Merge pull request #13154 from webpack/perf/iterable

sokra · web-flow · commit 28d9589d45b1 · 2021-04-19T16:29:45.000+02:00
cheaper getIterator
diff --git a/lib/FileSystemInfo.js b/lib/FileSystemInfo.js
@@ -77,6 +77,92 @@ const DONE_ITERATOR_RESULT = new Set().keys().next();
 // Tsh = Timestamp + Hash
 // Tshs = Timestamp + Hash combinations
 
+class SnapshotIterator {
+	constructor(next) {
+		this.next = next;
+	}
+}
+
+class SnapshotIterable {
+	constructor(snapshot, getMaps) {
+		this.snapshot = snapshot;
+		this.getMaps = getMaps;
+	}
+
+	[Symbol.iterator]() {
+		let state = 0;
+		/** @type {IterableIterator<string>} */
+		let it;
+		/** @type {(Snapshot) => (Map<string, any> | Set<string>)[]} */
+		let getMaps;
+		/** @type {(Map<string, any> | Set<string>)[]} */
+		let maps;
+		/** @type {Snapshot} */
+		let snapshot;
+		let queue;
+		return new SnapshotIterator(() => {
+			for (;;) {
+				switch (state) {
+					case 0:
+						snapshot = this.snapshot;
+						getMaps = this.getMaps;
+						maps = getMaps(snapshot);
+						state = 1;
+					/* falls through */
+					case 1:
+						if (maps.length > 0) {
+							const map = maps.pop();
+							if (map !== undefined) {
+								it = map.keys();
+								state = 2;
+							} else {
+								break;
+							}
+						} else {
+							state = 3;
+							break;
+						}
+					/* falls through */
+					case 2: {
+						const result = it.next();
+						if (!result.done) return result;
+						state = 1;
+						break;
+					}
+					case 3: {
+						const children = snapshot.children;
+						if (children !== undefined) {
+							if (children.size === 1) {
+								// shortcut for a single child
+								// avoids allocation of queue
+								for (const child of children) snapshot = child;
+								maps = getMaps(snapshot);
+								state = 1;
+								break;
+							}
+							if (queue === undefined) queue = [];
+							for (const child of children) {
+								queue.push(child);
+							}
+						}
+						if (queue !== undefined && queue.length > 0) {
+							snapshot = queue.pop();
+							maps = getMaps(snapshot);
+							state = 1;
+							break;
+						} else {
+							state = 4;
+						}
+					}
+					/* falls through */
+					case 4:
+						return DONE_ITERATOR_RESULT;
+				}
+			}
+		});
+	}
+}
+
 class Snapshot {
 	constructor() {
 		this._flags = 0;
@@ -283,63 +369,7 @@ class Snapshot {
 	 * @returns {Iterable<string>} iterable
 	 */
 	_createIterable(getMaps) {
-		let snapshot = this;
-		return {
-			[Symbol.iterator]() {
-				let state = 0;
-				/** @type {IterableIterator<string>} */
-				let it;
-				let maps = getMaps(snapshot);
-				const queue = [];
-				return {
-					next() {
-						for (;;) {
-							switch (state) {
-								case 0:
-									if (maps.length > 0) {
-										const map = maps.pop();
-										if (map !== undefined) {
-											it = map.keys();
-											state = 1;
-										} else {
-											break;
-										}
-									} else {
-										state = 2;
-										break;
-									}
-								/* falls through */
-								case 1: {
-									const result = it.next();
-									if (!result.done) return result;
-									state = 0;
-									break;
-								}
-								case 2: {
-									const children = snapshot.children;
-									if (children !== undefined) {
-										for (const child of children) {
-											queue.push(child);
-										}
-									}
-									if (queue.length > 0) {
-										snapshot = queue.pop();
-										maps = getMaps(snapshot);
-										state = 0;
-										break;
-									} else {
-										state = 3;
-									}
-								}
-								/* falls through */
-								case 3:
-									return DONE_ITERATOR_RESULT;
-							}
-						}
-					}
-				};
-			}
-		};
+		return new SnapshotIterable(this, getMaps);
 	}
 
 	/**
