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)