AWR1642: How to understand MMWave_spawn in Mmwave link

Hi champion,
   My customer is looking at the mmwave demo in mmwave_sdk_01_00_00_05. I got a question about the MMWave_spawn funciton in the code. This function is registered to rlDevicePowerOn in below code.

  /* Initialize OSI Queue Interface */
    RlApp_ClientCtx.osiCb.queue.rlOsiSpawn      = &MMWave_spawn;

1. Inside this function it saved input function point and parameter in gMMWave_MCB.ptrSpawnFxnFreeList, and then post a semaphore to other task. My questiton is when

MMWave_spawn is called and what is the funciton point and parameter it used.

static rlInt32_t MMWave_spawn
(
    RL_P_OSI_SPAWN_ENTRY    fxn,
    const void*             pValue,
    uint32_t                flags
)
{
    MMWave_SpawnFxnNode*    ptrSpawnFxnNode;
    uintptr_t               key;
    int32_t                 retVal = 0;

    /* Critical Section: The spawn free list is a critical resource which is accessed
     * from multiple contexts */
    key = HwiP_disable();
    ptrSpawnFxnNode = (MMWave_SpawnFxnNode*)MMWave_listRemove ((MMWave_ListNode**)&gMMWave_MCB.ptrSpawnFxnFreeList);
    HwiP_restore (key);

    /* Did we get an entry? */
    if (ptrSpawnFxnNode != NULL)
    {
        /* YES: Populate the entry */
        ptrSpawnFxnNode->spawnEntry = fxn;
        ptrSpawnFxnNode->arg        = pValue;

        /* Critical Section: The spawn active list is a critical resource which is accessed
         * from multiple contexts */
        key = HwiP_disable();
        MMWave_listAdd ((MMWave_ListNode**)&gMMWave_MCB.ptrSpawnFxnActiveList, (MMWave_ListNode*)ptrSpawnFxnNode);
        HwiP_restore (key);

        /* Keep track of the number of spawn messages which have been received */
        gMMWave_MCB.spawnCounter++;

        /* Wake up the mmWave execution thread  */
        SemaphoreP_post (gMMWave_MCB.linkSemHandle);
    }
    else
    {
        /* Error: No span free node was present. This can happen if all the spawn functions
         * have been taken up and the execute mmWave control API has not been invoked. Increment
         * statistics to report this condition */
        gMMWave_MCB.spawnOverflow++;

        /* Setup the return value to indicate an error. */
        retVal = -1;
    }
    return retVal;
}



2. why we define the spwan list size to 4 (MMWAVE_MAX_NUM_SPAWN_LIST)? In which case we need to use this list to save more than one funciton call.