Experimental Physics and
Industrial Control System

After looking at the source code and doing some tests using PvaClient::setDebug(), I’ve learned that PvaClientNTMultiMonitor->poll() doesn’t bring the data structure for the channels that had no change since the last poll. For these channels the data at the vectors looks like is only garbage.

The only way that I’ve managed to check if the channel was changed is by looking if “values[i]” is none. PvaClientNTMultiMonitor doesn’t provide a sort of hasChanged bool vector. If checking for “none” is what is expected I would suggest it to be written on the documentation.

I’ve placed an issue on the PvaClientCPP module on GitHub suggesting this feature.

Thank you,

Márcio Paduan Donadio

Control Systems Engineer - SLAC

I’m playing with PvaClientNTMulti and can’t understand some of the behaviors. I’m using EPICS 7.0.3.

Please, check part of the source code in the end of this email. I’ve created a PvaClientMultiChannel with 4 existent PVs. In a loop I’ve issued a multiMonitor waitEvent(1), got some data, print it, then issued a multiGet get(), got the same data, and printed it. In the first pass of the loop the data from the monitor agree with the get(). But in the second pass, the message from the monitor says “Not connected” and the message from get() still shows “UDF” for the last channel. Even though, isConnected[3] is still true. Also, the value for the last channel come as (none) and the timestamp as zero in the second pass of the monitor, different from get().

Return from multiMonitor, item 0

any[] value

    any

        double value 5.27338e-13

    any

        double value 5.73043e-13

    any

        double value 1.10038e-12

    any

        double value 0

Severity: [0,0,0,3]

["NO_ALARM", "NO_ALARM", "NO_ALARM", "UDF"]

isConnected: [true,true,true,true]

secondsPastEpoch: [1610078476,1610078476,1610078476,631152000]

Return from multiGet, item 0

any[] value

    any

        double value 5.27338e-13

    any

        double value 5.73043e-13

    any

        double value 1.10038e-12

    any

        double value 0

Severity: [0,0,0,3]

["NO_ALARM", "NO_ALARM", "NO_ALARM", "UDF"]

isConnected: [true,true,true,true]

secondsPastEpoch: [1610078476,1610078476,1610078476,631152000]

Return from multiMonitor, item 1

any[] value

    any

        double value 5.12687e-13

    any

        double value 5.38479e-13

    any

        double value 1.05117e-12

    (none)

Severity: [0,0,0,3]

["NO_ALARM", "NO_ALARM", "NO_ALARM", "not connected"]

isConnected: [true,true,true,true]

secondsPastEpoch: [1610078477,1610078477,1610078477,0]

Return from multiGet, item 1

any[] value

    any

        double value 5.12687e-13

    any

        double value 5.38479e-13

    any

        double value 1.05117e-12

    any

        double value 0

Severity: [0,0,0,3]

["NO_ALARM", "NO_ALARM", "NO_ALARM", "UDF"]

isConnected: [true,true,true,true]

secondsPastEpoch: [1610078477,1610078477,1610078477,631152000]

In another experiment, I commented out the get() part of the loop, having only the waitEvent one. Now I get almost nothing in the prints:

Return from multiMonitor, item 0

any[] value

    (none)

    (none)

    (none)

    any

        double value 0

Severity: [3,3,3,3]

["not connected", "not connected", "not connected", "UDF"]

isConnected: [true,true,true,true]

secondsPastEpoch: [0,0,0,631152000]

Return from multiMonitor, item 1

any[] value

    (none)

    (none)

    (none)

    (none)

Severity: [3,3,3,3]

["not connected", "not connected", "not connected", "not connected"]

isConnected: [true,true,true,true]

secondsPastEpoch: [0,0,0,0]

So, something happens when I call multiGet->get() before multiMonitor->waitEvent(). I’m probably missing something here. What is the right way to use waitEvent()? What about waitEvent() vs poll()?

Another thing is that I’d like to have waitEvent() bringing the full contents of the channels, but I see that internally it calls poll() using the default “value only” option. Don’t you think it would be useful to have waitEvent with 2 parameters: timeout and valueOnly?

/*

Code to create the multi channel with the PV names are not shown

PvaClientMultiChannelPtr multichannel (…)

*/

PvaClientNTMultiGetPtr multiGet(multiChannel->createNTGet());

PvaClientNTMultiMonitorPtr multiMonitor(multiChannel->createNTMonitor());

PVUnionArrayPtr values;

PVIntArrayPtr severity;

PVStringArrayPtr message;

PVBooleanArrayPtr isConnected;

PVLongArrayPtr secondsPastEpoch;

bool result;

int channelSize;

NTMultiChannelPtr multiPtr;

for (int iii=0; iii<2; ++iii) {

            result = multiMonitor->waitEvent(1);

            if(result) {

                multiPtr = multiMonitor->getData()->getNTMultiChannel();

                values = multiPtr->getValue();

                severity = multiPtr->getSeverity();

                message = multiPtr->getMessage();

                isConnected = multiPtr->getIsConnected();

                secondsPastEpoch = multiPtr->getSecondsPastEpoch();

                cout << endl << "Return from multiMonitor, item " << iii << endl;

                cout << values << endl;

                cout << "Severity: " << severity << endl;

                cout << message << endl;

                cout << "isConnected: " << isConnected << endl;

                cout << "secondsPastEpoch: " << secondsPastEpoch << endl;

            }

            multiGet->get(true);

            multiPtr = multiGet->getData()->getNTMultiChannel();

            values = multiPtr->getValue();

            severity = multiPtr->getSeverity();

            message = multiPtr->getMessage();

            isConnected = multiPtr->getIsConnected();

            secondsPastEpoch = multiPtr->getSecondsPastEpoch();

            cout << endl << "Return from multiGet, item " << iii << endl;

            cout << values << endl;

            cout << "Severity: " << severity << endl;

            cout << message << endl;

            cout << "isConnected: " << isConnected << endl;

            cout << "secondsPastEpoch: " << secondsPastEpoch << endl;

}

Thank you,

Márcio Paduan Donadio

Control Systems Engineer - SLAC