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PROLOG
This manual page is part of the POSIX Programmer's Manual. The Linux implementation of
this interface may differ (consult the corresponding Linux manual page for details of
Linux behavior), or the interface may not be implemented on Linux.
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_wrlock() function may fail if:
EDEADLK
A deadlock condition was detected or 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 POSIX.1‐2008, Section 3.287, Priority Inversion.
RATIONALE
If an implementation detects that the value specified by the rwlock argument to
pthread_rwlock_trywrlock() or pthread_rwlock_wrlock() does not refer to an initialized
read-write lock object, it is recommended that the function should fail and report an
[EINVAL] error.
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_rwlock_destroy(), pthread_rwlock_rdlock(), pthread_rwlock_timedrdlock(),
pthread_rwlock_timedwrlock(), pthread_rwlock_unlock()
The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority Inversion, Section
4.11, Memory Synchronization, <pthread.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2013 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/online.html .
Any typographical or formatting errors that appear in this page are most likely to have
been introduced during the conversion of the source files to man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .