rw_tryrdlock(SYNCH)

rw_tryrdlock -- conditionally acquire a reader-writer lock in read mode

Synopsis

   cc [options] -Kthread file
   
   #include <synch.h>
   

   int rw_tryrdlock(rwlock_t *lock);

Description

rw_tryrdlock attempts once to acquire the reader-writer lock pointed to by lock in read mode; it does not block the caller if the lock is unavailable.

A reader-writer lock can be held by any number of readers at one time, but only one writer at a time can hold the lock.

If the lock is free or is currently held by another reader and there are no writers waiting, rw_tryrdlock increments the reader count and the caller proceeds.

If the lock is currently held by a writer, or there are writers waiting, rw_tryrdlock immediately returns EBUSY to the caller, without acquiring the lock.

lock must previously have been initialized (see rwlock_init(SYNCH)).

Parameters

lock: pointer to the lock to be acquired

Usage

rw_tryrdlock is used when the caller does not want to block if the lock is unavailable.

Return values

rw_tryrdlock returns zero for success and an error number for failure.

Errors

If the following condition occurs, rw_tryrdlock fails and returns the corresponding value:

EBUSY: the reader-writer lock pointed to by lock cannot be acquired

If the following condition is detected, rw_tryrdlock returns the corresponding value:

EINVAL: invalid argument specified

For consistency, locks acquired with rw_tryrdlock should be released with rw_unlock.

References

Intro(SYNCH), rwlock(SYNCH), rwlock_destroy(SYNCH), rwlock_init(SYNCH), rw_rdlock(SYNCH), rw_trywrlock(SYNCH), rw_unlock(SYNCH), rw_wrlock(SYNCH)