pthread_rwlock_timedrdlock

, pthread_rwlock_reltimedrdlock_np

- lock a read-write lock for reading

Synopsis

cc -mt [ flag... ] file... [ library... ]
#include <pthread.h>
#include <time.h>

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

int pthread_rwlock_reltimedrdlock_np(pthread_rwlock_t *restrict rwlock,
     const struct timespec *restrict rel_timeout);

Description

The pthread_rwlock_timedrdlock() function applies a read lock to the read-write lock referenced by rwlock as in the pthread_rwlock_rdlock(3C) function. 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 pthread_rwlock_reltimedrdlock_np() function is identical to the pthread_rwlock_timedrdlock() function, except that the timeout is specified as a relative time interval. The timeout expires when the time interval specified by rel_timeout passes, as measured by the CLOCK_REALTIME clock, or if the time interval specified by rel_timeout is negative 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 either 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() or pthread_rwlock_reltimedrdlock_np(), 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 results are undefined if this function is called with an uninitialized read-write lock.

Return Values

The pthread_rwlock_timedrdlock() and pthread_rwlock_reltimedrdlock_np() functions return 0 if the lock for reading on the read-write lock object referenced by rwlock is acquired. Otherwise, an error number is returned to indicate the error.

Errors

The pthread_rwlock_timedrdlock() and and pthread_rwlock_reltimedrdlock_np() functions will fail if:

ETIMEDOUT

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

The pthread_rwlock_timedrdlock() and pthread_rwlock_reltimedrdlock_np() functions may fail if:

EAGAIN

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

EDEADLK

The calling thread already holds a write lock on rwlock.

EINVAL

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.

Attributes

See attributes(5) for descriptions of the following attributes:

See Also

pthread_rwlock_destroy(3C), pthread_rwlock_rdlock(3C), pthread_rwlock_timedwrlock(3C), pthread_rwlock_trywrlock(3C), pthread_rwlock_unlock(3C), pthread_rwlock_wrlock(3C), attributes(5), standards(5)