线程管理

thread管理基础

thread_join_detach.cpp

• 线程启动后,销毁前要调用join或detach，否则std::thread的析构函数会调用std::terminate终止程序.
• 线程都有入口函数,入口main/foo 函数.
• 线程会在函数结束时完会退出.
• 使用join即可保证局部变量在线程结束后才被销毁.
• 将函数添加为std::thread的参数即可启动线程
• join过的std::thread joinable()为false,故不能再次被join
• 分离线程称为守护线程，即没有任何显式接口并运行在后台的线程，其特点是长时间运行。

class A{
    int _value;
public:
    A(int value):_value(value){std::cout<<"A("<<_value<<")"<<endl;}
    ~A(){std::cout<<"~A("<<_value<<")"<<endl;}
    int value() const { return _value; }
};

void foo(int value){
    system_clock::time_point  startTimer  = std::chrono::high_resolution_clock::now();
    std::cout << "starting sub thread =" << std::this_thread::get_id()<<"\tvalue =" << value<<endl;
    std::this_thread::sleep_for(std::chrono::seconds(value));
    PrintExitInfo(startTimer);
}
void foo_join(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    thread1.join();   // foo_join所在线程,等待线程thread1完成执行
    //保证局部变量obj在线程thread1结束后才被销毁.
}

void foo_detach(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    thread1.detach();   // 允许线程独立于foo_detach所在线程执行
    //变量obj被销毁,thread1可能还在运行.
}
void test_terminate(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    //thread1的析构函数会调用std::terminate终止程序,obj未被销毁.
}
int main()
{
    A obj{0};
    std::cout << "starting main thread =" << std::this_thread::get_id()<<endl;
    system_clock::time_point startTimer = std::chrono::high_resolution_clock::now();
//    test_terminate(1);
    foo_detach(5);
    foo_join(3);
    PrintExitInfo(startTimer);

    return 0;
}

• A(0)
  starting main thread =1
  A(5)
  ~A(5)
  A(3)
  starting sub thread =2	value =5
  starting sub thread =3	value =3
  Exiting thread =3	duration:3011.49 ms
  ~A(3)
  Exiting thread =1	duration:3011.55 ms
  ~A(0)
  

为线程函数传递参数

• 有参数的函数也能传给std::thread，参数的默认实参会被忽略
• std::thread会无视参数的引用类型，因此需要使用std::ref来生成一个引用包裹对象以传入引用类型
• 也可以传递类成员函数
• 如果参数是move-only对象则需要使用std::move

void f(int i = 1){  std::cout << i <<endl;}
void Func(int& n) { ++n; std::cout << n <<endl; }
struct AA {
    void f(int i) { std::cout << i<<endl; }
};
void FuncPoint(std::unique_ptr<int> p)
{
    std::cout << *p<<endl;
}
int main()
{
    int i = 1;
    std::thread t(f, i); // 第一个参数为函数名，其余参数为函数的参数
    t.join();

    std::thread t2(Func, std::ref(i));
    t2.join();

    AA a;
    std::thread t3(&AA::f, &a, 42); // 第一个参数为成员函数地址，第二个参数为实例地址
    t3.join();

    std::unique_ptr<int> p(new int(43));
    std::thread t4(FuncPoint, std::move(p));
    t4.join();
}

线程标识

//std::thread::hardware_concurrency();  //支持的并发线程数
std::thread::id masterThread; // 主线程
int main()
{
    masterThread = std::this_thread::get_id();
}

转移线程所有权

void g();
void f(int i) { std::cout << i; }

std::thread gg()
{
  return std::thread(f, 42);
}
int main()
{
  std::thread t1(f);
std::thread t2 = std::move(t1); // t1所有权给t2，t2关联执行f的线程
t1 = std::thread(g); // t1重新关联一个执行g的线程
std::thread t3;
t3 = std::move(t2); // t3关联t2的线程，t2无关联
t1 = std::move(t3); // t1已有关联g的线程，调用std::terminate终止程序
  
  std::thread t{gg()};
  t.join();
}

#include <iostream>
#include <thread>
#include <chrono>
using namespace std;
using namespace std::chrono;

class A{
    int _value;
public:
    A(int value):_value(value){std::cout<<"A("<<_value<<")"<<endl;}
    ~A(){std::cout<<"~A("<<_value<<")"<<endl;}
    int value() const { return _value; }
};

void PrintExitInfo(system_clock::time_point startTimer)
{
    auto EndTimer = high_resolution_clock::now();
    duration<double, std::milli> fp_ms = EndTimer - startTimer;
    std::cout << "Exiting thread =" << std::this_thread::get_id() << "\tduration:"<< fp_ms.count() << " ms"<<endl;
}

void foo(int value){
    system_clock::time_point  startTimer  = std::chrono::high_resolution_clock::now();
    std::cout << "starting sub thread =" << std::this_thread::get_id()<<"\tvalue =" << value<<endl;
    std::this_thread::sleep_for(std::chrono::seconds(value));
    PrintExitInfo(startTimer);
}

void foo_join(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    thread1.join();   // foo_join所在线程,等待线程thread1完成执行
    //保证局部变量obj在线程thread1结束后才被销毁.
}

void foo_detach(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    thread1.detach();   // 允许线程独立于foo_detach所在线程执行
    //变量obj被销毁,thread1可能还在运行.
}
void test_terminate(int value){
    A obj{value};
    std::thread thread1(foo,obj.value());
    //thread1的析构函数会调用std::terminate终止程序,obj未被销毁.
}

int main()
{
    std::thread::id masterThread; // 主线程
    masterThread = std::this_thread::get_id();

    A obj{0};
    std::cout << "starting main thread =" << masterThread <<endl;
    system_clock::time_point startTimer = std::chrono::high_resolution_clock::now();
    //    test_terminate(1);
    foo_detach(5);
    foo_join(3);
    PrintExitInfo(startTimer);

    return 0;
}