SEM_GETVALUE(3C) Standard C Library Functions SEM_GETVALUE(3C)

NAME

sem_getvalue - get the value of a semaphore

SYNOPSIS

#include <semaphore.h>

int sem_getvalue(sem_t *restrict sem, int *restrict sval);

DESCRIPTION

The sem_getvalue() function updates the location referenced by the sval
argument to have the value of the semaphore referenced by sem without
affecting the state of the semaphore. The updated value represents an
actual semaphore value that occurred at some unspecified time during the
call, but it need not be the actual value of the semaphore when it is
returned to the calling process.


If sem is locked, then the value returned by sem_getvalue() is either
zero or a negative number whose absolute value represents the number of
processes waiting for the semaphore at some unspecified time during the
call.


The value set in sval may be 0 or positive. If sval is 0, there may be
other processes (or LWPs or threads) waiting for the semaphore; if sval
is positive, no process is waiting.

RETURN VALUES

Upon successful completion, sem_getvalue() returns 0. Otherwise, it
returns -1 and sets errno to indicate the error.

ERRORS

The sem_getvalue() function will fail if:

EINVAL
The sem argument does not refer to a valid semaphore.


ENOSYS
The sem_getvalue() function is not supported by the system.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+

SEE ALSO

semctl(2), semget(2), semop(2), sem_post(3C), sem_wait(3C),
attributes(7), standards(7)


February 5, 2008 SEM_GETVALUE(3C)