[js][utility] add AsyncLock

shared/utility/async-lock.mjs

@@ -0,0 +1,82 @@
+import { Queue } from './queue.mjs';
+
+import { Queue } from './queue.mjs';
+
+/**
+ * Represents an asynchronous lock for managing access to a shared resource.
+ * @class
+ */
+export class AsyncLock {
+    /**
+     * Creates an instance of AsyncLock.
+	 * @constructor
+     */
+    constructor() {
+        /**
+         * A queue to store pending requests for acquiring the lock.
+         * @type {Queue}
+		 * @private
+         */
+        this.pending_queue = new Queue();
+
+        /**
+         * The current state of the lock.
+         * @type {boolean}
+		 * @private
+         */
+        this.state = false;
+
+        /**
+         * The ID associated with the current lock holder.
+         * @type {number}
+		 * @private
+         */
+        this.lock_id = 0;
+    }
+
+    /**
+     * Checks the current state of the lock.
+     * @returns {boolean} True if the lock is acquired; otherwise, false.
+     */
+    query() {
+        return this.state;
+    }
+
+    /**
+     * Acquires the lock asynchronously.
+     * @returns {Promise<number>} A promise that resolves with the unique ID associated with the acquired lock.
+     */
+    acquire() {
+        if (!this.state) {
+            this.state = true;
+            this.lock_id += 1;
+            return Promise.resolve(this.lock_id);
+        }
+        return new Promise((resolve, _reject) => this.pending_queue.push(resolve));
+    }
+
+    /**
+     * Releases the lock with the specified ID.
+     * @param {number} lock_id The ID of the lock to release.
+     */
+    release(lock_id) {
+        if (!this.state || lock_id !== this.lock_id) { return; }
+        if (this.pending_queue.empty()) {
+            this.state = false;
+            return;
+        }
+
+        let resolve = this.pending_queue.front();
+        this.pending_queue.popFront();
+        this.lock_id += 1;
+        resolve(this.lock_id);
+    }
+
+    /**
+     * Releases the lock forcefully even you are not the owner.
+	 * BE CAREFUL WHAT YOU WISH FOR!!
+     */
+    forceRelease() {
+        this.release(this.lock_id);
+    }
+};

shared/utility/index.mjs

@@ -1,2 +1,3 @@
 export { areArrayBuffersEqual } from './buffer.mjs';
 export { Queue, QueueEmptyError } from './queue.mjs';
+export { AsyncLock } from './async-lock.mjs';