in reply to Re^5: Is this absurd, or have I not RTFM?
in thread Is this absurd, or have I not RTFM?

Missing autoflushing may (as discussed else in this thread) explain why the "END DESTROY" line is not always printed. It doesn't explain the blow output of 2 different references being given to 2 calls to DESTROY in the same process though: 
^C======= BEGIN DESTROY:11632========
2014/05/19-10:36:43 Server closing!
SV = IV(0x11ba5d8) at 0x11ba5e8
  REFCNT = 1
  FLAGS = (ROK,READONLY)
  RV = 0xe462b8
  SV = PVHV(0xcf8880) at 0xe462b8
    REFCNT = 1
    FLAGS = (OBJECT,SHAREKEYS)
    STASH = 0xd10d40    "MyModule"
    ARRAY = 0x0
    KEYS = 0
    FILL = 0
    MAX = 7
    RITER = -1
    EITER = 0x0
======= BEGIN DESTROY:11632========
SV = IV(0x11ba4d0) at 0x11ba4e0
  REFCNT = 1
  FLAGS = (ROK,READONLY)
  RV = 0xe462b8
  SV = PVHV(0xcf8880) at 0xe462b8
    REFCNT = 1
    FLAGS = (OBJECT,OOK,SHAREKEYS)
    STASH = 0xd10d40    "MyModule"
    ARRAY = 0xfa0e30
    KEYS = 0
    FILL = 0
    MAX = 7
    RITER = -1
    EITER = 0x0
============ END DESTROY:11632========
======= BEGIN DESTROY:11631========
SV = IV(0xd103a0) at 0xd103b0
  REFCNT = 1
  FLAGS = (ROK,READONLY)
  RV = 0xe462b8
  SV = PVHV(0xcf8880) at 0xe462b8
    REFCNT = 1
    FLAGS = (OBJECT,SHAREKEYS)
    STASH = 0xd10d40    "MyModule"
    ARRAY = 0x0
    KEYS = 0
    FILL = 0
    MAX = 7
    RITER = -1
    EITER = 0x0
============ END DESTROY:11631========

[download]
The actual Perl object is also slightly changed... in a way I don't find meaningful... but then... I don't know the perlguts that well. I would primarily suspect a memory corruption reason for trashing the data. But it would be strange if such a problem never gave other symptoms with Net::Server::Prefork.

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Re^7: Is this absurd, or have I not RTFM?
by Anonymous Monk on May 19, 2014 at 09:30 UTC

    Please try this 

    #!/usr/bin/perl --
package MyModule;
use Devel::Peek;

sub new {
    my $obj = bless { '$$' => $$ }, shift;
    print "## $$ IN NEW $obj ##\n";
    return $obj;
}

sub DESTROY {
    print "#### BEGIN DESTROY: $$ : @_ ####\n";
    print Dump( @_ );
    print "###### END DESTROY: $$ : @_ ######\n";
}

1;

package MyServer;
use parent qw[ Net::Server::PreFork ];
our $hardtodestroy = MyModule->new;

sub child_finish_hook {
    undef $hardtodestroy;
}
1;

package main;
STDOUT->autoflush(1);
print "## this is perl $]\n";
MyServer->run(
    max_servers       => 1,
    min_servers       => 1,
    min_spare_servers => 0,
    max_spare_servers => 0
);

    [download]
[reply]
[d/l]
      2014/05/19-11:57:52 Server closing!
#### BEGIN DESTROY: 13138 : MyModule=HASH(0x1441b78) ####
SV = IV(0x190cba0) at 0x190cbb0
  REFCNT = 1
  FLAGS = (ROK,READONLY)
#### BEGIN DESTROY: 13138 : MyModule=HASH(0x1441b78) ####
SV = IV(0x190c810) at 0x190c820
  REFCNT = 1
  FLAGS = (ROK,READONLY)
  RV = 0x1441b78
  SV = PVHV(0x1448880) at 0x1441b78
    REFCNT = 1
    FLAGS = (OBJECT,SHAREKEYS)
    STASH = 0x1460d40   "MyModule"
    ARRAY = 0x1459360  (0:7, 1:1)
    hash quality = 100.0%
    KEYS = 1
    FILL = 1
    MAX = 7
    RITER = -1
    EITER = 0x0
    Elt "$$" HASH = 0x7f8f5659
    SV = IV(0x1460268) at 0x1460278
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 13137
###### END DESTROY: 13138 : MyModule=HASH(0x1441b78) ######
#### BEGIN DESTROY: 13137 : MyModule=HASH(0x1441b78) ####
SV = IV(0x150bd48) at 0x150bd58
  REFCNT = 1
  FLAGS = (ROK,READONLY)
  RV = 0x1441b78
  SV = PVHV(0x1448880) at 0x1441b78
    REFCNT = 1
    FLAGS = (OBJECT,SHAREKEYS)
    STASH = 0x1460d40   "MyModule"
    ARRAY = 0x1459360  (0:7, 1:1)
    hash quality = 100.0%
    KEYS = 1
    FILL = 1
    MAX = 7
    RITER = -1
    EITER = 0x0
    Elt "$$" HASH = 0x7f8f5659
    SV = IV(0x1460268) at 0x1460278
      REFCNT = 1
      FLAGS = (IOK,pIOK)
      IV = 13137
###### END DESTROY: 13137 : MyModule=HASH(0x1441b78) ######

      [download]

      So ... as it shows process 13138 is calling DESTROY twice for the same object. Apparently it gets interrupted by shutdown half way through the first invocation (but gets far enough to crash in other ways **). What I'm wondering about is what makes Perl retry the DESTROY method for the object at a later time.

      **: This means, that if the objects DESTROY method is an XS function you can manage to call free() on a C pointer during the first invocation before you get interrupted. ... and then calling free() again in the second invocation will cause glibc to complain loudly.

[reply]
[d/l]
        On current perl versions XS functions are not interrupted unless you activate the "unsafe" signals in some way (see perlipc).
[reply]

        Um, so where is the part about the perl version?

[reply]
        Might also need to add 
         
sub post_child_cleanup_hook {
    undef $hardtodestroy;
}

        [download]
[reply]
[d/l]

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