Connecting to non-existent channel in matlab "freezes" Matlab

[aswyatt]

The following is really bad:

javaaddpath("ca-1.3.2-all.jar")

con = org.epics.ca.Context();
ch = org.epics.ca.Channels.create(con, "NON_EXISTANT_PV");

% You can do nothing from here on other than kill Matlab
ch.get()

ch.close()
con.close()

An alternative is to connect via async, but I'm not sure of the consequences of this:

%	Only do this once per Matlab session!
javaaddpath("ca-1.3.2-all.jar")

con = org.epics.ca.Context();

ch = con.createChannel("NON_EXISTANT_STRING_PV", java.lang.String().getClass());
ch.connectAsync();
pause(1)	%	There can be a better way of waiting for connection
if ~strcmp(ch.getConnectionState, "CONNECTED")
  warning("PV does not exist")
end

ch = con.createChannel("EXISTANT_STRING_PV", java.lang.String().getClass());
ch.connectAsync();
pause(1)	%	There can be a better way of waiting for connection
if ~strcmp(ch.getConnectionState(), "CONNECTED")
  warning("PV does not exist")
end

ch.get()

ch.close()
con.close()

However, the connect method should allow one to specify a timeout value (and not use an infinite timeout as default).

[simondelabici]

@aswyatt sorry it took me a while to respond to you... I'm afraid I didn't see the original email notification of your issue.

The good news is there is a relatively straightforward way of achieving the "synchronous-connect-with-timeout" behaviour that you desire. This is described in the README file. Basically the asynchronous connect returns a Java CompletableFuture, then you simply invoke a get() on that with the timeout you desire. There is also a construct for achieving this on multiple channels.

I reproduced the details below.

Please let me know whether this solves your problem.

Thanks and best regards

Simon Rees
Software Engineer
PSI

connectAsync()
connectAsync() will return a CompletableFuture. To check whether the connect was successful call .get() on it. The synchronous way to connect will block until the channel can be connected. If you want to specify a timeout for a connect use the asynchronous connect as follows:

channel.connectAsync().get(1, java.util.concurrent.TimeUnit.SECONDS);

For connecting multiple channels in parallel use:

Channel<Integer> channel1 = context.createChannel("adc02", Integer.class);
Channel<String> channel2 = context.createChannel("adc03", String.class);

// Wait for all channels to be connected
CompletableFuture.allOf(channel1.connectAsync(), channel2.connectAsync()).get();

A timeout for the multiple connect is realized the same way as with the single connectAsync().