c++11并发之std::thread

知识链接：

https://www.cnblogs.com/lidabo/p/7852033.html

构造函数如下：

default ()

    thread() noexcept;

initialization()

    template <class Fn, class... Args> explicit thread (Fn&& fn, Args&&... args);

copy [deleted] ()

    thread (const thread&) = delete;

move []

    thread (thread&& x) noexcept;

().默认构造函数，创建一个空的 thread 执行对象。

().初始化构造函数，创建一个 thread 对象，该 thread 对象可被 joinable，新产生的线程会调用 fn 函数，该函数的参数由 args 给出。

().拷贝构造函数（被禁用），意味着 thread 不可被拷贝构造。

().move 构造函数，move 构造函数，调用成功之后 x 不代表任何 thread 执行对象。

注意：可被 joinable 的 thread 对象必须在他们销毁之前被主线程 join 或者将其设置为 detached

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

void fun1(int n)  //初始化构造函数

{

   cout << "Thread " << n << " executing\n";

   n += ;

   this_thread::sleep_for(chrono::milliseconds());

}

void fun2(int & n) //拷贝构造函数

{

    cout << "Thread " << n << " executing\n";

    n += ;

    this_thread::sleep_for(chrono::milliseconds());

}

int main()

{

    int n = ;

    thread t1;               //t1不是一个thread

    thread t2(fun1, n + );  //按照值传递

    t2.join();

    cout << "n=" << n << '\n';

    n = ;

    thread t3(fun2, ref(n)); //引用

    thread t4(move(t3));     //t4执行t3，t3不是thread

    t4.join();

    cout << "n=" << n << '\n';

    system("pause");

    return ;

} 

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

void running()

{

    cout << "thread is running..." << endl;

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    // 栈上

    thread t1(running); // 根据函数初始化执行

    thread t2(running);

    thread t3(running);

    // 线程数组

    thread th[] {thread(running), thread(running), thread(running)}; // 执行

    // 堆上

    thread* pt1(new thread(running));

    thread* pt2(new thread(running));

    thread* pt3(new thread(running));

    // 线程指针数组

    thread* pth(new thread[]{thread(running), thread(running), thread(running)});

    return a.exec();

}

多线程传递参数

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

void running(const char* str,const int id)

{

    cout << "thread" << id << "is running..."<< str << endl;

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    // 栈上

    thread t1(running,"hello1",); // 根据函数初始化执行

    thread t2(running,"hello2",);

    thread t3(running,"hello3",);

    return a.exec();

}

join

join 是让当前主线程等待所有的子线程执行完，才能退出。

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

void running(const char* str,const int id)

{

    cout << "thread" << id << "is running..."<< str << endl;

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    // 栈上

    thread t1(running,"hello1",); // 根据函数初始化执行

    thread t2(running,"hello2",);

    thread t3(running,"hello3",);

    cout << t1.joinable() << endl;

    cout << t2.joinable() << endl;

    cout << t3.joinable() << endl;

    t1.join(); // 主线程等待当前线程执行完成再退出

    t2.join();

    t3.join();

    return a.exec();

}

detach

线程 detach 脱离主线程的绑定，主线程挂了，子线程不报错，子线程执行完自动退出。

线程 detach以后，子线程会成为孤儿线程，线程之间将无法通信。

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

void running(const char* str,const int id)

{

    cout << "thread" << id << "is running..."<< str << endl;

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    // 栈上

    thread t1(running,"hello1",); // 根据函数初始化执行

    thread t2(running,"hello2",);

    thread t3(running,"hello3",);

    cout << t1.joinable() << endl;

    cout << t2.joinable() << endl;

    cout << t3.joinable() << endl;

    t1.detach();

    t2.detach();

    t3.detach();

    return a.exec();

}

获取cpu核心个数

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    auto n = thread::hardware_concurrency();//获取cpu核心个数

    cout << n << endl; #

    return a.exec();

}

CPP原子变量与线程安全。

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

using namespace std;

const int N = ;

int num = ;

void run()

{

    for (int i = ; i < N; ++i){

        num++;

    }

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    clock_t start = clock();

    thread t1(run);

    thread t2(run);

    t1.join();

    t2.join();

    clock_t end = clock();

    cout << "num=" << num << ",spend time:" << end - start << "ms" << endl;

    return a.exec();

}

运行结果：num=1157261,spend time:9ms
结果并不是200000，这是由于线程之间的冲突

互斥量

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

#include <mutex>

using namespace std;

const int N = ;

int num = ;

mutex m;

void run()

{

    m.lock();

    for (int i = ; i < N; ++i){

        num++;

    }

    m.unlock();

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    clock_t start = clock();

    thread t1(run);

    thread t2(run);

    t1.join();

    t2.join();

    clock_t end = clock();

    cout << "num=" << num << ",spend time:" << end - start << "ms" << endl;

    return a.exec();

}

运行结果：num=2,spend time:5ms

原子变量。

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

#include <mutex>

using namespace std;

const int N = ;

atomic_int num {}; // 不会发生线程冲突，线程安全

void run()

{

    for (int i = ; i < N; ++i){

        num++;

    }

}

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    clock_t start = clock();

    thread t1(run);

    thread t2(run);

    t1.join();

    t2.join();

    clock_t end = clock();

    cout << "num=" << num << ",spend time:" << end - start << "ms" << endl;

    return a.exec();

}

C++11 并发之std::atomic。

lambda与多线程

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

#include <mutex>

using namespace std;

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    auto fun = [](const char* str){cout << str << endl;};

    thread t1(fun,"hello world");

    thread t2(fun,"hello C++");

    return a.exec();

}

时间等待相关

#include <QCoreApplication>

#include<thread>

#include<chrono>

#include <iostream>

#include <mutex>

using namespace std;

int main(int argc, char *argv[])

{

    QCoreApplication a(argc, argv);

    auto fun = [](const char* str){

        this_thread::sleep_for(chrono::seconds());

        this_thread::yield();// 让cpu执行其他空闲线程

        cout << this_thread::get_id() << endl;

        cout << str << endl;

    };

    thread t1(fun,"hello world");

    return a.exec();

}