07-04-2010
Quote:
Therefore, it is possible that pthread_cond_timedwait would block for ever, which is exactly what one is trying to avoid by using a timed version of 'wait'.
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.
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?
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LEARN ABOUT MOJAVE
pthread_cond_timedwait
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
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.
Values for struct timespec can be obtained by adding the required time interval to the the current time obtained using gettimeofday(2).
Note that struct timeval and struct timespec use different units to specify the time. Hence, the user should always take care to perform the
time unit conversions accordingly.
EXAMPLE
struct timeval tv;
struct timespec ts;
gettimeofday(&tv, NULL);
ts.tv_sec = tv.tv_sec + 0;
ts.tv_nsec = 0;
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.
SEE ALSO
pthread_cond_broadcast(3), pthread_cond_destroy(3), pthread_cond_init(3), pthread_cond_signal(3), pthread_cond_wait(3), gettimeofday(2)
STANDARDS
The pthread_cond_timedwait() function conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').
BSD
May 9, 2010 BSD