[BRLTTY] How does a BrlAPI client detect that brltty has quit?

[Willie Walker]

Hi All:

I'm chasing down a problem where the Python process for Orca goes 
ballistic when someone kills brltty.  The net result is that the desktop 
hangs, which is bad news.

Orca does a gobject.io_add_watch on the brlAPI.fileDescriptor and then 
calls brlAPI.readKey in the callback that is notified when there is 
activity.

Using the trace facility of Python, I'm not sure I'm seeing any loops 
happening and I'm also not getting any exceptions from BrlAPI calls from 
what I can tell.  I'm also not seeing any abnormal condition value being 
sent to the io callback.  I've tried doing an os.fstat on the BrlAPI 
file descriptor before doing the BrlAPI readKey call, and it seems fine, 
too.

Attached is a simple application that doesn't exhibit the same hang as 
Orca, but it does seg fault.  What I do is run brltty in a terminal 
window, and then this app in another.  I then kill brltty and observe 
what happens to this app.  Ideally, the application should be able to 
detect that brltty has disappeared.

Any ideas on what I should be able to do in Python to detect that brltty 
has been killed?

Will
import os

import brlapi
import gobject
import pyatspi

brlAPI = None
brlAPIRunning = False
brlAPISourceId = 0

def printBrailleEvent(command):
    print("BRAILLE EVENT: %s" % repr(command))

def brlAPIKeyReader(source, condition):
    """Method to read a key from the BrlAPI bindings.  This is a
    gobject IO watch handler.
    """
    global brlAPIRunning
    print "HERE"
    try:
        print os.fstat(brlAPI.fileDescriptor)
    except:
        print "BAD FILE DESCRIPTOR!!!"
        return False
    try:
        key = brlAPI.readKey(False)
        if key:
            printBrailleEvent(brlAPI.expandKeyCode(key))
    except:
        print "OOPS!"
        brlAPIRunning = False
    return brlAPIRunning

def init(tty=7):
    global brlAPI
    global brlAPIRunning
    global brlAPISourceId

    gobject.threads_init()
    brlAPI = brlapi.Connection()

    try:
        brlAPI.enterTtyModeWithPath()
        brlAPIRunning = True
    except:
        brlAPI.enterTtyMode(tty)
        brlAPIRunning = True

    if brlAPIRunning:
        brlAPISourceId = gobject.io_add_watch(brlAPI.fileDescriptor,
                                              gobject.IO_IN,
                                              brlAPIKeyReader)

if __name__ == "__main__":
    init()
    pyatspi.Registry.start(gil=False) 
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