WebWorkers: Implement initial WebWorkers API

Summary:
public

Implements a basic WebWorkers API that allows posting messages between the main JS thread and a worker background thread. It follows the existing webworkers API from JS. Currently passed memory needs to be JSON serializable and is copied (unfortunately, this is what webkit does as well, but with a more advanced serialization/deserialization process).

There are a lot of TODO's: I'll add tasks for them once this is accepted.

Reviewed By: lexs

Differential Revision: D2779349

fb-gh-sync-id: 8ed04c115d36acf0264ef1f6a12a65dd0c14ff18

ReactAndroid/src/main/jni/react/JSCWebWorker.cpp

@@ -0,0 +1,115 @@
+// Copyright 2004-present Facebook. All Rights Reserved.
+
+#include <unistd.h>
+#include <mutex>
+#include <pthread.h>
+#include <unordered_map>
+
+#include <fb/assert.h>
+#include <fb/log.h>
+#include <folly/Memory.h>
+#include <jni/fbjni/Exceptions.h>
+#include <jni/LocalReference.h>
+
+#include "JSCWebWorker.h"
+#include "JSCHelpers.h"
+#include "jni/JMessageQueueThread.h"
+#include "jni/JSLoader.h"
+#include "jni/WebWorkers.h"
+#include "Value.h"
+
+#include <JavaScriptCore/JSValueRef.h>
+
+using namespace facebook::jni;
+
+namespace facebook {
+namespace react {
+
+// TODO(9604425): thread safety
+static std::unordered_map<JSContextRef, JSCWebWorker*> s_globalContextRefToJSCWebWorker;
+
+JSCWebWorker::JSCWebWorker(int id, JSCWebWorkerOwner *owner, std::string scriptSrc) :
+    id_(id),
+    scriptName_(std::move(scriptSrc)),
+    owner_(owner) {
+  ownerMessageQueueThread_ = owner->getMessageQueueThread();
+  FBASSERTMSGF(ownerMessageQueueThread_, "Owner MessageQueueThread must not be null");
+  workerMessageQueueThread_ = WebWorkers::createWebWorkerThread(id, ownerMessageQueueThread_.get());
+  FBASSERTMSGF(workerMessageQueueThread_, "Failed to create worker thread");
+
+  workerMessageQueueThread_->runOnQueue([this] () {
+    initJSVMAndLoadScript();
+  });
+}
+
+JSCWebWorker::~JSCWebWorker() {
+  // TODO(9604430): Implement tear down
+}
+
+void JSCWebWorker::postMessage(JSValueRef msg) {
+  std::string msgString = Value(owner_->getContext(), msg).toJSONString();
+
+  workerMessageQueueThread_->runOnQueue([this, msgString] () {
+    if (isFinished()) {
+      return;
+    }
+    Value rebornJSMsg = Value::fromJSON(context_, String(msgString.c_str()));
+    JSValueRef args[] = { rebornJSMsg };
+    Value onmessageValue = Object::getGlobalObject(context_).getProperty("onmessage");
+    onmessageValue.asObject().callAsFunction(1, args);
+  });
+}
+
+void JSCWebWorker::finish() {
+  isFinished_ = true;
+  // TODO(9604430): Implement tear down
+}
+
+bool JSCWebWorker::isFinished() {
+  return isFinished_;
+}
+
+void JSCWebWorker::initJSVMAndLoadScript() {
+  FBASSERTMSGF(!isFinished(), "Worker was already finished!");
+  FBASSERTMSGF(!context_, "Worker JS VM was already created!");
+
+  context_ = JSGlobalContextCreateInGroup(
+      NULL, // use default JS 'global' object
+      NULL // create new group (i.e. new VM)
+  ); 
+  s_globalContextRefToJSCWebWorker[context_] = this;
+  
+  // TODO(9604438): Protect against script does not exist
+  std::string script = loadScriptFromAssets(scriptName_);
+  evaluateScript(context_, String(script.c_str()), String(scriptName_.c_str()));
+
+  installGlobalFunction(context_, "postMessage", nativePostMessage);
+}
+
+void JSCWebWorker::postMessageToOwner(JSValueRef msg) {
+  std::string msgString = Value(context_, msg).toJSONString();
+  ownerMessageQueueThread_->runOnQueue([this, msgString] () {
+      owner_->onMessageReceived(id_, msgString);
+  });
+}
+
+JSValueRef JSCWebWorker::nativePostMessage(
+    JSContextRef ctx,
+    JSObjectRef function,
+    JSObjectRef thisObject,
+    size_t argumentCount,
+    const JSValueRef arguments[],
+    JSValueRef *exception) {
+  if (argumentCount != 1) {
+    *exception = makeJSCException(ctx, "postMessage got wrong number of arguments");
+    return JSValueMakeUndefined(ctx);
+  }
+  JSValueRef msg = arguments[0];
+  JSCWebWorker *webWorker = s_globalContextRefToJSCWebWorker.at(JSContextGetGlobalContext(ctx));
+  webWorker->postMessageToOwner(msg);
+  
+  return JSValueMakeUndefined(ctx);
+}
+
+}
+}