JAVASCRIPT semaphore.js

//#region src/promise/semaphore.ts
/**
* A counting semaphore for async functions that manages available permits.
* Semaphores are mainly used to limit the number of concurrent async tasks.
*
* Each `acquire` operation takes a permit or waits until one is available.
* Each `release` operation adds a permit, potentially allowing a waiting task to proceed.
*
* The semaphore ensures fairness by maintaining a FIFO (First In, First Out) order for acquirers.
*
* @example
* const sema = new Semaphore(2);
*
* async function task() {
*   await sema.acquire();
*   try {
*     // This code can only be executed by two tasks at the same time
*   } finally {
*     sema.release();
*   }
* }
*
* task();
* task();
* task(); // This task will wait until one of the previous tasks releases the semaphore.
*/
var Semaphore = class {
	/**
	* The maximum number of concurrent operations allowed.
	* @type {number}
	*/
	capacity;
	/**
	* The number of available permits.
	* @type {number}
	*/
	available;
	deferredTasks = [];
	/**
	* Creates an instance of Semaphore.
	* @param capacity - The maximum number of concurrent operations allowed.
	*
	* @example
	* const sema = new Semaphore(3); // Allows up to 3 concurrent operations.
	*/
	constructor(capacity) {
		this.capacity = capacity;
		this.available = capacity;
	}
	/**
	* Acquires a semaphore, blocking if necessary until one is available.
	* @returns A promise that resolves when the semaphore is acquired.
	*
	* @example
	* const sema = new Semaphore(1);
	*
	* async function criticalSection() {
	*   await sema.acquire();
	*   try {
	*     // This code section cannot be executed simultaneously
	*   } finally {
	*     sema.release();
	*   }
	* }
	*/
	async acquire() {
		if (this.available > 0) {
			this.available--;
			return;
		}
		return new Promise((resolve) => {
			this.deferredTasks.push(resolve);
		});
	}
	/**
	* Releases a semaphore, allowing one more operation to proceed.
	*
	* @example
	* const sema = new Semaphore(1);
	*
	* async function task() {
	*   await sema.acquire();
	*   try {
	*     // This code can only be executed by two tasks at the same time
	*   } finally {
	*     sema.release(); // Allows another waiting task to proceed.
	*   }
	* }
	*/
	release() {
		const deferredTask = this.deferredTasks.shift();
		if (deferredTask != null) {
			deferredTask();
			return;
		}
		if (this.available < this.capacity) this.available++;
	}
};
//#endregion
exports.Semaphore = Semaphore;