Question

While reading about binary semaphore and mutex I found the following difference:

Both can have value 0 and 1, but mutex can be unlocked by the same
thread which has acquired the mutex lock. A thread which acquires
mutex lock can have priority inversion in case a higher priority
process wants to acquire the same mutex whereas this is not the case
with binary semaphore.

So where should I use binary semaphores? Can anyone cite an example?

EDIT: I think I have figured out the working of both. Basically binary semaphore offer synchronization whereas mutex offer locking mechanism. I read some examples from Galvin OS book to make it more clear.

Answer 1

One typical situation where I find binary semaphores very useful is for thread initialization where the thread will read from a structure owned by the parent thread. The parent thread needs to wait for the new thread to read the shared data from the structure before it can let the structure’s lifetime end (by leaving its scope, for instance). With a binary semaphore, all you have to do is initialize the semaphore value to zero and have the child post it while the parent waits on it. Without semaphores, you’d need a mutex and condition variable and much uglier program logic for using them.