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

> semaphore.h - semaphores (REALTIME)

#### SYNOPSIS

> `[SEM] #include <semaphore.h>`

#### DESCRIPTION

> The <semaphore.h> header shall define the sem_t type, used in performing semaphore operations. The semaphore may be implemented using a file descriptor, in which case applications are able to open up at least a total of {OPEN_MAX} files and semaphores. The symbol SEM_FAILED shall be defined (see sem_open()).

> The following shall be declared as functions and may also be defined as macros. Function prototypes shall be provided.

>     int    sem_close(sem_t *);
>     int    sem_destroy(sem_t *);
>     int    sem_getvalue(sem_t *restrict, int *restrict);
>     int    sem_init(sem_t *, int, unsigned);
>     sem_t *sem_open(const char *, int, ...);
>     int    sem_post(sem_t *);
>     [TMO]
>     int    sem_timedwait(sem_t *restrict, const struct timespec *restrict);

>     int    sem_trywait(sem_t *);
>     int    sem_unlink(const char *);
>     int    sem_wait(sem_t *);

> Inclusion of the <semaphore.h> header may make visible symbols defined in the headers <fcntl.h> and <sys/types.h>.

The following sections are informative.

#### APPLICATION USAGE

> None.

#### RATIONALE

> None.

#### FUTURE DIRECTIONS

> None.

#### SEE ALSO

> <fcntl.h>, <sys/types.h>, the System Interfaces volume of IEEE Std 1003.1-2001, sem_destroy(), sem_getvalue(), sem_init(), sem_open(), sem_post(), sem_timedwait(), sem_trywait(), sem_unlink(), sem_wait()

#### CHANGE HISTORY

> First released in Issue 5. Included for alignment with the POSIX Realtime Extension.

#### Issue 6

> The <semaphore.h> header is marked as part of the Semaphores option.

> The Open Group Corrigendum U021/3 is applied, adding a description of SEM_FAILED.

> The sem_timedwait() function is added for alignment with IEEE Std 1003.1d-1999.

> The restrict keyword is added to the prototypes for sem_getvalue() and sem_timedwait().

End of informative text.

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