parallel-universe/Lock.js

The set of async flow control structures and promise utils.

'use strict';

/**
 * Promise-based lock implementation.
 *
 * When someone tries to acquire a {@link Lock} they receive a promise for a release callback that is fulfilled as soon
 * as previous lock owner invokes their release callback.
 *
 * @see https://en.wikipedia.org/wiki/Lock_(computer_science) Lock (computer science)
 */
class Lock {
    /**
     * `true` if {@link Lock} was acquired and wasn't released yet.
     */
    get isLocked() {
        return this._promise !== undefined;
    }
    /**
     * Waits for the {@link Lock} to become available and fulfills it with the callback that releases the lock.
     */
    acquire() {
        const { _promise } = this;
        let promise;
        const release = () => {
            if (this._promise === promise) {
                this._promise = undefined;
            }
        };
        if (_promise !== undefined) {
            this._promise = promise = _promise.then(() => release);
        }
        else {
            this._promise = promise = Promise.resolve(release);
        }
        return promise;
    }
}

exports.Lock = Lock;