_LWP_SEMA_WAIT(2) System Calls _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)

May 8, 1998 _LWP_SEMA_WAIT(2)