mutex-js

Provides a promise-based mechanism for locking around code which requires synchronization (i.e. you may want to synchronize functions that span multiple iterations of the event loop).

Install

npm install --save mutex-js

Getting started

const Mutex = requires('mutex-js');
 
const mutex = new Mutex();
mutex.lock(() => {...});

Example

Below, we call an async function run several times with different args (the calls will run in parallel). The function reads data from a file, appends the input to the data and finally writes the modified data back to the file. Without synchronization, each call to run may overlap the results of the previous one. Wrapping the function implementation in a locking mechanism ensures that only one call is executing the critical section at a time.

const mutex = new Mutex();
 
// reads file, returns a promise with file data
const readFromFile = () => {...}
// appends arg to data, returns a promise with modified data
const appendData = (data, arg) => {...}
// writes data to file, returns a promise
const writeToFile = (data) => {...}
 
const run = (arg) =>
  mutex.lock(
    readFromFile()
    .then(data => appendData(data, arg))
    .then(writeToFile)
  );
 
Promise.all([
  run('foo'),
  run('bar')
])
.then(...)
.catch(...)