[C++知识库]std::thread

1. std::thread创建和使用

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

void func(int num, string str)
{
	for (int i = 0; i < 10; ++i)
	{
		cout << "子线程: i = " << i << "num: "
			<< num << ", str: " << str << endl;
	}
}

void func1()
{
	for (int i = 0; i < 10; ++i)
	{
		cout << "子线程: i = " << i << endl;
	}
}


int main()
{
	//bug:没有回收子线程
	cout << "主线程的线程ID: " << this_thread::get_id() << endl;
	thread t(func, 520, "i love you");
	thread t1(func1);
	cout << "线程t 的线程ID: " << t.get_id() << endl;
	cout << "线程t1的线程ID: " << t1.get_id() << endl;

	return 0;
}

2. join()

阻塞当前线程直至 *this 所标识的线程结束其执行。

int main()
{
	cout << "主线程的线程ID: " << this_thread::get_id() << endl;
	thread t(func, 520, "i love you");
	thread t1(func1);
	cout << "线程t 的线程ID: " << t.get_id() << endl;
	cout << "线程t1的线程ID: " << t1.get_id() << endl;
	t.join();
	t1.join();

	return 0;
}

3. detach()

从 thread 对象分离执行线程，允许执行独立地持续。一旦该线程退出，则释放任何分配的资源。
调用 detach 后 *this 不再占有任何线程。

int main()
{
	cout << "主线程的线程ID: " << this_thread::get_id() << endl;
	thread t(func, 520, "i love you");
	thread t1(func1);
	cout << "线程t 的线程ID: " << t.get_id() << endl;
	cout << "线程t1的线程ID: " << t1.get_id() << endl;
	t.detach();
	t1.detach();
	// 让主线程休眠, 等待子线程执行完毕
	this_thread::sleep_for(chrono::seconds(5));
}

4. joinable()

检查 std::thread 对象是否标识活跃的执行线程。具体而言，若 get_id() != std::thread::id() 则返回 true 。故默认构造的 thread 不可结合。
结束执行代码，但仍未结合的线程仍被当作活跃的执行线程，从而可结合。

#include <iostream>
#include <thread>
#include <chrono>
 
void foo()
{
    std::this_thread::sleep_for(std::chrono::seconds(1));
}
 
int main()
{
    std::thread t;
    std::cout << "before starting, joinable: " << std::boolalpha << t.joinable()
              << '\n';
 
    t = std::thread(foo);
    std::cout << "after starting, joinable: " << t.joinable() 
              << '\n';
 
    t.join();
    std::cout << "after joining, joinable: " << t.joinable() 
              << '\n';
}

输出

before starting, joinable: false
after starting, joinable: true
after joining, joinable: false

5. 静态函数 hardware_concurrency

int main()
{
	int num = thread::hardware_concurrency();
	cout << "CPU number: " << num << endl;
}

输出

//当前机器cpu个数
CPU NUMBER: 8

参考

高效程序员 C++ 线程的使用
cppreference.com std::thread