refactor: Only promisify read and write locks once

Change-type: patch
Signed-off-by: Cameron Diver <cameron@balena.io>

src/config/configJson.ts

@@ -2,18 +2,15 @@ import * as Promise from 'bluebird';
 import * as _ from 'lodash';
 import { fs } from 'mz';
 import * as path from 'path';
-import * as Lock from 'rwlock';
 
 import { ConfigSchema, ConfigValue } from '../lib/types';
+import { readLock, writeLock } from '../lib/update-lock';
 
 import * as constants from '../lib/constants';
 import { writeAndSyncFile, writeFileAtomic } from '../lib/fs-utils';
 import * as osRelease from '../lib/os-release';
 
-type LockCallback = (file: string) => Promise<() => void>;
-
 export default class ConfigJsonConfigBackend {
-	private lock: Lock;
 	private readLockConfigJson: () => Promise.Disposer<() => void>;
 	private writeLockConfigJson: () => Promise.Disposer<() => void>;
 
@@ -25,12 +22,7 @@ export default class ConfigJsonConfigBackend {
 	public constructor(schema: ConfigSchema, configPath?: string) {
 		this.configPath = configPath;
 		this.schema = schema;
-		this.lock = new Lock();
 
-		const writeLock: LockCallback = Promise.promisify(
-			this.lock.async.writeLock,
-		);
-		const readLock: LockCallback = Promise.promisify(this.lock.async.readLock);
 		this.writeLockConfigJson = () =>
 			writeLock('config.json').disposer(release => release());
 		this.readLockConfigJson = () =>

src/device-state.coffee

@@ -1,6 +1,5 @@
 Promise = require 'bluebird'
 _ = require 'lodash'
-Lock = require 'rwlock'
 EventEmitter = require 'events'
 fs = Promise.promisifyAll(require('fs'))
 express = require 'express'
@@ -122,9 +121,8 @@ module.exports = class DeviceState extends EventEmitter
 		@on 'error', (err) ->
 			console.error('Error in deviceState: ', err, err.stack)
 		@_currentVolatile = {}
-		_lock = new Lock()
-		@_writeLock = Promise.promisify(_lock.async.writeLock)
-		@_readLock = Promise.promisify(_lock.async.readLock)
+		@_writeLock = updateLock.writeLock
+		@_readLock = updateLock.readLock
 		@lastSuccessfulUpdate = null
 		@failedUpdates = 0
 		@applyInProgress = false

src/lib/update-lock.ts

@@ -46,8 +46,14 @@ process.on('exit', () => {
 	}
 });
 
+type LockFn = (key: string | number) => Bluebird<() => void>;
 const locker = new Lock();
-const writeLock = Bluebird.promisify(locker.async.writeLock).bind(locker);
+export const writeLock: LockFn = Bluebird.promisify(locker.async.writeLock, {
+	context: locker,
+});
+export const readLock: LockFn = Bluebird.promisify(locker.async.readLock, {
+	context: locker,
+});
 
 function dispose(release: () => void): Bluebird<void> {
 	return Bluebird.map(_.keys(locksTaken), lockName => {
@@ -101,5 +107,10 @@ export function lock(
 			.disposer(dispose);
 	};
 
-	return Bluebird.using(takeTheLock(), fn);
+	const disposer = takeTheLock();
+	if (disposer) {
+		return Bluebird.using(disposer, fn);
+	} else {
+		return Bluebird.resolve(fn());
+	}
 }

src/logger.ts

@@ -1,11 +1,11 @@
 import * as Bluebird from 'bluebird';
 import * as es from 'event-stream';
 import * as _ from 'lodash';
-import * as Lock from 'rwlock';
 
 import { EventTracker } from './event-tracker';
 import Docker = require('./lib/docker-utils');
 import { LogType } from './lib/log-types';
+import { writeLock } from './lib/update-lock';
 import {
 	LocalLogBackend,
 	LogBackend,
@@ -34,10 +34,6 @@ interface LoggerConstructOptions {
 }
 
 export class Logger {
-	private writeLock: (key: string) => Bluebird<() => void> = Bluebird.promisify(
-		new Lock().async.writeLock,
-	);
-
 	private backend: LogBackend | null = null;
 	private balenaBackend: BalenaLogBackend | null = null;
 	private localBackend: LocalLogBackend | null = null;
@@ -130,7 +126,7 @@ export class Logger {
 	}
 
 	public lock(containerId: string): Bluebird.Disposer<() => void> {
-		return this.writeLock(containerId).disposer(release => {
+		return writeLock(containerId).disposer(release => {
 			release();
 		});
 	}