pthread_rwlock_trywrlock(3)pthread_rwlock_trywrlock(3)NAMEpthread_rwlock_trywrlock - Attempts to acquire a read-write lock for
write access without waiting
SYNOPSIS
#include <pthread.h>
int pthread_rwlock_trywrlock(
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 the read-write lock referenced by
rwlock for write access. If any thread already holds that lock for
write access or read access, this routine fails and returns [EBUSY] and
the calling thread does not wait for the lock to become available.
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.
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 read-write lock could not be acquired for
write access because it was already locked for write access or for read
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 write or read access.
ERRORS
None
SEE ALSO
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
pthread_rwlock_trywrlock(3)