Wire up custom event loop interop for the GLFW embedder. (#9089)

Author: chinmaygarde

ci/licenses_golden/licenses_flutter

@@ -918,6 +918,8 @@ FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/flutte
 FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/flutter_window_controller.h
 FILE: ../../../flutter/shell/platform/glfw/client_wrapper/include/flutter/plugin_registrar_glfw.h
 FILE: ../../../flutter/shell/platform/glfw/flutter_glfw.cc
+FILE: ../../../flutter/shell/platform/glfw/glfw_event_loop.cc
+FILE: ../../../flutter/shell/platform/glfw/glfw_event_loop.h
 FILE: ../../../flutter/shell/platform/glfw/key_event_handler.cc
 FILE: ../../../flutter/shell/platform/glfw/key_event_handler.h
 FILE: ../../../flutter/shell/platform/glfw/keyboard_hook_handler.h

shell/platform/glfw/BUILD.gn

@@ -33,6 +33,8 @@ source_set("flutter_glfw_headers") {
 source_set("flutter_glfw") {
   sources = [
     "flutter_glfw.cc",
+    "glfw_event_loop.cc",
+    "glfw_event_loop.h",
     "key_event_handler.cc",
     "key_event_handler.h",
     "keyboard_hook_handler.h",
@@ -65,6 +67,11 @@ source_set("flutter_glfw") {
       "$flutter_root/shell/platform/linux/config:gtk3",
       "$flutter_root/shell/platform/linux/config:x11",
     ]
+  } else if (is_mac) {
+    libs = [
+      "CoreVideo.framework",
+      "IOKit.framework",
+    ]
   }
 }
 

shell/platform/glfw/flutter_glfw.cc

@@ -15,6 +15,7 @@
 #include "flutter/shell/platform/common/cpp/client_wrapper/include/flutter/plugin_registrar.h"
 #include "flutter/shell/platform/common/cpp/incoming_message_dispatcher.h"
 #include "flutter/shell/platform/embedder/embedder.h"
+#include "flutter/shell/platform/glfw/glfw_event_loop.h"
 #include "flutter/shell/platform/glfw/key_event_handler.h"
 #include "flutter/shell/platform/glfw/keyboard_hook_handler.h"
 #include "flutter/shell/platform/glfw/platform_handler.h"
@@ -79,8 +80,11 @@ struct FlutterDesktopWindowControllerState {
   // Handler for the flutter/platform channel.
   std::unique_ptr<flutter::PlatformHandler> platform_handler;
 
-  // Whether or not the pointer has been added (or if tracking is enabled, has
-  // been added since it was last removed).
+  // The event loop for the main thread that allows for delayed task execution.
+  std::unique_ptr<flutter::GLFWEventLoop> event_loop;
+
+  // Whether or not the pointer has been added (or if tracking is enabled,
+  // has been added since it was last removed).
   bool pointer_currently_added = false;
 
   // The screen coordinates per inch on the primary monitor. Defaults to a sane
@@ -489,11 +493,13 @@ static void GLFWErrorCallback(int error_code, const char* description) {
 // provided).
 //
 // Returns a caller-owned pointer to the engine.
-static FlutterEngine RunFlutterEngine(GLFWwindow* window,
-                                      const char* assets_path,
-                                      const char* icu_data_path,
-                                      const char** arguments,
-                                      size_t arguments_count) {
+static FlutterEngine RunFlutterEngine(
+    GLFWwindow* window,
+    const char* assets_path,
+    const char* icu_data_path,
+    const char** arguments,
+    size_t arguments_count,
+    const FlutterCustomTaskRunners* custom_task_runners) {
   // FlutterProjectArgs is expecting a full argv, so when processing it for
   // flags the first item is treated as the executable and ignored. Add a dummy
   // value so that all provided arguments are used.
@@ -528,6 +534,7 @@ static FlutterEngine RunFlutterEngine(GLFWwindow* window,
   args.command_line_argc = static_cast<int>(argv.size());
   args.command_line_argv = &argv[0];
   args.platform_message_callback = GLFWOnFlutterPlatformMessage;
+  args.custom_task_runners = custom_task_runners;
   FlutterEngine engine = nullptr;
   auto result =
       FlutterEngineRun(FLUTTER_ENGINE_VERSION, &config, &args, window, &engine);
@@ -578,9 +585,38 @@ FlutterDesktopWindowControllerRef FlutterDesktopCreateWindow(
   // GLFWMakeResourceContextCurrent immediately.
   state->resource_window = CreateShareWindowForWindow(window);
 
+  // Create an event loop for the window. It is not running yet.
+  state->event_loop = std::make_unique<flutter::GLFWEventLoop>(
+      std::this_thread::get_id(),  // main GLFW thread
+      [state = state.get()](const auto* task) {
+        if (FlutterEngineRunTask(state->engine, task) != kSuccess) {
+          std::cerr << "Could not post an engine task." << std::endl;
+        }
+      });
+
+  // Configure task runner interop.
+  FlutterTaskRunnerDescription platform_task_runner = {};
+  platform_task_runner.struct_size = sizeof(FlutterTaskRunnerDescription);
+  platform_task_runner.user_data = state.get();
+  platform_task_runner.runs_task_on_current_thread_callback =
+      [](void* state) -> bool {
+    return reinterpret_cast<FlutterDesktopWindowControllerState*>(state)
+        ->event_loop->RunsTasksOnCurrentThread();
+  };
+  platform_task_runner.post_task_callback =
+      [](FlutterTask task, uint64_t target_time_nanos, void* state) -> void {
+    reinterpret_cast<FlutterDesktopWindowControllerState*>(state)
+        ->event_loop->PostTask(task, target_time_nanos);
+  };
+
+  FlutterCustomTaskRunners custom_task_runners = {};
+  custom_task_runners.struct_size = sizeof(FlutterCustomTaskRunners);
+  custom_task_runners.platform_task_runner = &platform_task_runner;
+
   // Start the engine.
-  state->engine = RunFlutterEngine(window, assets_path, icu_data_path,
-                                   arguments, argument_count);
+  state->engine =
+      RunFlutterEngine(window, assets_path, icu_data_path, arguments,
+                       argument_count, &custom_task_runners);
   if (state->engine == nullptr) {
     return nullptr;
   }
@@ -704,15 +740,17 @@ void FlutterDesktopRunWindowLoop(FlutterDesktopWindowControllerRef controller) {
   // Necessary for GTK thread safety.
   XInitThreads();
 #endif
+
   while (!glfwWindowShouldClose(window)) {
-    glfwPollEvents();
+    auto wait_duration = std::chrono::milliseconds::max();
 #ifdef FLUTTER_USE_GTK
+    // If we are not using GTK, there is no point in waking up.
+    wait_duration = std::chrono::milliseconds(10);
     if (gtk_events_pending()) {
       gtk_main_iteration();
     }
 #endif
-    // TODO(awdavies): This will be deprecated soon.
-    __FlutterEngineFlushPendingTasksNow();
+    controller->event_loop->WaitForEvents(wait_duration);
   }
   FlutterDesktopDestroyWindow(controller);
 }
@@ -738,8 +776,9 @@ FlutterDesktopEngineRef FlutterDesktopRunEngine(const char* assets_path,
                                                 const char* icu_data_path,
                                                 const char** arguments,
                                                 size_t argument_count) {
-  auto engine = RunFlutterEngine(nullptr, assets_path, icu_data_path, arguments,
-                                 argument_count);
+  auto engine =
+      RunFlutterEngine(nullptr, assets_path, icu_data_path, arguments,
+                       argument_count, nullptr /* custom task runners */);
   if (engine == nullptr) {
     return nullptr;
   }

shell/platform/glfw/glfw_event_loop.cc

@@ -0,0 +1,114 @@
+// 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/shell/platform/glfw/glfw_event_loop.h"
+
+#include <GLFW/glfw3.h>
+
+#include <atomic>
+#include <utility>
+
+namespace flutter {
+
+GLFWEventLoop::GLFWEventLoop(std::thread::id main_thread_id,
+                             TaskExpiredCallback on_task_expired)
+    : main_thread_id_(main_thread_id),
+      on_task_expired_(std::move(on_task_expired)) {}
+
+GLFWEventLoop::~GLFWEventLoop() = default;
+
+bool GLFWEventLoop::RunsTasksOnCurrentThread() const {
+  return std::this_thread::get_id() == main_thread_id_;
+}
+
+void GLFWEventLoop::WaitForEvents(std::chrono::nanoseconds max_wait) {
+  const auto now = TaskTimePoint::clock::now();
+  std::vector<FlutterTask> expired_tasks;
+
+  // Process expired tasks.
+  {
+    std::lock_guard<std::mutex> lock(task_queue_mutex_);
+    while (!task_queue_.empty()) {
+      const auto& top = task_queue_.top();
+      // If this task (and all tasks after this) has not yet expired, there is
+      // nothing more to do. Quit iterating.
+      if (top.fire_time > now) {
+        break;
+      }
+
+      // Make a record of the expired task. Do NOT service the task here
+      // because we are still holding onto the task queue mutex. We don't want
+      // other threads to block on posting tasks onto this thread till we are
+      // done processing expired tasks.
+      expired_tasks.push_back(task_queue_.top().task);
+
+      // Remove the tasks from the delayed tasks queue.
+      task_queue_.pop();
+    }
+  }
+
+  // Fire expired tasks.
+  {
+    // Flushing tasks here without holing onto the task queue mutex.
+    for (const auto& task : expired_tasks) {
+      on_task_expired_(&task);
+    }
+  }
+
+  // Sleep till the next task needs to be processed. If a new task comes
+  // along, the wait in GLFW will be resolved early because PostTask posts an
+  // empty event.
+  {
+    // Make sure the seconds are not integral.
+    using Seconds = std::chrono::duration<double, std::ratio<1>>;
+
+    std::lock_guard<std::mutex> lock(task_queue_mutex_);
+    const auto next_wake = task_queue_.empty() ? TaskTimePoint::max()
+                                               : task_queue_.top().fire_time;
+
+    const auto duration_to_wait = std::chrono::duration_cast<Seconds>(
+        std::min(next_wake - now, max_wait));
+
+    if (duration_to_wait.count() > 0.0) {
+      ::glfwWaitEventsTimeout(duration_to_wait.count());
+    } else {
+      // Avoid engine task priority inversion by making sure GLFW events are
+      // always processed even when there is no need to wait for pending engine
+      // tasks.
+      ::glfwPollEvents();
+    }
+  }
+}
+
+GLFWEventLoop::TaskTimePoint GLFWEventLoop::TimePointFromFlutterTime(
+    uint64_t flutter_target_time_nanos) {
+  const auto now = TaskTimePoint::clock::now();
+  const auto flutter_duration =
+      flutter_target_time_nanos - FlutterEngineGetCurrentTime();
+  return now + std::chrono::nanoseconds(flutter_duration);
+}
+
+void GLFWEventLoop::PostTask(FlutterTask flutter_task,
+                             uint64_t flutter_target_time_nanos) {
+  static std::atomic_uint64_t sGlobalTaskOrder(0);
+
+  Task task;
+  task.order = ++sGlobalTaskOrder;
+  task.fire_time = TimePointFromFlutterTime(flutter_target_time_nanos);
+  task.task = flutter_task;
+
+  {
+    std::lock_guard<std::mutex> lock(task_queue_mutex_);
+    task_queue_.push(task);
+
+    // Make sure the queue mutex is unlocked before waking up the loop. In case
+    // the wake causes this thread to be descheduled for the primary thread to
+    // process tasks, the acquisition of the lock on that thread while holding
+    // the lock here momentarily till the end of the scope is a pessimization.
+  }
+
+  ::glfwPostEmptyEvent();
+}
+
+}  // namespace flutter

shell/platform/glfw/glfw_event_loop.h

@@ -0,0 +1,73 @@
+// 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.
+
+#ifndef FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_
+#define FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_
+
+#include <chrono>
+#include <deque>
+#include <mutex>
+#include <queue>
+#include <thread>
+
+#include "flutter/shell/platform/embedder/embedder.h"
+
+namespace flutter {
+
+// An event loop implementation that supports Flutter Engine tasks scheduling in
+// the GLFW event loop.
+class GLFWEventLoop {
+ public:
+  using TaskExpiredCallback = std::function<void(const FlutterTask*)>;
+  GLFWEventLoop(std::thread::id main_thread_id,
+                TaskExpiredCallback on_task_expired);
+
+  ~GLFWEventLoop();
+
+  // Returns if the current thread is the thread used by the GLFW event loop.
+  bool RunsTasksOnCurrentThread() const;
+
+  // Wait for an any GLFW or pending Flutter Engine events and returns when
+  // either is encountered. Expired engine events are processed. The optional
+  // timeout should only be used when non-GLFW or engine events need to be
+  // processed in a polling manner.
+  void WaitForEvents(
+      std::chrono::nanoseconds max_wait = std::chrono::nanoseconds::max());
+
+  // Post a Flutter engine tasks to the event loop for delayed execution.
+  void PostTask(FlutterTask flutter_task, uint64_t flutter_target_time_nanos);
+
+ private:
+  using TaskTimePoint = std::chrono::steady_clock::time_point;
+  struct Task {
+    uint64_t order;
+    TaskTimePoint fire_time;
+    FlutterTask task;
+
+    struct Comparer {
+      bool operator()(const Task& a, const Task& b) {
+        if (a.fire_time == b.fire_time) {
+          return a.order > b.order;
+        }
+        return a.fire_time > b.fire_time;
+      }
+    };
+  };
+  std::thread::id main_thread_id_;
+  TaskExpiredCallback on_task_expired_;
+  std::mutex task_queue_mutex_;
+  std::priority_queue<Task, std::deque<Task>, Task::Comparer> task_queue_;
+  std::condition_variable task_queue_cv_;
+
+  GLFWEventLoop(const GLFWEventLoop&) = delete;
+
+  GLFWEventLoop& operator=(const GLFWEventLoop&) = delete;
+
+  static TaskTimePoint TimePointFromFlutterTime(
+      uint64_t flutter_target_time_nanos);
+};
+
+}  // namespace flutter
+
+#endif  // FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_

tools/gn

@@ -253,6 +253,7 @@ def to_gn_args(args):
 
     if sys.platform == 'darwin':
       gn_args['mac_sdk_path'] = args.mac_sdk_path
+      gn_args['build_glfw_shell'] = args.build_glfw_shell
       if gn_args['mac_sdk_path'] == '':
         gn_args['mac_sdk_path'] = os.getenv('FLUTTER_MAC_SDK_PATH', '')
 
@@ -323,6 +324,9 @@ def parse_args(args):
                       help='The IDE files to generate using GN. Use `gn gen help` and look for the --ide flag to' +
                       ' see supported IDEs. If this flag is not specified, a platform specific default is selected.')
 
+  parser.add_argument('--build-glfw-shell', dest='build_glfw_shell', default=False, action='store_true',
+                      help='Force building the GLFW shell on desktop platforms where it is not built by default.')
+
   return parser.parse_args(args)
 
 def main(argv):