Global, MySQL-backed lock. This is a high-reliability, low-performance global lock.

The lock is maintained by using GET_LOCK() in MySQL, and automatically released when the connection terminates. Thus, this lock can safely be used to control access to shared resources without implementing any sort of timeout or override logic: the lock can't normally be stuck in a locked state with no process actually holding the lock.

However, acquiring the lock is moderately expensive (several network roundtrips). This makes it unsuitable for tasks where lock performance is important.

$lock = PhabricatorGlobalLock::newLock('example');
$lock->lock();
  do_contentious_things();
$lock->unlock();