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Increment a semaphore
#include <semaphore.h>
int sem_post( sem_t * sem );
- sem
- A pointer to the sem_t object for the semaphore whose
value you want to increment.
libc
Use the -l c option to
qcc
to link against this library.
This library is usually included automatically.
The sem_post() function increments the semaphore referenced by
the sem argument. If any processes are currently blocked
waiting for the semaphore, then one of these processes will
return successfully from its call to sem_wait.
The process to be unblocked is determined in accordance with the
scheduling policies in effect for the blocked processes. The
highest priority waiting process is unblocked, and if there is
more than one highest priority process blocked waiting for the
semaphore, then the highest priority process that has been
waiting the longest is unblocked.
The sem_post() function is reentrant with respect to signals, and
can be called from a signal handler.
- 0
- Success.
- -1
- An error occurred (errno is set).
- EINVAL
- Invalid semaphore descriptor sem.
- ENOSYS
- The sem_post() function isn't supported.
POSIX 1003.1 SEM
Safety: | |
Cancellation point |
No |
Interrupt handler |
No |
Signal handler |
Yes |
Thread |
Yes |
errno,
sem_destroy(),
sem_init(),
sem_trywait(),
sem_wait()
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