Suppose 10 processes are waiting on a semaphore using sem_wait().
and an 11th process calls sem_post on that semaphore.
which of the 10 processes will enter the critical block?
Is it like random? All the process will wake up and strive to achieve a lock.
and CPU will provide a lock to one of the processes and the rest will go back to waiting for state
Does sem_post wake up a random process
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1 Answers
The POSIX standard doesn't specify which thread will be woken up. Moreover, without artificial delays it's impossible for threads to start waiting on a semaphore in a well-defined order.
In practice, it's likely to be the thread which has been waiting the longest, as a queue structure is used to record threads waiting on a synchronization object. It definitely won't be a 'random' thread. But it's also not something you should depend on for the correctness of your code.
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