Multithreaded Programming Guide

Acquiring a Read Lock on a Read-Write Lock Before a Specified Absolute Time

The pthread_rwlock_timedrdlock(3C) function applies a read lock to the read-write lock referenced by rwlock as in the pthread_rwlock_rdlock() function.

pthread_rwlock_timedrdlock Syntax

#include <pthread.h>
#include <time.h>

int  pthread_rwlock_timedrdlock(pthread_rwlock_t *restrict rwlock,
          const struct timespec *restrict abs_timeout);

If the lock cannot be acquired without waiting for other threads to unlock the lock, this wait will be terminated when the specified timeout expires. The timeout expires when the absolute time specified by abs_timeout passes, as measured by the CLOCK_REALTIME clock (that is, when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the call.

The resolution of the timeout is the resolution of the CLOCK_REALTIME clock. The timespec data type is defined in the <time.h> header. Under no circumstances does the function fail with a timeout if the lock can be acquired immediately. The validity of the timeout parameter need not be checked if the lock can be immediately acquired.

If a signal that causes a signal handler to be executed is delivered to a thread blocked on a read-write lock with a call to pthread_rwlock_timedrdlock(), upon return from the signal handler the thread resumes waiting for the lock as if it was not interrupted.

The calling thread might deadlock if at the time the call is made it holds a write lock on rwlock.

The pthread_rwlock_reltimedrdlock_np() function is identical to the pthread_rwlock_timedrdlock() function, except that the timeout is specified as a relative time interval.

pthread_rwlock_timedrdlock Return Values

If successful, returns 0 if the lock for writing on the read-write lock object referenced by rwlock is acquired. Otherwise, an error number is returned to indicate the error.



The lock could not be acquired before the specified timeout expired.



The read lock could not be acquired because the maximum number of read locks for lock would be exceeded.



The calling thread already holds the rwlock.



The value specified by rwlock does not refer to an initialized read-write lock object, or the timeout nanosecond value is less than zero or greater than or equal to 1,000 million.