Semaphore example

semaphore.php

//Semaphore properties
$key         = 1111; // Key can be any unique number
$max         = 1; // Max number of connections
$permissions = 0666; // default permissions
$autoRelease = 1; // To keep from a deadlock
 
// Begin Semaphore locking
$semaphore = sem_get( $key, $max, $permissions, $autoRelease );
if( !$semaphore ) {
	// Probably best to log vs. error message. But should exit or return to prevent execution if we can't get the semaphore. 
     echo "Something went wrong. Could not access semaphore.\n";
     exit;
}
sem_acquire($semaphore);
// If we get to here then the below code will execute. 

// Code to execute goes here

// Release the semaphore lock so the next process can run. 
sem_release($semaphore);