多線程之互斥鎖（By C++）

時間 2019-12-09

標籤多線程互斥 c++ 欄目 Java 简体版

原文原文鏈接

　　首先貼一段win32API實現的多線程的代碼，使用CreateThread實現，若是不要傳參數，就把第四個參數設爲NULLios

#include<Windows.h>
#include<iostream>
using namespace std;

//有參數
DWORD WINAPI MyThread_lpParamter(LPVOID lpParamter)
{
    string *lp = (string *)lpParamter;
    while (1)
    {

        cout << "MyThread1 Runing :"<<lp->c_str()<<""<< endl;
        Sleep(5000);
    }
}

int main()
{
    string parameter = "我是參數";
    HANDLE hThread2 = CreateThread(NULL, 0, MyThread_lpParamter, &parameter, 0, NULL);
    CloseHandle(hThread2);
    while(1);
    return 0;
}

下面是執行的結果多線程

互斥鎖：spa

　　當一個全局的共有資源被多個線程同時調用會出現意想不到的問題，好比你去銀行取出全部錢，同時又轉全部錢到支付寶，若是這兩塊同時執行，就有可能轉出雙倍的錢，這是不容許的。線程

這時候要使用的這個線程須要將這個資源（取錢這個過程）先「鎖」起來，而後用好以後再解鎖，這期間別的線程就沒法使用了，其餘線程的也是相似的過程。code

#include<Windows.h>
#include<iostream>
using namespace std;
//互斥鎖
HANDLE hMutex1;
int flag;

DWORD WINAPI MyThread2(LPVOID lpParamter)
{
    while (1)
    {
　　　　//沒上鎖的話就本身鎖上，不然等着
        WaitForSingleObject(hMutex1,INFINITE);
        flag=!flag;
        cout << "MyThread1 Runing :"<<"線程2"<<" "<<flag<< endl;
        Sleep(1000);
　　　　　//解鎖
        ReleaseMutex(hMutex1);
    }
}
DWORD WINAPI MyThread1(LPVOID lpParamter)
{
    while (1)
    {
        WaitForSingleObject(hMutex1,INFINITE);
        flag=!flag;
        cout << "MyThread2 Runing"<<"線程1" <<" "<<flag<< endl;
        Sleep(10);
        ReleaseMutex(hMutex1);

    }
}

int main()
{
    //建立一個鎖
    hMutex1  =CreateMutex(NULL,FALSE,NULL);
    HANDLE hThread1 = CreateThread(NULL, 0, MyThread1, NULL, 0, NULL);
    CloseHandle(hThread1);

    HANDLE hThread2 = CreateThread(NULL, 0, MyThread2, NULL, 0, NULL);
    CloseHandle(hThread2);
    while(1);
    return 0;
}

能夠看到結果，就算線程1延時的時間很是短，可是因爲線程2執行的時候，就被鎖住了，線程1就處於等待。結果就是線程1和線程2會交替執行blog

多進程互斥：進程

若是某個文件不容許被多個進程用時使用，這時候也能夠採用進程間互斥。當一個進程建立一個進程後建立一個鎖，第二個進程使用OpenMutex獲取第一個進程建立的互斥鎖的句柄。支付寶

第一個進程：資源

#include<Windows.h>
#include<iostream>
using namespace std;
//互斥鎖
HANDLE hMutex1;
int flag;
DWORD WINAPI MyThread(LPVOID lpParamter)
{
    while (1)
    {
        WaitForSingleObject(hMutex1,INFINITE);
        flag=!flag;
        cout << "MyThread2 Runing"<<"進程1" <<" "<<flag<< endl;
        Sleep(500);
        //此時鎖1被鎖，沒法在下面解鎖2
        ReleaseMutex(hMutex1);

    }
}
int main()
{
    //建立一個鎖
    hMutex1  =CreateMutex(NULL,false,LPCWSTR("hMutex1"));
    HANDLE hThread1 = CreateThread(NULL, 0, MyThread, NULL, 0, NULL);
    CloseHandle(hThread1);
    while(1);
    return 0;
}

第二個進程：string

#include<Windows.h>
#include<iostream>
using namespace std;
//互斥鎖
HANDLE hMutex1;
int flag;
//無參數
DWORD WINAPI MyThread(LPVOID lpParamter)
{
    while (1)
    {
        WaitForSingleObject(hMutex1,INFINITE);
        flag=!flag;
        cout << "MyThread2 Runing"<<"進程2" <<" "<<flag<< endl;
        Sleep(5000);
        ReleaseMutex(hMutex1);
    }
}

int main()
{
    //打開
    hMutex1  = OpenMutex(MUTEX_ALL_ACCESS,false,LPCWSTR("hMutex1"));
    if(hMutex1!=NULL)
        cout<<"鎖打開成功"<<endl;
    HANDLE hThread1 = CreateThread(NULL, 0, MyThread, NULL, 0, NULL);
    CloseHandle(hThread1);
    while(1);
    return 0;
}

結果能夠看到，之運行進程1，消息打印的很是快，可是把進程2打開以後，進程1的消息打印速度就跟進程2變得同樣了。

死鎖：

何爲死鎖，舉個例子，兩個櫃子，兩個鎖，兩把鑰匙，把兩把鑰匙放進另一個櫃子，而後鎖上，結果呢，兩個都打不開了。在程序內部，這樣就會致使兩個進程死掉。

看例子

#include<Windows.h>
#include<iostream>
using namespace std;
//互斥鎖
HANDLE hMutex1;
HANDLE hMutex2;
int flag;
DWORD WINAPI MyThread2(LPVOID lpParamter)
{
    while (1)
    {
        WaitForSingleObject(hMutex1,INFINITE);
        flag=!flag;
        cout << "MyThread1 Runing :"<<"線程1"<<" "<<flag<< endl;
        Sleep(1000);

        //此時鎖2被鎖，沒法在下面解鎖1
        WaitForSingleObject(hMutex2,INFINITE);
        ReleaseMutex(hMutex2);
        ReleaseMutex(hMutex1);
    }
}
DWORD WINAPI MyThread1(LPVOID lpParamter)
{
    while (1)
    {
        WaitForSingleObject(hMutex2,INFINITE);
        flag=!flag;
        cout << "MyThread2 Runing"<<"線程1" <<" "<<flag<< endl;
        Sleep(1000);

        //此時鎖1被鎖，沒法在下面解鎖2
        WaitForSingleObject(hMutex1,INFINITE);
        ReleaseMutex(hMutex1);
        ReleaseMutex(hMutex2);

    }
}


int main()
{
    //建立一個鎖
    hMutex1  =CreateMutex(NULL,FALSE,NULL);
    hMutex2  =CreateMutex(NULL,FALSE,NULL);
    HANDLE hThread1 = CreateThread(NULL, 0, MyThread1, NULL, 0, NULL);
    CloseHandle(hThread1);

    HANDLE hThread2 = CreateThread(NULL, 0, MyThread2,NULL, 0, NULL);
    CloseHandle(hThread2);
    while(1);
    return 0;
}