react-context-mutex

A mutex implementation using React and React context. It will prevent a function from running multiple times, until you allow it to run again. Works in browser and NodeJS.

This was created because I wanted to prevent a fetch from running multiple times after implementing a custom hook in multiple components. The custom hook had a useEffect which ran the fetch function.

Install

$ npm install react-context-mutex

Demo

How to use

import { useMutex } from 'react-context-mutex';

const useFetchHook = () => {
    const MutexRunner = useMutex();
    const mutex = new MutexRunner('myUniqueKey1');

    mutex.run(async () => {
        mutex.lock();
        try {
            const response = await fetch('http://myurl');
            const data = await response.json();
            mutex.unlock();
        } catch (e) {
            mutex.unlock();
        }
    });
};

The useFetchHook hook can runs multiple times but the actual fetch is only done once. When the mutex is unlocked again, the fetch can also be executed again.

API

Create a new instance of the mutex runner:

const mutex = new MutexRunner('myUniqueKey1');

Try to run a function. If the mutex is not locked, the resolveCallback will run. If it is locked, the optional rejectCallback will run:

mutex.run(resolveCallback: () => void, rejectCallback?: () => void) => void 
/*
    Usage: mutex.run(() => { yourFunction(); });
    or: 
    mutex.run(
        () => { yourFunction(); }, 
        () => { myMutexIsLocked(); }
    );
    returns void
*/

Lock a mutex:

mutex.lock() // returns void

Unlock a mutex:

mutex.unlock() // returns void

Check if a mutex is locked:

mutex.isLocked() // returns a boolean

Behind the scenes

Behind the scenes there's an array of strings, representing the mutex keys, registered using React context. A new record is added to the array when a process should be locked. Likewise, the record is removed when the process is unlocked.

When using the mutex.run method, there's a check to see if the process is locked or not. If it is, the callback within the mutex.run is abandoned. If the provided key does not reference to a locked process, the callback is executed.

Why React context? Because that way the "mutex store" array will only be initiated once, thus able to use throughout multiple components without causing unwanted collisions.