POSIX_SEMAPHORES

POSIX Semaphores option group. More...

Files
file	semaphore.h
	POSIX semaphores API (<semaphore.h>)

Macros
#define	SEM_FAILED   ((sem_t *) 0)
	Returned by sem_open() on failure.

Typedefs
typedef struct sys_sem	sem_t
	Semaphore object type.

Functions
int	sem_destroy (sem_t *semaphore)
	Destroy an unnamed semaphore.
int	sem_getvalue (sem_t *ZRESTRICT semaphore, int *ZRESTRICT value)
	Get the current value of a semaphore.
int	sem_init (sem_t *semaphore, int pshared, unsigned int value)
	Initialise an unnamed semaphore.
int	sem_post (sem_t *semaphore)
	Unlock a semaphore (increment its count).
int	sem_timedwait (sem_t *ZRESTRICT semaphore, struct timespec *ZRESTRICT abstime)
	Lock a semaphore with an absolute timeout.
int	sem_trywait (sem_t *semaphore)
	Try to lock a semaphore without blocking.
int	sem_wait (sem_t *semaphore)
	Lock a semaphore, blocking until it becomes available.
sem_t *	sem_open (const char *name, int oflags,...)
	Open or create a named semaphore.
int	sem_unlink (const char *name)
	Remove a named semaphore.
int	sem_close (sem_t *sem)
	Close a named semaphore.

Detailed Description

POSIX Semaphores option group.

Macro Definition Documentation

SEM_FAILED

#define SEM_FAILED   ((sem_t *) 0)

Returned by sem_open() on failure.

Definition at line 31 of file semaphore.h.

Typedef Documentation

sem_t

typedef struct sys_sem sem_t

Semaphore object type.

A sem_t may live in any memory the calling thread can access (static, stack, or heap). Sharing one between threads requires memory every participant can access: with CONFIG_USERSPACE enabled, a user thread's stack is private to it, so a shared sem_t belongs in static storage, a common memory partition, or the malloc arena.

Definition at line 44 of file semaphore.h.

Function Documentation

sem_close()

int sem_close

(

sem_t *

sem

)

Close a named semaphore.

Parameters

sem	Semaphore to close.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_close.html

sem_destroy()

int sem_destroy

(

sem_t *

semaphore

)

Destroy an unnamed semaphore.

Parameters

semaphore

Semaphore to destroy.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_destroy.html

sem_getvalue()

int sem_getvalue	(	sem_t *ZRESTRICT	semaphore,
		int *ZRESTRICT	value
	)

Get the current value of a semaphore.

Parameters

semaphore	Semaphore to query.
value	Output: current count (implementation may report 0 if waiters are present).

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_getvalue.html

sem_init()

int sem_init	(	sem_t *	semaphore,
		int	pshared,
		unsigned int	value
	)

Initialise an unnamed semaphore.

Parameters

semaphore	Semaphore to initialise.
pshared	Non-zero if the semaphore is shared between processes.
value	Initial count (must be <= SEM_VALUE_MAX).

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_init.html

sem_open()

sem_t * sem_open	(	const char *	name,
		int	oflags,
			...
	)

Open or create a named semaphore.

Parameters

name	Semaphore name (implementation-defined path).
oflags	Flags: O_CREAT, O_EXCL.
...	If O_CREAT is set: mode_t mode, unsigned int value.

Returns

Pointer to the semaphore on success, or SEM_FAILED on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_open.html

sem_post()

int sem_post

(

sem_t *

semaphore

)

Unlock a semaphore (increment its count).

Parameters

semaphore

Semaphore to post.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_post.html

sem_timedwait()

int sem_timedwait	(	sem_t *ZRESTRICT	semaphore,
		struct timespec *ZRESTRICT	abstime
	)

Lock a semaphore with an absolute timeout.

Parameters

semaphore	Semaphore to wait on.
abstime	Absolute timeout (CLOCK_REALTIME).

Returns

0 on success, -1 with errno = ETIMEDOUT on timeout, or -1 with errno set on another failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_timedwait.html

sem_trywait()

int sem_trywait

(

sem_t *

semaphore

)

Try to lock a semaphore without blocking.

Parameters

semaphore

Semaphore to try.

Returns

0 on success, -1 with errno = EAGAIN if the count is zero, or -1 with errno set on another failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_trywait.html

sem_unlink()

int sem_unlink

(

const char *

name

)

Remove a named semaphore.

Parameters

name	Semaphore name.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_unlink.html

sem_wait()

int sem_wait

(

sem_t *

semaphore

)

Lock a semaphore, blocking until it becomes available.

Parameters

semaphore

Semaphore to wait on.

Returns

0 on success, or -1 with errno set on failure.

See also

https://pubs.opengroup.org/onlinepubs/9699919799/functions/sem_wait.html