Small socket problem

[John O'Hagan]

On Mon, 9 Feb 2009, Gabriel Genellina wrote:
> En Mon, 09 Feb 2009 07:43:36 -0200, John O'Hagan <research at johnohagan.com>
>
> escribió:
> > I'm using the socket module (python 2.5) like this (where 'options'
> > refers to
> > an optparse object) to connect to the Fluidsynth program:
> >
> >             host = "localhost"
> >             port = 9800
> >             fluid = socket(AF_INET, SOCK_STREAM)
> >             try:
> >                 fluid.connect((host, port))  #Connect if fluidsynth is
> > running
> >             except BaseException:
> >                 print "Connecting to fluidsynth..." #Or start fluidsynth
> >                 soundfont =  options.soundfont
> >                 driver = options.driver
> >                 Popen(["fluidsynth", "-i", "-s", "-g", "0.5",
> >                 "-C", "1",  "-R", "1", "-l", "-a", driver, "-j",
> > soundfont])
> >                 timeout = 50
> >                 while 1:
> >                     timeout -= 1
> >                     if timeout == 0:
> >                         print "Problem with fluidsynth: switching to
> > synth."
> >                         play_method = "synth"
> >                         break
> >                     try:
> >                         fluid.connect((host, port))
> >                     except BaseException:
> >                         sleep(0.05)
> >                         continue
> >                     else:
> >                         break
> >
> > (I'm using BaseException because I haven't been able to discover what
> > exception class[es] socket uses).
>
> Usually socket.error, which is a subclass of IOError, but others might
> happen too I think. In any case, the most generic except clause you should
> use is
> try:
> except Exception: ...
> (because you usually don't want to catch KeyboardInterrupt nor SystemExit,
> that is, let Ctrl-C and sys.exit() do their work)

Thanks, I had been doing "from socket import foo, bar" without 
importing "error", that now works. I think I should use that specific 
exception in the try clause for now so I can see any other exceptions that 
may occur, a good idea?

>
> > The problem is that this fails to connect ( the error is "111: Connection
> > refused") the first time I run it after booting if fluidsynth is not
> > already
> > running, no matter how long the timeout is; after Ctrl-C'ing out of the
> > program, all subsequent attempts succeed. Note that fluidsynth need not
> > be
> > running for a success to occur.
>
> Always the same exception? In both lines?

Yes; I'm sure this is obvious, but just for clarity: if fluidsynth is not 
running I expect that error at the first line where connection is attempted, 
and at the second line during the loop while fluidsynth is loading (this 
takes 0.5-5 seconds depending on the size of the soundfont it's using). But I 
don't understand why the connection is still refused once fluidsynth has 
finished loading.

I received an off-list reply to this post to the effect that attempting to 
reuse a socket on which a connection attempt has failed, will fail, and that 
I needed to create a new socket for each attempt. It seemed very plausible, 
so I tried inserting a fresh

fluid = socket(AF_INET, SOCK_STREAM)

before the second fluid.connect() in the loop; but this still behaved the same 
way. Is that the way to do it?

Annoyingly, I've so far only been able reproduce the problem by rebooting.

Regards,

John