Re: [EXTERNAL] How to check if a PV is initially disconnected using org.phoebus.pv.PV.onValueEvent().subscribe()

["Kasemir, Kay via Tech-talk" <tech-talk at aps.anl.gov>]

> if the initial status of the PV is already disconnected

 

Each PV starts out in the disconnected state.

Ideally, it will then connect “real soon” and you get the first value update, but if you never hear anything, that means it was and remains disconnected.

 

-Kay

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Wang, Lin via Tech-talk <tech-talk at aps.anl.gov>
Date: Thursday, May 16, 2024 at 11:29 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] How to check if a PV is initially disconnected using org.phoebus.pv.PV.onValueEvent().subscribe()

Dear all,

 

When monitoring a PV using the following Java code snippet, if the status of the PV changes from connected to disconnected, valueChanged() will be invoked and the disconnected status can be checked. However, if the initial status of the PV is already disconnected, then valueChanged() will not be invoked, thus I do not know if the PV is disconnected or "connected but has no new value".

 

import org.epics.vtype.VType;

import org.phoebus.pv.PV;

import org.phoebus.pv.PVPool;

import io.reactivex.rxjava3.disposables.Disposable;

 

public class Test {

    public void start() throws Exception

    {

        PV pv = PVPool.getPV("test:123");

        Disposable pv_flow = pv.onValueEvent().subscribe(this::valueChanged);

    }

 

    private void valueChanged(final VType value)

    {

        if (PV.isDisconnected(value))

        {

            System.out.println("PV is disconnected");

        }

    }

}

 

How can I check if the PV is initially disconnected or is not available at all using this monitoring approach?

 

 

Thanks,

Lin