threads, tie and segmentation fault

petesmiley has asked for the wisdom of the Perl Monks concerning the following question:

Has anyone tried using DB_File or SDBM_File or modules of that sort with threads in perl 5.8? I keep getting a segmentation fault when my program exits.

I provided a short code sample that produces the problem on my machine. I don't think it even makes it to the untie. To get rid of the segfault all I have to do is comment out the tie.

Maybe someone could point out something I'm doing wrong, or suggest a module that works better for this. Any advice would be appreciated.

smiles

#!/usr/bin/perl

use strict;
use threads;
use threads::shared;
use Thread::Queue;
use SDBM_File;
use Fcntl;

# initialize some stuff
my $q = Thread::Queue->new();
my %items : shared;
tie %items,'SDBM_File','itemdb',O_CREAT|O_RDWR,0640 or die "Could not 
+open SDBM file: $!\n";
$items{$_} = 1 for 1..10;

# play with 3 threads
for (1..3) { threads->new(\&ttest) }
my @threadlist = threads->list;
$q->enqueue($_) for 1..10;
$q->enqueue(undef) for @threadlist;
$_->join for @threadlist;

# clean up mess
untie %items;
unlink 'itemdb.pag','itemdb.dir';

sub ttest {
    while (my $qthingie = $q->dequeue) {
        print "$items{$qthingie}\n"
    }
}
[download]

Comment on threads, tie and segmentation fault Download Code

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Re: threads, tie and segmentation fault by pg (Canon) on Feb 04, 2003 at 20:49 UTC
Just like I said, Perl should start to state what are thread-safe. I am planning to give a example of thread-safe OO module in meditations. I will do this ASAP, whenever I have some spare time. I am hoping that would be useful.	[reply]
Re: Re: threads, tie and segmentation fault by petesmiley (Friar) on Feb 04, 2003 at 21:10 UTC
I agree, and thanks. I look forward to reading it. That still doesn't quite help with my current quandary though. :)	[reply]
Re: threads, tie and segmentation fault by petesmiley (Friar) on Feb 05, 2003 at 17:40 UTC
Now that I have a slightly clearer understanding of how perl threads work, I have a piece of code that resolves this problem. Note that tying and untying with locks solves the problem. Apparently a tie will not carry well when spawning threads so each one would have to do its own tying and untying. #!/usr/bin/perl use strict; use threads; use threads::shared; use Thread::Queue; use DB_File::Lock; use Fcntl; my $q = Thread::Queue->new(); my %items; my $DB = tie %items,'DB_File::Lock','itemdb',O_CREAT\|O_RDWR,0640,$DB_H +ASH,'write' or die "Could not open SDBM file: $!\n"; $items{$_} = 1 for 1..10; untie %items; undef $DB; for (1..3) { threads->new(\&ttest) } my @threadlist = threads->list; $q->enqueue($_) for 1..10; $q->enqueue(undef) for @threadlist; $_->join for @threadlist; unlink 'itemdb.pag','itemdb.dir'; sub ttest { my %db; while (my $qthingie = $q->dequeue) { my %items; my $DB = tie %items,'DB_File::Lock','itemdb',O_CREAT\|O +_RDWR,0640,$DB_HASH,'write' or die "Could not open SDBM file: $!\n"; print "$qthingie $items{$qthingie}\n"; untie %items; } } [download]	[reply] [d/l]
Re: threads, tie and segmentation fault by perrin (Chancellor) on Feb 04, 2003 at 17:51 UTC
Those are XS modules. Did someone tell you they were thread safe? I assume they are not.	[reply]
Re: Re: threads, tie and segmentation fault by petesmiley (Friar) on Feb 04, 2003 at 20:42 UTC
I kind of figured :) But is there a nice alternative to these?	[reply]