Get the value of a named or unnamed semaphore
Synopsis:
#include <semaphore.h>
int sem_getvalue( sem_t * sem,
int * value );
Arguments:
- sem
- A pointer to the sem_t object for the semaphore whose
value you want to get.
- value
- A pointer to a location where the function can store the semaphore's value.
A positive value indicates the number of semaphore wait operations (e.g.,
sem_wait())
that will return without blocking.
A zero or negative value indicates that any subsequent semaphore wait operations will block.
For the unnamed
(sem_init())
semaphore implementation, a negative value represents the number of threads currently blocked waiting
on the semaphore.
Library:
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
Description:
The sem_getvalue() function takes a snapshot of the value of the
semaphore, sem, and stores it in value. This
value can change at any time, and is guaranteed valid only at some
point in the sem_getvalue() call.
This function is provided for debugging semaphore code.
Returns:
- 0
- Success.
- -1
- An error occurred
(errno is set).
Errors:
- EINVAL
- Invalid semaphore descriptor sem.
Classification:
POSIX 1003.1
| Safety: |
|
|---|
| Cancellation point |
No |
| Interrupt handler |
No |
| Signal handler |
Yes |
| Thread |
Yes |