Re^2: Slow worker threads

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 ?

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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]

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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]

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