close watchers correctly when closing watching

lib/Compiler.js

@@ -16,6 +16,7 @@ function Watching(compiler, watchOptions, handler) {
 	this.error = null;
 	this.stats = null;
 	this.handler = handler;
+	this.closed = false;
 	if(typeof watchOptions === "number") {
 		this.watchOptions = {
 			aggregateTimeout: watchOptions
@@ -92,12 +93,14 @@ Watching.prototype._done = function(err, compilation) {
 	else
 		this.compiler.applyPlugins("failed", this.error);
 	this.handler(this.error, this.stats);
-	if(!this.error)
+	if(!this.error && !this.closed)
 		this.watch(compilation.fileDependencies, compilation.contextDependencies, compilation.missingDependencies);
 };
 
 Watching.prototype.watch = function(files, dirs, missing) {
+	this.pausedWatcher = null;
 	this.watcher = this.compiler.watchFileSystem.watch(files, dirs, missing, this.startTime, this.watchOptions, function(err, filesModified, contextModified, missingModified, fileTimestamps, contextTimestamps) {
+		this.pausedWatcher = this.watcher;
 		this.watcher = null;
 		if(err) return this.handler(err);
 
@@ -111,6 +114,7 @@ Watching.prototype.watch = function(files, dirs, missing) {
 
 Watching.prototype.invalidate = function() {
 	if(this.watcher) {
+		this.pausedWatcher = this.watcher;
 		this.watcher.pause();
 		this.watcher = null;
 	}
@@ -125,10 +129,15 @@ Watching.prototype.invalidate = function() {
 Watching.prototype.close = function(callback) {
 	if(callback === undefined) callback = function() {};
 
+	this.closed = true;
 	if(this.watcher) {
 		this.watcher.close();
 		this.watcher = null;
 	}
+	if(this.pausedWatcher) {
+		this.pausedWatcher.close();
+		this.pausedWatcher = null;
+	}
 	if(this.running) {
 		this.invalid = true;
 		this._done = () => {

lib/node/NodeWatchFileSystem.js

@@ -55,10 +55,15 @@ class NodeWatchFileSystem {
 		}
 		return {
 			close: () => {
-				this.watcher.close();
+				if(this.watcher) {
+					this.watcher.close();
+					this.watcher = null;
+				}
 			},
 			pause: () => {
-				this.watcher.pause();
+				if(this.watcher) {
+					this.watcher.pause();
+				}
 			}
 		};
 	}

test/WatchDetection.test.js

@@ -102,9 +102,9 @@ describe("WatchDetection", () => {
 				function step4() {
 					onChange = null;
 
-					watcher.close();
-
-					done();
+					watcher.close(() => {
+						setTimeout(done, 1000);
+					});
 				}
 
 				function handleError(err) {