Hello Monks, I have encountered a big issue with perl threads, and I truly hope someone can help me to solve it. In brief: in certain situations, if you spawn threads, and within each thread you execute a shell command (either via system() or backticks), you see a significant loss of performances. Most importantly, if you check with "top", you will immediately see that not all threads are actually executing the system call simultaneously, but at most 1 or 2 of them. Here what I noticed so far by making a few tests:

1. The behaviour is triggered when the shell command is executed "very quickly" (a few milliseconds)
2. If from within the thread you fork a process, and execute the system call in there, this behaviour is not observed

So, it seems like all threads are competing for some resource. Any idea on how this can be prevented/fixed?

Many thanks to all of you in advance for your advice!

Daniel 

# runs smoothly
 
use threads;
use strict;
 
my @pool = map { threads->create(\&mysub) } 1 .. 50;
$_->join for (@pool);
 
sub mysub {
    
    print "spawned " . threads->tid . "\n";
 
    for (1 .. 100) { `sleep 1`; }
 
}

__END__
 
 
# after the first threads have been spawned, it starts slowing down
 
use threads;
use strict;
 
my @pool = map { threads->create(\&mysub) } 1 .. 50;
$_->join for (@pool);
 
sub mysub {
    
    print "spawned " . threads->tid . "\n";
 
 
    for (1 .. 100) { `sleep 0.0001`; }
 
}
 
__END__

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In reply to Perl threads loss of performance with system call by daniel85

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