015 volatile关键字 线程函数的lParam 原子操作和旋转锁.

　　● 对全局变量进行 volatile 可以阻止编译器对变量的优化

　　● lparam 线程函数的传参  1 #include <windows.h>

#include <stdio.h>
#include <tchar.h>
#include <process.h>

int gNum = 0;
const int LOOPCOUNT = 1000;
const int THREADCONUT = 1000;

unsigned __stdcall ThreadFun(void *lParam)
{
    int nThreadNo = (int)lParam;
    gNum = 0;
    for( int i = 0; i < LOOPCOUNT; ++i)
    {
        gNum += i;
    }
    printf("Threaad%4d:gNum=gNum=%d
",nThreadNo,gNum);
    return 0;
}
int main()
{
    HANDLE hThreads[THREADCONUT] = {0};
    for(int i=0; i<THREADCONUT; ++i)
    {
        hThreads[i] = (HANDLE)_beginthreadex(nullptr, 0, ThreadFun, (void*)i, 0, nullptr);
    }　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　
    WaitForMultipleObjects(THREADCONUT, hThreads, TRUE, INFINITE);
    
    for(int i = 0; i< THREADCONUT; ++i)
    {
        CloseHandle(hThreads[i]);
    }
    return 0;
}

　　● (void*)i, 临时变量i 强制转换位 void* 然后在 线程函数内 再转换回int

● 另外一种传参的方法

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <process.h>

int gNum = 0;
const int LOOPCOUNT = 1000;
const int THREADCONUT = 1000;

unsigned __stdcall ThreadFun(void *lParam)
{
    int *nThreadNo = (int*)lParam;
    gNum = 0;
    for( int i = 0; i < LOOPCOUNT; ++i)
    {
        gNum += i;
    }
    printf("Threaad%4d:gNum=gNum=%d
",*nThreadNo,gNum);
    return 0;
}
int main()
{
    HANDLE hThreads[THREADCONUT] = {0};
    for(int i=0; i<THREADCONUT; ++i)
    {
        hThreads[i] = (HANDLE)_beginthreadex(nullptr, 0, ThreadFun, &i, 0, nullptr);
    }
    WaitForMultipleObjects(THREADCONUT, hThreads, TRUE, INFINITE);
    
    for(int i = 0; i< THREADCONUT; ++i)
    {
        CloseHandle(hThreads[i]);
    }
    return 0;
}

●  执行结果黑诡异

●  线程是同时执行的不分先后顺序

● 原子操作

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <process.h>

volatile int gNum = 0;
const int LOOPCOUNT = 1000;
const int THREADCONUT = 1000;

unsigned __stdcall ThreadFun(void *lParam)
{
    int nThreadNo = (int)lParam;
    gNum = 0;
    for( int i = 0; i < LOOPCOUNT; ++i)
    {
        //gNum += i;
        InterlockedExchangeAdd((long*)&gNum,i);
    }
    printf("Threaad%4d:gNum=gNum=%d
",nThreadNo,gNum);
    return 0;
}
int main()
{
    HANDLE hThreads[THREADCONUT] = {0};
    for(int i=0; i<THREADCONUT; ++i)
    {
        hThreads[i] = (HANDLE)_beginthreadex(nullptr, 0, ThreadFun, (void*)i, 0, nullptr);
    }
    WaitForMultipleObjects(THREADCONUT, hThreads, TRUE, INFINITE);
    
    for(int i = 0; i< THREADCONUT; ++i)
    {
        CloseHandle(hThreads[i]);
    }
    return 0;
}

●  反而错误更多了

#include <windows.h>
#include <stdio.h>
#include <tchar.h>
#include <process.h>

volatile int gNum = 0;
volatile BOOL gbUseing = FALSE;
const int LOOPCOUNT = 1000;
const int THREADCONUT = 1000;

unsigned __stdcall ThreadFun(void *lParam)
{
    int nThreadNo = (int)lParam;

        //gNum += i;
        while(InterlockedExchangeAdd((long*)&gbUseing,TRUE)==TRUE)
        {
            Sleep(0);
        }
    printf("Entry Thread%4d
",nThreadNo);
    gNum = 0;
    printf("Threaad%4d:gNum=gNum=%d
",nThreadNo,gNum);
    InterlockedExchangeAdd((long*)&gbUseing,FALSE);
    return 0;
}
int main()
{
    HANDLE hThreads[THREADCONUT] = {0};
    for(int i=0; i<THREADCONUT; ++i)
    {
        hThreads[i] = (HANDLE)_beginthreadex(nullptr, 0, ThreadFun, (void*)i, 0, nullptr);
    }
    WaitForMultipleObjects(THREADCONUT, hThreads, TRUE, INFINITE);
    
    for(int i = 0; i< THREADCONUT; ++i)
    {
        CloseHandle(hThreads[i]);
    }
    return 0;
}