65 lines
1.4 KiB
JavaScript
65 lines
1.4 KiB
JavaScript
/*
|
|
MIT License http://www.opensource.org/licenses/mit-license.php
|
|
Author Tobias Koppers @sokra
|
|
*/
|
|
|
|
"use strict";
|
|
|
|
/**
|
|
* Simple counting semaphore used to limit how many asynchronous tasks may run
|
|
* concurrently.
|
|
*/
|
|
class Semaphore {
|
|
/**
|
|
* Initializes the semaphore with the number of permits that may be held at
|
|
* the same time.
|
|
* @param {number} available the amount available number of "tasks"
|
|
* in the Semaphore
|
|
*/
|
|
constructor(available) {
|
|
this.available = available;
|
|
/** @type {(() => void)[]} */
|
|
this.waiters = [];
|
|
/** @private */
|
|
this._continue = this._continue.bind(this);
|
|
}
|
|
|
|
/**
|
|
* Acquires a permit for the callback immediately when one is available or
|
|
* queues the callback until another task releases its permit.
|
|
* @param {() => void} callback function block to capture and run
|
|
* @returns {void}
|
|
*/
|
|
acquire(callback) {
|
|
if (this.available > 0) {
|
|
this.available--;
|
|
callback();
|
|
} else {
|
|
this.waiters.push(callback);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Releases a permit and schedules the next waiting callback, if any.
|
|
*/
|
|
release() {
|
|
this.available++;
|
|
if (this.waiters.length > 0) {
|
|
process.nextTick(this._continue);
|
|
}
|
|
}
|
|
|
|
/**
|
|
* Drains the next waiting callback after a permit becomes available.
|
|
*/
|
|
_continue() {
|
|
if (this.available > 0 && this.waiters.length > 0) {
|
|
this.available--;
|
|
const callback = /** @type {(() => void)} */ (this.waiters.pop());
|
|
callback();
|
|
}
|
|
}
|
|
}
|
|
|
|
module.exports = Semaphore;
|