How to avoid file deadlocks when PHP process/server crashes?

Question

I am new to PHP. I understand I can use flock() to lock a file and avoid race conditions when two users reach the same php file adding content to the lockable file.

However, what happens if a php process crashes? What happens to the next user waiting for the lockable file? What happens if the server crashes (someone pulls the plug)? Is the lock automatically released? Will the file remain locked after rebooting the server?

To make it short, does PHP make sure such critical situations (i.e., lock not explicitly released) are handled properly? If not, how should one deal with these situations? How to recover from these?