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pthread_mutex_timedlock.3p (6617B)

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.TH PTHREAD_MUTEX_TIMEDLOCK "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH 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.
.\"
.SH NAME
pthread_mutex_timedlock
\(em lock a mutex
.SH SYNOPSIS
.LP
.nf
#include <pthread.h>
#include <time.h>
.P
int pthread_mutex_timedlock(pthread_mutex_t *restrict \fImutex\fP,
    const struct timespec *restrict \fIabstime\fP);
.fi
.SH DESCRIPTION
The
\fIpthread_mutex_timedlock\fR()
function shall lock the mutex object referenced by
.IR mutex .
If the mutex is already locked, the calling thread shall block
until the mutex becomes available as in the
\fIpthread_mutex_lock\fR()
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.
.P
The timeout shall expire when the absolute time specified by
.IR abstime
passes, as measured by the clock on which timeouts are based (that is,
when the value of that clock equals or exceeds
.IR abstime ),
or if the absolute time specified by
.IR abstime
has already been passed at the time of the call.
.P
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
.BR timespec
data type is defined in the
.IR <time.h> 
header.
.P
Under no circumstance shall the function fail with a timeout if the
mutex can be locked immediately. The validity of the
.IR abstime
parameter need not be checked if the mutex can be locked immediately.
.P
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.
.P
If
.IR mutex
is a robust mutex and the process containing the owning thread
terminated while holding the mutex lock, a call to
\fIpthread_mutex_timedlock\fR()
shall return the error value
.BR [EOWNERDEAD] .
If
.IR mutex
is a robust mutex and the owning thread terminated while holding the
mutex lock, a call to
\fIpthread_mutex_timedlock\fR()
may return the error value
.BR [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
\fIpthread_mutex_consistent\fR().
If the application is unable to recover the state, it should unlock the
mutex without a prior call to
\fIpthread_mutex_consistent\fR(),
after which the mutex is marked permanently unusable.
.P
If
.IR mutex
does not refer to an initialized mutex object, the behavior is undefined.
.SH "RETURN VALUE"
If successful, the
\fIpthread_mutex_timedlock\fR()
function shall return zero; otherwise, an error number shall be
returned to indicate the error.
.SH ERRORS
The
\fIpthread_mutex_timedlock\fR()
function shall fail if:
.TP
.BR EAGAIN
The mutex could not be acquired because the maximum number of recursive
locks for
.IR mutex
has been exceeded.
.TP
.BR EDEADLK
The mutex type is PTHREAD_MUTEX_ERRORCHECK and the current
thread already owns the mutex.
.TP
.BR 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.
.TP
.BR EINVAL
The process or thread would have blocked, and the
.IR abstime
parameter specified a nanoseconds field value less than zero or greater
than or equal to 1\|000 million.
.TP
.BR ENOTRECOVERABLE
.br
The state protected by the mutex is not recoverable.
.TP
.BR EOWNERDEAD
.br
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.
.TP
.BR ETIMEDOUT
The mutex could not be locked before the specified timeout expired.
.P
The
\fIpthread_mutex_timedlock\fR()
function may fail if:
.TP
.BR EDEADLK
A deadlock condition was detected.
.TP
.BR EOWNERDEAD
.br
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.
.P
This function shall not return an error code of
.BR [EINTR] .
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "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
.BR [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.
.SH RATIONALE
Refer to
.IR "\fIpthread_mutex_lock\fR\^(\|)".
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIpthread_mutex_destroy\fR\^(\|)",
.IR "\fIpthread_mutex_lock\fR\^(\|)",
.IR "\fItime\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 4.12" ", " "Memory Synchronization",
.IR "\fB<pthread.h>\fP",
.IR "\fB<time.h>\fP"
.\"
.SH 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 .
.PP
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 .