Only trigger language server auto update once (#623)

Previously the extension would trigger a new auto-update whenever it was
activated. However this can causes issues when a user deactivates-activates the
language server quickly multiple times, as it cause multiple timeouts to be
created. Additionally, when disabled, it would not clear any active timeouts.

This commit adds a small wrapper around the setTimeout function to track usage.
In particular, it will silently ignore calls to add a timeout if a timeout is
already active.  This commit also clears any timeouts when the language server
is disabled.

src/extension.ts

@@ -23,7 +23,10 @@ import {
 	prunedFolderNames,
 	sortedWorkspaceFolders
 } from './vscodeUtils';
-import { sleep } from './utils';
+import {
+	SingleInstanceTimeout,
+	sleep
+} from './utils';
 
 interface terraformLanguageClient {
 	commandPrefix: string,
@@ -40,6 +43,7 @@ const appInsightsKey = '885372d2-6f3c-499f-9d25-b8b219983a52';
 let reporter: TelemetryReporter;
 
 let installPath: string;
+let languageServerUpdater = new SingleInstanceTimeout();
 
 export async function activate(context: vscode.ExtensionContext): Promise<any> {
 	const extensionVersion = vscode.extensions.getExtension(extensionId).packageJSON.version;
@@ -70,6 +74,7 @@ export async function activate(context: vscode.ExtensionContext): Promise<any> {
 				const current = config('terraform').get('languageServer');
 				await config('terraform').update('languageServer', Object.assign(current, { external: false }), vscode.ConfigurationTarget.Global);
 			}
+			languageServerUpdater.clear();
 			return stopClients();
 		}),
 		vscode.commands.registerCommand('terraform.apply', async () => {
@@ -168,7 +173,7 @@ export function deactivate(): Promise<void[]> {
 
 async function updateLanguageServer() {
 	const delay = 1000 * 60 * 60 * 24;
-	setTimeout(updateLanguageServer, delay); // check for new updates every 24hrs
+	languageServerUpdater.timeout(updateLanguageServer, delay); // check for new updates every 24hrs
 
 	// skip install if a language server binary path is set
 	if (!config('terraform').get('languageServer.pathToBinary')) {

src/utils.ts

@@ -34,3 +34,22 @@ export function httpsRequest(url: string, options: https.RequestOptions = {}, en
 export async function sleep(ms: number): Promise<void> {
 	return new Promise(resolve => setTimeout(resolve, ms));
 }
+
+// A small wrapper around setTimeout which ensures that only a single timeout
+// timer can be running at a time. Attempts to add a new timeout silently fail.
+export class SingleInstanceTimeout {
+	private timerLock = false;
+	private timerId: NodeJS.Timeout;
+
+	public timeout(fn, delay, ...args) {
+		if (!this.timerLock) {
+			this.timerLock = true;
+			this.timerId = setTimeout(function () { this.timerLock = false; fn() }, delay, args)
+		}
+	}
+
+	public clear() {
+		if (this.timerId) { clearTimeout(this.timerId) }
+		this.timerLock = false;
+	}
+}