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man pages section 2: System Calls

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Updated: Thursday, June 13, 2019
 
 

_lwp_sema_wait(2)

Name

_lwp_sema_wait, _lwp_sema_trywait, _lwp_sema_init, _lwp_sema_post - semaphore operations

Synopsis

#include <sys/lwp.h>

int _lwp_sema_wait(lwp_sema_t *sema);
int _lwp_sema_trywait(lwp_sema_t *sema);
int _lwp_sema_init(lwp_sema_t *sema, int count);
int _lwp_sema_post(lwp_sema_t *sema);

Description

Conceptually, a semaphore is an non-negative integer count that is atomically incremented and decremented. Typically this represents the number of resources available. The _lwp_sema_init () function initializes the count, _lwp_sema_post() atomically increments the count, and _lwp_sema_wait() waits for the count to become greater than 0 and then atomically decrements it.

LWP semaphores must be initialized before use. The _lwp_sema_init() function initializes the count associated with the LWP semaphore pointed to by sema to count.

The _lwp_sema_wait() function blocks the calling LWP until the semaphore count becomes greater than 0 and then atomically decrements it.

The _lwp_sema_trywait() function atomically decrements the count if it is greater than zero. Otherwise it returns an error.

The _lwp_sema_post() function atomically increments the semaphore count. If there are any LWPs blocked on the semaphore, one is unblocked.

Return Values

Upon successful completion, 0 is returned. A non-zero value indicates an error.

Errors

The _lwp_sema_init(), _lwp_sema_trywait(), _lwp_sema_wait(), and _lwp_sema_post() functions will fail if:

EINVAL

The sema argument points to an invalid semaphore.

EFAULT

The sema argument points to an illegal address.

The _lwp_sema_wait() function will fail if:

EINTR

The function execution was interrupted by a signal or fork(2).

The _lwp_sema_trywait() function will fail if:

EBUSY

The function was called on a semaphore with a zero count.

The _lwp_sema_post() function will fail if:

EOVERFLOW

The value of the sema argument exceeds SEM_VALUE_MAX .

See Also

fork(2)