File Locking vs. Semaphores

c linux unix interprocess
Blagovest Buyukliev picture Blagovest Buyukliev · Aug 25, 2010 · Viewed 11k times · Source

Just out of curiosity, what is the preferred way to achieve interprocess synchronization on Linux? The sem*(2) family of system calls seem to have a very clunky and dated interface, while there are three ways to lock files - fcntl(), flock() and lockf().

What are the internal differences (if any) and how would you justify the usage of each?

Answer

Jens Gustedt picture Jens Gustedt · Aug 25, 2010

Neither. The actual versions of pthread_* (eg. phtread_mutex_t) all allow to place the variables in shared segments that are created via shm_open. You just have to place some extra parameter to the init calls.

Don't use semaphores (sem_t) if you don't have to, they are too low level and are interupted by IO etc.

Don't abuse file locking for interprocess control. It is not made for that. In particular, you don't have a possibility to flush file meta-data such as locks, so you never know when a lock / unlock will become visible to a second process.

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