Merge pull request #15991 from gluxon/cached-Snapshot-iterables

Improve watch performance by using stable identities for Snapshot iterables
webpack · Jul 5, 2022 · 1132eb3 · 1132eb3
2 parents 21ead2f + 7b3f4c0
commit 1132eb3
Show file tree

Hide file tree

Showing 2 changed files with 77 additions and 13 deletions.
diff --git a/lib/FileSystemInfo.js b/lib/FileSystemInfo.js
@@ -208,6 +208,12 @@ class SnapshotIterable {
 class Snapshot {
 	constructor() {
 		this._flags = 0;
+		/** @type {Iterable<string> | undefined} */
+		this._cachedFileIterable = undefined;
+		/** @type {Iterable<string> | undefined} */
+		this._cachedContextIterable = undefined;
+		/** @type {Iterable<string> | undefined} */
+		this._cachedMissingIterable = undefined;
 		/** @type {number | undefined} */
 		this.startTime = undefined;
 		/** @type {Map<string, FileSystemInfoEntry | null> | undefined} */
@@ -418,31 +424,43 @@ class Snapshot {
 	 * @returns {Iterable<string>} iterable
 	 */
 	getFileIterable() {
-		return this._createIterable(s => [
-			s.fileTimestamps,
-			s.fileHashes,
-			s.fileTshs,
-			s.managedFiles
-		]);
+		if (this._cachedFileIterable === undefined) {
+			this._cachedFileIterable = this._createIterable(s => [
+				s.fileTimestamps,
+				s.fileHashes,
+				s.fileTshs,
+				s.managedFiles
+			]);
+		}
+		return this._cachedFileIterable;
 	}
 
 	/**
 	 * @returns {Iterable<string>} iterable
 	 */
 	getContextIterable() {
-		return this._createIterable(s => [
-			s.contextTimestamps,
-			s.contextHashes,
-			s.contextTshs,
-			s.managedContexts
-		]);
+		if (this._cachedContextIterable === undefined) {
+			this._cachedContextIterable = this._createIterable(s => [
+				s.contextTimestamps,
+				s.contextHashes,
+				s.contextTshs,
+				s.managedContexts
+			]);
+		}
+		return this._cachedContextIterable;
 	}
 
 	/**
 	 * @returns {Iterable<string>} iterable
 	 */
 	getMissingIterable() {
-		return this._createIterable(s => [s.missingExistence, s.managedMissing]);
+		if (this._cachedMissingIterable === undefined) {
+			this._cachedMissingIterable = this._createIterable(s => [
+				s.missingExistence,
+				s.managedMissing
+			]);
+		}
+		return this._cachedMissingIterable;
 	}
 }
 

diff --git a/test/FileSystemInfo.unittest.js b/test/FileSystemInfo.unittest.js
@@ -363,4 +363,50 @@ ${details(snapshot)}`)
 			}
 		});
 	}
+
+	describe("stable iterables identity", () => {
+		const options = { timestamp: true };
+
+		/**
+		 * @param {function((WebpackError | null)=, (Snapshot | null)=): void} callback callback function
+		 */
+		function getSnapshot(callback) {
+			const fs = createFs();
+			const fsInfo = createFsInfo(fs);
+			fsInfo.createSnapshot(
+				Date.now() + 10000,
+				files,
+				directories,
+				missing,
+				options,
+				callback
+			);
+		}
+
+		it("should return same iterable for getFileIterable()", done => {
+			getSnapshot((err, snapshot) => {
+				if (err) done(err);
+				expect(snapshot.getFileIterable()).toEqual(snapshot.getFileIterable());
+				done();
+			});
+		});
+
+		it("should return same iterable for getContextIterable()", done => {
+			getSnapshot((err, snapshot) => {
+				if (err) done(err);
+				expect(snapshot.getContextIterable()).toEqual(
+					snapshot.getContextIterable()
+				);
+				done();
+			});
+		});
+
+		it("should return same iterable for getMissingIterable()", done => {
+			getSnapshot((err, snapshot) => {
+				if (err) done(err);
+				expect(snapshot.getFileIterable()).toEqual(snapshot.getFileIterable());
+				done();
+			});
+		});
+	});
 });