Fix possible TerminalInstance leak (microsoft#203390)

* Fix possible TerminalInstance leak

Fixes microsoft#200400

Two fixes:

- Make sure an event is disposed of
- In EventMultiplexer, explicitly dispose of all listeners when the multiplexer is disposed

* Remove extra import

Author: mjbvz

src/vs/base/common/event.ts

@@ -1456,14 +1456,17 @@ export class EventMultiplexer<T> implements IDisposable {
 	}
 
 	private unhook(e: { event: Event<T>; listener: IDisposable | null }): void {
-		if (e.listener) {
-			e.listener.dispose();
-		}
+		e.listener?.dispose();
 		e.listener = null;
 	}
 
 	dispose(): void {
 		this.emitter.dispose();
+
+		for (const e of this.events) {
+			e.listener?.dispose();
+		}
+		this.events = [];
 	}
 }
 

src/vs/workbench/api/browser/mainThreadTerminalService.ts

@@ -3,7 +3,7 @@
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
 
-import { DisposableStore, Disposable, IDisposable, MutableDisposable } from 'vs/base/common/lifecycle';
+import { DisposableStore, Disposable, IDisposable, MutableDisposable, combinedDisposable } from 'vs/base/common/lifecycle';
 import { ExtHostContext, ExtHostTerminalServiceShape, MainThreadTerminalServiceShape, MainContext, TerminalLaunchConfig, ITerminalDimensionsDto, ExtHostTerminalIdentifier, TerminalQuickFix, ITerminalCommandDto } from 'vs/workbench/api/common/extHost.protocol';
 import { extHostNamedCustomer, IExtHostContext } from 'vs/workbench/services/extensions/common/extHostCustomers';
 import { URI } from 'vs/base/common/uri';
@@ -236,7 +236,7 @@ export class MainThreadTerminalService implements MainThreadTerminalServiceShape
 		}
 
 		const multiplexer = this._terminalService.createOnInstanceCapabilityEvent(TerminalCapability.CommandDetection, capability => capability.onCommandFinished);
-		multiplexer.event(e => {
+		const sub = multiplexer.event(e => {
 			this._onDidExecuteCommand(e.instance.instanceId, {
 				commandLine: e.data.command,
 				// TODO: Convert to URI if possible
@@ -245,7 +245,7 @@ export class MainThreadTerminalService implements MainThreadTerminalServiceShape
 				output: e.data.getOutput()
 			});
 		});
-		this._sendCommandEventListener.value = multiplexer;
+		this._sendCommandEventListener.value = combinedDisposable(multiplexer, sub);
 	}
 
 	public $stopSendingCommandEvents(): void {