include/semaphore.h File Reference

Interface: POSIX 1003.1b semaphores for task synchronization. More...

#include <config.h>
#include <time.h>
#include <atomic.h>

Include dependency graph for semaphore.h:

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Defines
#define	EAGAIN   0xffff
	the error code
Typedefs
typedef atomic_t	sem_t
	the semaphore data-type
Functions
int	sem_init (sem_t *sem, int pshared, unsigned int value)
	Initialize a semaphore.
int	sem_wait (sem_t *sem)
	Wait for semaphore (blocking).
int	sem_timedwait (sem_t *sem, const time_t abs_timeout)
	Wait for semaphore (blocking with timeout).
int	sem_trywait (sem_t *sem)
	Try a wait for semaphore (non-blocking).
int	sem_post (sem_t *sem)
	Post a semaphore.
int	sem_getvalue (sem_t *sem, int *sval)
	Get the semaphore value.
int	sem_destroy (sem_t *sem)
	We're done with the semaphore, destroy it.

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Detailed Description

Interface: POSIX 1003.1b semaphores for task synchronization.

Author:

Markus L. Noga <markus@noga.de>

Definition in file semaphore.h.

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Define Documentation

#define EAGAIN   0xffff

the error code Definition at line 48 of file semaphore.h.

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Typedef Documentation

typedef atomic_t sem_t

the semaphore data-type Definition at line 46 of file semaphore.h. Referenced by sem_init().

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Function Documentation

int sem_destroy (  sem_t *  sem  )  [inline]

We're done with the semaphore, destroy it. sem_destroy() destroys a semaphore object, freeing the resources it might hold. Parameters: sem  a pointer to the semaphore to be destroyed Returns: (always returns 0) NOTE: No tasks should be waiting on the semaphore at the time sem_destroy is called. Definition at line 147 of file semaphore.h.

int sem_getvalue (  sem_t *  sem, int *  sval )  [inline]

Get the semaphore value. Definition at line 132 of file semaphore.h.

int sem_init (  sem_t *  sem, int  pshared, unsigned int  value )  [inline]

Initialize a semaphore. sem_init() initializes the semaphore object pointed to by {sem} by setting its internal count to {value} Parameters: sem  a pointer to the semaphore to be initialized value  the initial value for count pshared  (this argument is ignored) Returns: (always 0) Definition at line 64 of file semaphore.h. References sem_t.

int sem_post (  sem_t *  sem  )  [inline]

Post a semaphore. sem_post() atomically increases the count of the semaphore pointed to by {sem}. This function never blocks and can safely be used in asynchronous signal handlers. Parameters: sem  a pointer to the semaphore to be signaled Returns: (always returns 0) Definition at line 123 of file semaphore.h. References atomic_inc().

int sem_timedwait (  sem_t *  sem, const time_t  abs_timeout )

Wait for semaphore (blocking with timeout). sem_timedwait() suspends the calleing task until either the semaphore pointed to by {sem} has non-zero count or the given absolute timeout passed. Note the timeout is an ABSOLUTE time not relative (yes the standard is that stupid); so if you want a relative waiting time, call the function with get_system_up_time() + relativeTime. If the semaphore reached a non-zero count its value is then atomically decreased. Parameters: sem  a pointer to the semaphore on which to wait abs_timeout  the absolute timeout of this operation. If the semaphore cannot be locked up to this time, this function returns. Returns: 0 if the semaphore could successfully be locked; -1 if the timeout has been reached. Note: in IEEE 1003.1, the timeout is passed as a struct timeval not a time_t.

int sem_trywait (  sem_t *  sem  )

Try a wait for semaphore (non-blocking). sem_trywait() is a non-blocking variant of sem_wait(). If the semaphore pointed to by {sem} has non-zero count, the count is atomically decreased and sem_trywait immediately returns 0. If the semaphore count is zero, sem_trywait immediately returns with error EAGAIN. Parameters: sem  a pointer to the semaphore on which to attempt a wait Returns: 0 if decremented the semaphore or EAGAIN if can't NOTE: this is IRQ handler safe.

int sem_wait (  sem_t *  sem  )

Wait for semaphore (blocking). sem_wait() suspends the calling task until the semaphore pointed to by {sem} has non-zero count. It then atomically decreases the semaphore count. Parameters: sem  a pointer to the semaphore on which to wait Returns: 0 if wait returned immediately, EAGAIN if task did have to wait for the semaphore.

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