c++多線程執行個體

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#include <windows.h>#include <stdio.h>#include <process.h>int g_ntotal = 100;int g_thread_counter;int g_sum;//計算結果HANDLE g_thread_lock;//HANDLE 被類型定義為 void *struct THREAD_DATA{    int num_threads;    int thread_id;};void sum_func(void *pdata){    THREAD_DATA *ptdata = (THREAD_DATA *)pdata;    int i, sum = 0;    for (i = ptdata->thread_id; i <= g_ntotal; i += ptdata->num_threads)        sum += i;    delete ptdata;    WaitForSingleObject(g_thread_lock, INFINITE);    g_sum += sum;    --g_thread_counter;    ReleaseMutex(g_thread_lock);}void main(void){    LARGE_INTEGER hfreq, hcounter1, hcounter2;//這三個貨是64位的整數    QueryPerformanceFrequency(&hfreq);    //printf("%ld",hfreq);    SYSTEM_INFO sys_info;//這貨是結構體變數    GetSystemInfo(&sys_info);//實參為指向結構體的指標    int num_processors = sys_info.dwNumberOfProcessors;//值為2，是一個DWORD類型的成員變數，DWORD被定義為無符號長整型    //num_processors = 1;        printf("Number of processors=%d\n", num_processors);//機器支援的線程數目    g_thread_lock = CreateMutex(NULL, FALSE, NULL);//傳回值為無類型指標，CreateMutex作用是找出當前系統是否已經存在指定進程的執行個體。如果沒有則建立一個互斥體。    g_thread_counter = num_processors;//系統支援的線程數    g_sum = 0;//計算結果初始化    QueryPerformanceCounter(&hcounter1);//擷取目前時間儲存到 hcounter1 中，實參是指向64位整數的指標    int i;    THREAD_DATA *pdata;//THREAD_DATA是本程式中自己定義的結構體    for (i = 1; i < num_processors; ++i)    {        pdata = new THREAD_DATA;        pdata->thread_id = i + 1;        pdata->num_threads = num_processors;//值為2        _beginthread(sum_func, 0, pdata);    }    pdata = new THREAD_DATA;    pdata->thread_id = 1;    pdata->num_threads = num_processors;//值為2    sum_func(pdata);    while (1)    {        int itemp;        WaitForSingleObject(g_thread_lock, INFINITE);        itemp = g_thread_counter;//系統支援的線程數，值為2        ReleaseMutex(g_thread_lock);        if (itemp == 0) break;    }    QueryPerformanceCounter(&hcounter2);//擷取結束時間，儲存到 hcounter2 中    double dt = (double)(hcounter2.QuadPart - hcounter1.QuadPart)        / (double)hfreq.QuadPart;//運算式中涉及的三個變數是共用體類型（8位元組），其中QuadPart是共用體的 long long類型成員，在此處被毫無節操地轉換成了double類型，double也是佔用8位元組    printf("sum=%d\n", g_sum);    printf("Calculation time=%f\n", dt);//此處將%g改為了%f，這裡是代碼的已耗用時間    //printf("%d", sizeof(double));    getchar();    CloseHandle(g_thread_lock); //將CreateMutex建立的互斥體關閉}

 

c++多線程執行個體