C++多线程编程一

1.C++多线程初步：

#include <iostream>
#include <thread>
#include <Windows.h>

using namespace std;

void run()
{
    MessageBoxA(, "hello world", "hello china", );

}

void main0101()
{
    //同步（阻塞）
    run();
    run();
    run();

    cin.get();
}

void main0102()
{
    //并行，异步，非阻塞
    thread t1(run);        //根据函数初始化并执行,t1在栈上
    thread t2(run);
    thread t3(run);
    thread t4(run);

    cin.get();
}

void main0103()
{
    //并行，异步，非阻塞
    //thread t[5]{ run,run,run,run,run };    //error C2440: “初始化”: 无法从“void (__cdecl *)(void)”转换为“std::thread”
    thread t[]{ thread(run),thread(run), thread(run), thread(run), thread(run) };    //初始化线程数组（线程池）

    cin.get();
}

void main0104()
{
    //堆上
    thread *pthread1(new thread(run));
    thread *pthread2(new thread(run));
    thread *pthread3(new thread(run));

    cin.get();
}

void main()
{
    //堆上开辟了线程数组
    thread *pthread1(new thread[]{ thread(run),thread(run), thread(run), thread(run), thread(run) });

    cin.get();
}

2. 线程冻结与解冻调试：

#include <iostream>
#include <thread>
#include <Windows.h>
#include <cstdlib>

using namespace std;

void test()
{
    int i = ;
    while ()
    {
        cout << ++i << endl;
        Sleep();
    }
}

void main()
{
    thread *p(new thread(test));    //堆上

    system("pause");

    system("pause");

    system("pause");

    system("pause");

    cin.get();
}

3. 多线程传参：

#include <iostream>
#include <thread>
#include <Windows.h>

using namespace std;

void showmsg(const char *str1, const char *str2)
{
    MessageBoxA(, str1, str2, );
}

void main()
{
    thread th1(showmsg, "", "");
    thread th2(showmsg, "", "");
    thread th3(showmsg, "", "");
    cin.get();
}

4. 多线程的join 和detach：

#include <iostream>
#include <thread>
#include <array>
#include <Windows.h>

using namespace std;

//join让当前主线程等待所有子线程执行完成才能退出
//detach脱离主线程的绑定，主线程退出的时候，不影响子线程。
void show()
{
    MessageBoxA(, "", "", );
}

void main0401()
{
    array<thread, > threads{ thread(show),thread(show),thread(show) };

    for (int i = ; i < ; i++)
    {
        cout << threads[i].joinable() << endl;    //判断是否可以join
        threads[i].join();    //主线程等待子线程执行完成再退出
    }

    auto n = thread::hardware_concurrency();    //获取CPU是几核
    cout << n << endl;

    cin.get();
}

void main()
{
    thread th(show);
    //th.join();
    th.detach();    //脱离主线程，主线程挂了不报错
    //detach以后线程无法通信

    th.joinable();
}

5. 原子变量与线程安全：

#include <iostream>
#include <thread>
#include <mutex>    //互斥量
#include <atomic>    //原子变量

using namespace std;

//线程安全，多线程访问不冲突就是线程安全，冲突则不安全
//int num = 0;

//mutex m;    //互斥，加锁解锁浪费时间

atomic_int num();    //原子变量不会发生线程冲突，属于线程安全

void run()
{
    for (int i = ; i < ; i++)
    {
        //m.lock();
        num++;
        //m.unlock();
    }
}

void main()
{
    clock_t start = clock();

    thread th1(run);
    thread th2(run);
    th1.join();
    th2.join();

    clock_t end = clock();
    cout << num << endl;
    cout << end - start << "ms" << endl;

    cin.get();
}
//全局变量，会发生冲突，结果不正确，速度快
//mutex，结果正确，速度慢
//atomic，结果正确，速度比mutex快

6. lambda 表达式与多线程：

#include <iostream>
#include <thread>
#include <Windows.h>
#include <chrono>

using namespace std;

void main0701()
{
    //auto fun = []() {MessageBoxA(0, "1", "2", 0); };
    //thread th1(fun);
    //thread th2(fun);

    thread th1([]() {MessageBoxA(, "", "", ); });
    thread th2([]() {MessageBoxA(, "", "", ); });

    cin.get();
}

void main()
{
    //thread th1([]() {cout << this_thread::get_id() << endl; });    //获取当前线程的id
    //thread th2([]() {cout << this_thread::get_id() << endl; });

    thread th1([]() {
        this_thread::sleep_for(chrono::seconds());    //等待3秒
        this_thread::yield();        //让CPU先执行其他线程，空闲了再执行我
        cout << this_thread::get_id() << endl;        //获取当前线程的id
        //this_thread::sleep_until();    //某个时刻到来之前一直等待
    });
    thread th2([]() {
        this_thread::sleep_for(chrono::seconds());    //等待10秒
        cout << this_thread::get_id() << endl;
    });

    cin.get();
}

7. 伪函数与多线程：

　　（1）伪函数概念：

#include <iostream>
using namespace std;

struct func
{
    void operator ()()    //伪函数，可以将对象名当做函数名来使用
    {
        cout << "hello china hello cpp" << endl;
    }

    void operator ()(int i)    //伪函数，可以将对象名当做函数名来使用
    {
        cout << "hello china hello cpp! " << i << endl;
    }
};

void main()
{
    func f1;
    f1();

    func f2;
    f2();

    cin.get();
}

　　（2）伪函数与多线程：

#include <iostream>
#include <thread>
#include <Windows.h>

using namespace std;

struct MyStruct
{
    MyStruct()
    {
        cout << "create" << endl;
    }
    ~MyStruct()
    {
        cout << "end" << endl;
    }

    void operator ()()    //对象名当做函数名使用，重载了()，但()只适用于当前结构体对象
    {
        MessageBoxA(, "", "", );

    }
};

void main()
{
    MyStruct go1;
    thread t1(go1);

    MyStruct go2;
    thread t2(go2);

    //MyStruct()是构造函数，创建一个临时对象,匿名对象
    //MyStruct()();
    //thread t3(MyStruct());//匿名的对象,不适合作为多线程参数，销毁太快

    //MyStruct *p = new MyStruct;
    MyStruct *p = new MyStruct();//多一个()就是构造函数

    cin.get();
}

8. 成员函数构建多线程：

#include <iostream>
#include <thread>
#include <Windows.h>

using namespace std;

struct fun
{
    void run1()
    {
        MessageBoxA(, "", "ABCDE", );
        cout << "hello china" << endl;
    }

    void run2(const char *str)
    {
        MessageBoxA(, str, str, );
        cout << "hello china" << endl;
    }
};

void main()
{
    //fun *p(nullptr);
    //p->run1();            //空类指针可以引用没有调用内部变量的成员函数

    fun fun1;
    //&fun::run引用成员函数
    thread th1(&fun::run1, fun1);
    thread th2(&fun::run1, fun1);

    thread th3(&fun::run2, fun1,"run2-1");
    thread th4(&fun::run2, fun1, "run2-2");

    cin.get();
}

9. 多线程通信future：

#include <iostream>
#include <thread>
#include <future>
#include <string>
#include <cstdlib>

using namespace std;

void main0401()
{
    string str1("");
    string str2("");
    string str3(str1 + str2);    //C++风格的字符串
    cout << str3 << endl;

    cin.get();
}

promise<string>val;    //全局通信变量

void main()
{
    thread th1([]()
    {
        future<string> fu = val.get_future();//获取未来的状态
        cout << "等待中..." << endl;
        cout << fu.get() << endl;
    });

    thread th2([]()
    {
        system("pause");
        val.set_value("I love CPP");
        system("pause");
    }); 

    th1.join();
    th2.join();

}

10. 基于继承的多线程：

#include <iostream>
#include <thread>

using namespace std;

class zhangthread :public thread //C++代码重用-->继承
{
public:
    zhangthread() :thread()    //子类调父类的构造函数
    {

    }

    template <typename T, typename...Args>    //子类调父类的构造函数,可变参数的构造
    zhangthread(T && func,Args &&...args):thread(   forward<T>(func),    forward<Args>(args)...   )
    {

    }

    void run(const char *cmd)    //新增的功能
    {
        system(cmd);
    }
};

void main()
{
    zhangthread t1([](){cout << "hello this is Zhang"<<endl;});
    t1.run("calc");

    zhangthread t2([](int num)    {cout << "hello this is Zhang"<<num<<endl; },   );
    t2.run("notepad");

    cin.get();
}

11. 条件变量：

#include <iostream>
#include <thread>
#include <mutex>
#include <condition_variable>    //条件变量

using namespace std;

//线程通信，结合mutex
//一个线程，多个线程处于等待，通知一个或通知多个

mutex m;                //线程互相排斥
condition_variable cv;    //线程通信

void main()
{
    thread **th = new thread * [];//开辟线程的指针数组

    for (int i = ; i < ; i++)
    {
        th[i] = new thread([](int index)
        {
            unique_lock<mutex> lck(m);    //锁定
            cv.wait_for(lck, chrono::hours());    //一直等待
            cout << index << endl;        //打印编号
        }  ,   i );    //传递参数

        this_thread::sleep_for(chrono::milliseconds());    //错开
    }

    for (int i = ; i < ; i++)
    {
        lock_guard<mutex> lckg(m);//解锁向导
        cv.notify_one();    //挨个通知
    }

    for (int i = ; i < ; i++)
    {
        th[i]->join();
        delete th[i];
    }

    delete[]th;    //释放指针数组

    cin.get();
}

12. 获取线程的结果：

#include <iostream>
#include <thread>
#include <future>//线程将来结果
#include <chrono>//时间
#include <mutex>

using namespace std;

mutex g_m;

void main()
{
    auto run = [=](int index)->int
    {
        lock_guard<mutex> lckg(g_m);    //加锁
        cout << this_thread::get_id() << " " << index << endl;    //获取线程id
        this_thread::sleep_for(chrono::seconds());    //等待10秒
        return index * ;    //返回结果
    };

    packaged_task<int(int)> pt1(run);
    packaged_task<int(int)> pt2(run);    //创建两个任务包

    thread t1([&]() {pt1(); });
    thread t2([&]() {pt2(); });    //开启线程

    cout << pt1.get_future().get() << endl;
    cout << pt2.get_future().get() << endl;    //获取结果

    t1.join();
    t2.join();

    cin.get();
}

13. 可变参数实现多线程：

#include <iostream>
#include <cstdarg>
#include <thread>

using namespace std;

//可变参数
int go(const char *fmt, ...)
{
    va_list ap;            //第一个数据（指针）
    va_start(ap, fmt);    //开始

    vprintf(fmt, ap);    //调用

    va_end(ap);            //结束

    return ;
}

void main()
{
    thread th(go, "%sABCD%d____%c____%x", "12345abc", , 'A', );

    cin.get();
}

14. 多线程实现并行计算：

#include <iostream>
#include <thread>
#include <future>
#include <vector>
#include <cstdlib>

using namespace std;

#define COUNT 1000000

//线程函数：
int add(vector<int> *arr, int start, int count)
{
    static mutex m;    //静态局部变量，只会初始化一次
    int sum();//保存结果

    for (int i = ; i < count; i++)
    {
        sum += (*arr)[start + i];//实现累加
    }

    {    //此处仅仅是计算过程中的显示，更清楚查看
        lock_guard<mutex> lckg(m);//加锁,不让其他线程干涉

        cout << "thread" << this_thread::get_id() << ",count=" << count << ",sum=" << sum << endl;
    }

    return sum;
}

void main()
{
    vector<int> data(COUNT);    //数组，100万的大小
    for (int i = ; i < COUNT; i++)
    {
        data[i] = i % ;    //0-999
    }

    vector< future<int> > result;//结果数组

    int cpus = thread::hardware_concurrency();//CPU核心的个数

    for (int i = ; i < cpus * ; i++)
    {
        //1000 10= 100 * 10
        //1000 9 = 1000 - 111*8
        int batch_each = COUNT / (cpus * );

        if (i == (cpus * ) - )
        {
            batch_each = COUNT - COUNT / (cpus * )*i;//最后一个承担的多一点
        }

        //不断压入结果
        result.push_back(async(add, &data, i*batch_each, batch_each));//async直接返回结果

    }

    //汇总
    int lastresult();
    for (int i = ; i < cpus * ; i++)
    {
        lastresult += result[i].get();//汇总结果，累加
    }
    cout << "lastresule=" << lastresult << endl;

    cin.get();
}