NAME

pthread_rwlock_trywrlock − Attempts to acquire a read-write lock for write access without waiting. 

LIBRARY

DECthreads POSIX 1003.1c Library (libpthread.so)

SYNOPSIS

#include <pthread.h>

int   pthread_rwlock_trywrlock(
                      pthread_rwlock_t         ∗rwlock);

PARAMETERS

rwlockAddress 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. 

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:

0Successful completion. 

[EBUSY]The read-write lock could not be acquired for write access because it was already locked for write access or for read access. 

[EINVAL]The value specified by rwlock does not refer to an initialized read-write lock object. 

[EDEADLCK]
The current thread already owns the read-write lock for write or read access.

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