Traffic

A node.js semaphore implementation.

Single node semaphore

Usage

var traffic = require('node-traffic');

traffic.enter(function criticalZone () {
// ...
traffic.leave();  
});

Example with web servers

app.post('/resource', function (req, res) {
  traffic.enter(function () {
    // DB stuff...
    traffic.leave();
    res.respond();
  });
});

Namespaced semaphores

traffic.enter('changeResource', function criticalZone () {
  // ...
  traffic.leave('changeResource');
});

Example for web servers

app.post('/resource/:id', function (req, res) {
  traffic.enter('changeResource-' + req.params.id, function () {
    // DB stuff...
    traffic.leave('changeResource-' + req.params.id);
    res.respond();
  });
});

Distributed semaphore

Traffic allows to have a distributed semaphore across multiples nodes using Zookeeper.

Configure

var config = {
  zkHost: 'localhost:2181', // host:port
  zkRoot: '/', // znode path
  zkTimeout: 4000 // 4 seconds
};
var traffic = require('node-traffic').distributed(config);
traffic.on('connectionTimeout', function (err) {
  // handle Zookeeper connection timeout
});

zkRoot will be created if it doesn't exists.

Usage

traffic.enter(function criticalZone () {
  // ...
  traffic.leave();
});

// Namespaced
traffic.enter('myNamespace', function () {
  // ...
  traffic.leave('myNamespace');
});

Note: Using namespaces creates znodes under config.zkRoot.

Don't forget to close the Zookeeper connection...

process.on('exit',function(){
  traffic.close();
});

Common patterns

If traffic fails to connect to Zookeeper you can fallback into normal semaphores.

traffic.on('connectionTimeout', function (err) {
  traffic = require('node-traffic');
});

Run tests

Install jasmine

npm install -g jasmine

Run specs

npm test
jasmine spec/semaphore_spec.js
jasmine spec/distributed_semaphore_spec.js