使用信号量进行线程同步

 

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

#define NUMTHREADS 4

HANDLE hSemaphore;

void UseSemaphore(void);
DWORD WINAPI SemaphoreThread(LPVOID lpParam);

int main(void){
    UseSemaphore();
}

void UseSemaphore(void){
    HANDLE hThread[NUMTHREADS];
    INT i;
    LONG lMax;
    CHAR cMax;
    printf("将创建%d个线程,获得信号量的线程可以向屏幕打印.\n请输入信号量的最大计数1-%d:",NUMTHREADS,NUMTHREADS);
    cMax = getch();
    printf("%c\n",cMax);
    lMax = cMax & 0xF;
    if(lMax<0 || lMax>NUMTHREADS){
        printf("请输入1-%d.\n",NUMTHREADS);
    }
    hSemaphore = CreateSemaphore(NULL,lMax,lMax,NULL);
    if(hSemaphore == NULL){
        printf("Create Semaphorec error.(%d)\n",GetLastError());
    }
    for(i=0;i<NUMTHREADS;i++){
        hThread[i] = CreateThread(NULL,0,SemaphoreThread,&i,0,NULL);
        if(hThread[i] == NULL){
            printf("Create Threads error.(%d)\n",GetLastError());
            return;
        }
    }
    WaitForMultipleObjects(NUMTHREADS,hThread,TRUE,INFINITE);
}

DWORD WINAPI SemaphoreThread(LPVOID lpParam){
    DWORD dwWaitResult;
    BYTE lpRead[16];
    DWORD j = 0;
    DWORD dwPreviousCount;

    for(;j<3;j++){
        Sleep(rand()%1000);
        dwWaitResult = WaitForSingleObject(hSemaphore,INFINITE);
        switch(dwWaitResult){
        case WAIT_OBJECT_0:
            printf("\nProcess %d Gets Semaphore",GetCurrentThreadId());
            break;
        default:
            printf("\nprocess %u wait error:%u",GetCurrentThreadId(),GetLastError());
        }
        Sleep(rand()%1000);
        if(!ReleaseSemaphore(hSemaphore,1,&dwPreviousCount))
        {
            printf("\nprocess %u Release Semaphore error:%d",GetCurrentProcessId(),GetLastError());
        }else
        {
            printf("\nProcess %u Release Semaphore,previous count is %u",GetCurrentProcessId(),dwPreviousCount);
        }
    }
    return 1;
}