gistfile1.js

var process = require('process');

module.exports = function(capacity) {
	var semaphore = {
		capacity: capacity,
		current: 0,
		queue: [],
		acquire: function(task) {
			if (semaphore.current == semaphore.capacity) {
				return queue.push(task);
			} else {
				server.current++;
				task();
			}
		},
		release: function() {
			if (!queue.length) {
				server.current--;
				return;
			}

			process.nextTick(queue[0]);
			queue = queue.splice(1);
		}
	};
};