Wrap concurrent message loop tasks in an autorelease pool on iOS/Mac platforms (flutter/engine#42459)

See https://github.com/flutter/flutter/issues/127482

engine/src/flutter/ci/licenses_golden/licenses_flutter

@@ -863,6 +863,7 @@ ORIGIN: ../../../flutter/fml/command_line.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/compiler_specific.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/concurrent_message_loop.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/concurrent_message_loop.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/fml/concurrent_message_loop_factory.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/container.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/dart/dart_converter.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/dart/dart_converter.h + ../../../flutter/LICENSE
@@ -921,6 +922,7 @@ ORIGIN: ../../../flutter/fml/platform/android/scoped_java_ref.cc + ../../../flut
 ORIGIN: ../../../flutter/fml/platform/android/scoped_java_ref.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/cf_utils.cc + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/cf_utils.h + ../../../flutter/LICENSE
+ORIGIN: ../../../flutter/fml/platform/darwin/concurrent_message_loop_factory.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/message_loop_darwin.h + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/message_loop_darwin.mm + ../../../flutter/LICENSE
 ORIGIN: ../../../flutter/fml/platform/darwin/paths_darwin.mm + ../../../flutter/LICENSE
@@ -3534,6 +3536,7 @@ FILE: ../../../flutter/fml/command_line.h
 FILE: ../../../flutter/fml/compiler_specific.h
 FILE: ../../../flutter/fml/concurrent_message_loop.cc
 FILE: ../../../flutter/fml/concurrent_message_loop.h
+FILE: ../../../flutter/fml/concurrent_message_loop_factory.cc
 FILE: ../../../flutter/fml/container.h
 FILE: ../../../flutter/fml/dart/dart_converter.cc
 FILE: ../../../flutter/fml/dart/dart_converter.h
@@ -3592,6 +3595,7 @@ FILE: ../../../flutter/fml/platform/android/scoped_java_ref.cc
 FILE: ../../../flutter/fml/platform/android/scoped_java_ref.h
 FILE: ../../../flutter/fml/platform/darwin/cf_utils.cc
 FILE: ../../../flutter/fml/platform/darwin/cf_utils.h
+FILE: ../../../flutter/fml/platform/darwin/concurrent_message_loop_factory.mm
 FILE: ../../../flutter/fml/platform/darwin/message_loop_darwin.h
 FILE: ../../../flutter/fml/platform/darwin/message_loop_darwin.mm
 FILE: ../../../flutter/fml/platform/darwin/paths_darwin.mm

engine/src/flutter/fml/BUILD.gn

@@ -131,9 +131,15 @@ source_set("fml") {
   libs = []
 
   if (is_ios || is_mac) {
-    sources += [ "platform/posix/shared_mutex_posix.cc" ]
+    sources += [
+      "platform/darwin/concurrent_message_loop_factory.mm",
+      "platform/posix/shared_mutex_posix.cc",
+    ]
   } else {
-    sources += [ "synchronization/shared_mutex_std.cc" ]
+    sources += [
+      "concurrent_message_loop_factory.cc",
+      "synchronization/shared_mutex_std.cc",
+    ]
   }
 
   if (is_ios || is_mac) {

engine/src/flutter/fml/concurrent_message_loop.cc

@@ -11,12 +11,6 @@
 
 namespace fml {
 
-std::shared_ptr<ConcurrentMessageLoop> ConcurrentMessageLoop::Create(
-    size_t worker_count) {
-  return std::shared_ptr<ConcurrentMessageLoop>{
-      new ConcurrentMessageLoop(worker_count)};
-}
-
 ConcurrentMessageLoop::ConcurrentMessageLoop(size_t worker_count)
     : worker_count_(std::max<size_t>(worker_count, 1ul)) {
   for (size_t i = 0; i < worker_count_; ++i) {
@@ -60,7 +54,7 @@ void ConcurrentMessageLoop::PostTask(const fml::closure& task) {
         << "Tried to post a task to shutdown concurrent message "
            "loop. The task will be executed on the callers thread.";
     lock.unlock();
-    task();
+    ExecuteTask(task);
     return;
   }
 
@@ -103,12 +97,12 @@ void ConcurrentMessageLoop::WorkerMain() {
     TRACE_EVENT0("flutter", "ConcurrentWorkerWake");
     // Execute the primary task we woke up for.
     if (task) {
-      task();
+      ExecuteTask(task);
     }
 
     // Execute any thread tasks.
     for (const auto& thread_task : thread_tasks) {
-      thread_task();
+      ExecuteTask(thread_task);
     }
 
     if (shutdown_now) {
@@ -117,6 +111,10 @@ void ConcurrentMessageLoop::WorkerMain() {
   }
 }
 
+void ConcurrentMessageLoop::ExecuteTask(const fml::closure& task) {
+  task();
+}
+
 void ConcurrentMessageLoop::Terminate() {
   std::scoped_lock lock(tasks_mutex_);
   shutdown_ = true;

engine/src/flutter/fml/concurrent_message_loop.h

@@ -24,7 +24,7 @@ class ConcurrentMessageLoop
   static std::shared_ptr<ConcurrentMessageLoop> Create(
       size_t worker_count = std::thread::hardware_concurrency());
 
-  ~ConcurrentMessageLoop();
+  virtual ~ConcurrentMessageLoop();
 
   size_t GetWorkerCount() const;
 
@@ -36,6 +36,10 @@ class ConcurrentMessageLoop
 
   bool RunsTasksOnCurrentThread();
 
+ protected:
+  explicit ConcurrentMessageLoop(size_t worker_count);
+  virtual void ExecuteTask(const fml::closure& task);
+
  private:
   friend ConcurrentTaskRunner;
 
@@ -48,8 +52,6 @@ class ConcurrentMessageLoop
   std::map<std::thread::id, std::vector<fml::closure>> thread_tasks_;
   bool shutdown_ = false;
 
-  explicit ConcurrentMessageLoop(size_t worker_count);
-
   void WorkerMain();
 
   void PostTask(const fml::closure& task);

engine/src/flutter/fml/concurrent_message_loop_factory.cc

@@ -0,0 +1,15 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/concurrent_message_loop.h"
+
+namespace fml {
+
+std::shared_ptr<ConcurrentMessageLoop> ConcurrentMessageLoop::Create(
+    size_t worker_count) {
+  return std::shared_ptr<ConcurrentMessageLoop>{
+      new ConcurrentMessageLoop(worker_count)};
+}
+
+}  // namespace fml

engine/src/flutter/fml/platform/darwin/concurrent_message_loop_factory.mm

@@ -0,0 +1,26 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "flutter/fml/concurrent_message_loop.h"
+
+namespace fml {
+
+class ConcurrentMessageLoopDarwin : public ConcurrentMessageLoop {
+  friend class ConcurrentMessageLoop;
+
+ protected:
+  explicit ConcurrentMessageLoopDarwin(size_t worker_count) : ConcurrentMessageLoop(worker_count) {}
+
+  void ExecuteTask(const fml::closure& task) override {
+    @autoreleasepool {
+      task();
+    }
+  }
+};
+
+std::shared_ptr<ConcurrentMessageLoop> ConcurrentMessageLoop::Create(size_t worker_count) {
+  return std::shared_ptr<ConcurrentMessageLoop>{new ConcurrentMessageLoopDarwin(worker_count)};
+}
+
+}  // namespace fml