hydrogen-web/src/utils/LockMap.ts

/*
Copyright 2020 The Matrix.org Foundation C.I.C.

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

import {Lock} from "./Lock";

export class LockMap<T> {
    private readonly _map: Map<T, Lock> = new Map();

    async takeLock(key: T): Promise<Lock> {
        let lock = this._map.get(key);
        if (lock) {
            await lock.take();
        } else {
            lock = new Lock();
            lock.tryTake();
            this._map.set(key, lock);
        }
        // don't leave old locks lying around
        lock.released()!.then(() => {
            // give others a chance to take the lock first
            Promise.resolve().then(() => {
                if (!lock!.isTaken) {
                    this._map.delete(key);
                }
            });
        });
        return lock;
    }
}

export function tests() {
    return {
        "taking a lock on the same key blocks": async assert => {
            const lockMap = new LockMap();
            const lock = await lockMap.takeLock("foo");
            let second = false;
            const prom = lockMap.takeLock("foo").then(() => {
                second = true;
            });
            assert.equal(second, false);
            // do a delay to make sure prom does not resolve on its own
            await Promise.resolve();
            lock.release();
            await prom;
            assert.equal(second, true);
        },
        "lock is not cleaned up with second request": async assert => {
            const lockMap = new LockMap();
            const lock = await lockMap.takeLock("foo");
            let ranSecond = false;
            const prom = lockMap.takeLock("foo").then(returnedLock => {
                ranSecond = true;
                assert.equal(returnedLock.isTaken, true);
                // peek into internals, naughty
                // @ts-ignore
                assert.equal(lockMap._map.get("foo"), returnedLock);
            });
            lock.release();
            await prom;
            // double delay to make sure cleanup logic ran
            await Promise.resolve();
            await Promise.resolve();
            assert.equal(ranSecond, true);
        },
        "lock is cleaned up without other request": async assert => {
            const lockMap = new LockMap();
            const lock = await lockMap.takeLock("foo");
            await Promise.resolve();
            lock.release();
            // double delay to make sure cleanup logic ran
            await Promise.resolve();
            await Promise.resolve();
            // @ts-ignore
            assert.equal(lockMap._map.has("foo"), false);
        },
        
    };
}