sem.h File Reference

Asterisk semaphore API. More...

#include "asterisk/lock.h"
#include <limits.h>

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Data Structures
struct	ast_sem

Macros
#define	AST_SEM_VALUE_MAX   INT_MAX

Functions
int	ast_sem_destroy (struct ast_sem *sem)
	Destroy a semaphore. More...
int	ast_sem_getvalue (struct ast_sem *sem, int *sval)
	Gets the current value of the semaphore. More...
int	ast_sem_init (struct ast_sem *sem, int pshared, unsigned int value)
	Initialize a semaphore. More...
int	ast_sem_post (struct ast_sem *sem)
	Increments the semaphore, unblocking a waiter if necessary. More...
int	ast_sem_timedwait (struct ast_sem *sem, const struct timespec *abs_timeout)
	Decrements the semaphore, waiting until abs_timeout. More...
int	ast_sem_wait (struct ast_sem *sem)
	Decrements the semaphore. More...

Detailed Description

Asterisk semaphore API.

This API is a thin wrapper around the POSIX semaphore API (when available), so see the POSIX documentation for further details.

Definition in file sem.h.

Macro Definition Documentation

AST_SEM_VALUE_MAX

#define AST_SEM_VALUE_MAX   INT_MAX

Definition at line 92 of file sem.h.

Function Documentation

ast_sem_destroy()

int ast_sem_destroy

(

struct ast_sem *

sem

)

Destroy a semaphore.

Destroying a semaphore that other threads are currently blocked on produces undefined behavior.

Parameters

sem	Semaphore to destroy.

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by bridge_sync_cleanup(), and default_listener_pvt_destroy().

ast_sem_getvalue()

int ast_sem_getvalue	(	struct ast_sem *	sem,
		int *	sval
	)

Gets the current value of the semaphore.

If threads are blocked on this semaphore, POSIX allows the return value to be either 0 or a negative number whose absolute value is the number of threads blocked. Don't assume that it will give you one or the other; Asterisk has been ported to just about everything.

Parameters

	sem	Semaphore to query.
[out]	sval	Output value.

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by default_tps_processing_function().

ast_sem_init()

int ast_sem_init	(	struct ast_sem *	sem,
		int	pshared,
		unsigned int	value
	)

Initialize a semaphore.

Parameters

sem	Semaphore to initialize.
pshared	Pass true (nonzero) to share this thread between processes. Not be supported on all platforms, so be wary! But leave the parameter, to be compatible with the POSIX ABI in case we need to add support in the future.
value	Initial value of the semaphore.

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by bridge_sync_init(), and default_listener_pvt_alloc().

ast_sem_post()

int ast_sem_post

(

struct ast_sem *

sem

)

Increments the semaphore, unblocking a waiter if necessary.

Parameters

sem	Semaphore to increment.

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by bridge_sync_signal(), and default_task_pushed().

ast_sem_timedwait()

int ast_sem_timedwait	(	struct ast_sem *	sem,
		const struct timespec *	abs_timeout
	)

Decrements the semaphore, waiting until abs_timeout.

If the semaphore's current value is zero, this function blocks until another thread posts (ast_sem_post()) to the semaphore (or is interrupted by a signal handler, which sets errno to EINTR).

Parameters

sem	Semaphore to decrement.
abs_timeout

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by bridge_sync_wait().

ast_sem_wait()

int ast_sem_wait

(

struct ast_sem *

sem

)

Decrements the semaphore.

If the semaphore's current value is zero, this function blocks until another thread posts (ast_sem_post()) to the semaphore (or is interrupted by a signal handler, which sets errno to EINTR).

Parameters

sem	Semaphore to decrement.

Return values

0	on success.
-1	on error, errno set to indicate error.

Referenced by default_tps_processing_function().