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Re: pthread_mutex_unlock not permitted in signal handler?

Hi,

Is it *at all possible* to unlock a mutex following the interruption of a thread on Tiger? (I haven't tried this on Leopard yet -- since I don't need to do the signal hack there, hopefully this is moot) Basically, I'm reading from a socket, and need a way to kill the thread if there's no response. But I also need to maintain a lock on the socket while I'm waiting for a response so other tasks don't try to send their own queries. I'm polling relatively frequently, so I don't want to have to take the lock, launch a new thread, and monitor the other thread every time. (this is a real-time task with a hardware device)

Is there any particular reason you don't do the semi-standard unix method of using select() or equivalent on your socket together with a pipe, and then write a byte to the other end of the pipe from whoever wanted to stop the thread in the first place? No messing with signals needed.

On a related note, don't use pthread_mutex_* from a signal handler if you use the same mutex outside signals in the same thread. You may not be allowed to enter pthread_mutex_* twice in the same thread, even if the mutex is recursive. Let's say the socket reader quits at just the right time and enters pthread_mutex_*, and just then your signal arrives, and also attempts to execute pthread_mutex_*. Now your program would have entered the mutex twice in the same thread. On some systems this results in a failure or a dead-lock.

Lassi
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 >pthread_mutex_unlock not permitted in signal handler? (From: Ethan Tira-Thompson <email@hidden>)



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