c++多线程（十四） - std::future_status

朱雀 2022-02-09 10:53 835阅读 0赞

c++中， std::future\_status的定义如下：

enum class future_status
    {
    	ready,      //成功
    	timeout,    //超时
    	deferred    //延迟
    };

### 1. future\_status::ready   ###

线程myThread执行5秒，wait\_for等待了6s，所以线程myThread已经执行完毕，future\_status的值为ready 。

#include<iostream>
    #include<thread>
    #include<mutex>
    #include<future>
    using namespace std;
    
    int myThread()
    {
    	cout << "Thread start id = " << this_thread::get_id() << endl;
    	chrono::milliseconds time(5000); //休息5秒
    	this_thread::sleep_for(time);
    	cout << "Thread end id = " << this_thread::get_id() << endl;
    	return 5;
    }
    
    int main()
    {
    	cout << "Main start id = " << this_thread::get_id() << endl;
    	future<int> result = async(myThread);
    	cout << "continue......" << endl;
    	//等待6秒
    	std::future_status status = result.wait_for(std::chrono::seconds(6));
    	//超时，线程还没执行完
    	if (status == std::future_status::ready)
    	{
    		cout << "线程执行完" << endl;
    	}	 
    	//成功，线程已经执行完
    	else if (status == std::future_status::timeout)
    	{
    		cout << "线程超时" << endl;
    	}
    	//延迟，async第一个参数被设置为std::launch::deferred
    	else if (status == std::future_status::deferred)
    	{
    		cout << "线程延迟执行" << endl;
    	}
    	return 0;
    }

执行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70][]

### 2. future\_status::timeout ###

线程myThread执行5秒，wait\_for等待了1s，所以线程myThread超时，future\_status的值为timeout。

//等待1秒
    std::future_status status = result.wait_for(std::chrono::seconds(1));

执行结果

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70 1][]

### 3. future\_status::deferred ###

线程myThread延迟执行，future\_status的值为deferred。

//线程延迟执行
    future<int> result = async(std::launch::deferred, myThread);

执行结果

![2019050217261211.png][]

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70]: /images/20220206/90758467fe6e42cb935dc6ee3a068450.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2xpeWF6aGVuMjAxMQ_size_16_color_FFFFFF_t_70 1]: /images/20220206/b3e1d89a6ef74be5ad63a8b6eac3e07a.png
[2019050217261211.png]: /images/20220206/ab7facd5894a4fdcb61ebfa9ba8a9f90.png