Segfaults with threading

[rottmanja]

I am working on a perl app that uses multiple threads to handle multiple instances of the same sub routine. During testing, I have run into an issue with segfaults after the first thread is created and the sub routines have started to process. During the creation of the second thread is where I run into the segfault.

Any help with this is greatly appreciated. It is frustrating as hell.

Here is the code that I use to create the threads.

use Lib:LSInstance;
use Lib:LSParse qw(parseMain);
use Lib:aemon;
use Data:umper;
use strict;
use threads;


#Lib:aemon::daemonize();


my @thisVar = Lib:LSInstance::getInstances();

for(my $i = 0; $i < @thisVar; $i++){
my $thr1 = threads->new(\&threadTest, $thisVar[$i][2],$thisVar[$i][1] )->join();
}





sub threadTest{
print "Child Thread $_[0] \n";
print "********************************************************************************\n";
my @thatVar = parseMain($_[0],$_[1]);
#print Dumper(@thatVar);
}

And here is what I get with a stack trace after the first thread has been started.


) = 0
stat64("/usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0x9d51270) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.8/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.7/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.6/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.5/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.8/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.7/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.6/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/5.8.5/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/site_perl/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.8/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.7/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.6/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.5/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.8/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.7/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.6/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/5.8.5/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/vendor_perl/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/5.8.8/i386-linux-thread-multi/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("/usr/lib/perl5/5.8.8/auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
stat64("./auto/DBI/DESTROY.al", 0xbf91fb6c) = -1 ENOENT (No such file or directory)
close(3) = 0
munmap(0xb7cba000, 135168) = 0
ioctl(0, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
_llseek(0, 0, 0xbf91ff20, SEEK_CUR) = -1 ESPIPE (Illegal seek)
ioctl(1, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
_llseek(1, 0, 0xbf91ff20, SEEK_CUR) = -1 ESPIPE (Illegal seek)
ioctl(2, SNDCTL_TMR_TIMEBASE or TCGETS, {B38400 opost isig icanon echo ...}) = 0
_llseek(2, 0, 0xbf91ff20, SEEK_CUR) = -1 ESPIPE (Illegal seek)
ioctl(6, SNDCTL_TMR_TIMEBASE or TCGETS, 0xbf91fef8) = -1 ENOTTY (Inappropriate ioctl for device)
_llseek(6, 0, [6019], SEEK_CUR) = 0
mmap2(NULL, 528384, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7238000
munmap(0xb7238000, 528384) = 0
clone(Child Thread HS_INT2_BASE
********************************************************************************
child_stack=0xb7cb94b4, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0xb7cb9bd8, {entry_number:6, base_addr:0xb7cb9b90, limit:1048575, seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1, seg_not_present:0, useable:1}, child_tidptr=0xb7cb9bd8) = 4146
futex(0xb7cb9bd8, FUTEX_WAIT, 4146, NULL <unfinished ...>
+++ killed by SIGSEGV +++

 

[Kirsle]

I don't see why it would segfault, but I did notice something you're not doing right:

my $thr1 = threads->new(\&threadTest, $thisVar[$i][2],$thisVar[$i][1] )->join();

The join() method on threads will block execution until the thread you're joining has finished and stopped execution. So instead of your threads running in parallel, you're simply spawning a single thread and waiting for it to finish before iterating through your loop and spawning thread #2.

A better way of dealing with threads would be this:

use threads;

# spawn all 20 threads and let them run in parallel
my @thr = ();
for (my $i = 0; $i < 10; $i++) {
   print "Spawning thread number $i\n";
   $thr[$i] = threads->new (\&threadcode, $i);
}

# start rejoining the threads
for (my $i = 0; $i < 10; $i++) {
   print "Joining thread $i\n";
   $thr[$i]->join();
   print "\tThread $i joined back with the parent\n";
}

sub threadcode {
   my $id = shift;

   print "-->Thread $id has started<--\n";

   # sleep $id seconds
   sleep ($id);

   # return to end execution
   print "-->Thread $id is ending<--\n";
   return 1;
}

That should spawn off 10 threads pretty rapidly and each thread will sleep one second longer than the previous one. Here's my output:

[kirsle@eclipse ~]$ perl threads.pl 
Spawning thread number 0
Spawning thread number 1
-->Thread 0 has started<--
-->Thread 0 is ending<--
-->Thread 1 has started<--
Spawning thread number 2
Spawning thread number 3
-->Thread 2 has started<--
Spawning thread number 4
-->Thread 3 has started<--
Spawning thread number 5
-->Thread 4 has started<--
Spawning thread number 6
-->Thread 5 has started<--
Spawning thread number 7
-->Thread 6 has started<--
Spawning thread number 8
-->Thread 7 has started<--
Spawning thread number 9
-->Thread 9 has started<--
Joining thread 0
	Thread 0 joined back with the parent
Joining thread 1
-->Thread 8 has started<--
-->Thread 1 is ending<--
	Thread 1 joined back with the parent
Joining thread 2
-->Thread 2 is ending<--
	Thread 2 joined back with the parent
Joining thread 3
-->Thread 3 is ending<--
	Thread 3 joined back with the parent
Joining thread 4
-->Thread 4 is ending<--
	Thread 4 joined back with the parent
Joining thread 5
-->Thread 5 is ending<--
	Thread 5 joined back with the parent
Joining thread 6
-->Thread 6 is ending<--
	Thread 6 joined back with the parent
Joining thread 7
-->Thread 7 is ending<--
	Thread 7 joined back with the parent
Joining thread 8
-->Thread 8 is ending<--
	Thread 8 joined back with the parent
Joining thread 9
-->Thread 9 is ending<--
	Thread 9 joined back with the parent

Anyway, try making a simpler threading test. If your Perl segfaults then, you might just have a faulty installation of Perl and/or threads.

Also, keep in mind that some modules are not "thread-safe". IIRC there's a section on the threads documentation that talks about what thread-safe means.

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