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sem就是信号量，其使用如下所示：在使用sem之前先要创建semLOS_SemCreate(0, &g_usSemID);创建后，就可以调用LOS_SemPend 来得到一个信号量，调用LOS_SemPost 释放一个信号量static VOID Example_SemTask1(VOID){    UINT32 uwRet;    dprintf("Example_SemTask1 try get sem g_usSemID ,timeout 10 ticks.\n");    /* get sem, timeout is 10 ticks */#获取信号量    uwRet = LOS_SemPend(g_usSemID, 10);    /* get sem ok */    if (LOS_OK == uwRet)    {#成功获取后释放信号量        LOS_SemPost(g_usSemID);        return;    }}下来我们具体看看如何获取信号量LITE_OS_SEC_TEXT UINT32 LOS_SemPend(UINT32 uwSemHandle, UINT32 uwTimeout){    UINT32      uwIntSave;    SEM_CB_S    *pstSemPended;    UINT32      uwRetErr;    LOS_TASK_CB *pstRunTsk;    pstSemPended = GET_SEM(uwSemHandle);  #得到正在运行的task    pstRunTsk = (LOS_TASK_CB *)g_stLosTask.pstRunTask;#将要得到的信号量赋值给当前进程    pstRunTsk->pTaskSem = (VOID *)pstSemPended;#将这个进程插入到pendlist中，并建立一个timer来唤醒这个进程得到信号量    osTaskWait(&pstSemPended->stSemList, OS_TASK_STATUS_PEND, uwTimeout);    (VOID)LOS_IntRestore(uwIntSave);#释放cpu    LOS_Schedule();    if (pstRunTsk->usTaskStatus & OS_TASK_STATUS_TIMEOUT)    {        uwIntSave = LOS_IntLock();        pstRunTsk->usTaskStatus &= (~OS_TASK_STATUS_TIMEOUT);        uwRetErr = LOS_ERRNO_SEM_TIMEOUT;        goto errre_uniSemPend;    }#规定的时间内信号量被唤醒，没有timeout则返回成功    return LOS_OK;#否则返回失败，获取信号量失败errre_uniSemPend:    (VOID)LOS_IntRestore(uwIntSave);    OS_RETURN_ERROR(uwRetErr);}LITE_OS_SEC_TEXT VOID osTaskWait(LOS_DL_LIST *pstList, UINT32 uwTaskStatus, UINT32 uwTimeOut){    LOS_TASK_CB *pstRunTsk;    LOS_DL_LIST *pstPendObj;    pstRunTsk = g_stLosTask.pstRunTask;    osPriqueueDequeue(&pstRunTsk->stPendList);    pstRunTsk->usTaskStatus &= (~OS_TASK_STATUS_READY);    pstPendObj = &pstRunTsk->stPendList;    pstRunTsk->usTaskStatus |= uwTaskStatus;#将这个进程插入到pendlist中    LOS_ListTailInsert(pstList,pstPendObj);    if (uwTimeOut != LOS_WAIT_FOREVER)    {        pstRunTsk->usTaskStatus |= OS_TASK_STATUS_TIMEOUT;#建立一个timer在规定时间内唤醒这个进程        osTaskAdd2TimerList((LOS_TASK_CB *)pstRunTsk, uwTimeOut);    }}释放信号量的函数分析如下：LITE_OS_SEC_TEXT UINT32 LOS_SemPost(UINT32 uwSemHandle){    UINT32      uwIntSave;    SEM_CB_S    *pstSemPosted = GET_SEM(uwSemHandle);    LOS_TASK_CB *pstResumedTask;#需要释放的信号量不为null的话     if (!LOS_ListEmpty(&pstSemPosted->stSemList))    {#从需要释放信号量的list中找到第一个task        pstResumedTask = OS_TCB_FROM_PENDLIST(LOS_DL_LIST_FIRST(&(pstSemPosted->stSemList))); /*lint !e413*/#将要唤醒的task的sem置空        pstResumedTask->pTaskSem = NULL;#开始唤醒task        osTaskWake(pstResumedTask, OS_TASK_STATUS_PEND);#恢复中断        (VOID)LOS_IntRestore(uwIntSave);#启动调度        LOS_Schedule();    }    else    {#从这里可以知道信号量可以分别获取和释放多次        pstSemPosted->usSemCount++;        (VOID)LOS_IntRestore(uwIntSave);    }    return LOS_OK;}

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