Re: areaDetector with 'empty' array output

[Phil Atkin <phil.atkin@pixelanalytics.co.uk>]

Perhaps a better example: suppose we want to plot the events as each camera frame is processed?  If there are no events, we want to clear the display.

Phil

On 25/07/2016 13:44, Mark Rivers wrote:

I'm not sure I understand the question.  If count is 0 then is there any point in allocating the NDArray and doing callbacks?  Do you still want to pass NDAttributes to downstream plugins?  If not, then why not just skip the NDArray allocation and callbacks when count is 0?

Mark

________________________________
From: tech-talk-bounces@aps.anl.gov [tech-talk-bounces@aps.anl.gov] on behalf of Phil Atkin [phil.atkin@pixelanalytics.co.uk]
Sent: Monday, July 25, 2016 5:35 AM
To: tech-talk@aps.anl.gov
Subject: areaDetector with 'empty' array output

Hi,

My areaDetector plugin has an option to generate an array containing a 'list' of events.  In pseudocode, it does something like the following in the processCallbacks method:

    if (this->pArrays[0]) {
        this->pArrays[0]->release();
        this->pArrays[0] = NULL;
    }

    this->unlock();

        // Copy the events list to the output array
        size_t count = events.size();
        dims[xDim] = count;
        dims[yDim] = 3; // x, y and type
        this->pArrays[0] = pNDArrayPool->alloc(2, dims, NDFloat32, 0, nullptr);

    this->pArrays[0]->timeStamp = pArray->timeStamp;
    this->pArrays[0]->epicsTS = pArray->epicsTS;
    this->pArrays[0]->uniqueId = pArray->uniqueId;
    pArray->pAttributeList->copy(this->pArrays[0]->pAttributeList);

    this->lock();
    // [Set some parameter values, including NDArraySizeX,Y,Z]
    this->getAttributes(this->pArrays[0]->pAttributeList);
    this->unlock();
    doCallbacksGenericPointer(this->pArrays[0], NDArrayData, 0);
    this->lock();
    callParamCallbacks();
Currently I'm experiencing a crash if there are no events in the list.  pNDArrayPool->alloc returns null if count is zero.  I guess this is neither surprising nor unreasonable, but it leaves me with the question of what I should (and should not) do if the list is empty.  I somehow need to 'output' something, otherwise plugins downstream won't be called, will they?

Thanks in advance,

Phil

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