WebWorkers: Add ExecutorToken to route native module calls to/from workers

Summary:To support native modules in web workers, native modules need to have an notion of the JS executor/thread that called into them in order to respond via Callback or JS module call to the right executor on the right thread.

ExecutorToken is an object that only serves as a token that can be used to identify an executor/message queue thread in the bridge. It doesn't expose any methods. Native modules Callback objects automatically have this ExecutionContext attached -- JSModule calls for modules that support workers will need to supply an appropriate ExecutorToken when retrieving the JSModule implementation from the ReactContext.

Reviewed By: mhorowitz

Differential Revision: D2965458

fb-gh-sync-id: 6e354d4df8536d40b12d02bd055f6d06b4ca595d
shipit-source-id: 6e354d4df8536d40b12d02bd055f6d06b4ca595d

ReactAndroid/src/main/java/com/facebook/react/bridge/NativeModule.java

@@ -23,7 +23,7 @@ import com.fasterxml.jackson.core.JsonGenerator;
  */
 public interface NativeModule {
   interface NativeMethod {
-    void invoke(CatalystInstance catalystInstance, ReadableNativeArray parameters);
+    void invoke(CatalystInstance catalystInstance, ExecutorToken executorToken, ReadableNativeArray parameters);
     String getType();
   }
 
@@ -74,7 +74,25 @@ public interface NativeModule {
   void onCatalystInstanceDestroy();
 
   /**
-   * Whether this native module supports calls from web workers. Ignored for now.
+   * In order to support web workers, a module must be aware that it can be invoked from multiple
+   * different JS VMs. Supporting web workers means recognizing things like:
+   *
+   * 1) ids (e.g. timer ids, request ids, etc.) may only unique on a per-VM basis
+   * 2) the module needs to make sure to enqueue callbacks and JS module calls to the correct VM
+   *
+   * In order to facilitate this, modules that support web workers will have all their @ReactMethod-
+   * annotated methods passed a {@link ExecutorToken} as the first parameter before any arguments
+   * from JS. This ExecutorToken internally maps to a specific JS VM and can be used by the
+   * framework to route calls appropriately. In order to make JS module calls correctly, start using
+   * the version of {@link ReactContext#getJSModule(ExecutorToken, Class)} that takes an
+   * ExecutorToken. It will ensure that any calls you dispatch to the returned object will go to
+   * the right VM. For Callbacks, you don't have to do anything special -- the framework
+   * automatically tags them with the correct ExecutorToken when the are created.
+   *
+   * Note: even though calls can come from multiple JS VMs on multiple threads, calls to this module
+   * will still only occur on a single thread.
+   *
+   * @return whether this module supports web workers.
    */
   boolean supportsWebWorkers();
 }