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Wire up custom event loop interop for the GLFW embedder. #9089
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| Original file line number | Diff line number | Diff line change |
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| // 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. | ||
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| #include "flutter/shell/platform/glfw/glfw_event_loop.h" | ||
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| #include <GLFW/glfw3.h> | ||
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| #include <atomic> | ||
| #include <utility> | ||
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| namespace flutter { | ||
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| 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)) {} | ||
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| GLFWEventLoop::~GLFWEventLoop() = default; | ||
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| bool GLFWEventLoop::RunsTasksOnCurrentThread() const { | ||
| return std::this_thread::get_id() == main_thread_id_; | ||
| } | ||
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| void GLFWEventLoop::WaitForEvents(std::chrono::nanoseconds max_wait) { | ||
| const auto now = TaskTimePoint::clock::now(); | ||
| std::vector<FlutterTask> expired_tasks; | ||
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| // 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; | ||
| } | ||
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| // 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); | ||
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| // Remove the tasks from the delayed tasks queue. | ||
| task_queue_.pop(); | ||
| } | ||
| } | ||
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| // Fire expired tasks. | ||
| { | ||
|
There was a problem hiding this comment. There's no scoped lock; why is there a scope block? (I would argue that the fact that you did this despite in not being any mechanical reason I can see is an indication that it should be broken into helpers.) There was a problem hiding this comment. Yeah, you are right. I wrote the comments first as pseudocode then filled it out with real code. As noted earlier, I don't think adding scopes means that the block should necessarily be extracted into its own helper routine. |
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| // Flushing tasks here without holing onto the task queue mutex. | ||
| for (const auto& task : expired_tasks) { | ||
| on_task_expired_(&task); | ||
| } | ||
| } | ||
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| // 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>>; | ||
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| std::lock_guard<std::mutex> lock(task_queue_mutex_); | ||
| const auto next_wake = task_queue_.empty() ? TaskTimePoint::max() | ||
| : task_queue_.top().fire_time; | ||
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| const auto duration_to_wait = std::chrono::duration_cast<Seconds>( | ||
| std::min(next_wake - now, max_wait)); | ||
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| 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(); | ||
| } | ||
| } | ||
| } | ||
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| 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); | ||
| } | ||
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| void GLFWEventLoop::PostTask(FlutterTask flutter_task, | ||
| uint64_t flutter_target_time_nanos) { | ||
| static std::atomic_uint64_t sGlobalTaskOrder(0); | ||
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| Task task; | ||
| task.order = ++sGlobalTaskOrder; | ||
| task.fire_time = TimePointFromFlutterTime(flutter_target_time_nanos); | ||
| task.task = flutter_task; | ||
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| { | ||
| std::lock_guard<std::mutex> lock(task_queue_mutex_); | ||
| task_queue_.push(task); | ||
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| // 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. | ||
| } | ||
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| ::glfwPostEmptyEvent(); | ||
| } | ||
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| } // namespace flutter | ||
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -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. | ||
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| #ifndef FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_ | ||
| #define FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_ | ||
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| #include <chrono> | ||
| #include <deque> | ||
| #include <mutex> | ||
| #include <queue> | ||
| #include <thread> | ||
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| #include "flutter/shell/platform/embedder/embedder.h" | ||
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| namespace flutter { | ||
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| // An event loop implementation that supports Flutter Engine tasks scheduling in | ||
| // the GLFW event loop. | ||
| class GLFWEventLoop { | ||
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| public: | ||
| using TaskExpiredCallback = std::function<void(const FlutterTask*)>; | ||
| GLFWEventLoop(std::thread::id main_thread_id, | ||
| TaskExpiredCallback on_task_expired); | ||
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| ~GLFWEventLoop(); | ||
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| // Returns if the current thread is the thread used by the GLFW event loop. | ||
| bool RunsTasksOnCurrentThread() const; | ||
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| // 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()); | ||
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| // Post a Flutter engine tasks to the event loop for delayed execution. | ||
| void PostTask(FlutterTask flutter_task, uint64_t flutter_target_time_nanos); | ||
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| private: | ||
| using TaskTimePoint = std::chrono::steady_clock::time_point; | ||
| struct Task { | ||
| uint64_t order; | ||
| TaskTimePoint fire_time; | ||
| FlutterTask task; | ||
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| 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_; | ||
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| GLFWEventLoop(const GLFWEventLoop&) = delete; | ||
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| GLFWEventLoop& operator=(const GLFWEventLoop&) = delete; | ||
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| static TaskTimePoint TimePointFromFlutterTime( | ||
| uint64_t flutter_target_time_nanos); | ||
| }; | ||
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| } // namespace flutter | ||
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| #endif // FLUTTER_SHELL_PLATFORM_GLFW_GLFW_EVENT_LOOP_H_ | ||
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This seems unrelated to the PR?
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This is necessary after
--build-glfw-shellon Mac.