/* 永久等待条件变量返回 */
int
SDL_CondWait(SDL_cond * cond, SDL_mutex * mutex)
{
    return SDL_CondWaitTimeout(cond, mutex, SDL_MUTEX_MAXWAIT);
}


/**
 *  设置的超时时间永远都不会到达
 */
#define SDL_MUTEX_MAXWAIT   (~(Uint32)0)


    /* 等待信号量 */
    if (ms == SDL_MUTEX_MAXWAIT) {
        retval = SDL_SemWait(cond->wait_sem);
    } else {
        retval = SDL_SemWaitTimeout(cond->wait_sem, ms);
    }


int
SDL_SemWait(SDL_sem * sem)
{
    return SDL_SemWaitTimeout(sem, SDL_MUTEX_MAXWAIT);
}


int
SDL_SemWaitTimeout(SDL_sem * sem, Uint32 timeout)
{
    int retval;
    DWORD dwMilliseconds;

    if (!sem) {
        return SDL_SetError("Passed a NULL sem");
    }

    if (timeout == SDL_MUTEX_MAXWAIT) {
        dwMilliseconds = INFINITE;
    } else {
        dwMilliseconds = (DWORD) timeout;
    }
    switch (WaitForSingleObjectEx(sem->id, dwMilliseconds, FALSE)) {
    case WAIT_OBJECT_0:
        InterlockedDecrement(&sem->count);
        retval = 0;
        break;
    case WAIT_TIMEOUT:
        retval = SDL_MUTEX_TIMEDOUT;
        break;
    default:
        retval = SDL_SetError("WaitForSingleObject() failed");
        break;
    }
    return retval;
}


最终调用了Windows的信号量函数，这个函数跟Sleep函数在线程等待过程中，是否有优势？？