NAME

pthread_mutex_clocklock, pthread_mutex_timedlock — lock a mutex

SYNOPSIS

#include <pthread.h>

int pthread_mutex_clocklock(pthread_mutex_t *restrict mutex,
       clockid_t clock_id, const struct timespec *restrict abstime);
int pthread_mutex_timedlock(pthread_mutex_t *restrict mutex,
       const struct timespec *restrict abstime);


DESCRIPTION

The pthread_mutex_clocklock() and pthread_mutex_timedlock() functions 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.

For pthread_mutex_timedlock(), the timeout shall be based on the CLOCK_REALTIME clock. For pthread_mutex_clocklock(), the timeout shall be based on the clock specified by the clock_id argument. The resolution of the timeout shall be the resolution of the clock on which it is based. Implementations shall support passing CLOCK_REALTIME and CLOCK_MONOTONIC to pthread_mutex_clocklock() as the clock_id argument.

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.

^[RPI|TPI] 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_clocklock() or 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_clocklock() or 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_clocklock() and pthread_mutex_timedlock() functions shall return zero; otherwise, an error number shall be returned to indicate the error.

ERRORS

The pthread_mutex_clocklock() and pthread_mutex_timedlock() functions shall fail if:

[EAGAIN]

The mutex could not be acquired because the maximum number of recursive locks for mutex has been exceeded.

[EAGAIN]

The mutex is a robust mutex and the system resources available for robust mutexes owned would be 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 either the abstime parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million, or the pthread_mutex_clocklock() function was passed an invalid or unsupported clock_id value.

[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_clocklock() and pthread_mutex_timedlock() functions 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.

These functions shall not return an error code of [EINTR].

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

XBD 4.15.2 Memory Synchronization, <pthread.h>, <time.h>

CHANGE HISTORY

First released in Issue 6. Derived from IEEE Std 1003.1d-1999.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/99 is applied, marking the last paragraph in the DESCRIPTION as part of the Thread Priority Inheritance option.

IEEE Std 1003.1-2001/Cor 2-2004, item XSH/TC2/D6/100 is applied, updating the ERRORS section so that the [EDEADLK] error includes detection of a deadlock condition.

Issue 7

Changes are made from The Open Group Technical Standard, 2006, Extended API Set Part 3.

The pthread_mutex_timedlock() function is moved from the Timeouts option to the Base.

Functionality relating to the Timers option is moved to the Base.

The DESCRIPTION is updated to clarify the behavior when mutex does not refer to an initialized mutex.

The ERRORS section is updated to account properly for all of the various mutex types.

Issue 8

Austin Group Defect 354 is applied, adding the [EAGAIN] error for exceeding system resources available for robust mutexes owned.

Austin Group Defect 592 is applied, removing text relating to <time.h> from the SYNOPSIS and DESCRIPTION sections.

Austin Group Defects 1216 and 1472 are applied, adding pthread_mutex_clocklock().