Expose locks utils

frontend/sync-client/src/index.ts

@@ -20,3 +20,8 @@ export type { ClientCursors } from "./services/types/ClientCursors";
 export type { NetworkConnectionStatus } from "./types/network-connection-status";
 export { DocumentUpdateStatus } from "./types/document-update-status";
 export { SyncClient } from "./sync-client";
+
+import { Locks } from "./utils/locks";
+export const helpers = {
+	Locks
+};

frontend/sync-client/src/utils/locks.ts

@@ -1,14 +1,27 @@
 import type { Logger } from "../tracing/logger";
 
-// Manages locks on T to prevent concurrent modifications
-// allowing the client's FileOperations implementation to be simpler.
-// Locks are granted in a first-in-first-out order.
+/**
+ * Manages exclusive locks on items to prevent concurrent modifications.
+ * Locks are granted in FIFO order.
+ *
+ * @template T The type of the key used for locking
+ */
 export class Locks<T> {
+	/** Currently locked keys */
 	private readonly locked = new Set<T>();
+
+	/** Queue of resolve functions waiting for each key */
 	private readonly waiters = new Map<T, (() => unknown)[]>();
 
 	public constructor(private readonly logger: Logger) {}
 
+	/**
+	 * Attempts to acquire a lock immediately without waiting.
+	 * Must call `unlock()` if successful.
+	 *
+	 * @param key The key to lock
+	 * @returns `true` if lock acquired, `false` if already locked
+	 */
 	public tryLock(key: T): boolean {
 		if (this.locked.has(key)) {
 			return false;
@@ -19,6 +32,13 @@ export class Locks<T> {
 		return true;
 	}
 
+	/**
+	 * Waits to acquire a lock, blocking until available.
+	 * Operations are queued in FIFO order. Must call `unlock()` when done.
+	 *
+	 * @param key The key to wait for and lock
+	 * @returns Promise that resolves when lock is acquired
+	 */
 	public async waitForLock(key: T): Promise<void> {
 		if (this.tryLock(key)) {
 			return Promise.resolve();
@@ -27,6 +47,7 @@ export class Locks<T> {
 		this.logger.debug(`Waiting for lock on ${key}`);
 
 		return new Promise((resolve) => {
+			// DefaultDict behavior
 			let waiting = this.waiters.get(key);
 			if (!waiting) {
 				waiting = [];
@@ -37,12 +58,19 @@ export class Locks<T> {
 		});
 	}
 
+	/**
+	 * Releases a lock and grants access to the next waiting operation in FIFO order.
+	 * Removes the key from locked set if no waiters.
+	 *
+	 * @param key The key to unlock
+	 * @throws {Error} If key is not currently locked
+	 */
 	public unlock(key: T): void {
 		if (!this.locked.has(key)) {
-			throw new Error(`Document ${key} is not locked, cannot unlock`);
+			throw new Error(`Key ${key} is not locked, cannot unlock`);
 		}
 
-		// Remove the first element to ensure FIFO unblocking order
+		// Remove first waiter to ensure FIFO order
 		const nextWaiting = this.waiters.get(key)?.shift();
 
 		if (nextWaiting) {
@@ -53,6 +81,10 @@ export class Locks<T> {
 		}
 	}
 
+	/**
+	 * Clears all locks and waiters. Causes waiting operations to hang indefinitely.
+	 * Use with caution.
+	 */
 	public reset(): void {
 		this.locked.clear();
 		this.waiters.clear();