Bug 1539039 keep WorkletGlobalScope as long as its Worklet is usable r=baku

Depends on D25353

Differential Revision: https://phabricator.services.mozilla.com/D25354

--HG--
extra : moz-landing-system : lando

dom/worklet/Worklet.cpp

@@ -326,7 +326,8 @@ NS_IMETHODIMP
 ExecutionRunnable::Run() {
   // WorkletThread::IsOnWorkletThread() cannot be used here because it depends
   // on a WorkletJSContext having been created for this thread.  That does not
-  // happen until the first time RunOnWorkletThread() is called.
+  // happen until the global scope is created the first time
+  // RunOnWorkletThread() is called.
   if (!NS_IsMainThread()) {
     RunOnWorkletThread();
     return NS_DispatchToMainThread(this);
@@ -339,11 +340,7 @@ ExecutionRunnable::Run() {
 void ExecutionRunnable::RunOnWorkletThread() {
   WorkletThread::EnsureCycleCollectedJSContext(mParentRuntime);
 
-  AutoJSAPI jsapi;
-  jsapi.Init();
-
-  RefPtr<WorkletGlobalScope> globalScope =
-      mWorkletImpl->CreateGlobalScope(jsapi.cx());
+  WorkletGlobalScope* globalScope = mWorkletImpl->GetGlobalScope();
   MOZ_ASSERT(globalScope);
 
   AutoEntryScript aes(globalScope, "Worklet");

dom/worklet/WorkletImpl.cpp

@@ -11,6 +11,7 @@
 
 #include "mozilla/BasePrincipal.h"
 #include "mozilla/dom/RegisterWorkletBindings.h"
+#include "mozilla/dom/ScriptSettings.h"
 #include "mozilla/dom/WorkletBinding.h"
 
 namespace mozilla {
@@ -42,7 +43,7 @@ WorkletLoadInfo::~WorkletLoadInfo() {
 WorkletImpl::WorkletImpl(nsPIDOMWindowInner* aWindow, nsIPrincipal* aPrincipal)
     : mWorkletLoadInfo(aWindow, aPrincipal), mTerminated(false) {}
 
-WorkletImpl::~WorkletImpl() = default;
+WorkletImpl::~WorkletImpl() { MOZ_ASSERT(!mGlobalScope); }
 
 JSObject* WorkletImpl::WrapWorklet(JSContext* aCx, dom::Worklet* aWorklet,
                                    JS::Handle<JSObject*> aGivenProto) {
@@ -50,30 +51,46 @@ JSObject* WorkletImpl::WrapWorklet(JSContext* aCx, dom::Worklet* aWorklet,
   return dom::Worklet_Binding::Wrap(aCx, aWorklet, aGivenProto);
 }
 
-already_AddRefed<dom::WorkletGlobalScope> WorkletImpl::CreateGlobalScope(
-    JSContext* aCx) {
+dom::WorkletGlobalScope* WorkletImpl::GetGlobalScope() {
   dom::WorkletThread::AssertIsOnWorkletThread();
 
-  RefPtr<dom::WorkletGlobalScope> scope = ConstructGlobalScope();
+  if (mGlobalScope) {
+    return mGlobalScope;
+  }
 
-  JS::Rooted<JSObject*> global(aCx);
-  NS_ENSURE_TRUE(scope->WrapGlobalObject(aCx, &global), nullptr);
+  dom::AutoJSAPI jsapi;
+  jsapi.Init();
+  JSContext* cx = jsapi.cx();
 
-  JSAutoRealm ar(aCx, global);
+  mGlobalScope = ConstructGlobalScope();
+
+  JS::Rooted<JSObject*> global(cx);
+  NS_ENSURE_TRUE(mGlobalScope->WrapGlobalObject(cx, &global), nullptr);
+
+  JSAutoRealm ar(cx, global);
 
   // Init Web IDL bindings
-  if (!dom::RegisterWorkletBindings(aCx, global)) {
+  if (!dom::RegisterWorkletBindings(cx, global)) {
     return nullptr;
   }
 
-  JS_FireOnNewGlobalObject(aCx, global);
+  JS_FireOnNewGlobalObject(cx, global);
 
-  return scope.forget();
+  return mGlobalScope;
 }
 
 void WorkletImpl::NotifyWorkletFinished() {
   MOZ_ASSERT(NS_IsMainThread());
 
+  if (mTerminated) {
+    return;
+  }
+
+  // Release global scope on its thread.
+  SendControlMessage(NS_NewRunnableFunction(
+      "WorkletImpl::NotifyWorkletFinished",
+      [self = RefPtr<WorkletImpl>(this)]() { self->mGlobalScope = nullptr; }));
+
   mTerminated = true;
   if (mWorkletThread) {
     mWorkletThread->Terminate();

dom/worklet/WorkletImpl.h

@@ -74,7 +74,7 @@ class WorkletImpl {
   void NotifyWorkletFinished();
 
   // Execution thread only.
-  already_AddRefed<dom::WorkletGlobalScope> CreateGlobalScope(JSContext* aCx);
+  dom::WorkletGlobalScope* GetGlobalScope();
 
   // Any thread.
 
@@ -93,6 +93,9 @@ class WorkletImpl {
   // Parent thread only.
   RefPtr<dom::WorkletThread> mWorkletThread;
   bool mTerminated;
+
+  // Execution thread only.
+  RefPtr<dom::WorkletGlobalScope> mGlobalScope;
 };
 
 }  // namespace mozilla