Adding support to cancel a headless task

Libraries/ReactNative/AppRegistry.js

@@ -21,6 +21,9 @@ const renderApplication = require('renderApplication');
 
 type Task = (taskData: any) => Promise<void>;
 type TaskProvider = () => Task;
+type TaskCanceller = () => void;
+type TaskCancelProvider = () => TaskCanceller;
+
 /* $FlowFixMe(>=0.90.0 site=react_native_fb) This comment suppresses an
  * error found when Flow v0.90 was deployed. To see the error, delete this
  * comment and run Flow. */
@@ -50,7 +53,8 @@ export type WrapperComponentProvider = any => React$ComponentType<*>;
 const runnables: Runnables = {};
 let runCount = 1;
 const sections: Runnables = {};
-const tasks: Map<string, TaskProvider> = new Map();
+const taskProviders: Map<string, TaskProvider> = new Map();
+const taskCancelProviders: Map<string, TaskCancelProvider> = new Map();
 let componentProviderInstrumentationHook: ComponentProviderInstrumentationHook = (
   component: ComponentProvider,
 ) => component();
@@ -212,13 +216,23 @@ const AppRegistry = {
    *
    * See http://facebook.github.io/react-native/docs/appregistry.html#registerheadlesstask
    */
-  registerHeadlessTask(taskKey: string, task: TaskProvider): void {
-    if (tasks.has(taskKey)) {
+  registerHeadlessTask(taskKey: string, taskProvider: TaskProvider): void {
+    this.registerCancellableHeadlessTask(taskKey, taskProvider, () => () => { /* Cancel is no-op */ });
+  },
+
+  /**
+   * Register a cancellable headless task. A headless task is a bit of code that runs without a UI.
+   *
+   * See http://facebook.github.io/react-native/docs/appregistry.html#registercancellableheadlesstask
+   */
+  registerCancellableHeadlessTask(taskKey: string, taskProvider: TaskProvider, taskCancelProvider: TaskCancelProvider): void {
+    if (taskProviders.has(taskKey)) {
       console.warn(
-        `registerHeadlessTask called multiple times for same key '${taskKey}'`,
+        `registerHeadlessTask or registerCancellableHeadlessTask called multiple times for same key '${taskKey}'`,
       );
     }
-    tasks.set(taskKey, task);
+    taskProviders.set(taskKey, taskProvider);
+    taskCancelProviders.set(taskKey, taskCancelProvider);
   },
 
   /**
@@ -227,7 +241,7 @@ const AppRegistry = {
    * See http://facebook.github.io/react-native/docs/appregistry.html#startheadlesstask
    */
   startHeadlessTask(taskId: number, taskKey: string, data: any): void {
-    const taskProvider = tasks.get(taskKey);
+    const taskProvider = taskProviders.get(taskKey);
     if (!taskProvider) {
       throw new Error(`No task registered for key ${taskKey}`);
     }
@@ -240,6 +254,19 @@ const AppRegistry = {
         NativeModules.HeadlessJsTaskSupport.notifyTaskFinished(taskId);
       });
   },
+
+  /**
+   * Only called from native code. Cancels a headless task.
+   *
+   * See http://facebook.github.io/react-native/docs/appregistry.html#cancelheadlesstask
+   */
+  cancelHeadlessTask(taskId: number, taskKey: string): void {
+    const taskCancelProvider = taskCancelProviders.get(taskKey);
+    if (!taskCancelProvider) {
+      throw new Error(`No task canceller registered for key '${taskKey}'`);
+    }
+    taskCancelProvider()();
+  }
 };
 
 BatchedBridge.registerCallableModule('AppRegistry', AppRegistry);