labwindows:关于自带例子DirectPtrAccess线程安全队列的疑问

路径在：..samplesutilityThreadingThreadSafeQueueDirectPtrAccess中
/*---------------------------------------------------------------------------*/
/* Generate random data and write it to the queue.        */
/*---------------------------------------------------------------------------*/
static int CVICALLBACK AcquireTSQDataWithPtrsThreadFunction (void *unused)
{
int numToWrite;
int index;
double *writePtr;
while (running)
  {
  /* Use direct pointers to write data to the thread-safe queue. */
  if (CmtGetTSQWritePtr (tsqHandle, &writePtr, &numToWrite) >= 0)
   {
   /* Ensure we do not overflow the queue. */
   if (numToWrite > NUM_ITEMS_IN_QUEUE_WRITE_BLOCK)
    numToWrite = NUM_ITEMS_IN_QUEUE_WRITE_BLOCK;
   
   for (index = 0; index < numToWrite; ++index)
    {
    *writePtr++ = rand() * 100.0 / (double)RAND_MAX;
    }
   
   CmtReleaseTSQWritePtr (tsqHandle, numToWrite);
   }
  Delay(.01);
  }
return 0;
}
为何CmtGetTSQWritePtr (tsqHandle, &writePtr, &numToWrite) 中numToWrite获得的值为5？如何理解？

/*---------------------------------------------------------------------------*/
/* Read data from the queue and plot it to the stripchart.      */
/*---------------------------------------------------------------------------*/
static void CVICALLBACK PlotDataFromQueueCallback (CmtTSQHandle queueHandle,
  unsigned int event, int value, void *callbackData)
{
double *readPtr;
int numItemsInQueue;

/* Use direct pointers to read the data from the queue. */
CmtGetTSQReadPtr (queueHandle, &readPtr, &numItemsInQueue);
PlotStripChart (panelHandle, PANEL_TSQPLOT, readPtr,
     NUM_ITEMS_IN_QUEUE_READ_BLOCK, 0, 0, VAL_DOUBLE);
CmtReleaseTSQReadPtr (queueHandle, NUM_ITEMS_IN_QUEUE_READ_BLOCK);
}
为何CmtGetTSQReadPtr (queueHandle, &readPtr, &numItemsInQueue);中numItemsInQueue获得的值则每次都变化？何解？

AcquireTSQDataWithPtrsThreadFunction与PlotDataFromQueueCallback是同步进行的？



/*---------------------------------------------------------------------------*/
/* Create threads to generate data and to display the data.      */
/*---------------------------------------------------------------------------*/中

/* Install a callback to read and plot the generated data. */
   CmtInstallTSQCallback (tsqHandle, EVENT_TSQ_ITEMS_IN_QUEUE,
           NUM_ITEMS_IN_QUEUE_READ_BLOCK,
           PlotDataFromQueueCallback, NULL,
           CmtGetCurrentThreadID(), &plotDataCallbackID);
上面的CmtInstallTSQCallback中有一个回调函数PlotDataFromQueueCallback
后面怎跟着一个
/* Start the writer thread. */
   CmtScheduleThreadPoolFunction (DEFAULT_THREAD_POOL_HANDLE,
             AcquireTSQDataWithPtrsThreadFunction,
             0, 0);

上面这2个函数的是不是这个意思：
首先安装一个读数据与绘制曲线的回调函数，但是当前还没有数据可以处理
后面则开始一个写随机数的CmtScheduleThreadPoolFunction发起写线程函数AcquireTSQDataWithPtrsThreadFunction
写完了循环数据之后来一句CmtReleaseTSQWritePtr (tsqHandle, numToWrite); 释放了写指针
这时就会自动回调PlotDataFromQueueCallback函数来绘制曲线？


PlotDataFromQueueCallback与AcquireTSQDataWithPtrsThreadFunction之间的关系应该如何理解线程在处理过程中的关系?