Support for log file locking

[bobrik]

Closes #379.

Not sure how to test failing flock. Any ideas?

[bobrik]

I've fixed bad test, btw.

[Seldaek]

Thanks!

[mta59066]

Locking for who? Flock is an advisory lock and does not enforce anything. It is only useful if you look for it. So what this does is place an advisory lock on the file against other possible writers who might check for this lock.

It does not do anything about #379 and the existence of it gives the false assumption that there is a locking mechanism between different processes utilizing monolog.

[stof]

hmm indeed. Ignoring the locking error makes the locking useless to solve the issue. But please open an issue instead of commenting on a 4.5 year old merged PR. Most people won't ever look at it.

[IMSoP]

@mta59066 (and anyone else that comes upon this comment) The lock is "advisory" in terms of code that never requests a lock, but it is still blocking for all code that does request a lock. If you have two instances of the same code, and both call flock, one process will be forced to wait until the other process releases the lock. That should be enough to stop two log messages interrupting each other in the same file.

You can demonstrate this for yourself with a simple test script like this:

$fh = fopen('/tmp/example.log', 'a');
echo getmypid(), " acquiring lock...\n";
flock($fh, LOCK_EX);
echo getmypid(), " lock acquired; sleeping for 10 seconds...\n";
sleep(10);
echo getmypid(), " releasing lock...\n";
flock($fh, LOCK_UN);
echo getmypid(), " done.\n";

Running that 3 times gives the following output:

3458 acquiring lock...
3458 lock acquired; sleeping for 10 seconds...
3468 acquiring lock...
3475 acquiring lock...
3458 releasing lock...
3458 done.
3475 lock acquired; sleeping for 10 seconds...
3475 releasing lock...
3475 done.
3468 lock acquired; sleeping for 10 seconds...
3468 releasing lock...
3468 done.