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pthread_rwlock_rdlock(3) [osf1 man page]

pthread_rwlock_rdlock(3)				     Library Functions Manual					  pthread_rwlock_rdlock(3)

NAME
pthread_rwlock_rdlock - Acquires a read-write lock for read access. LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so) SYNOPSIS
#include <pthread.h> int pthread_rwlock_rdlock( pthread_rwlock_t *rwlock); PARAMETERS
Address of the read-write lock object to acquire for read access. DESCRIPTION
This routine acquires a read-write lock for read access. 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 routine returns. If a thread already holds the lock for read access, the lock is granted and this routine returns. 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 corresponding call to pthread_rwlock_unlock must be issued. If some thread already holds the lock for write access, the calling thread will not acquire the read lock. If the read lock is not acquired, the calling thread blocks until it can acquire the lock for read access. Results are undefined if the calling thread has already acquired a lock for write access on rwlock when this routine is called. If the read-write lock object referenced by rwlock is not initialized, the results of calling this routine are undefined. If a thread is interrupted (via a Tru64 UNIX signal or an OpenVMS AST) while waiting for a read-write lock for read access, upon return from the interrupt routine the thread resumes waiting for the lock as if it had not been interrupted. 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 lock for read access could not be acquired because the maximum number of read lock acquisitions for rwlock has been exceeded. The current thread already owns the read-write lock for writing. The value specified by rwlock does not refer to an ini- tialized read-write lock object. ERRORS
None RELATED INFORMATION
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_tryrdlock(3), pthread_rwlock_wrlock(3), pthread_rwlock_unlock(3) Manuals: Guide to DECthreads and Programmer's Guide delim off pthread_rwlock_rdlock(3)

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pthread_rwlock_wrlock(3)				     Library Functions Manual					  pthread_rwlock_wrlock(3)

NAME
pthread_rwlock_wrlock - Acquires a read-write lock for write access. LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so) SYNOPSIS
#include <pthread.h> int pthread_rwlock_wrlock( pthread_rwlock_t *rwlock); PARAMETERS
Address of the read-write lock object to acquire for write access. DESCRIPTION
This routine attempts to acquire a read-write lock for write access. If any thread already has acquired the lock for write access or read access, the lock is not granted and the calling thread blocks until it can acquire the lock. A thread can hold only one lock for write access on a read-write lock. Results are undefined if the calling thread holds the read-write lock (whether for read or write access) at the time this routine is called. If the read-write lock object referenced by rwlock is not initialized, the results of calling this routine are undefined. If a thread is interrupted (via a Tru64 UNIX signal or an OpenVMS AST) while waiting for a read-write lock for write access, upon return from the interrupt routine the thread resumes waiting for the lock as if it had not been interrupted. Realtime applications can encounter priority inversion when using read-write locks. The problem occurs when a high-priority thread acquires a read-write lock that is about to be unlocked (that is, posted) by a low-priority thread, but the low-priority thread is preempted by a medium-priority thread. This scenario leads to priority inversion in that a high-priority thread is blocked by lower-priority threads for an unlimited period of time. During system design, realtime programmers must take into account the possibility of priority inversion and can deal with it in a number of ways, such as by having critical sections that are guarded by read-write locks execute at a high priority, so that a thread cannot be preempted while executing in its critical section. 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 current thread already owns the read-write lock for write or read access. The value specified by rwlock does not refer to an initialized read-write lock object. ERRORS
None RELATED INFORMATION
Functions: pthread_rwlock_init(3), pthread_rwlockattr_init(3), pthread_rwlock_rdlock(3), pthread_rwlock_trywrlock(3), pthread_rwlock_unlock(3) Manuals: Guide to DECthreads and Programmer's Guide delim off pthread_rwlock_wrlock(3)
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