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C++線程之thread詳解_C 語(yǔ)言

作者：早睡的葉子 ? 更新時(shí)間： 2022-05-19 編程語(yǔ)言

1.創(chuàng)建線程

直接初始話thread類對(duì)象進(jìn)行創(chuàng)建線程，創(chuàng)建線程后調(diào)用join()方法，讓主線程等待子線程完成工程。

#include 
#include 
void thread_function()
{
    std::cout << "thread function\n";
}
int main()
{
    std::thread t(&thread_function);   // t starts running
    std::cout << "main thread\n";
    t.join();   // main thread waits for the thread t to finish
    return 0;
}

2.守護(hù)線程

我們可以調(diào)用detach()方法，將線程變?yōu)槭刈o(hù)線程，完成線程和主線程的分離。一旦線程分離，我們不能強(qiáng)迫它再次加入主線程，再次調(diào)用join()方法會(huì)報(bào)錯(cuò)的。

一旦分離，線程應(yīng)該永遠(yuǎn)以這種方式存在。調(diào)用join()函數(shù)之前可以使用函數(shù)joinable()檢查線程是否可以加入主線程，加強(qiáng)程序健壯性。

// t2.cpp
int main()
{
    std::thread t(&thread_function);
    std::cout << "main thread\n";
    if( t.joinable( ) ) 
        // t.join();
    // t.join();
    t.detach();
    return 0;
}

3. 可調(diào)用對(duì)象

線程可以調(diào)用

  • 函數(shù)指針
  • 類對(duì)象
  • lamda表達(dá)式

1.函數(shù)指針

就像之前舉例的樣子

2.類對(duì)象

#include 
#include 
class MyFunctor
{
public:
    void operator()() {
        std::cout << "functor\n";
    }
};
int main()
{
    MyFunctor fnctor;
    // 這樣是不能運(yùn)行的，
    // std::thread t(fnctor);
    // 必須按照這樣進(jìn)行初始話。
    // MyFunctor fnctor;  Note that we had to add () to enclose the MyFunctor(). 
    std::thread t((MyFunctor())); // it's related to the function declaration convention in C++.
    std::cout << "main thread\n";
    t.join();
    return 0;
}

3.lamda表達(dá)式

#include 
#include 
class MyFunctor
{
public:
    void operator()() {
        std::cout << "functor\n";
    }
};
int main()
{
    MyFunctor fnctor;
    // 這樣是不能運(yùn)行的，
    // std::thread t(fnctor);
    // 必須按照這樣進(jìn)行初始話。
    // MyFunctor fnctor;  Note that we had to add () to enclose the MyFunctor(). 
    std::thread t((MyFunctor())); // it's related to the function declaration convention in C++.
    std::cout << "main thread\n";
    t.join();
    return 0;
}

4. 傳參

傳參分為三種

1.值傳遞

2.引用傳遞

3.不復(fù)制，也不共享內(nèi)存的傳參方式move()

#include 
#include 
#include 
void thread_function(std::string s)
{
    std::cout << "thread function ";
    std::cout << "message is = " << s << std::endl;
}
int main()
{
    std::string s = "Kathy Perry";
    // 1. 值傳遞
    std::thread t(&thread_function, s);
    // 2. 引用傳遞
    std::thread t(&thread_function, std::ref(s));
    // 3. 不復(fù)制，也不共享內(nèi)存的傳參方式`move()
    std::thread t(&thread_function, std::move(s));
    std::cout << "main thread message = " << s << std::endl;
    t.join();
    return 0;
}

5. 線程的移動(dòng)和復(fù)制

// t5.cpp
#include 
#include 
void thread_function()
{
    std::cout << "thread function\n";
}
int main()
{
    std::thread t(&thread_function);
    std::cout << "main thread\n";
    //  transfer the ownership of the thread by moving it:
    std::thread t2 = move(t);
    t2.join();
    return 0;
}

6.線程id

獲取線程的id：?this_thread::get_id()

總共有多少個(gè)線程：std::thread::hardware_concurrency()

程序

int main()
{
    std::string s = "Kathy Perry";
    std::thread t(&thread_function, std::move(s));
    std::cout << "main thread message = " << s << std::endl;
    std::cout << "main thread id = " << std::this_thread::get_id() << std::endl;
    std::cout << "child thread id = " << t.get_id() << std::endl;
    t.join();
    return 0;
}

輸出

thread function message is = Kathy Perry
main thread message =
main thread id = 1208
child thread id = 5224

7. 互斥mutex

互斥鎖可能是 C++ 中使用最廣泛的數(shù)據(jù)保護(hù)機(jī)制，但重要的是構(gòu)造我們的代碼以保護(hù)正確的數(shù)據(jù)并避免接口中固有的競(jìng)爭(zhēng)條件。互斥鎖也有自己的問(wèn)題，表現(xiàn)為死鎖和保護(hù)太多或太少的數(shù)據(jù)

標(biāo)準(zhǔn) C++ 庫(kù)提供了std::lock_guard類模板，它實(shí)現(xiàn) 了互斥鎖的RAII習(xí)慣用法。它在構(gòu)造時(shí)鎖定提供的互斥鎖并在銷毀時(shí)解鎖它，從而確保始終正確解鎖鎖定的互斥鎖。

#include 
#include 
#include 
#include 
#include 
using namespace std;
// a global variable
std::listmyList;
// a global instance of std::mutex to protect global variable
std::mutex myMutex;
void addToList(int max, int interval)
{
	// the access to this function is mutually exclusive
	std::lock_guard guard(myMutex);
	for (int i = 0; i < max; i++) {
		if( (i % interval) == 0) myList.push_back(i);
	}
}
void printList()
{
	// the access to this function is mutually exclusive
	std::lock_guard guard(myMutex);
	for (auto itr = myList.begin(), end_itr = myList.end(); itr != end_itr; ++itr ) {
		cout << *itr << ",";
	}
}
int main()
{
	int max = 100;
	std::thread t1(addToList, max, 1);
	std::thread t2(addToList, max, 10);
	std::thread t3(printList);
	t1.join();
	t2.join();
	t3.join();
	return 0;
}

總結(jié)

原文鏈接：https://blog.csdn.net/sexyluna/article/details/123531927
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