windows系统调用 semaphore信号量

#include "iostream"
#include "windows.h"
#include "cstring"
using namespace std;

HANDLE g_hSemThreads=INVALID_HANDLE_VALUE;

static DWORD WINAPI ThreadProc(LPVOID lpParam){
    LONG nPauseMs=reinterpret_cast<LONG>(lpParam);
    Sleep(nPauseMs);

    if(g_hSemThreads!=INVALID_HANDLE_VALUE){
        LONG nPrevCt(0);

        if(ReleaseSemaphore(
            g_hSemThreads,
            1,
            &nPrevCt
            )){
                printf("%d msec thread ended ,slots left:%d
",nPauseMs,nPrevCt+1);
        }
    }

    return(0);
}



void main(){
    g_hSemThreads=CreateSemaphore(
        NULL,
        5,
        5,
        NULL
        );
    for(int nTotal=20;nTotal>0;nTotal-=2){
        WaitForSingleObject(g_hSemThreads,INFINITE);
        LONG nPauseMs=nTotal*5;

        HANDLE hThread=CreateThread(
            NULL,
            0,
            ThreadProc,
            reinterpret_cast<LPVOID>(nPauseMs),
            0,
            NULL
            );

        printf("in the %d msec a thread is creates 
",nPauseMs);
        CloseHandle(hThread);
        hThread=INVALID_HANDLE_VALUE;
    }

    CloseHandle(g_hSemThreads);
    g_hSemThreads=INVALID_HANDLE_VALUE;
    getchar();
}