Bug 1646054 - P2. Always retain dispatch flags r=froydnj

When TaskQueue was first conceived; it was only used with AbstractThreads and with tail dispatch.
By default, AbstractThread::Dispatch dropped the flags , as it was dispatching all tasks via the tail dispatcher.

It was an oversight, there's no use-case where we wouldn't want the dispatch flags to be carried forward.

It also simplifies the code and TaskQueue's use.

Depends on D80351

Differential Revision: https://phabricator.services.mozilla.com/D80352

Author: Jean-Yves Avenard

xpcom/threads/TaskQueue.cpp

@@ -11,19 +11,17 @@
 namespace mozilla {
 
 TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
-                     const char* aName, bool aRequireTailDispatch,
-                     bool aRetainFlags)
+                     const char* aName, bool aRequireTailDispatch)
     : AbstractThread(aRequireTailDispatch),
       mTarget(aTarget),
       mQueueMonitor("TaskQueue::Queue"),
       mTailDispatcher(nullptr),
-      mShouldRetainFlags(aRetainFlags),
       mIsRunning(false),
       mIsShutdown(false),
       mName(aName) {}
 
 TaskQueue::TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
-                     bool aSupportsTailDispatch, bool aRetainFlags)
+                     bool aSupportsTailDispatch)
     : TaskQueue(std::move(aTarget), "Unnamed", aSupportsTailDispatch) {}
 
 TaskQueue::~TaskQueue() {
@@ -57,11 +55,8 @@ nsresult TaskQueue::DispatchLocked(nsCOMPtr<nsIRunnable>& aRunnable,
     return currentThread->TailDispatcher().AddTask(this, aRunnable.forget());
   }
 
-  // If the task queue cares about individual flags, retain them in the struct.
-  uint32_t retainFlags = mShouldRetainFlags ? aFlags : 0;
-
   LogRunnable::LogDispatch(aRunnable);
-  mTasks.push({std::move(aRunnable), retainFlags});
+  mTasks.push({std::move(aRunnable), aFlags});
 
   if (mIsRunning) {
     return NS_OK;

xpcom/threads/TaskQueue.h

@@ -53,11 +53,10 @@ class TaskQueue : public AbstractThread, public nsIDirectTaskDispatcher {
 
  public:
   explicit TaskQueue(already_AddRefed<nsIEventTarget> aTarget,
-                     bool aSupportsTailDispatch = false,
-                     bool aRetainFlags = false);
+                     bool aSupportsTailDispatch = false);
 
   TaskQueue(already_AddRefed<nsIEventTarget> aTarget, const char* aName,
-            bool aSupportsTailDispatch = false, bool aRetainFlags = false);
+            bool aSupportsTailDispatch = false);
 
   NS_DECL_ISUPPORTS_INHERITED
   NS_DECL_NSIDIRECTTASKDISPATCHER
@@ -196,11 +195,6 @@ class TaskQueue : public AbstractThread, public nsIDirectTaskDispatcher {
 
   TaskDispatcher* mTailDispatcher;
 
-  // TaskQueues should specify if they want all tasks to dispatch with their
-  // original flags included, which means the flags will be retained in the
-  // TaskStruct.
-  bool mShouldRetainFlags;
-
   // True if we've dispatched an event to the target to execute events from
   // the queue.
   bool mIsRunning;

xpcom/threads/nsThreadManager.cpp

@@ -184,9 +184,7 @@ already_AddRefed<nsISerialEventTarget>
 BackgroundEventTarget::CreateBackgroundTaskQueue(const char* aName) {
   MutexAutoLock lock(mMutex);
 
-  RefPtr<TaskQueue> queue = new TaskQueue(do_AddRef(this), aName,
-                                          /*aSupportsTailDispatch=*/false,
-                                          /*aRetainFlags=*/true);
+  RefPtr<TaskQueue> queue = new TaskQueue(do_AddRef(this), aName);
   mTaskQueues.AppendElement(queue);
 
   return queue.forget();