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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_MUTEX_TIMEDLOCK(3)				   BSD Library Functions Manual 				PTHREAD_MUTEX_TIMEDLOCK(3)

NAME
pthread_mutex_timedlock -- lock a mutex without blocking indefinitely LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> #include <time.h> int pthread_mutex_timedlock(pthread_mutex_t *mutex, const struct timespec *abs_timeout); DESCRIPTION
The pthread_mutex_timedlock() function will lock mutex. If it is already locked the calling thread will block until the mutex becomes avail- able or the timeout, specified by abs_timeout, expires. The time of the timeout is an absolute time and is not relative to the current time. RETURN VALUES
If successful, pthread_mutex_timedlock() will return zero, otherwise an error number will be returned to indicate the error. ERRORS
The pthread_mutex_timedlock() function will fail if: [EINVAL] The mutex was created with the protocol attribute having the value PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than the mutex's current priority ceiling. [EINVAL] The process or thread would have blocked, and abs_timeout specified a nanosecond value less than zero or greater than or equal to 1 billion. [EINVAL] The mutex parameter is invalid. [ETIMEDOUT] The mutex could not be locked before the timeout expired. [EAGAIN] The mutex could not be acquired because the maximum number of recursive locks for the mutex has been exceeded. [EDEADLK] The current thread already owns the mutex. SEE ALSO
pthread_mutex_destroy(3), pthread_mutex_init(3), pthread_mutex_lock(3), pthread_mutex_trylock(3), pthread_mutex_unlock(3) STANDARDS
The pthread_mutex_timedlock() function is expected to conform to ISO/IEC 9945-1:1996 (``POSIX.1''). BSD
December 30, 2003 BSD
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