SEM_GETVALUE(3C) Standard C Library Functions SEM_GETVALUE(3C)
sem_getvalue - get the value of a semaphore
#include <semaphore.h>
int sem_getvalue(sem_t *restrict sem, int *restrict sval);
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.
Upon successful completion, sem_getvalue() returns 0. Otherwise, it
returns -1 and sets errno to indicate the error.
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.
See attributes(7) for descriptions of the following attributes:
+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Committed |
+--------------------+-------------------+
|MT-Level | MT-Safe |
+--------------------+-------------------+
|Standard | See standards(7). |
+--------------------+-------------------+
semctl(2), semget(2), semop(2), sem_post(3C), sem_wait(3C),
attributes(7), standards(7)
February 5, 2008 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)