I'm having an issue when waiting on a pthread condition variable from the main thread and then a signal handler runs, which should cancel the wait since I have cancellation points enabled, however this did not happen. While debugging I see the main thread blocked when standing inside the signal handler. Here's the call graph at that point:
There are two semaphores associated with a condition variable wait: a) One for the conditional variable and b) one for a mutex that protects the condition variable. When you wait for a condition, the mutex (b) is unlocked and the logic waits on (a). After (a) wakes up, then mutex (b) is re-relocked. So there can be two waits.
What is not clear from the call graph is if the sem_wait() is the first for the condition variable or the second for the mutex. nxsem_wait_interruptible() is fine for for the first, but not for the second if ECANCELED was returned.
