improve how polling is scheduled to reduce load

Author: sokra

lib/DirectoryWatcher.js

@@ -79,6 +79,7 @@ class DirectoryWatcher extends EventEmitter {
 				: options.poll
 				? 5007
 				: false;
+		this.timeout = undefined;
 		this.initialScanRemoved = new Set();
 		this.initialScanFinished = undefined;
 		/** @type {Map<string, Set<Watcher>>} */
@@ -104,13 +105,12 @@ class DirectoryWatcher extends EventEmitter {
 	createWatcher() {
 		try {
 			if (this.polledWatching) {
-				// Poll for changes
-				const interval = setInterval(() => {
-					this.doScan(false);
-				}, this.polledWatching);
 				this.watcher = {
 					close: () => {
-						clearInterval(interval);
+						if (this.timeout) {
+							clearTimeout(this.timeout);
+							this.timeout = undefined;
+						}
 					}
 				};
 			} else {
@@ -466,6 +466,16 @@ class DirectoryWatcher extends EventEmitter {
 		if (err) {
 			console.error("Watchpack Error (initial scan): " + err);
 		}
+		this.onScanFinished();
+	}
+
+	onScanFinished() {
+		if (this.polledWatching) {
+			this.timeout = setTimeout(() => {
+				if (this.closed) return;
+				this.doScan(false);
+			}, this.polledWatching);
+		}
 	}
 
 	onDirectoryRemoved(reason) {
@@ -528,6 +538,10 @@ class DirectoryWatcher extends EventEmitter {
 			return;
 		}
 		this.scanning = true;
+		if (this.timeout) {
+			clearTimeout(this.timeout);
+			this.timeout = undefined;
+		}
 		process.nextTick(() => {
 			if (this.closed) return;
 			fs.readdir(this.path, (err, items) => {
@@ -606,6 +620,7 @@ class DirectoryWatcher extends EventEmitter {
 						this.doScan(this.scanAgainInitial);
 					} else {
 						this.scanning = false;
+						this.onScanFinished();
 					}
 				});
 				for (const itemPath of itemPaths) {