Re: Slow worker threads

This is not related to your performance problem, but I wonder if flock is doing what you think it is. Consider the following:

use strict;
use warnings;
use threads;
use Fcntl qw(:flock);

open(FILE, ">>/tmp/test.txt");

for(0..9) {
    threads->new(\&worker, $_);
}

$_->join for threads->list;

sub worker {
    my $x = shift;

    flock(FILE, LOCK_EX);
    print "$x: locked file\n";
    sleep(10);
    flock(FILE, LOCK_UN);
    print "$x: unlocked file\n";
    return;
}
[download]

Which produces

0: locked file
1: locked file
2: locked file
3: locked file
4: locked file
5: locked file
6: locked file
7: locked file
8: locked file
9: locked file
0: unlocked file
1: unlocked file
2: unlocked file
3: unlocked file
4: unlocked file
5: unlocked file
6: unlocked file
7: unlocked file
8: unlocked file
9: unlocked file
[download]

If you are locking against other processes changing the file between your writes, you should probably be seeking to end of file between locking and writing.

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Re^2: Slow worker threads by spx2 (Deacon) on Jul 18, 2009 at 17:56 UTC
Let's consider NONBLOCKING flock , there's something really wrong going on : `use strict; use warnings; use threads; use feature 'say' ; use Fcntl qw(:flock); open(FILE, ">>/tmp/test.txt"); for(0..9) { threads->new(\&worker, $_); } $_->join for threads->list; sub worker { my $x = shift; my $locked; $locked = flock(FILE, LOCK_EX\|LOCK_NB ); if( $locked ) { say "$x: lock acquired"; sleep 4; } else { say "$x: cannot acquire lock"; } flock( FILE, LOCK_UN ); print "$x: lock released\n"; return; }` [download] `0: lock acquired 1: lock acquired 2: lock acquired 3: lock acquired 4: lock acquired 5: lock acquired 6: lock acquired 7: lock acquired 8: lock acquired 9: lock acquired 0: lock released 1: lock released 2: lock released 3: lock released 4: lock released 5: lock released 6: lock released 7: lock released 8: lock released 9: lock released` [download] How come the lock is acquired again and again without being released anywhere in between ?! Isn't this what a lock is supposed to do ? Lock something and not give access to anyone else until released ?	[reply] [d/l] [select]
Re^3: Slow worker threads by spx2 (Deacon) on Jul 18, 2009 at 19:20 UTC
it didn't occur to me that the threads were actually sharing the FILE filehandle , so if one acquired the lock , each of them actually acquired the lock because FILE was shared amongst them( thanks tye for pointing that out ) I managed to pull of a quick replacement for that which works as one would expect. Notice the 9-$x , that is to make sure that `time(thread1)>time(thread2)>time(thread3)>...` . Also notice that $thread_lock are thread-specific locks use strict; use warnings; use threads; use feature 'say' ; use Fcntl qw(:flock); my $file_path = ">>/tmp/test.txt"; open(FILE, $file_path); for(0..9) { threads->new(\&worker, $_); } $_->join for threads->list; sub worker { my $x = shift; my $locked; open(my $thread_lock,$file_path); $locked = flock($thread_lock, LOCK_EX\|LOCK_NB ); if( $locked ) { say "$x: lock acquired"; sleep 9-$x; } else { say "$x: cannot acquire lock"; }; if($locked) { flock( $thread_lock, LOCK_UN ); print "$x: lock released\n"; } return; } [download] `0: lock acquired 1: cannot acquire lock 2: cannot acquire lock 3: cannot acquire lock 4: cannot acquire lock 5: cannot acquire lock 6: cannot acquire lock 7: cannot acquire lock 8: cannot acquire lock 9: cannot acquire lock 0: lock released` [download]	[reply] [d/l] [select]