Implementation of two or more threads merging for multiple platform v…

…iews (flutter#27662)

Implementation of two or more threads merging for both lightweight multiple engines and standalone multiple engines.

ci/licenses_golden/licenses_flutter

@@ -259,6 +259,8 @@ FILE: ../../../flutter/fml/posix_wrappers.h
 FILE: ../../../flutter/fml/raster_thread_merger.cc
 FILE: ../../../flutter/fml/raster_thread_merger.h
 FILE: ../../../flutter/fml/raster_thread_merger_unittests.cc
+FILE: ../../../flutter/fml/shared_thread_merger.cc
+FILE: ../../../flutter/fml/shared_thread_merger.h
 FILE: ../../../flutter/fml/size.h
 FILE: ../../../flutter/fml/status.h
 FILE: ../../../flutter/fml/synchronization/atomic_object.h

fml/BUILD.gn

@@ -57,6 +57,8 @@ source_set("fml") {
     "posix_wrappers.h",
     "raster_thread_merger.cc",
     "raster_thread_merger.h",
+    "shared_thread_merger.cc",
+    "shared_thread_merger.h",
     "size.h",
     "synchronization/atomic_object.h",
     "synchronization/count_down_latch.cc",

fml/memory/task_runner_checker.cc

@@ -8,7 +8,7 @@ namespace fml {
 
 TaskRunnerChecker::TaskRunnerChecker()
     : initialized_queue_id_(InitTaskQueueId()),
-      subsumed_queue_id_(
+      subsumed_queue_ids_(
           MessageLoopTaskQueues::GetInstance()->GetSubsumedTaskQueueId(
               initialized_queue_id_)){};
 
@@ -17,8 +17,15 @@ TaskRunnerChecker::~TaskRunnerChecker() = default;
 bool TaskRunnerChecker::RunsOnCreationTaskRunner() const {
   FML_CHECK(fml::MessageLoop::IsInitializedForCurrentThread());
   const auto current_queue_id = MessageLoop::GetCurrentTaskQueueId();
-  return RunsOnTheSameThread(current_queue_id, initialized_queue_id_) ||
-         RunsOnTheSameThread(current_queue_id, subsumed_queue_id_);
+  if (RunsOnTheSameThread(current_queue_id, initialized_queue_id_)) {
+    return true;
+  }
+  for (auto& subsumed : subsumed_queue_ids_) {
+    if (RunsOnTheSameThread(current_queue_id, subsumed)) {
+      return true;
+    }
+  }
+  return false;
 };
 
 bool TaskRunnerChecker::RunsOnTheSameThread(TaskQueueId queue_a,

fml/memory/task_runner_checker.h

@@ -22,7 +22,7 @@ class TaskRunnerChecker final {
 
  private:
   TaskQueueId initialized_queue_id_;
-  TaskQueueId subsumed_queue_id_;
+  std::set<TaskQueueId> subsumed_queue_ids_;
 
   TaskQueueId InitTaskQueueId();
 };

fml/memory/task_runner_checker_unittest.cc

@@ -94,14 +94,14 @@ TEST(TaskRunnerCheckerTests, MergedTaskRunnersRunsOnTheSameThread) {
   fml::TaskQueueId qid2 = loop2->GetTaskRunner()->GetTaskQueueId();
   const auto raster_thread_merger_ =
       fml::MakeRefCounted<fml::RasterThreadMerger>(qid1, qid2);
-  const int kNumFramesMerged = 5;
+  const size_t kNumFramesMerged = 5;
 
   raster_thread_merger_->MergeWithLease(kNumFramesMerged);
 
   // merged, running on the same thread
   EXPECT_EQ(TaskRunnerChecker::RunsOnTheSameThread(qid1, qid2), true);
 
-  for (int i = 0; i < kNumFramesMerged; i++) {
+  for (size_t i = 0; i < kNumFramesMerged; i++) {
     ASSERT_TRUE(raster_thread_merger_->IsMerged());
     raster_thread_merger_->DecrementLease();
   }
@@ -154,7 +154,7 @@ TEST(TaskRunnerCheckerTests,
   });
   latch3.Wait();
 
-  fml::MessageLoopTaskQueues::GetInstance()->Unmerge(qid1);
+  fml::MessageLoopTaskQueues::GetInstance()->Unmerge(qid1, qid2);
 
   fml::AutoResetWaitableEvent latch4;
   loop2->GetTaskRunner()->PostTask([&]() {

fml/memory/weak_ptr_unittest.cc

@@ -212,14 +212,14 @@ TEST(TaskRunnerAffineWeakPtrTest, ShouldNotCrashIfRunningOnTheSameTaskRunner) {
   fml::TaskQueueId qid2 = loop2->GetTaskRunner()->GetTaskQueueId();
   const auto raster_thread_merger_ =
       fml::MakeRefCounted<fml::RasterThreadMerger>(qid1, qid2);
-  const int kNumFramesMerged = 5;
+  const size_t kNumFramesMerged = 5;
 
   raster_thread_merger_->MergeWithLease(kNumFramesMerged);
 
   loop2_task_start_latch.Signal();
   loop2_task_finish_latch.Wait();
 
-  for (int i = 0; i < kNumFramesMerged; i++) {
+  for (size_t i = 0; i < kNumFramesMerged; i++) {
     ASSERT_TRUE(raster_thread_merger_->IsMerged());
     raster_thread_merger_->DecrementLease();
   }

fml/message_loop_task_queues.cc

@@ -8,9 +8,9 @@
 
 #include <iostream>
 #include <memory>
+#include <optional>
 
 #include "flutter/fml/make_copyable.h"
-#include "flutter/fml/message_loop_impl.h"
 #include "flutter/fml/task_source.h"
 #include "flutter/fml/thread_local.h"
 
@@ -25,7 +25,7 @@ fml::RefPtr<MessageLoopTaskQueues> MessageLoopTaskQueues::instance_;
 
 namespace {
 
-// iOS prior to version 9 prevents c++11 thread_local and __thread specefier,
+// iOS prior to version 9 prevents c++11 thread_local and __thread specifier,
 // having us resort to boxed enum containers.
 class TaskSourceGradeHolder {
  public:
@@ -41,9 +41,7 @@ FML_THREAD_LOCAL ThreadLocalUniquePtr<TaskSourceGradeHolder>
     tls_task_source_grade;
 
 TaskQueueEntry::TaskQueueEntry(TaskQueueId created_for_arg)
-    : owner_of(_kUnmerged),
-      subsumed_by(_kUnmerged),
-      created_for(created_for_arg) {
+    : subsumed_by(_kUnmerged), created_for(created_for_arg) {
   wakeable = NULL;
   task_observers = TaskObservers();
   task_source = std::make_unique<TaskSource>(created_for);
@@ -76,20 +74,21 @@ void MessageLoopTaskQueues::Dispose(TaskQueueId queue_id) {
   std::lock_guard guard(queue_mutex_);
   const auto& queue_entry = queue_entries_.at(queue_id);
   FML_DCHECK(queue_entry->subsumed_by == _kUnmerged);
-  TaskQueueId subsumed = queue_entry->owner_of;
-  queue_entries_.erase(queue_id);
-  if (subsumed != _kUnmerged) {
+  auto& subsumed_set = queue_entry->owner_of;
+  for (auto& subsumed : subsumed_set) {
     queue_entries_.erase(subsumed);
   }
+  // Erase owner queue_id at last to avoid &subsumed_set from being invalid
+  queue_entries_.erase(queue_id);
 }
 
 void MessageLoopTaskQueues::DisposeTasks(TaskQueueId queue_id) {
   std::lock_guard guard(queue_mutex_);
   const auto& queue_entry = queue_entries_.at(queue_id);
   FML_DCHECK(queue_entry->subsumed_by == _kUnmerged);
-  TaskQueueId subsumed = queue_entry->owner_of;
+  auto& subsumed_set = queue_entry->owner_of;
   queue_entry->task_source->ShutDown();
-  if (subsumed != _kUnmerged) {
+  for (auto& subsumed : subsumed_set) {
     queue_entries_.at(subsumed)->task_source->ShutDown();
   }
 }
@@ -170,8 +169,8 @@ size_t MessageLoopTaskQueues::GetNumPendingTasks(TaskQueueId queue_id) const {
   size_t total_tasks = 0;
   total_tasks += queue_entry->task_source->GetNumPendingTasks();
 
-  TaskQueueId subsumed = queue_entry->owner_of;
-  if (subsumed != _kUnmerged) {
+  auto& subsumed_set = queue_entry->owner_of;
+  for (auto& subsumed : subsumed_set) {
     const auto& subsumed_entry = queue_entries_.at(subsumed);
     total_tasks += subsumed_entry->task_source->GetNumPendingTasks();
   }
@@ -205,8 +204,8 @@ std::vector<fml::closure> MessageLoopTaskQueues::GetObserversToNotify(
     observers.push_back(observer.second);
   }
 
-  TaskQueueId subsumed = queue_entries_.at(queue_id)->owner_of;
-  if (subsumed != _kUnmerged) {
+  auto& subsumed_set = queue_entries_.at(queue_id)->owner_of;
+  for (auto& subsumed : subsumed_set) {
     for (const auto& observer : queue_entries_.at(subsumed)->task_observers) {
       observers.push_back(observer.second);
     }
@@ -230,22 +229,41 @@ bool MessageLoopTaskQueues::Merge(TaskQueueId owner, TaskQueueId subsumed) {
   std::lock_guard guard(queue_mutex_);
   auto& owner_entry = queue_entries_.at(owner);
   auto& subsumed_entry = queue_entries_.at(subsumed);
-
-  if (owner_entry->owner_of == subsumed) {
+  auto& subsumed_set = owner_entry->owner_of;
+  if (subsumed_set.find(subsumed) != subsumed_set.end()) {
     return true;
   }
 
-  std::vector<TaskQueueId> owner_subsumed_keys = {
-      owner_entry->owner_of, owner_entry->subsumed_by, subsumed_entry->owner_of,
-      subsumed_entry->subsumed_by};
+  // Won't check owner_entry->owner_of, because it may contains items when
+  // merged with other different queues.
 
-  for (auto key : owner_subsumed_keys) {
-    if (key != _kUnmerged) {
-      return false;
-    }
+  // Ensure owner_entry->subsumed_by being _kUnmerged
+  if (owner_entry->subsumed_by != _kUnmerged) {
+    FML_LOG(WARNING) << "Thread merging failed: owner_entry was already "
+                        "subsumed by others, owner="
+                     << owner << ", subsumed=" << subsumed
+                     << ", owner->subsumed_by=" << owner_entry->subsumed_by;
+    return false;
   }
-
-  owner_entry->owner_of = subsumed;
+  // Ensure subsumed_entry->owner_of being empty
+  if (!subsumed_entry->owner_of.empty()) {
+    FML_LOG(WARNING)
+        << "Thread merging failed: subsumed_entry already owns others, owner="
+        << owner << ", subsumed=" << subsumed
+        << ", subsumed->owner_of.size()=" << subsumed_entry->owner_of.size();
+    return false;
+  }
+  // Ensure subsumed_entry->subsumed_by being _kUnmerged
+  if (subsumed_entry->subsumed_by != _kUnmerged) {
+    FML_LOG(WARNING) << "Thread merging failed: subsumed_entry was already "
+                        "subsumed by others, owner="
+                     << owner << ", subsumed=" << subsumed
+                     << ", subsumed->subsumed_by="
+                     << subsumed_entry->subsumed_by;
+    return false;
+  }
+  // All checking is OK, set merged state.
+  owner_entry->owner_of.insert(subsumed);
   subsumed_entry->subsumed_by = owner;
 
   if (HasPendingTasksUnlocked(owner)) {
@@ -255,16 +273,37 @@ bool MessageLoopTaskQueues::Merge(TaskQueueId owner, TaskQueueId subsumed) {
   return true;
 }
 
-bool MessageLoopTaskQueues::Unmerge(TaskQueueId owner) {
+bool MessageLoopTaskQueues::Unmerge(TaskQueueId owner, TaskQueueId subsumed) {
   std::lock_guard guard(queue_mutex_);
   const auto& owner_entry = queue_entries_.at(owner);
-  const TaskQueueId subsumed = owner_entry->owner_of;
-  if (subsumed == _kUnmerged) {
+  if (owner_entry->owner_of.empty()) {
+    FML_LOG(WARNING)
+        << "Thread unmerging failed: owner_entry doesn't own anyone, owner="
+        << owner << ", subsumed=" << subsumed;
+    return false;
+  }
+  if (owner_entry->subsumed_by != _kUnmerged) {
+    FML_LOG(WARNING)
+        << "Thread unmerging failed: owner_entry was subsumed by others, owner="
+        << owner << ", subsumed=" << subsumed
+        << ", owner_entry->subsumed_by=" << owner_entry->subsumed_by;
+    return false;
+  }
+  if (queue_entries_.at(subsumed)->subsumed_by == _kUnmerged) {
+    FML_LOG(WARNING) << "Thread unmerging failed: subsumed_entry wasn't "
+                        "subsumed by others, owner="
+                     << owner << ", subsumed=" << subsumed;
+    return false;
+  }
+  if (owner_entry->owner_of.find(subsumed) == owner_entry->owner_of.end()) {
+    FML_LOG(WARNING) << "Thread unmerging failed: owner_entry didn't own the "
+                        "given subsumed queue id, owner="
+                     << owner << ", subsumed=" << subsumed;
     return false;
   }
 
   queue_entries_.at(subsumed)->subsumed_by = _kUnmerged;
-  owner_entry->owner_of = _kUnmerged;
+  owner_entry->owner_of.erase(subsumed);
 
   if (HasPendingTasksUnlocked(owner)) {
     WakeUpUnlocked(owner, GetNextWakeTimeUnlocked(owner));
@@ -280,11 +319,14 @@ bool MessageLoopTaskQueues::Unmerge(TaskQueueId owner) {
 bool MessageLoopTaskQueues::Owns(TaskQueueId owner,
                                  TaskQueueId subsumed) const {
   std::lock_guard guard(queue_mutex_);
-  return owner != _kUnmerged && subsumed != _kUnmerged &&
-         subsumed == queue_entries_.at(owner)->owner_of;
+  if (owner == _kUnmerged || subsumed == _kUnmerged) {
+    return false;
+  }
+  auto& subsumed_set = queue_entries_.at(owner)->owner_of;
+  return subsumed_set.find(subsumed) != subsumed_set.end();
 }
 
-TaskQueueId MessageLoopTaskQueues::GetSubsumedTaskQueueId(
+std::set<TaskQueueId> MessageLoopTaskQueues::GetSubsumedTaskQueueId(
     TaskQueueId owner) const {
   std::lock_guard guard(queue_mutex_);
   return queue_entries_.at(owner)->owner_of;
@@ -318,13 +360,11 @@ bool MessageLoopTaskQueues::HasPendingTasksUnlocked(
     return true;
   }
 
-  const TaskQueueId subsumed = entry->owner_of;
-  if (subsumed == _kUnmerged) {
-    // this is not an owner and queue is empty.
-    return false;
-  } else {
-    return !queue_entries_.at(subsumed)->task_source->IsEmpty();
-  }
+  auto& subsumed_set = entry->owner_of;
+  return std::any_of(
+      subsumed_set.begin(), subsumed_set.end(), [&](const auto& subsumed) {
+        return !queue_entries_.at(subsumed)->task_source->IsEmpty();
+      });
 }
 
 fml::TimePoint MessageLoopTaskQueues::GetNextWakeTimeUnlocked(
@@ -336,32 +376,35 @@ TaskSource::TopTask MessageLoopTaskQueues::PeekNextTaskUnlocked(
     TaskQueueId owner) const {
   FML_DCHECK(HasPendingTasksUnlocked(owner));
   const auto& entry = queue_entries_.at(owner);
-  const TaskQueueId subsumed = entry->owner_of;
-  if (subsumed == _kUnmerged) {
+  if (entry->owner_of.empty()) {
+    FML_CHECK(!entry->task_source->IsEmpty());
     return entry->task_source->Top();
   }
 
+  // Use optional for the memory of TopTask object.
+  std::optional<TaskSource::TopTask> top_task;
+
+  std::function<void(const TaskSource*)> top_task_updater =
+      [&top_task](const TaskSource* source) {
+        if (source && !source->IsEmpty()) {
+          TaskSource::TopTask other_task = source->Top();
+          if (!top_task.has_value() || top_task->task > other_task.task) {
+            top_task.emplace(other_task);
+          }
+        }
+      };
+
   TaskSource* owner_tasks = entry->task_source.get();
-  TaskSource* subsumed_tasks = queue_entries_.at(subsumed)->task_source.get();
-
-  // we are owning another task queue
-  const bool subsumed_has_task = !subsumed_tasks->IsEmpty();
-  const bool owner_has_task = !owner_tasks->IsEmpty();
-  fml::TaskQueueId top_queue_id = owner;
-  if (owner_has_task && subsumed_has_task) {
-    const auto owner_task = owner_tasks->Top();
-    const auto subsumed_task = subsumed_tasks->Top();
-    if (owner_task.task > subsumed_task.task) {
-      top_queue_id = subsumed;
-    } else {
-      top_queue_id = owner;
-    }
-  } else if (owner_has_task) {
-    top_queue_id = owner;
-  } else {
-    top_queue_id = subsumed;
+  top_task_updater(owner_tasks);
+
+  for (TaskQueueId subsumed : entry->owner_of) {
+    TaskSource* subsumed_tasks = queue_entries_.at(subsumed)->task_source.get();
+    top_task_updater(subsumed_tasks);
   }
-  return queue_entries_.at(top_queue_id)->task_source->Top();
+  // At least one task at the top because PeekNextTaskUnlocked() is called after
+  // HasPendingTasksUnlocked()
+  FML_CHECK(top_task.has_value());
+  return top_task.value();
 }
 
 }  // namespace fml