pthread_rwlock_wrlock(3)pthread_rwlock_wrlock(3)NAMEpthread_rwlock_wrlock - Acquires a read-write lock for write access
SYNOPSIS
#include <pthread.h>
int pthread_rwlock_wrlock(
pthread_rwlock_t *rwlock );
LIBRARY
DECthreads POSIX 1003.1c Library (libpthread.so)
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.
Real-time 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 pre‐
empted 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, real-
time 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
SEE ALSO
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
pthread_rwlock_wrlock(3)
