_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)

SunOS 5.11							    8 May 1998							 _lwp_sema_wait(2)