pthread_rwlock_tryrdlock(3) [osf1 man page]
pthread_rwlock_tryrdlock(3) Library Functions Manual pthread_rwlock_tryrdlock(3) NAME
pthread_rwlock_tryrdlock - Attempts to acquire a read-write lock for read access without waiting. LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so) SYNOPSIS
#include <pthread.h> int pthread_rwlock_tryrdlock( pthread_rwlock_t *rwlock); PARAMETERS
Address of the read-write lock object to acquire for read access. DESCRIPTION
This routine attempts to acquire a read-write lock for read access, but does not wait for the lock if it not immediately available. If a thread already holds the lock for read access, the lock is granted and this routine returns. If no thread already holds the lock for write access and there are no writers waiting to acquire the lock, the lock for read access is granted to the calling thread and this rou- tine returns. If some thread already holds the lock for write access, the calling thread will not acquire the read lock. Results are undefined if the calling thread has already acquired a lock for write access on rwlock when this routine is called. A thread can hold multiple, concurrent locks for read access on the same read-write lock. In a given thread, for each call to this routine that successfully acquires the same read-write lock for read access, a corrresponding call to pthread_rwlock_unlock must be issued. If the read-write lock object referenced by rwlock is not initialized, the results of calling this routine are undefined. RETURN VALUES
If an error condition occurs, this routine returns an integer value indicating the type of error. Possible return values are as follows: Successful completion. The read-write lock could not be acquired for read access because another thread already acquired it for write access or is blocked and waiting for it for write access. The value specified by rwlock does not refer to an initialized read-write lock object. The current thread already owns the read-write lock for writing. The lock for read access could not be acquired because the maxi- mum number of read lock acquisitions for rwlock has been exceeded. ERRORS
None RELATED INFORMATION
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_rdlock(3), pthread_rwlock_wrlock(3), pthread_rwlock_unlock(3) Manuals: Guide to DECthreads and Programmer's Guide delim off pthread_rwlock_tryrdlock(3)
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pthread_rwlock_rdlock(3C) pthread_rwlock_rdlock(3C) NAME
pthread_rwlock_rdlock, pthread_rwlock_tryrdlock - lock or attempt to lock read-write lock object for reading SYNOPSIS
cc -mt [ flag... ] file... -lpthread [ library... ] #include <pthread.h> int pthread_rwlock_rdlock(pthread_rwlock_t *rwlock); int pthread_rwlock_tryrdlock(pthread_rwlock_t *rwlock); The pthread_rwlock_rdlock() function applies a read lock to the read-write lock referenced by rwlock. The calling thread acquires the read lock if a writer does not hold the lock and there are no writers blocked on the lock. The calling thread does not acquire the lock if a writer holds the lock or if writers of higher or equal priority are blocked on the lock; otherwise, the calling thread acquires the lock. If the read lock is not acquired, the calling thread blocks until it can acquire the lock. A thread can hold multiple concurrent read locks on rwlock (that is, successfully call the pthread_rwlock_rdlock() function n times). If so, the thread must perform matching unlocks (that is, it must call the pthread_rwlock_unlock() function n times). The maximum number of concurrent read locks that a thread can hold on one read-write lock is currently set at 100,000, though this number could change in a future release. There is no imposed limit on the number of different threads that can apply a read lock to one read-write lock. The pthread_rwlock_tryrdlock() function applies a read lock like the pthread_rwlock_rdlock() function, with the exception that the function fails if the equivalent pthread_rwlock_rdlock() call would have blocked the calling thread. In no case will the pthread_rwlock_tryrdlock() function ever bloc. It always either acquires the lock or fails and returns immediately. Results are undefined if any of these functions are called with an uninitialized read-write lock. If a signal is delivered to a thread waiting for a read-write lock for reading, upon return from the signal handler the thread resumes waiting for the read-write lock for reading as if it was not interrupted. If successful, the pthread_rwlock_rdlock() function returns 0. Otherwise, an error number is returned to indicate the error. The pthread_rwlock_tryrdlock() function returns 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. The pthread_rwlock_rdlock() and pthread_rwlock_tryrdlock() functions will fail if: EAGAIN The read lock could not be acquired because the maximum number of read locks by the current thread for rwlock has been exceeded. The pthread_rwlock_rdlock() function will fail if: EDEADLK The current thread already owns the read-write lock for writing. The pthread_rwlock_tryrdlock() function will fail if: EBUSY The read-write lock could not be acquired for reading because a writer holds the lock or a writer with the appropriate pri- ority was blocked on it. See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ |MT-Level |MT-Safe | +-----------------------------+-----------------------------+ pthread_rwlock_init(3C), pthread_rwlock_wrlock(3C), pthread_rwlockattr_init(3C), pthread_rwlock_unlock(3C), attributes(5), standards(5) 23 Mar 2005 pthread_rwlock_rdlock(3C)