semaphore.js

Asynchronous semaphore for Javascript.

An asynchronous semaphore limits the number of asynchronous functions running at any given time.

Installation

The component can be used as a Common JS module, an AMD module, or a global.

Install with Bower:

bower install --save semaphore.js

Install with npm:

npm install --save semaphore.js

API

Initialization

Simple semaphore creation

/* Creates a semaphore of size 3 */
var sem = new Semaphore(3);

Semaphore creation with timeout, if calling function doesn't release within timeout

/* Creates a semaphore of size 2, and if the calling function doesn't
release, auto-releases in 100 ms */
var sem = new Semaphore(2, 100);

Acquiring and releasing semaphore

The acquire method takes in a function that has a release method with it. The release method releases the semaphore the first time it is invoked. Subsequent invocations have no effect (they do not create extra semaphore capacity).

var sem = new Semaphore(2, 100);
sem.acquire(function(release) {
  // do stuff
  // release after 50 ms
  console.log("first callback acquiring");
  setTimeout(function() {
    console.log("first callback releasing");
    release();
    release(); // only the first invocation matters
  }, 150);
});

sem.acquire(function(release) {
  console.log("first callback acquiring");
  setTimeout(function() {
    console.log("first callback releasing");
    release();
  }, 1);
});

Look at example/example.js for a demo. You can run it as

node example/example.js

Testing

Install Node (which comes with npm).

Install the development dependencies:

npm install

Run the tests:

npm test