Lockal

Lockal is a bespoke localStorage based locking system, allowing atomic* actions to be performed across tabs and browser windows.

Usage

var Lock = require('lockal').Lock;
var lock = new Lock('myAtomicAction');

lock.acquire(function (err, unlock) {
    if (err) {
        console.log('Unable to get lock!');
    } else{
        doSomethingAtomically();
        unlock();
    }
});

* This is not atomic in the true sense, of course, since Javascript doesn't provide the kind of concurrency necessary to ensure entirely thread-safe operations across multiple tabs. This is as close as we can get, though, and should be "good enough" for 99% of use cases.

lockal.isEnabled

A boolean to indicate whether localStorage is available on the current platform. Attempting to instantiate a Lock class if isEnabled is false will result in an error being thrown.

Class: lockal.Lock(key[, options])

Each Lock class is used to interact with a single lock "key". Options usually need not be given, but may be useful if you want to tweak some internals.

• lockCheck - Time to wait after a lock to ensure it's not going to be written over by another tab.
• retryInterval - Duration between retries on mustAcquire.
• maintainInterval - How often the maintainer should touch the lock.

lock.acquire([ttl][, callback])

Attempts to lock on the key. The lock will remain in place for the TTL, given in milliseconds, or until explicitly unlocked.

Callback will be called with:

• an Error as its first argument if a lock wasn't made,
• otherwise, an unlock function as its second argument,
• and a maintain function as its third argument.

lock.mustAcquire([ttl][, callback])

Similar to lock.acquire, but only runs the callback after a lock was successfully established.

lock.unlock([force])

Unlocks a key if it was locked by this Locker instance. If force is given to be true, the key is unlocked even if the original lock was not put in place by this locker instance.

Returns whether or not the unlock was executed.

lock.maintain()

Keep updating a lock's TTL so long as the instance in in existence, and the lock is maintained. Calling unlock or closing the tab will cause the maintenance to stop, and the lock to therefore be released.