report tree).

   A reference to a hash
       The following shows the raw form of a reference to a hash.

               use Devel::Peek;
               $a = {hello=>42};
               Dump $a;

       The output:

               SV = IV(0x8177858) at 0x816a618
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0x814fc10
                 SV = PVHV(0x8167768) at 0x814fc10
                   REFCNT = 1
                   FLAGS = (SHAREKEYS)
                   ARRAY = 0x816c5b8  (0:7, 1:1)
                   hash quality = 100.0%
                   KEYS = 1
                   FILL = 1
                   MAX = 7
                   RITER = -1
                   EITER = 0x0
                   Elt "hello" HASH = 0xc8fd181b
                   SV = IV(0x816c030) at 0x814fcf4
                     REFCNT = 1
                     FLAGS = (IOK,pIOK)
                     IV = 42

       This shows $a is a reference pointing to an SV.  That SV is a PVHV, a hash. Fields RITER and EITER
       are used by ""each" in perlfunc".

       The "quality" of a hash is defined as the total number of comparisons needed to access every element
       once, relative to the expected number needed for a random hash. The value can go over 100%.

       The total number of comparisons is equal to the sum of the squares of the number of entries in each
       bucket.  For a random hash of "<n"> keys into "<k"> buckets, the expected value is:

                       n + n(n-1)/2k

   Dumping a large array or hash
       The "Dump()" function, by default, dumps up to 4 elements from a toplevel array or hash.  This number
       can be increased by supplying a second argument to the function.

               use Devel::Peek;
               $a = [10,11,12,13,14];
               Dump $a;

       Notice that "Dump()" prints only elements 10 through 13 in the above code.  The following code will
       print all of the elements.

               use Devel::Peek 'Dump';
               $a = [10,11,12,13,14];
               Dump $a, 5;

   A reference to an SV which holds a C pointer
       This is what you really need to know as an XS programmer, of course.  When an XSUB returns a pointer
       to a C structure that pointer is stored in an SV and a reference to that SV is placed on the XSUB
       stack.  So the output from an XSUB which uses something like the T_PTROBJ map might look something
       like this:

               SV = IV(0xf381c) at 0xc859a8
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0xb8ad8
                 SV = PVMG(0xbb3c8) at 0xc859a0
                   REFCNT = 1
                   FLAGS = (OBJECT,IOK,pIOK)
                   IV = 729160
                   NV = 0
                   PV = 0
                   STASH = 0xc1d10       "CookBookB::Opaque"

       This shows that we have an SV which is a reference, which points at another SV.  In this case that
       second SV is a PVMG, a blessed scalar.  Because it is blessed it has the "OBJECT" flag set.  Note
       that an SV which holds a C pointer also has the "IOK" flag set.  The "STASH" is set to the package
       name which this SV was blessed into.

       The output from an XSUB which uses something like the T_PTRREF map, which doesn't bless the object,
       might look something like this:

               SV = IV(0xf381c) at 0xc859a8
                 REFCNT = 1
                 FLAGS = (ROK)
                 RV = 0xb8ad8
                 SV = PVMG(0xbb3c8) at 0xc859a0
                   REFCNT = 1
                   FLAGS = (IOK,pIOK)
                   IV = 729160
                   NV = 0
                   PV = 0

   A reference to a subroutine
       Looks like this:

               SV = IV(0x24d2dd8) at 0x24d2de8
                 REFCNT = 1
                 FLAGS = (TEMP,ROK)
                 RV = 0x24e79d8
                 SV = PVCV(0x24e5798) at 0x24e79d8
                   REFCNT = 2
                   FLAGS = ()
                   COMP_STASH = 0x22c9c50      "main"
                   START = 0x22eed60 ===> 0
                   ROOT = 0x22ee490
                   GVGV::GV = 0x22de9d8        "MY" :: "top_targets"
                   FILE = "(eval 5)"
                   DEPTH = 0
                   FLAGS = 0x0
                   OUTSIDE_SEQ = 93
                   PADLIST = 0x22e9ed8
                   PADNAME = 0x22e9ec0(0x22eed00) PAD = 0x22e9ea8(0x22eecd0)
                   OUTSIDE = 0x22c9fb0 (MAIN)

       This shows that

       •   the subroutine is not an XSUB (since "START" and "ROOT" are non-zero, and "XSUB" is not listed,
           and is thus null);

       •   that it was compiled in the package "main";

       •   under the name "MY::top_targets";

       •   inside a 5th eval in the program;

       •   it is not currently executed (see "DEPTH");

       •   it has no prototype ("PROTOTYPE" field is missing).

EXPORTS
       "Dump", "mstat", "DeadCode", "DumpArray", "DumpWithOP" and "DumpProg", "fill_mstats",
       "mstats_fillhash", "mstats2hash" by default. Additionally available "SvREFCNT", "SvREFCNT_inc" and
       "SvREFCNT_dec".

BUGS
       Readers have been known to skip important parts of perlguts, causing much frustration for all.

AUTHOR
       Ilya Zakharevich    ilya@math.ohio-state.edu

       Copyright (c) 1995-98 Ilya Zakharevich. All rights reserved.  This program is free software; you can
       redistribute it and/or modify it under the same terms as Perl itself.

       Author of this software makes no claim whatsoever about suitability, reliability, edability,
       editability or usability of this product, and should not be kept liable for any damage resulting from
       the use of it. If you can use it, you are in luck, if not, I should not be kept responsible. Keep a
       handy copy of your backup tape at hand.

SEE ALSO
       perlguts, and perlguts, again.



perl v5.16.2                                     2012-10-25                                 Devel::Peek(3pm)