request method

JSPromise<JSAny?> request(String name, JSObject callbackOrOptions, [ LockGrantedCallback callback ])

The request() method of the LockManager interface requests a Lock object with parameters specifying its name and characteristics. The requested Lock is passed to a callback, while the function itself returns a Promise that resolves (or rejects) with the result of the callback after the lock is released, or rejects if the request is aborted.

The mode property of the options parameter may be either "exclusive" or "shared".

Request an "exclusive" lock when it should only be held by one code instance at a time. This applies to code in both tabs and workers. Use this to represent mutually exclusive access to a resource. When an "exclusive" lock for a given name is held, no other lock with the same name can be held.

Request a "shared" lock when multiple instances of the code can share access to a resource. When a "shared" lock for a given name is held, other "shared" locks for the same name can be granted, but no "exclusive" locks with that name can be held or granted.

This shared/exclusive lock pattern is common in database transaction architecture, for example to allow multiple simultaneous readers (each requests a "shared" lock) but only one writer (a single "exclusive" lock). This is known as the readers-writer pattern. In the IndexedDB API, this is exposed as "readonly" and "readwrite" transactions which have the same semantics.

Implementation

external JSPromise<JSAny?> request(
  String name,
  JSObject callbackOrOptions, [
  LockGrantedCallback callback,
]);