Experimental Physics and
Industrial Control System

Mark Rivers <[email protected]> · Sun, 9 Oct 2016 22:16:10 +0000

Hi Michael,

Thanks for the quick response.

I have another newbie question.

My class has

private:
    std::string m_pvName;
    std::string m_request;
    short m_priority;
    ChannelProviderPtr m_provider;
    ChannelPtr m_channel;

How do I initialize m_channel in my constructor so that I know that 

  m_channel = m_provider->createChannel(m_pvName, m_thisPtr, m_priority);

has not yet been call, so I should not call m_channel->destroy()?  If this were a normal pointer I would initialize it to 0 and test that, but that does not work for a ChannelPtr.

If I unconditionally call m->channel->destroy() before m_channel has been created the first time I get an access violation.

Thanks,
Mark

________________________________________
From: Michael Davidsaver [[email protected]]
Sent: Sunday, October 09, 2016 1:37 PM
To: Mark Rivers; EPICS Tech-Talk
Subject: Re: EPICS V4 question

Mark,

First, the *Requester classes are somewhat "transient", so it's probably
not a good idea to combine this with ADDriver, which isn't.  You may
also get into trouble should you wish to have one ADDriver associated
with more than on PVA channel (as you have inadvertently done).

Disconnecting is done with Channel::destory(), not the ChannelRequester.
 For various annoying reasons it is *not* sufficient to let a connected
Channel be destroyed (as in c++ destructor).  Calling Channel::destory()
is mandatory.

You may (or not) find the following test code useful in understanding
the Channel/Monitor lifecycle.

https://github.com/mdavidsaver/pva2pva/blob/master/testApp/testtest.cpp

Michael

On 10/09/2016 01:24 PM, Mark Rivers wrote:
> I have some EPICS V4 client code that basically does the following:
>
>
>
> class epicsShareClass pvaDriver : public ADDriver,
>
>         public virtual epics::pvAccess::ChannelRequester,
>
>         public virtual epics::pvData::MonitorRequester
>
>
>
> …
>
>
>
>     try
>
>     {
>
>         ClientFactory::start();
>
>         m_provider = getChannelProviderRegistry()->getProvider("pva");
>
>         m_channel = m_provider->createChannel(m_pvName, m_thisPtr,
> m_priority);
>
>         m_pvRequest = CreateRequest::create()->createRequest(m_request);
>
>         m_monitor = m_channel->createMonitor(m_thisPtr, m_pvRequest);
>
>     }
>
>     catch (exception &ex)
>
>     {
>
> …
>
>     }
>
>
>
> The monitorConnect() and monitorEvent() methods are being called as
> expected, and everything is working.
>
>
>
> Now I want to extend the code to allow the current channel to be
> disconnected, and call m_provider->createChannel() to a different
> channel.  What do I need to do for this?  I found that if I just call
> m_provider->createChannel with a different p_pvName it does not throw an
> exception, but it appears to simply stay connected to the existing channel.
>
>
>
> Thanks,
>
> Mark
>
>
>

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System