fcntl() for thread or process synchronization?

Question

Is it possible to use fcntl() system call on a file to achieve thread/process synchronization (instead of semaphoress)?

Answer 1

Yes. Unix fcntl locks (and filesystem resources in general) are system-wide, so any two threads of execution (be they separate processes or not) can use them. Whether that's a good idea or not is context-dependent.

Answer 2

That's one way of synchronizing between processes, but if you don't want to use semaphores, you could use process shared mutexes, such as mutexes and condition variables created with the PTHREAD_PROCESS_SHARED attribute on POSIX based platforms (see pthread_mutexattr_setpshared() and pthread_condattr_setpshared()). Another option is to use an event based IPC (sockets, etc) mechanism that blocks until an event you define is demultiplexed (e.g. via select()). There are several other shared memory based options as well.

However, since you're using C++ I'd recommend using a C++ framework that greatly simplifies this sort of interprocess synchronization across multiple platforms like boost.interprocess or ACE.

Answer 3

The fcntl and flock are not for thread, but for process, so they cannot be used for thread synchronization.