(PHP 4, PHP 5)
sem_acquire — Acquire a semaphore
$sem_identifier
   [, bool $nowait = false
  ] )sem_acquire() by default blocks (if necessary) until the semaphore can be acquired. A process attempting to acquire a semaphore which it has already acquired will block forever if acquiring the semaphore would cause its maximum number of semaphore to be exceeded.
After processing a request, any semaphores acquired by the process but not explicitly released will be released automatically and a warning will be generated.
sem_identifier
       sem_identifier is a semaphore resource,
       obtained from sem_get().
      
nowaitSpecifies if the process shouldn't wait for the semaphore to be acquired. If set to true, the call will return false immediately if a semaphore cannot be immediately acquired.
   Returns TRUE on success or FALSE on failure.
  
| Version | Description | 
|---|---|
| 5.6.1 | The $nowaitparameter was added. |