semaphore.h File Reference

Semaphores. More...

#include "FreeRTOS_POSIX/time.h"
#include "FreeRTOS_POSIX_types.h"

Go to the source code of this file.

Typedefs
typedef PosixSemType_t	sem_t
	Semaphore type.

Functions
int	sem_destroy (sem_t *sem)
	Destroy an unnamed semaphore. More...
int	sem_getvalue (sem_t *sem, int *sval)
	Get the value of a semaphore. More...
int	sem_init (sem_t *sem, int pshared, unsigned value)
	Initialize an unnamed semaphore. More...
int	sem_post (sem_t *sem)
	Unlock a semaphore. More...
int	sem_timedwait (sem_t *sem, const struct timespec *abstime)
	Lock a semaphore with timeout. More...
int	sem_trywait (sem_t *sem)
	Lock a semaphore if available. More...
int	sem_wait (sem_t *sem)
	Lock a semaphore. More...

Detailed Description

Semaphores.

http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/semaphore.h.html

Function Documentation

sem_destroy()

int sem_destroy

(

sem_t *

sem

)

Destroy an unnamed semaphore.

See also

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

Return values

0	- upon successful completion

Note

Semaphore is destroyed regardless of whether there is any thread currently blocked on this semaphore.

sem_getvalue()

int sem_getvalue	(	sem_t *	sem,
		int *	sval
	)

Get the value of a semaphore.

See also

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

Return values

0	- Upon successful completion

Note

If sem is locked, then the object to which sval points is set to zero.

sem_init()

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

Initialize an unnamed semaphore.

See also

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

Note

pshared is ignored. Semaphores will always be considered "shared".

Return values

0	- upon successful completion
-1	- otherwise. System error variable errno is also set in this case.

Side Effects Possible errno values

EINVAL - The value argument exceeds {SEM_VALUE_MAX}.
ENOSPC - A resource required to initialize the semaphore has been exhausted.

sem_post()

int sem_post

(

sem_t *

sem

)

Unlock a semaphore.

See also

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

Return values

0	- upon successful completion

sem_timedwait()

int sem_timedwait	(	sem_t *	sem,
		const struct timespec *	abstime
	)

Lock a semaphore with timeout.

See also

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

Return values

0	- upon successful completion
-1	- otherwise. System error variable errno is also set in this case.

Side Effects Possible errno values

EINVAL - 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.

Note

Deadlock detection is not implemented.

sem_trywait()

int sem_trywait

(

sem_t *

sem

)

Lock a semaphore if available.

See also

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

Return values

0	- upon successful completion
-1	- otherwise. System error variable errno is also set in this case.

Side Effects Possible errno values

EAGAIN - The semaphore was already locked, so it cannot be immediately locked by the sem_trywait() operation.

sem_wait()

int sem_wait

(

sem_t *

sem

)

Lock a semaphore.

See also

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

Return values

0	- upon successful completion
-1	- otherwise. System error variable errno is also set in this case.

Note

Deadlock detection is not implemented.