Initial commit 🎉

fbshipit-source-id: b6fc29740c6875d2e78953b8a7123890a67930f2
Co-authored-by: Sebastian McKenzie <sebmck@fb.com>
Co-authored-by: John Knox <jknox@fb.com>
Co-authored-by: Emil Sjölander <emilsj@fb.com>
Co-authored-by: Pritesh Nandgaonkar <prit91@fb.com>

src/ui/styled/gc.js

@@ -0,0 +1,114 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+
+import type {Tracker, RulesToClass} from './index.js';
+import type {StyleSheet} from './sheet.js';
+
+const invariant = require('invariant');
+
+export class GarbageCollector {
+  constructor(sheet: StyleSheet, tracker: Tracker, rulesToClass: RulesToClass) {
+    this.sheet = sheet;
+    this.tracker = tracker;
+
+    // used to keep track of what classes are actively in use
+    this.usedClasses = new Map();
+
+    // classes to be removed, we put this in a queue and perform it in bulk rather than straight away
+    // since by the time the next tick happens this style could have been reinserted
+    this.classRemovalQueue = new Set();
+
+    this.rulesToClass = rulesToClass;
+  }
+
+  tracker: Tracker;
+  sheet: StyleSheet;
+  usedClasses: Map<string, number>;
+  garbageTimer: ?TimeoutID;
+  classRemovalQueue: Set<string>;
+  rulesToClass: RulesToClass;
+
+  hasQueuedCollection(): boolean {
+    return Boolean(this.garbageTimer);
+  }
+
+  getReferenceCount(key: string): number {
+    return this.usedClasses.get(key) || 0;
+  }
+
+  // component has been mounted so make sure it's being depended on
+  registerClassUse(name: string) {
+    const count = this.usedClasses.get(name) || 0;
+    this.usedClasses.set(name, count + 1);
+    if (this.classRemovalQueue.has(name)) {
+      this.classRemovalQueue.delete(name);
+
+      if (this.classRemovalQueue.size === 0) {
+        this.haltGarbage();
+      }
+    }
+  }
+
+  // component has been unmounted so remove it's dependencies
+  deregisterClassUse(name: string) {
+    let count = this.usedClasses.get(name);
+    if (count == null) {
+      return;
+    }
+
+    count--;
+    this.usedClasses.set(name, count);
+
+    if (count === 0) {
+      this.classRemovalQueue.add(name);
+      this.scheduleGarbage();
+    }
+  }
+
+  scheduleGarbage() {
+    if (this.garbageTimer != null) {
+      return;
+    }
+
+    this.garbageTimer = setTimeout(() => {
+      this.collectGarbage();
+    }, 2000);
+  }
+
+  haltGarbage() {
+    if (this.garbageTimer) {
+      clearTimeout(this.garbageTimer);
+      this.garbageTimer = null;
+    }
+  }
+
+  getCollectionQueue() {
+    return Array.from(this.classRemovalQueue);
+  }
+
+  collectGarbage() {
+    this.haltGarbage();
+    for (const name of this.classRemovalQueue) {
+      const trackerInfo = this.tracker.get(name);
+      invariant(trackerInfo != null, 'trying to remove unknown class');
+
+      const {rules} = trackerInfo;
+      this.rulesToClass.delete(rules);
+
+      this.sheet.delete(name);
+      this.tracker.delete(name);
+      this.usedClasses.delete(name);
+    }
+    this.classRemovalQueue.clear();
+  }
+
+  flush() {
+    this.haltGarbage();
+    this.classRemovalQueue.clear();
+    this.usedClasses.clear();
+  }
+}