CPP 学习笔记-多线程

知识点１

转载自 https://www.ev0l.art/index.php/archives/9/

- Linux 下编译 带<thread> 的CPP需要加上 -pthread 编译选项。例如：

g++ -std=c++11 -pthread a.cpp

- QT Creator 编译带<thread>的CPP有ＢＵＧ，暂时不知道怎么去除！

代码1

#include <stdlib.h>v
#include <thread>

using namespace std;
void run(char* p)
{
    int i=0;
    i=system(p);
}

int main()
{
    char p[5][20]={
        "ls",
        "echo nihao",
        "gnome-terminal",
        "terminator",
        "ps -aux"

    };

    while("nimei")
    {
       static  int i(0);
        if(i<5){
            thread  *pt=new  thread(run,p[i]);
            i+=1;
            cout<<"I now is :\t"<<i<<endl;
        }
        else{
            break;
        }

        cout<<"Breaking...."<<endl;
    }




    cin.get();
    return 0;
}

 

知识点２

<li> 关于thread类的内部成

关键字	详细解释
id	Thread的iｄ
native_handle_type	native_handle_type
operator=	Move massive Thread
get_id	get Thread ID
joinable	get if joinable
join	join thread
detach	detach thread
swap	swap thread
native_handle	get native handle
hardware_concurrency[static]	Detect hardware concurrency (public static function)

<li> 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。

<li> 线程 detach以后，子线程会成为孤儿线程，线程之间将无法通信。

知识点３

<li>线程中变量的竞争控制是通过 mutex automic 来实现的

<li>mutex : 互斥量。需要包含头文件　<mutex> 来使用　-->速度慢

<li>atomic 原子变量。需要包含头文件<atomic>来实现　-->速度快，线程安全。

代码３

#include <iostream>
#include <stdlib.h>
#include <thread>
#include <atomic>

using namespace std;
int count(0);

void run()
{
    for(int i(0);i<1000000;i++)
    {
        count++;
        cout<<"\t"<<i<<"\t"<<count<<"\t";
    }
}

int main()
{
    auto n=thread::hardware_concurrency();

    thread* pt[n];
    for(int z=0;z<n;z++)
    {
        pt[z]=new thread(run);
        pt[z]->detach();

    }

    cout<<"Finally count is \t"<<count<<endl;
    cout<<"Used "<<n <<"threads"<<endl;




    cin.get();
    return 0;
}

 

运行结果不是1000000×２．

 1 #include <stdlib.h>
 2 #include <thread>
 3 #include <atomic>
 4 
 5 using namespace std;
 6 int count(0);
 7 
 8 void run()
 9 {
10     for(int i(0);i<1000000;i++)
11     {
12         count++;
13         cout<<"\t"<<i<<"\t"<<count<<"\t";
14     }
15 }
16 
17 int main()
18 {
19     auto n=thread::hardware_concurrency();
20 
21     thread* pt[n];
22     for(int z=0;z<n;z++)
23     {
24         pt[z]=new thread(run);
25         pt[z]->detach();
26 
27     }
28 
29     cout<<"Finally count is \t"<<count<<endl;
30     cout<<"Used "<<n <<"threads"<<endl;
31 
32 
33 
34 
35     cin.get();
36     return 0;
37 }

 

运行结果是1000000×２．正确

<li>atomic 声明方式为　atomic<int> a(100); 等号初始化会报错

<li>vim 按ＣＴＲＬ+S 后假死按　ＣＴＲＬ＋q 退出