Comserver - should I have one connection open at all times?

[Mastiff]

I finally got comserver working, with one second waits between opening the connection, sending the command and closing the connection. But I wonder if the best policy is not to close that communication at all, just keep it open at all times, or to close it after each event. Any thoughts? It may be a problem if one computer has to be rebooted, right? So there should be a check to see if the line is open. With list open connection from the demo, maybe?

[Rob H]

I'd say you should keep it open. Check the error return from con:SendEvent() and try reopening the connection if that fails.

[Mastiff]

OK, error checking is something I've never tried before...

con,err = con:SendEvent('comtest',200,1,'a','b',nil,'d')
if ( con == nil ) then
con,err = comserv.NewConnection( '192.168.0.25', 20005, 'girder', CallBack);
con,err = con:SendEvent('comtest',200,1,'a','b',nil,'d')
else
end

Of course that's wrong, but I like to at least show that I'm trying to do something by myself... ops: The error I get is:

[string "D:\Vidcap G4.GML:\Comservertest\Comserverte..."]:12: attempt to index global `con' (a number value)
stack traceback:
	[string "D:\Vidcap G4.GML:\Comservertest\Comserverte..."]:12: in main chunk

[Rob H]

Well, you need to open the connection first.

[Mastiff]

if con == nil then
function CallBack(Param1, Param2, Param3, Param4, Param5)

  print("called back:")
  
  print(Param1)
  print(Param2)
  print(Param3)
  print(Param4)
  print(Param5)
  
end
con = comserv.NewConnection( '192.168.0.25', 20005, 'girder', CallBack);
con = con:SendEvent('comtest',200,1,'a','b',nil,'d')
else
con = con:SendEvent('comtest',200,1,'a','b',nil,'d')
end

[string "D:\Vidcap G4.GML:\Comservertest\Comserverte..."]:16: attempt to index global `con' (a number value)
stack traceback:
	[string "D:\Vidcap G4.GML:\Comservertest\Comserverte..."]:16: in main chunk

Never said I was smart...

[Mastiff]

Another attempt, and this one seems to actually work:

if ( con == nil ) then
function CallBack(Param1, Param2, Param3, Param4, Param5)

  print("called back:")
  
  print(Param1)
  print(Param2)
  print(Param3)
  print(Param4)
  print(Param5)
  
end
con,err = comserv.NewConnection( '192.168.0.11', 20005, 'girder', CallBack);
win.Sleep (500)
print('Trigger Event Ref ID: '..con:SendEvent('comtest',200,1,'a','b',nil,'d'))
else
print('Trigger Event Ref ID: '..con:SendEvent('comtest',200,1,'a','b',nil,'d'))
win.Sleep (500)
end

Am I right? Is that sound?

[Rob H]

That's looking better, although I'm not sure I'd put the call definition inside the if statement.

You really need to check the sequence and error returned from SendEvent()
if you get an error then you want to drop the connection and try to re-establish it, possibly even caching any event strings until the connection has been remade.

[Mastiff]

OK, can we repeat that in english, please? :wink: Anyway, that callback function, is that really necessary for this stuff? I have another attempt here:

if ( con == nil ) then
con,err = comserv.NewConnection( '192.168.0.25', 20005, 'girder', CallBack);
win.Sleep (1000)
con:SendEvent('comtest',200,1,'a','b',nil,'d')
else
win.Sleep (1000)
con:SendEvent('comtest',200,1,'a','b',nil,'d')
win.Sleep (1000)
end

Here I can get the "pingpong" started, where G4 1 sends a command to G4 2 with a multigroup that shows the OSD on 2 plus a command from 2 to fire the thing again on 1 and so on. Seems to work all right.

The first time it takes a couple of seconds, from then on it flashes like crazy. I have it on 100 ms, with a wait command for 100 ms, and it can really be psychedelic if you look at a big red square flashing like that!

[Mastiff]

I just found a fatal flaw in my script. If one server is reset, the whole process stops. And the sender can't see that it's not getting anything through. Is that what error checking in SendEvent() would do?

[Rob H]

Yep, that's the whole point.

Something like this :-

if not con then
    con,err = comserv.NewConnection( '192.168.0.25', 20005, 'girder');
    win.Sleep (1000)  -- not sure this is required
end
local seq, err = con:SendEvent('comtest',200,1,'a','b',nil,'d')
if err then
    con:Close()
    con = nil
end