remove lock and use raw ptr for MessageLoopTaskQueues (flutter/engine#34249)

engine/src/flutter/fml/message_loop_impl.h

@@ -64,7 +64,7 @@ class MessageLoopImpl : public Wakeable,
   MessageLoopImpl();
 
  private:
-  fml::RefPtr<MessageLoopTaskQueues> task_queue_;
+  fml::MessageLoopTaskQueues* task_queue_;
   TaskQueueId queue_id_;
 
   std::atomic_bool terminated_;

engine/src/flutter/fml/message_loop_task_queues.cc

@@ -17,13 +17,8 @@
 
 namespace fml {
 
-std::mutex MessageLoopTaskQueues::creation_mutex_;
-
 const size_t TaskQueueId::kUnmerged = ULONG_MAX;
 
-// Guarded by creation_mutex_.
-fml::RefPtr<MessageLoopTaskQueues> MessageLoopTaskQueues::instance_;
-
 namespace {
 
 // iOS prior to version 9 prevents c++11 thread_local and __thread specifier,
@@ -37,7 +32,6 @@ class TaskSourceGradeHolder {
 };
 }  // namespace
 
-// Guarded by creation_mutex_.
 FML_THREAD_LOCAL ThreadLocalUniquePtr<TaskSourceGradeHolder>
     tls_task_source_grade;
 
@@ -48,14 +42,9 @@ TaskQueueEntry::TaskQueueEntry(TaskQueueId created_for_arg)
   task_source = std::make_unique<TaskSource>(created_for);
 }
 
-fml::RefPtr<MessageLoopTaskQueues> MessageLoopTaskQueues::GetInstance() {
-  std::scoped_lock creation(creation_mutex_);
-  if (!instance_) {
-    instance_ = fml::MakeRefCounted<MessageLoopTaskQueues>();
-    tls_task_source_grade.reset(
-        new TaskSourceGradeHolder{TaskSourceGrade::kUnspecified});
-  }
-  return instance_;
+MessageLoopTaskQueues* MessageLoopTaskQueues::GetInstance() {
+  static MessageLoopTaskQueues* instance = new MessageLoopTaskQueues;
+  return instance;
 }
 
 TaskQueueId MessageLoopTaskQueues::CreateTaskQueue() {
@@ -67,7 +56,10 @@ TaskQueueId MessageLoopTaskQueues::CreateTaskQueue() {
 }
 
 MessageLoopTaskQueues::MessageLoopTaskQueues()
-    : task_queue_id_counter_(0), order_(0) {}
+    : task_queue_id_counter_(0), order_(0) {
+  tls_task_source_grade.reset(
+      new TaskSourceGradeHolder{TaskSourceGrade::kUnspecified});
+}
 
 MessageLoopTaskQueues::~MessageLoopTaskQueues() = default;
 
@@ -95,7 +87,6 @@ void MessageLoopTaskQueues::DisposeTasks(TaskQueueId queue_id) {
 }
 
 TaskSourceGrade MessageLoopTaskQueues::GetCurrentTaskSourceGrade() {
-  std::scoped_lock creation(creation_mutex_);
   return tls_task_source_grade.get()->task_source_grade;
 }
 
@@ -145,11 +136,8 @@ fml::closure MessageLoopTaskQueues::GetNextTaskToRun(TaskQueueId queue_id,
   fml::closure invocation = top.task.GetTask();
   queue_entries_.at(top.task_queue_id)
       ->task_source->PopTask(top.task.GetTaskSourceGrade());
-  {
-    std::scoped_lock creation(creation_mutex_);
-    const auto task_source_grade = top.task.GetTaskSourceGrade();
-    tls_task_source_grade.reset(new TaskSourceGradeHolder{task_source_grade});
-  }
+  const auto task_source_grade = top.task.GetTaskSourceGrade();
+  tls_task_source_grade.reset(new TaskSourceGradeHolder{task_source_grade});
   return invocation;
 }
 

engine/src/flutter/fml/message_loop_task_queues.h

@@ -62,12 +62,11 @@ enum class FlushType {
 /// This also wakes up the loop at the required times.
 /// \see fml::MessageLoop
 /// \see fml::Wakeable
-class MessageLoopTaskQueues
-    : public fml::RefCountedThreadSafe<MessageLoopTaskQueues> {
+class MessageLoopTaskQueues {
  public:
   // Lifecycle.
 
-  static fml::RefPtr<MessageLoopTaskQueues> GetInstance();
+  static MessageLoopTaskQueues* GetInstance();
 
   TaskQueueId CreateTaskQueue();
 
@@ -152,9 +151,6 @@ class MessageLoopTaskQueues
 
   fml::TimePoint GetNextWakeTimeUnlocked(TaskQueueId queue_id) const;
 
-  static std::mutex creation_mutex_;
-  static fml::RefPtr<MessageLoopTaskQueues> instance_;
-
   mutable std::mutex queue_mutex_;
   std::map<TaskQueueId, std::unique_ptr<TaskQueueEntry>> queue_entries_;
 
@@ -162,8 +158,6 @@ class MessageLoopTaskQueues
 
   std::atomic_int order_;
 
-  FML_FRIEND_MAKE_REF_COUNTED(MessageLoopTaskQueues);
-  FML_FRIEND_REF_COUNTED_THREAD_SAFE(MessageLoopTaskQueues);
   FML_DISALLOW_COPY_ASSIGN_AND_MOVE(MessageLoopTaskQueues);
 };
 

engine/src/flutter/fml/message_loop_task_queues_merge_unmerge_unittests.cc

@@ -27,7 +27,7 @@ class TestWakeable : public fml::Wakeable {
   WakeUpCall wake_up_call_;
 };
 
-static int CountRemainingTasks(fml::RefPtr<MessageLoopTaskQueues> task_queue,
+static int CountRemainingTasks(fml::MessageLoopTaskQueues* task_queue,
                                const TaskQueueId& queue_id,
                                bool run_invocation = false) {
   const auto now = ChronoTicksSinceEpoch();

engine/src/flutter/fml/shared_thread_merger.h

@@ -57,7 +57,7 @@ class SharedThreadMerger
  private:
   fml::TaskQueueId owner_;
   fml::TaskQueueId subsumed_;
-  fml::RefPtr<fml::MessageLoopTaskQueues> task_queues_;
+  fml::MessageLoopTaskQueues* task_queues_;
   std::mutex mutex_;
   bool enabled_;