| Subject: | Issue using IPC::ShareLite (using segment size of 0 to open existing shared memory segment) |
| Date: | Wed, 5 Sep 2012 15:06:50 +0000 |
| To: | "bug-IPC-ShareLite [...] rt.cpan.org" <bug-IPC-ShareLite [...] rt.cpan.org> |
| From: | "Macke, Edward" <Edward.Macke [...] savvis.com> |
Distribution: IPC-ShareLite-0.17
Perl Version: perl 5, version 12, subversion 4 (v5.12.4) built for x86_64-linux-thread-multi
O/S: Linux dc2repappdv01.it.savvis.net 2.6.18-194.17.1.el5 #1 SMP Mon Sep 20 07:12:06 EDT 2010 x86_64 x86_64 x86_64 GNU/Linux
Description of issue:
The SysV shmget() C function allows one to retrieve the id of an existing shared memory segment for which the key is known but the size is not; ie:
shmid = shmget(key, 0, SHM_R);
is acceptable, provided the segment with this key already exists. However, one cannot use this paradigm with IPC::ShareLite:
use Test::More;
use IPC::SysV qw/SHM_RDONLY/;
use IPC::ShareLite;
my $ipc_key = 58972;
my $size = 80;
my $shmem;
eval {
$shmem = IPC::ShareLite->new(-key => $ipc_key,
-create => 'yes',
-destroy => 'no',
-exclusive => 'no',
-mode => 0700,
-size => $size);
};
isa_ok($shmem, "IPC::ShareLite", "IPC::ShareLite new create");
undef $shmem;
eval {
$shmem = IPC::ShareLite->new(-key => $ipc_key,
-create => 'no',
-destroy => 'no',
-exclusive => 'no',
-mode => SHM_RDONLY,
-size => 0,
);
};
isa_ok($shmem, "IPC::ShareLite", "IPC::ShareLite new reopen");
done_testing();
The first call to new() works, but the second call fails:
ok 1 - IPC::ShareLite new create isa IPC::ShareLite
not ok 2 - IPC::ShareLite new reopen isa IPC::ShareLite
# Failed test 'IPC::ShareLite new reopen isa IPC::ShareLite'
# at <test_code> line 28.
# IPC::ShareLite new reopen isn't defined
1..2
# Looks like you failed 1 test of 2.
Patch to fix the bug:
The following code (with fix shown) in sharestuff.c is the cause of the issue, as it changes a segmen_size value of 0 to SHM_SEGMENT_SIZE:
--- sharestuff.c.orig 2012-09-05 13:55:12.000000000 +0000
+++ sharestuff.c 2012-09-05 13:57:13.000000000 +0000
@@ -513,15 +513,10 @@
}
LOG1( "GET_EX_LOCK failed (%d)", errno );
return NULL;
}
- /* XXX IS THIS THE RIGHT THING TO DO? */
- if ( segment_size <= sizeof( Header ) ) {
- segment_size = SHM_SEGMENT_SIZE;
- }
-
Newxz( node, 1, Node );
if ( ( node->shmid = shmget( key, segment_size, flags ) ) < 0 ) {
LOG1( "shmget failed (%d)", errno );
return NULL;
I don't think there is a need to prevent small segment_size values; if they are invalid, the shmget() call should fail.
At the very least, a segment_size of 0 should be allowed, so that shared memory segments for which the key is known (but the size is not) may be used by IPC::ShareLite.
With this patch in place, the above code succeeds:
ok 1 - IPC::ShareLite new create isa IPC::ShareLite
ok 2 - IPC::ShareLite new reopen isa IPC::ShareLite
1..2
Let me know if you need additional information regarding the issue.
Thanks,
Ed Macke | Senior Software Development Engineer
Savvis, A CenturyLink Company
575 Maryville Centre Drive, Suite 400, Saint Louis, MO 63141
Office: 314.579.8622 | Mobile: 314.330.7656 | Fax: 314.579.8706
Email: edward.macke@savvis.com
www.savvis.com
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