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Top Forums Programming pthread_cond_timedwait relocks forever Post 302434696 by ramestica on Sunday 4th of July 2010 07:00:48 PM
Old 07-04-2010
Quote:
Originally Posted by fpmurphy
Yes, it is very possible for that to happen.

I am not sure what your understanding of how pthread_cond_timedwait works is. I would point out that once the wait time expires and is turned off, the thread is moved off the sleep queue. Likewise once a sleeping thread is signaled, even by error, it is taken off the sleep queue and the wait timer is turned off. This does not mean that it re-acquires the mutex, etc. If it takes another week before reacquiring the mutex, too bad. If it never gets the mutex back because the other thread has not released it, too bad.
i see that your understanding is then the same as mine.

realizing this detail in pthread (at least for the implementation i'm using) was a bit of a surprise. i try to use timed calls (pass timeout) just to be sure that the application will give a last sign of failure before giving up, instead of blocking there silent for ever.

Quote:
Originally Posted by fpmurphy
If you have the Lewis & Berg book on Pthreads, this issue is discussed on pages 94 -99. Dave Butenhof also discusses this issue in his book on Pthreads. See section 3.3.2 et al.

BTW, a thought just struck me, are you trying to port a Win32 application which uses eventing to GNU/Linux?
fortunately no!
 

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PTHREAD_COND_TIMEDWAIT(3)				   BSD Library Functions Manual 				 PTHREAD_COND_TIMEDWAIT(3)

NAME
pthread_cond_timedwait -- wait on a condition variable for a specific amount of time LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_cond_timedwait(pthread_cond_t *cond, pthread_mutex_t *mutex, const struct timespec *abstime); DESCRIPTION
The pthread_cond_timedwait() function atomically blocks the current thread waiting on the condition variable specified by cond, and releases the mutex specified by mutex. The waiting thread unblocks only after another thread calls pthread_cond_signal(3), or pthread_cond_broadcast(3) with the same condition variable, or if the system time reaches the time specified in abstime, and the current thread reacquires the lock on mutex. The clock used to measure abstime can be specified during creation of the condition variable using pthread_condattr_setclock(3). RETURN VALUES
If successful, the pthread_cond_timedwait() function will return zero. Otherwise an error number will be returned to indicate the error. ERRORS
The pthread_cond_timedwait() function will fail if: [EINVAL] The value specified by cond, mutex or abstime is invalid. [ETIMEDOUT] The system time has reached or exceeded the time specified in abstime. [EPERM] The specified mutex was not locked by the calling thread. SEE ALSO
pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_init(3), pthread_cond_signal(3), pthread_cond_wait(3), pthread_condattr_setclock(3) STANDARDS
The pthread_cond_timedwait() function conforms to ISO/IEC 9945-1:1996 (``POSIX.1''). BSD
May 9, 2010 BSD
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