On Wednesday, July 17, 2002, at 07:04 , George Schlossnagle wrote:
>>> The main problem appears to be that instead of taking a different branch
>>> if open() or flock() fails you continue on as if they had succeeded.
>
> flock($fh,LOCK_EX ) is a blocking call, so it won't return until the lock
> is available.
in lieu of going to semaphores... { not a bad solution for most }
{ there is also a race in there for 'grab the semaphore' but it
is probably still better than most solutions... }
you can get round that with an 'alarm()' - something on the form
my $timeout=5;
my $getLock=1;
my $alarmFlag=0;
local $SIG{ALRM} = sub { $alarmFlag=1;}
while( $getLock ) {
open(FH,....) or die ....;
alarm $timeout;
flock(....)
alarm 0;
if( $alarmFlag) {
$alarmFlag=0;
close(FH);
}else {
$getLock=0;
}
}
and/or stuff that in an eval block, and..... yadda yadda yadda
This way either you get in and out of there quickly or
block - but in a way that does not have the file open...
one is still in a race condition...
the other is to go with the 'symbolic link' type of trick of the
form of $filename.lockget -> $filename - and everyone checks
for the existence of that file first.... to try to avoid the
open for the flock()....
ciao
drieux
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