Question

我正在尝试了解Windows上的互斥体，但是在2012年的Visual Studio 2012上，波纹管代码无法正常工作。代码的目的不是检查错误条件，而是检查基本的api用法。我创建了100个线程，每个线程只有一个任务。增加全局变量testThisVariableIncr。每个线程调用的函数是MyThreadFunction（）。

请指导我哪里弄错了。

#include "stdafx.h"
#include <windows.h>
#include <tchar.h>
#include <strsafe.h>

#include "iostream"
using namespace std;

#define MAX_THREADS 100
#define BUF_SIZE 255
static int testThisVariableIncr;
DWORD  WINAPI  MyThreadFunction(LPVOID lpParam);

// Each thread will be sent this data structure
typedef struct MyData {
    int val1;
    int val2;
} MYDATA, *PMYDATA;

// al lhandles are usuly void POINTERS 
HANDLE ghMutex;


int _tmain()
{
    PMYDATA pDataArray[MAX_THREADS];
    DWORD   dwThreadIdArray[MAX_THREADS];
    HANDLE  hThreadArray[MAX_THREADS];

    // cretae a mutex but will be used by each thread 
    ghMutex = CreateMutex(
        NULL,              // default security attributes
        FALSE,             // initially not owned
        NULL);             // unnamed mutex


    // Create MAX_THREADS worker threads.



    for (int i = 0; i<MAX_THREADS; i++)
    {
        // CREATE DATA TOR EACH THREAD =============================================
        // Allocate memory for thread data. 
        pDataArray[i] = new MYDATA();
        pDataArray[i]->val1 = i;
        pDataArray[i]->val2 = i ;
        //=============================================


        // Create the thread to begin execution on its own.
        hThreadArray[i] = CreateThread(
            NULL,                   // default security attributes
            0,                      // use default stack size  
            MyThreadFunction,       // thread function name
            pDataArray[i],          // argument to thread function 
            0,                      // use default creation flags 
            &dwThreadIdArray[i]);   // returns the thread identifier 
    } // End of main thread creation loop.

    // Wait until all threads have terminated.something like join of linux
    WaitForMultipleObjects(MAX_THREADS, hThreadArray, TRUE, INFINITE);

    cout << "\n final value is : " << testThisVariableIncr;

    // Close all thread handles and free memory allocations.
    for (int i = 0; i<MAX_THREADS; i++)
    {
        CloseHandle(hThreadArray[i]);
        if (pDataArray[i] != NULL)
        {
            delete pDataArray[i];
            pDataArray[i] = NULL;    // Ensure address is not reused.
        }
    }

    CloseHandle(ghMutex);

    getchar();
    return 0;
}


DWORD WINAPI  MyThreadFunction(LPVOID lpParam)
{
    // Cast the parameter to the correct data type.
    // The pointer is known to be valid because 
    // it was checked for NULL before the thread was created.
    PMYDATA pDataArray;

    pDataArray = (PMYDATA)lpParam;

    while (1)
    {
        DWORD  dwWaitResult = WaitForSingleObject(
            ghMutex,    // handle to mutex
            INFINITE);  // no time-out interval
        if (WAIT_OBJECT_0 == dwWaitResult)
        {
            testThisVariableIncr++;
            ReleaseMutex(ghMutex);
            return 0;
        }
        Sleep(1);
    }
    return 0;
}

10次运行2-3次我获得97 95等而不是99次预期。

与waitforsingleobject的mutex无法按预期工作

0 个答案: