PTHREAD_MUTEX_TIMEDLOCK
Section: POSIX Programmer's Manual (3P)
Updated: 2017
Page Index
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_mutex_timedlock
--- lock a mutex
SYNOPSIS
#include <pthread.h>
#include <time.h>
int pthread_mutex_timedlock(pthread_mutex_t *restrict mutex,
const struct timespec *restrict abstime);
DESCRIPTION
The
pthread_mutex_timedlock()
function shall lock the mutex object referenced by
mutex.
If the mutex is already locked, the calling thread shall block
until the mutex becomes available as in the
pthread_mutex_lock()
function. If the mutex cannot be locked without waiting for another
thread to unlock the mutex, this wait shall be terminated when the
specified timeout expires.
The timeout shall expire when the absolute time specified by
abstime
passes, as measured by the clock on which timeouts are based (that is,
when the value of that clock equals or exceeds
abstime),
or if the absolute time specified by
abstime
has already been passed at the time of the call.
The timeout shall be based on the CLOCK_REALTIME clock.
The resolution of the timeout shall be the resolution of the clock on
which it is based. The
timespec
data type is defined in the
<time.h>
header.
Under no circumstance shall the function fail with a timeout if the
mutex can be locked immediately. The validity of the
abstime
parameter need not be checked if the mutex can be locked immediately.
As a consequence of the priority inheritance rules (for mutexes
initialized with the PRIO_INHERIT protocol), if a timed mutex wait is
terminated
because its timeout expires, the priority of the owner of the mutex
shall be adjusted as necessary to reflect the fact that this thread is
no longer among the threads waiting for the mutex.
If
mutex
is a robust mutex and the process containing the owning thread
terminated while holding the mutex lock, a call to
pthread_mutex_timedlock()
shall return the error value
[EOWNERDEAD].
If
mutex
is a robust mutex and the owning thread terminated while holding the
mutex lock, a call to
pthread_mutex_timedlock()
may return the error value
[EOWNERDEAD]
even if the process in which the owning thread resides has not
terminated. In these cases, the mutex is locked by the thread but the
state it protects is marked as inconsistent. The application should
ensure that the state is made consistent for reuse and when that is
complete call
pthread_mutex_consistent().
If the application is unable to recover the state, it should unlock the
mutex without a prior call to
pthread_mutex_consistent(),
after which the mutex is marked permanently unusable.
If
mutex
does not refer to an initialized mutex object, the behavior is undefined.
RETURN VALUE
If successful, the
pthread_mutex_timedlock()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
ERRORS
The
pthread_mutex_timedlock()
function shall fail if:
- EAGAIN
-
The mutex could not be acquired because the maximum number of recursive
locks for
mutex
has been exceeded.
- EDEADLK
-
The mutex type is PTHREAD_MUTEX_ERRORCHECK and the current
thread already owns the mutex.
- EINVAL
-
The mutex was created with the protocol attribute having the value
PTHREAD_PRIO_PROTECT and the calling thread's priority is higher than
the mutex' current priority ceiling.
- EINVAL
-
The process or thread would have blocked, and the
abstime
parameter specified a nanoseconds field value less than zero or greater
than or equal to 1000 million.
- ENOTRECOVERABLE
-
The state protected by the mutex is not recoverable.
- EOWNERDEAD
-
The mutex is a robust mutex and the process containing the previous
owning thread terminated while holding the mutex lock. The mutex lock
shall be acquired by the calling thread and it is up to the new owner
to make the state consistent.
- ETIMEDOUT
-
The mutex could not be locked before the specified timeout expired.
The
pthread_mutex_timedlock()
function may fail if:
- EDEADLK
-
A deadlock condition was detected.
- EOWNERDEAD
-
The mutex is a robust mutex and the previous owning thread terminated
while holding the mutex lock. The mutex lock shall be acquired by the
calling thread and it is up to the new owner to make the state consistent.
This function shall not return an error code of
[EINTR].
The following sections are informative.
EXAMPLES
None.
APPLICATION USAGE
Applications that have assumed that non-zero return values are errors
will need updating for use with robust mutexes, since a valid return
for a thread acquiring a mutex which is protecting a currently
inconsistent state is
[EOWNERDEAD].
Applications that do not check the error returns, due to ruling out the
possibility of such errors arising, should not use robust mutexes. If
an application is supposed to work with normal and robust mutexes, it
should check all return values for error conditions and if necessary
take appropriate action.
RATIONALE
Refer to
pthread_mutex_lock().
FUTURE DIRECTIONS
None.
SEE ALSO
pthread_mutex_destroy(),
pthread_mutex_lock(),
time()
The Base Definitions volume of POSIX.1-2017,
Section 4.12, Memory Synchronization,
<pthread.h>,
<time.h>
COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 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 .
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 .