Bug 1687597 - Ensure worker thread is reset before scheduling for deletion. r=dom-workers-and-storage-reviewers,asuth

Differential Revision: https://phabricator.services.mozilla.com/D102439

dom/workers/RuntimeService.cpp

@@ -2167,33 +2167,7 @@ WorkerThreadPrimaryRunnable::Run() {
 
   using mozilla::ipc::BackgroundChild;
 
-  class MOZ_STACK_CLASS SetThreadHelper final {
-    // Raw pointer: this class is on the stack.
-    WorkerPrivate* mWorkerPrivate;
-
-   public:
-    SetThreadHelper(WorkerPrivate* aWorkerPrivate, WorkerThread& aThread)
-        : mWorkerPrivate(aWorkerPrivate) {
-      MOZ_ASSERT(mWorkerPrivate);
-
-      mWorkerPrivate->SetWorkerPrivateInWorkerThread(&aThread);
-    }
-
-    ~SetThreadHelper() {
-      if (mWorkerPrivate) {
-        mWorkerPrivate->ResetWorkerPrivateInWorkerThread();
-      }
-    }
-
-    void Nullify() {
-      MOZ_ASSERT(mWorkerPrivate);
-      mWorkerPrivate->ResetWorkerPrivateInWorkerThread();
-      mWorkerPrivate = nullptr;
-    }
-  };
-
-  SetThreadHelper threadHelper(mWorkerPrivate, *mThread);
-
+  {
     auto failureCleanup = MakeScopeExit([&]() {
       // The creation of threadHelper above is the point at which a worker is
       // considered to have run, because the `mPreStartRunnables` are all
@@ -2202,6 +2176,14 @@ WorkerThreadPrimaryRunnable::Run() {
       mWorkerPrivate->RunLoopNeverRan();
     });
 
+    mWorkerPrivate->SetWorkerPrivateInWorkerThread(mThread.unsafeGetRawPtr());
+
+    const auto threadCleanup = MakeScopeExit([&] {
+      // This must be called before ScheduleDeletion, which is either called
+      // from failureCleanup leaving scope, or from the outer scope.
+      mWorkerPrivate->ResetWorkerPrivateInWorkerThread();
+    });
+
     mWorkerPrivate->AssertIsOnWorkerThread();
 
     // This needs to be initialized on the worker thread before being used on
@@ -2235,8 +2217,8 @@ WorkerThreadPrimaryRunnable::Run() {
         {
           // We're on the worker thread here, and WorkerPrivate's refcounting is
           // non-threadsafe: you can only do it on the parent thread.  What that
-        // means in practice is that we're relying on it being kept alive while
-        // we run.  Hopefully.
+          // means in practice is that we're relying on it being kept alive
+          // while we run.  Hopefully.
           MOZ_KnownLive(mWorkerPrivate)->DoRunLoop(cx);
           // The AutoJSAPI in DoRunLoop should have reported any exceptions left
           // on cx.
@@ -2268,8 +2250,7 @@ WorkerThreadPrimaryRunnable::Run() {
       // down the cycle collector. This breaks any remaining cycles and collects
       // any remaining C++ objects.
     }
-
-  threadHelper.Nullify();
+  }
 
   mWorkerPrivate->ScheduleDeletion(WorkerPrivate::WorkerRan);