The Open Group Base Specifications Issue 6
IEEE Std 1003.1, 2004 Edition
Copyright © 2001-2004 The IEEE and The Open Group, All Rights reserved.

#### NAME

> sem_timedwait - lock a semaphore (ADVANCED REALTIME)

#### SYNOPSIS

> ``[SEM TMO] #include <semaphore.h>
> #include <time.h>
> int sem_timedwait(sem_t *restrict` sem`,
> const struct timespec *restrict` abs_timeout`);``
> `
> `

#### DESCRIPTION

> The sem_timedwait() function shall lock the semaphore referenced by sem as in the sem_wait() function. However, if the semaphore cannot be locked without waiting for another process or thread to unlock the semaphore by performing a sem_post() function, this wait shall be terminated when the specified timeout expires.

> The timeout shall expire when the absolute time specified by abs_timeout passes, as measured by the clock on which timeouts are based (that is, when the value of that clock equals or exceeds abs_timeout), or if the absolute time specified by abs_timeout has already been passed at the time of the call.

> [TMR] If the Timers option is supported, the timeout shall be based on the CLOCK_REALTIME clock. If the Timers option is not supported, the timeout shall be based on the system clock as returned by the time() function. The resolution of the timeout shall be the resolution of the clock on which it is based. The timespec data type is defined as a structure in the <time.h> header.

> Under no circumstance shall the function fail with a timeout if the semaphore can be locked immediately. The validity of the abs_timeout need not be checked if the semaphore can be locked immediately.

#### RETURN VALUE

> The sem_timedwait() function shall return zero if the calling process successfully performed the semaphore lock operation on the semaphore designated by sem. If the call was unsuccessful, the state of the semaphore shall be unchanged, and the function shall return a value of -1 and set errno to indicate the error.

#### ERRORS

> The sem_timedwait() function shall fail if:

> [EINVAL]
>   The process or thread would have blocked, and the abs_timeout parameter specified a nanoseconds field value less than zero or greater than or equal to 1000 million.
> [ETIMEDOUT]
>   The semaphore could not be locked before the specified timeout expired.

> The sem_timedwait() function may fail if:

> [EDEADLK]
>   A deadlock condition was detected.
> [EINTR]
>   A signal interrupted this function.
> [EINVAL]
>   The sem argument does not refer to a valid semaphore.

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.

> The sem_timedwait() function is part of the Semaphores and Timeouts options and need not be provided on all implementations.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> sem_post(), sem_trywait(), sem_wait(), semctl(), semget(), semop(), time(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.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/D6/120 is applied, updating the ERRORS section so that the [EINVAL] error becomes optional.

End of informative text.

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