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0. 概要

对于C++应用编程，定时器模块是一个至关重要的组件。为了确保系统的可靠性和功能安全，我们需要设计一个高效、稳定的定时器。
本文将实现一个跨平台安全的C++ SafeTimer 定时器模块，并提供完整的gtest单元测试。

完整代码见 gitee_safe_timer

类似设计请参阅文章：C++编程： 线程池封装、任务异步执行以及任务延迟执行

1. 设计目标

目标是创建一个符合功能安全要求的定时器模块，具体包括以下几点：

1. 线程安全：确保多线程环境下的安全性。
2. 高可靠性：在异常情况下能够安全地停止定时器。
3. 高可维护性：代码结构清晰，易于扩展和维护。

2. SafeTimer 类的实现

SafeTimer 类是我们实现的核心，它提供了单次触发（SingleShot）和重复触发（Repeat）两种定时功能，同时还支持暂停（Pause）和恢复（Resume）。以下是 SafeTimer 类的完整实现。

2.1 头文件 safe_timer.h

#ifndef SAFE_TIMER_H
#define SAFE_TIMER_H#include <atomic>
#include <chrono>
#include <condition_variable>
#include <functional>
#include <memory>
#include <mutex>
#include <string>
#include <thread>// 定义SafeTimer类，用于管理定时任务
class SafeTimer {public:// 构造函数，可以指定定时器的名称，默认为"SafeTimer"explicit SafeTimer(const std::string& name = "SafeTimer") noexcept;// 析构函数virtual ~SafeTimer() noexcept;// 禁止复制构造和赋值操作SafeTimer(const SafeTimer&) = delete;SafeTimer& operator=(const SafeTimer&) = delete;// 返回定时器的名称std::string GetName() const noexcept;// 返回定时器是否处于循环模式bool IsLoop() const noexcept;// 设置一个一次性定时任务template <typename Callable, typename... Arguments>bool SingleShot(uint64_t interval_in_millis, Callable&& func, Arguments&&... args);// 设置一个可重复的定时任务template <typename Callable, typename... Arguments>bool Repeat(uint64_t interval_in_millis, Callable&& func, Arguments&&... args);// 设置一个可重复的定时任务，可以选择是否立即执行一次template <typename Callable, typename... Arguments>bool Repeat(uint64_t interval_in_millis, bool call_func_immediately, Callable&& func, Arguments&&... args);// 取消当前的定时任务void Cancel() noexcept;// 暂停当前的定时任务bool Pause() noexcept;// 恢复已暂停的定时任务void Resume() noexcept;// 判断定时器是否处于空闲状态bool IsTimerIdle() const noexcept;private:// 启动定时任务的核心函数bool Start(uint64_t interval_in_millis, std::function<void()> callback, bool loop, bool callback_immediately = false);// 尝试使定时器过期，用于取消或暂停任务void TryExpire() noexcept;// 销毁线程资源void DestroyThread() noexcept;private:// 定时器的名称std::string name_;// 标记定时器是否为循环模式bool is_loop_;// 原子布尔类型，标记定时器是否已经过期std::atomic_bool is_expired_;// 原子布尔类型，标记是否尝试使定时器过期std::atomic_bool try_to_expire_;// 独占所有权的线程智能指针std::unique_ptr<std::thread> thread_;// 互斥锁，用于线程同步std::mutex mutex_;// 条件变量，用于线程间的通信std::condition_variable condition_;// 定时器启动时的时间点std::chrono::time_point<std::chrono::steady_clock> start_time_;// 定时器结束时的时间点std::chrono::time_point<std::chrono::steady_clock> end_time_;// 剩余任务时间（毫秒）uint64_t task_remain_time_ms_;// 回调函数，当定时器过期时调用std::function<void()> callback_;
};// 实现模板成员函数// 单次定时任务的实现
template <typename Callable, typename... Arguments>
bool SafeTimer::SingleShot(uint64_t interval_in_millis, Callable&& func, Arguments&&... args) {// 创建一个绑定的函数对象，用于延迟执行auto action = std::bind(std::forward<Callable>(func), std::forward<Arguments>(args)...);// 调用私有的Start函数，设置一次性任务return Start(interval_in_millis, action, false);
}// 循环定时任务的实现
template <typename Callable, typename... Arguments>
bool SafeTimer::Repeat(uint64_t interval_in_millis, Callable&& func, Arguments&&... args) {// 创建一个绑定的函数对象，用于延迟执行auto action = std::bind(std::forward<Callable>(func), std::forward<Arguments>(args)...);// 调用私有的Start函数，设置循环任务return Start(interval_in_millis, action, true);
}// 循环定时任务的实现，允许指定是否立即执行一次
template <typename Callable, typename... Arguments>
bool SafeTimer::Repeat(uint64_t interval_in_millis, bool call_func_immediately, Callable&& func, Arguments&&... args) {// 创建一个绑定的函数对象，用于延迟执行auto action = std::bind(std::forward<Callable>(func), std::forward<Arguments>(args)...);// 调用私有的Start函数，设置循环任务，可选择立即执行return Start(interval_in_millis, action, true, call_func_immediately);
}#endif  // SAFE_TIMER_H

源文件 safe_timer.cpp

#include "safe_timer.h"
#include <iostream>SafeTimer::SafeTimer(const std::string& name) noexcept: name_(name), is_loop_(false), is_expired_(true), try_to_expire_(false), task_remain_time_ms_(0), callback_(nullptr) {}SafeTimer::~SafeTimer() noexcept {TryExpire();
}std::string SafeTimer::GetName() const noexcept {return name_;
}bool SafeTimer::IsLoop() const noexcept {return is_loop_;
}void SafeTimer::Cancel() noexcept {if (is_expired_ || try_to_expire_ || !thread_) {return;}TryExpire();
}bool SafeTimer::Pause() noexcept {if (is_expired_) {return false;}auto now = std::chrono::steady_clock::now();auto elapsed = std::chrono::duration_cast<std::chrono::milliseconds>(now - start_time_).count();auto remaining = std::chrono::duration_cast<std::chrono::milliseconds>(end_time_ - now).count();if (remaining <= 0) {return false;}Cancel();task_remain_time_ms_ = static_cast<uint64_t>(remaining);return true;
}void SafeTimer::Resume() noexcept {if (task_remain_time_ms_ > 0 && callback_) {Start(task_remain_time_ms_, callback_, false, false);task_remain_time_ms_ = 0;}
}bool SafeTimer::IsTimerIdle() const noexcept {return is_expired_ && !try_to_expire_;
}bool SafeTimer::Start(uint64_t interval_in_millis, std::function<void()> callback, bool loop, bool callback_immediately) {if (!is_expired_ || try_to_expire_) {return false;}is_expired_ = false;is_loop_ = loop;DestroyThread();thread_ = std::make_unique<std::thread>([this, interval_in_millis, callback, callback_immediately]() {if (callback_immediately) {callback();}while (!try_to_expire_) {callback_ = callback;start_time_ = std::chrono::steady_clock::now();end_time_ = start_time_ + std::chrono::milliseconds(interval_in_millis);std::unique_lock<std::mutex> lock(mutex_);condition_.wait_until(lock, end_time_);if (try_to_expire_) {break;}callback();if (!is_loop_) {break;}}is_expired_ = true;try_to_expire_ = false;});return true;
}void SafeTimer::TryExpire() noexcept {try_to_expire_ = true;DestroyThread();try_to_expire_ = false;
}void SafeTimer::DestroyThread() noexcept {if (thread_) {{std::lock_guard<std::mutex> lock(mutex_);condition_.notify_all();}if (thread_->joinable()) {thread_->join();}thread_.reset();}
}

3. 工作流程图

这个流程图分别展示了 SingleShot 和 Repeat 的流程，同时包括了暂停、恢复和取消操作。

4. 单元测试

为了验证 SafeTimer 的功能，我们编写了一组单元测试，覆盖了定时器的各种使用场景，包括单次触发、重复触发、暂停、恢复和取消等功能。

#include <gmock/gmock.h>
#include <gtest/gtest.h>#include <chrono>
#include <thread>#include "safe_timer.h"class CallbackMock {public:MOCK_METHOD(void, CallbackMethod, ());
};class SafeTimerTest : public testing::Test {protected:CallbackMock callback_mock;void SetUp() override {// Do nothing now}void TearDown() override {// Do nothing now}
};TEST_F(SafeTimerTest, SingleShot) {SafeTimer timer("TestSingleShot");EXPECT_CALL(callback_mock, CallbackMethod()).Times(1);int time_ms = 100;  // Delay time in millisecondsbool ret = timer.SingleShot(time_ms, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds(time_ms + 100));
}TEST_F(SafeTimerTest, RepeatWithParamCallImmediately) {SafeTimer timer("TestRepeatWithParamCallImmediately");int repeat_count = 3;  // Number of times repeat should executeint time_ms = 200;     // Delay time in millisecondsEXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count);// Execute once immediatelyauto ret = timer.Repeat(time_ms, true, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds((repeat_count - 1) * time_ms + 100));// Cancel previous timertimer.Cancel();EXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count);// Do not execute immediatelyret = timer.Repeat(time_ms, false, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds(repeat_count * time_ms + 100));
}TEST_F(SafeTimerTest, RepeatWithoutParamCallImmediately) {SafeTimer timer("TestRepeatWithoutParamCallImmediately");int repeat_count = 3;  // Number of times repeat should executeint time_ms = 500;     // Delay time in millisecondsEXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count);auto ret = timer.Repeat(time_ms, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds(repeat_count * time_ms + 100));
}TEST_F(SafeTimerTest, Cancel) {SafeTimer timer("Cancel");int repeat_count = 3;  // Number of times repeat should executeint time_ms = 500;  // Delay time in millisecondsEXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count - 1);// Execute once immediatelyauto ret = timer.Repeat(time_ms, true, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for 100ms less to ensure cancel is called in timestd::this_thread::sleep_for(std::chrono::milliseconds((repeat_count - 1) * time_ms - 100));timer.Cancel();
}// Test if cancelling immediately after timer creation causes any issues
// Expected: Cancelling immediately after timer creation should directly return and perform no operation
TEST_F(SafeTimerTest, CancelBeforeSingleShot) {SafeTimer timer("TestCancelBeforeSingleShot");EXPECT_CALL(callback_mock, CallbackMethod()).Times(1);timer.Cancel();int time_ms = 100;  // Delay time in millisecondsauto ret = timer.SingleShot(time_ms, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds(time_ms + 100));
}// Test if cancelling immediately after creating a SingleShot timer causes any issues
// Expected: Properly cancel without issues
TEST_F(SafeTimerTest, CancelImmediatelyAfterSingleShot) {SafeTimer timer("TestCancelImmediatelyAfterSingleShot");EXPECT_CALL(callback_mock, CallbackMethod()).Times(0);int time_ms = 100;  // Delay time in millisecondstimer.SingleShot(time_ms, &CallbackMock::CallbackMethod, &callback_mock);timer.Cancel();// Sleep for an additional 100ms to ensure callback is not calledstd::this_thread::sleep_for(std::chrono::milliseconds(time_ms + 100));
}TEST_F(SafeTimerTest, CancelAfterSingleShot) {SafeTimer timer("TestCancelAfterSingleShot");EXPECT_CALL(callback_mock, CallbackMethod()).Times(1);int time_ms = 100;  // Delay time in millisecondsauto ret = timer.SingleShot(time_ms, &CallbackMock::CallbackMethod, &callback_mock);EXPECT_TRUE(ret);// Sleep for an additional 100ms to ensure executionstd::this_thread::sleep_for(std::chrono::milliseconds(time_ms + 100));timer.Cancel();
}TEST_F(SafeTimerTest, Pause) {SafeTimer timer("Pause");int repeat_count = 2;  // Number of times repeat should executeint time_ms = 500;  // Delay time in millisecondsEXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count - 1);// Execute once immediatelytimer.Repeat(time_ms, true, &CallbackMock::CallbackMethod, &callback_mock);// Sleep for 100ms less to ensure pause is called in timestd::this_thread::sleep_for(std::chrono::milliseconds((repeat_count - 1) * time_ms - 100));auto ret = timer.Pause();EXPECT_TRUE(ret);
}TEST_F(SafeTimerTest, Resume) {SafeTimer timer("Resume");int repeat_count = 3;  // Number of times repeat should executeint time_ms = 100;  // Delay time in millisecondsEXPECT_CALL(callback_mock, CallbackMethod()).Times(repeat_count);// Execute once immediatelytimer.Repeat(time_ms, true, &CallbackMock::CallbackMethod, &callback_mock);int time_advance_pause = 50;  // Time in milliseconds to pause in advance// Sleep for time_advance_pause ms less to ensure pause is called in timestd::this_thread::sleep_for(std::chrono::milliseconds((repeat_count - 1) * time_ms - time_advance_pause));timer.Pause();timer.Resume();// Sleep for an additional 100ms to ensure timer execution is completedstd::this_thread::sleep_for(std::chrono::milliseconds(time_advance_pause + 100));
}int main(int argc, char** argv) {testing::InitGoogleMock(&argc, argv);return RUN_ALL_TESTS();
}

以上代码是使用Google Test和Google Mock进行单元测试，以下是几项要点：

1. 单次触发测试：

   • SingleShot测试了SafeTimer在设定的延时后只触发一次CallbackMethod。

2. 重复触发测试：

   • RepeatWithParamCallImmediately测试了计时器立即执行并重复触发回调的功能。
   • RepeatWithoutParamCallImmediately测试了计时器不立即执行，仅按照设定间隔重复触发回调的功能。

3. 取消计时器测试：

   • Cancel测试了在计时器执行过程中取消操作是否有效。
   • CancelBeforeSingleShot测试了在单次触发计时器创建后立即取消是否有效。
   • CancelImmediatelyAfterSingleShot测试了在单次触发计时器执行前立即取消的效果。
   • CancelAfterSingleShot测试了在单次触发计时器执行后再取消的效果。

4. 暂停与恢复计时器测试：

   • Pause测试了暂停计时器的功能。
   • Resume测试了暂停后恢复计时器的功能。

每个测试都使用EXPECT_CALL设置了预期的回调调用次数，并在适当的延时时间后检查回调是否按预期执行。

执行结果：

$ ./safe_timer_test 
[==========] Running 9 tests from 1 test suite.
[----------] Global test environment set-up.
[----------] 9 tests from SafeTimerTest
[ RUN      ] SafeTimerTest.SingleShot
[       OK ] SafeTimerTest.SingleShot (200 ms)
[ RUN      ] SafeTimerTest.RepeatWithParamCallImmediately
[       OK ] SafeTimerTest.RepeatWithParamCallImmediately (1201 ms)
[ RUN      ] SafeTimerTest.RepeatWithoutParamCallImmediately
[       OK ] SafeTimerTest.RepeatWithoutParamCallImmediately (1600 ms)
[ RUN      ] SafeTimerTest.Cancel
[       OK ] SafeTimerTest.Cancel (900 ms)
[ RUN      ] SafeTimerTest.CancelBeforeSingleShot
[       OK ] SafeTimerTest.CancelBeforeSingleShot (200 ms)
[ RUN      ] SafeTimerTest.CancelImmediatelyAfterSingleShot
[       OK ] SafeTimerTest.CancelImmediatelyAfterSingleShot (201 ms)
[ RUN      ] SafeTimerTest.CancelAfterSingleShot
[       OK ] SafeTimerTest.CancelAfterSingleShot (200 ms)
[ RUN      ] SafeTimerTest.Pause
[       OK ] SafeTimerTest.Pause (400 ms)
[ RUN      ] SafeTimerTest.Resume
[       OK ] SafeTimerTest.Resume (300 ms)
[----------] 9 tests from SafeTimerTest (5208 ms total)[----------] Global test environment tear-down
[==========] 9 tests from 1 test suite ran. (5208 ms total)
[  PASSED  ] 9 tests.