On Fri, March 23, 2007 7:52 pm, Yvan Strahm wrote:
> I am confused with the flock function and its usage. I have jobs which
> are
> stored in a database, these jobs are run by a series of job_runners
> scripts
> but sometimes the job_runners stop ( server or php crash-down). So i
> put a
> job_controller in crontab to check regularly if the runners run. But
> after
> a while I have a bunch of job_controller running, so to avoid that I
> tried
> to use flock.
>
> I try to put this in the job_controller:
>
> $wouldblock=1;
> $f=fopen("controller.lock", "r");
> flock($f, LOCK_EX+LOCK_NB, $wouldblock) or die("Error! cant lock!");
>
> hoping that as long as the first job_controller run or don't close the
> file
> handle, a second job_controller won't be able to lock the
> controller.lockfile and die, but it didn't work.
>
> I also try this:
>
> $wouldblock=1;
> $f=fopen("controller.php", "r");
> flock($f, LOCK_EX+LOCK_NB, $wouldblock) or die("Error! cant lock!");
>
> hoping the first job_controller will lock it-self, but it didn't work.
>
> I also thought of writing in the lock file the PID of the first
> job_controller and then compare it and if it doesn't match then die,
> but my
> main concern is , if the server crash down the "surviving" lock file
> will
> prevent any job_controller to start.
>
> So how could prevent multiple instance of the same script? Is flock
> the best
> way?
You can do it with flock, but then you end up sooner or later with a
locked file from an "exit" or killed script, and then you have to know
to remove locks older than X minutes.
You could also just do a "mkdir" for your lock, and check its
filemtime. You could even use "touch" within loop of the script to
make sure the script is still going, and safely assume that any lock
older than X seconds is stale and can be ignored/removed.
A final option is to use 'exec' to figure out if another process is
running already:
//bail out if it's already running:
$pid = getmypid();
$command = "/bin/ps auxwwww | grep " . __FILE__ . " | grep -v grep ";
exec($command, $existing, $error);
if ($error) die("OS Error: $error\n" . implode("\n", $existing) . "\n");
$other_count = 0;
foreach($existing as $procline){
if (!strstr($procline, " $pid ")) $other_count++;
}
if ($other_count) exit;
This allows you to be sure there is always one, and only one, running
prcess or this file, with no assumptions about lock files maybe being
stale.
I use different ones at different times, depending on what the process
needs to do, and how critical it is that it runs frequently.
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