Add a task system.

CMakeLists.txt

@@ -148,15 +148,16 @@ add_library(component
   src/ftxui/component/terminal_input_parser.hpp
   src/ftxui/component/util.cpp
   src/ftxui/component/window.cpp
+  src/ftxui/core/task.cpp
+  src/ftxui/core/task.hpp
+  src/ftxui/core/task_queue.cpp
+  src/ftxui/core/task_queue.hpp
+  src/ftxui/core/task_runner.cpp
+  src/ftxui/core/task_runner.hpp
 )
 
-target_link_libraries(dom
-  PUBLIC screen
-)
-
-target_link_libraries(component
-  PUBLIC dom
-)
+target_link_libraries(dom PUBLIC screen)
+target_link_libraries(component PUBLIC dom)
 
 if (NOT EMSCRIPTEN)
   find_package(Threads)

cmake/ftxui_test.cmake

@@ -19,13 +19,13 @@ add_executable(ftxui-tests
   src/ftxui/component/menu_test.cpp
   src/ftxui/component/modal_test.cpp
   src/ftxui/component/radiobox_test.cpp
-  src/ftxui/util/ref_test.cpp
   src/ftxui/component/receiver_test.cpp
   src/ftxui/component/resizable_split_test.cpp
   src/ftxui/component/screen_interactive_test.cpp
   src/ftxui/component/slider_test.cpp
   src/ftxui/component/terminal_input_parser_test.cpp
   src/ftxui/component/toggle_test.cpp
+  src/ftxui/core/task_test.cpp
   src/ftxui/dom/blink_test.cpp
   src/ftxui/dom/bold_test.cpp
   src/ftxui/dom/border_test.cpp
@@ -51,6 +51,7 @@ add_executable(ftxui-tests
   src/ftxui/dom/vbox_test.cpp
   src/ftxui/screen/color_test.cpp
   src/ftxui/screen/string_test.cpp
+  src/ftxui/util/ref_test.cpp
 )
 
 target_link_libraries(ftxui-tests

src/ftxui/core/task.cpp

@@ -0,0 +1,20 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include "task.hpp"
+
+namespace ftxui::task {
+bool PendingTask::operator<(const PendingTask& other) const {
+  if (!time && !other.time) {
+    return false;
+  }
+  if (!time) {
+    return true;
+  }
+  if (!other.time) {
+    return false;
+  }
+  return time.value() > other.time.value();
+}
+} // namespace ftxui::task
+

src/ftxui/core/task.hpp

@@ -0,0 +1,42 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#ifndef TASK_HPP
+#define TASK_HPP
+
+#include <chrono>
+#include <functional>
+#include <optional>
+
+namespace ftxui::task {
+
+/// A task represents a unit of work.
+using Task = std::function<void()>;
+
+/// A PendingTask represents a task that is scheduled to be executed at a
+/// specific time, or as soon as possible.
+struct PendingTask {
+  // Immediate task:
+  PendingTask(Task task) : task(std::move(task)) {}  // NOLINT
+
+  // Delayed task with a duration
+  PendingTask(Task task, std::chrono::steady_clock::duration duration)
+      : task(std::move(task)),
+        time(std::chrono::steady_clock::now() + duration) {}
+
+  /// The task to be executed.
+  Task task;
+
+  /// The time when the task should be executed. If the time is empty, the task
+  /// should be executed as soon as possible.
+  std::optional<std::chrono::steady_clock::time_point> time;
+
+  /// Compare two PendingTasks by their time.
+  /// If both tasks have no time, they are considered equal.
+  bool operator<(const PendingTask& other) const;
+};
+
+} // namespace ftxui::task
+
+
+#endif  // TASK_HPP_

src/ftxui/core/task_queue.cpp

@@ -0,0 +1,54 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include "task_queue.hpp"
+
+namespace ftxui::task {
+
+auto TaskQueue::PostTask(PendingTask task) -> void {
+  if (!task.time) {
+    immediate_tasks_.push(task);
+    return;
+  }
+
+  if (task.time.value() < std::chrono::steady_clock::now()) {
+    immediate_tasks_.push(task);
+    return;
+  }
+
+  delayed_tasks_.push(task);
+}
+
+auto TaskQueue::Get() -> MaybeTask {
+  // Attempt to execute a task immediately.
+  if (!immediate_tasks_.empty()) {
+    auto task = immediate_tasks_.front();
+    immediate_tasks_.pop();
+    return task.task;
+  }
+
+  // Move all tasks that can be executed to the immediate queue.
+  auto now = std::chrono::steady_clock::now();
+  while (!delayed_tasks_.empty() && delayed_tasks_.top().time.value() <= now) {
+    immediate_tasks_.push(delayed_tasks_.top());
+    delayed_tasks_.pop();
+  }
+
+  // Attempt to execute a task immediately.
+  if (!immediate_tasks_.empty()) {
+    auto task = immediate_tasks_.front();
+    immediate_tasks_.pop();
+    return task.task;
+  }
+
+  // If there are no tasks to execute, return the delay until the next task.
+  if (!delayed_tasks_.empty()) {
+    return delayed_tasks_.top().time.value() - now;
+  }
+
+  // If there are no tasks to execute, return the maximum duration.
+  return std::monostate{};
+}
+
+} // namespace ftxui::task
+

src/ftxui/core/task_queue.hpp

@@ -0,0 +1,36 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#ifndef TASK_QUEUE_HPP
+#define TASK_QUEUE_HPP
+
+#include <queue>
+#include <variant>
+
+#include "task.hpp"
+
+namespace ftxui::task {
+
+/// A task queue that schedules tasks to be executed in the future. Tasks can be
+/// scheduled to be executed immediately, or after a certain duration.
+/// - The tasks are executed in the order they were scheduled.
+/// - If multiple tasks are scheduled to be executed at the same time, they are
+///   executed in the order they were scheduled.
+/// - If a task is scheduled to be executed in the past, it is executed
+///   immediately.
+struct TaskQueue {
+  auto PostTask(PendingTask task) -> void;
+
+  using MaybeTask =
+      std::variant<Task, std::chrono::steady_clock::duration, std::monostate>;
+  auto Get() -> MaybeTask;
+
+ private:
+  std::queue<PendingTask> immediate_tasks_;
+  std::priority_queue<PendingTask> delayed_tasks_;
+};
+
+} // namespace ftxui::task
+
+
+#endif

src/ftxui/core/task_runner.cpp

@@ -0,0 +1,76 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include "task_runner.hpp"
+
+#include <cassert>
+#include <thread>
+
+namespace ftxui::task {
+
+static thread_local TaskRunner* current_task_runner = nullptr;  // NOLINT
+
+TaskRunner::TaskRunner() {
+  assert(!previous_task_runner_);
+  previous_task_runner_ = current_task_runner;
+  current_task_runner = this;
+}
+
+TaskRunner::~TaskRunner() {
+  current_task_runner = previous_task_runner_;
+}
+
+
+// static
+auto TaskRunner::Current() -> TaskRunner* {
+  assert(current_task_runner);
+  return current_task_runner;
+}
+
+auto TaskRunner::PostTask(Task task) -> void {
+  queue_.PostTask(PendingTask{std::move(task)});
+}
+
+auto TaskRunner::PostDelayedTask(Task task,
+                                 std::chrono::steady_clock::duration duration)
+    -> void {
+  queue_.PostTask(PendingTask{std::move(task), duration});
+}
+
+/// Runs the tasks in the queue.
+auto TaskRunner::RunUntilIdle()
+    -> std::optional<std::chrono::steady_clock::duration> {
+  while (true) {
+    auto maybe_task = queue_.Get();
+    if (std::holds_alternative<std::monostate>(maybe_task)) {
+      // No more tasks to execute, exit the loop.
+      return std::nullopt;
+    }
+
+    if (std::holds_alternative<Task>(maybe_task)) {
+      std::get<Task>(maybe_task)();
+      continue;
+    }
+
+    if (std::holds_alternative<std::chrono::steady_clock::duration>(
+            maybe_task)) {
+      return std::get<std::chrono::steady_clock::duration>(maybe_task);
+    }
+  }
+}
+
+auto TaskRunner::Run() -> void {
+  while (true) {
+    auto duration = RunUntilIdle();
+    if (!duration) {
+      // No more tasks to execute, exit the loop.
+      return;
+    }
+
+    // Sleep for the duration until the next task can be executed.
+    std::this_thread::sleep_for(duration.value());
+  }
+}
+
+} // namespace ftxui::task
+

src/ftxui/core/task_runner.hpp

@@ -0,0 +1,42 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#ifndef TASK_RUNNER_HPP
+#define TASK_RUNNER_HPP
+
+#include "task.hpp"
+#include "task_queue.hpp"
+
+namespace ftxui::task {
+
+class TaskRunner {
+ public:
+  TaskRunner();
+  ~TaskRunner();
+
+  // Returns the task runner for the current thread.
+  static auto Current() -> TaskRunner*;
+
+  /// Schedules a task to be executed immediately.
+  auto PostTask(Task task) -> void;
+
+  /// Schedules a task to be executed after a certain duration.
+  auto PostDelayedTask(Task task,
+                       std::chrono::steady_clock::duration duration) -> void;
+
+  /// Runs the tasks in the queue, return the delay until the next delayed task
+  /// can be executed.
+  auto RunUntilIdle() -> std::optional<std::chrono::steady_clock::duration>;
+
+  // Runs the tasks in the queue, blocking until all tasks are executed.
+  auto Run() -> void;
+
+ private:
+  TaskRunner* previous_task_runner_ = nullptr;
+  TaskQueue queue_;
+};
+
+} // namespace ftxui::task
+
+
+#endif  // TASK_RUNNER_HPP

src/ftxui/core/task_test.cpp

@@ -0,0 +1,95 @@
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+// Copyright 2024 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+#include "task.hpp"
+
+#include <gtest/gtest.h>
+
+#include "task_runner.hpp"
+
+namespace ftxui::task {
+
+TEST(TaskTest, Basic) {
+  std::vector<int> values;
+
+  auto task_1 = [&values] { values.push_back(1); };
+  auto task_2 = [&values] { values.push_back(2); };
+  auto task_3 = [&values] { values.push_back(3); };
+
+  auto runner = TaskRunner();
+
+  runner.PostTask(task_1);
+  runner.PostTask(task_2);
+  runner.PostTask(task_3);
+  while (true) {
+    auto duration = runner.RunUntilIdle();
+    if (!duration) {
+      break;
+    }
+    std::this_thread::sleep_for(duration.value());
+  }
+
+  EXPECT_EQ(values, (std::vector<int>{1, 2, 3}));
+}
+
+TEST(TaskTest, PostedWithinTask) {
+  std::vector<int> values;
+
+  auto task_1 = [&values] {
+    values.push_back(1);
+    auto task_2 = [&values] { values.push_back(5); };
+    TaskRunner::Current()->PostTask(std::move(task_2));
+    values.push_back(2);
+  };
+
+  auto task_2 = [&values] {
+    values.push_back(3);
+    auto task_2 = [&values] { values.push_back(6); };
+    TaskRunner::Current()->PostTask(std::move(task_2));
+    values.push_back(4);
+  };
+
+  auto runner = TaskRunner();
+
+  runner.PostTask(task_1);
+  runner.PostTask(task_2);
+  while (true) {
+    auto duration = runner.RunUntilIdle();
+    if (!duration) {
+      break;
+    }
+    std::this_thread::sleep_for(duration.value());
+  }
+
+  EXPECT_EQ(values, (std::vector<int>{1, 2, 3, 4, 5, 6}));
+}
+
+TEST(TaskTest, RunDelayedTask) {
+  std::vector<int> values;
+
+  auto task_1 = [&values] { values.push_back(1); };
+  auto task_2 = [&values] { values.push_back(2); };
+  auto task_3 = [&values] { values.push_back(3); };
+
+  auto runner = TaskRunner();
+
+  runner.PostDelayedTask(task_3, std::chrono::milliseconds(300));
+  runner.PostDelayedTask(task_1, std::chrono::milliseconds(100));
+  runner.PostDelayedTask(task_2, std::chrono::milliseconds(200));
+  while (true) {
+    auto duration = runner.RunUntilIdle();
+    if (!duration) {
+      break;
+    }
+    std::this_thread::sleep_for(duration.value());
+  }
+
+  EXPECT_EQ(values, (std::vector<int>{1, 2, 3}));
+}
+
+} // namespace ftxui::task
+
+