NAME
pthread_rwlock_trywrlock, pthread_rwlock_wrlock - lock a read-write
lock object for writing
SYNOPSIS
#include <pthread.h>
int pthread_rwlock_trywrlock(pthread_rwlock_t *rwlock);
int pthread_rwlock_wrlock(pthread_rwlock_t *rwlock);
DESCRIPTION
The pthread_rwlock_trywrlock() function shall apply a write lock like
the pthread_rwlock_wrlock() function, with the exception that the
function shall fail if any thread currently holds rwlock (for reading
or writing).
The pthread_rwlock_wrlock() function shall apply a write lock to the
read-write lock referenced by rwlock. The calling thread acquires the
write lock if no other thread (reader or writer) holds the read-write
lock rwlock. Otherwise, the thread shall block until it can acquire the
lock. The calling thread may deadlock if at the time the call is made
it holds the read-write lock (whether a read or write lock).
Implementations may favor writers over readers to avoid writer
starvation.
Results are undefined if any of these functions are called with an
uninitialized read-write lock.
If a signal is delivered to a thread waiting for a read-write lock for
writing, upon return from the signal handler the thread resumes waiting
for the read-write lock for writing as if it was not interrupted.
RETURN VALUE
The pthread_rwlock_trywrlock() function shall return zero if the lock
for writing on the read-write lock object referenced by rwlock is
acquired. Otherwise, an error number shall be returned to indicate the
error.
If successful, the pthread_rwlock_wrlock() function shall return zero;
otherwise, an error number shall be returned to indicate the error.
ERRORS
The pthread_rwlock_trywrlock() function shall fail if:
EBUSY The read-write lock could not be acquired for writing because it
was already locked for reading or writing.
The pthread_rwlock_trywrlock() and pthread_rwlock_wrlock() functions
may fail if:
EINVAL The value specified by rwlock does not refer to an initialized
read-write lock object.
The pthread_rwlock_wrlock() function may fail if:
EDEADLK
The current thread already owns the read-write lock for writing
or reading.
These functions shall not return an error code of [EINTR].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Applications using these functions may be subject to priority
inversion, as discussed in the Base Definitions volume of
IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_rwlock_destroy() , pthread_rwlock_rdlock() ,
pthread_rwlock_timedrdlock() , pthread_rwlock_timedwrlock() ,
pthread_rwlock_tryrdlock() , pthread_rwlock_unlock() , the Base
Definitions volume of IEEE Std 1003.1-2001, <pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2003 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 6, Copyright (C) 2001-2003 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group. In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online
at http://www.opengroup.org/unix/online.html .