c++11并发之std::thread
2024-09-22 02:46:41
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();
}
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