pthread_rwlock_timedrdlock(3) [freebsd man page]
PTHREAD_RWLOCK_TIMEDRDLOCK(3) BSD Library Functions Manual PTHREAD_RWLOCK_TIMEDRDLOCK(3) NAME
pthread_rwlock_timedrdlock -- acquire a read-write lock for reading or give up after a specified period LIBRARY
POSIX Threads Library (libpthread, -lpthread) SYNOPSIS
#include <pthread.h> int pthread_rwlock_timedrdlock(pthread_rwlock_t *rwlock, const struct timespec *abs_timeout); DESCRIPTION
This function acquires a read lock on the read-write lock rwlock. However, if the lock cannot be acquired without waiting for another thread to unlock the lock, this wait shall be terminated when abs_timeout expires. A thread may hold multiple concurrent read locks. The pthread_rwlock_unlock(3) function must be called once for each lock acquired. If the thread should be interrupted by a signal, the pthread_rwlock_timedrdlock() function will be automatically restarted after the thread returns from the signal handler. The calling thread may 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. IMPLEMENTATION NOTES
To prevent writer starvation, writers are favored over readers. RETURN VALUES
If successful, the pthread_rwlock_timedrdlock() function will return zero. Otherwise, an error number will be returned to indicate the error. This function shall not return an error code of EINTR. ERRORS
The pthread_rwlock_timedrdlock() function will fail if: [ETIMEDOUT] The lock could not be acquired before the specified timeout expired. The pthread_rwlock_timedrdlock() function may fail if: [EAGAIN] The read lock could not be acquired because the maximum number of read locks for rwlock 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 abs_timeout nanosecond value is less than zero or greater than or equal to 1 billion. SEE ALSO
pthread_rwlock_init(3), pthread_rwlock_timedwrlock(3), pthread_rwlock_unlock(3) STANDARDS
The pthread_rwlock_timedrdlock() function is expected to conform to ISO/IEC 9945-1:1996 (``POSIX.1''). HISTORY
The pthread_rwlock_timedrdlock() function first appeared in FreeBSD 5.2. BSD
January 16, 2004 BSD
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pthread_rwlock_timedrdlock(3C) Standard C Library Functions pthread_rwlock_timedrdlock(3C) NAME
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 spec- ified 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 param- eter 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: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |See below. | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ The pthread_rwlock_timedrdlock() function is Standard. The pthread_rwlock_reltimedrdlock_np() is Stable. 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) SunOS 5.10 30 Jan 2004 pthread_rwlock_timedrdlock(3C)