int sem_wait (
int sem_trywait (
The sem_wait function locks the semaphore referenced by sem by performing a semaphore lock operation on it. If the semaphore value is zero, the sem_wait function blocks until it either locks the semaphore or is interrupted by a signal.
The sem_trywait function locks a semaphore only if the semaphore is currently not locked. If the semaphore value is zero, the sem_trywait function returns without locking the semaphore.
These functions help ensure that the resource associated with the semaphore cannot be accessed by other processes. The semaphore remains locked until the process unlocks it with a call to the sem_post function.
Use the sem_wait function instead of the sem_trywait function if the process should wait for access to the semaphore.
If the sem_wait or sem_trywait function returns successfully, a value of 0 is returned and the function executes the semaphore lock operation.
On an unsuccessful call, a value of -1 is returned and errno is set to indicate that an error occurred. The state of the semaphore remains unchanged.
The sem_wait and sem_trywait functions fail under the following conditions:
Functions: sem_post(3) delim off