[patch][python] When an exception is raised by a signal handler, print it to stderr

[Simon McVittie]

This partially fixes a regression since 0.7x.

There need to be more checks for exceptions so they all at least get printed
to stderr - a lot of asynchronous code runs in slightly precarious
circumstances, so we can't necessarily provide full tracebacks, but it's
better than nothing. Places I can think of which may need exception
printing added:

- asynchronous method-call reply and error handlers
- the message filter mechanism (with which we implement signal handling,
  but this patch should be merged first anyway, since it's the most
  common case and the exception should be caught before it can disrupt
  other signal handlers)

>From 4f88700588d80861c8520e56407d3a40d5bd86e6 Mon Sep 17 00:00:00 2001
From: Simon McVittie <simon.mcvittie at collabora.co.uk>
Date: Mon, 19 Feb 2007 14:17:08 +0000
Subject: [PATCH] dbus/_dbus.py: When an exception is raised by a signal handler, print it to stderr

---
 dbus/_dbus.py |   54 ++++++++++++++++++++++++++++++++----------------------
 1 files changed, 32 insertions(+), 22 deletions(-)

diff --git a/dbus/_dbus.py b/dbus/_dbus.py
index 21ed122..8e3b536 100644
--- a/dbus/_dbus.py
+++ b/dbus/_dbus.py
@@ -33,7 +33,9 @@ BusImplementation = _dbus_bindings.BusImplementation
 
 import os
 import logging
+import sys
 import weakref
+from traceback import print_exc
 
 from dbus.proxies import ProxyObject, BUS_DAEMON_NAME, BUS_DAEMON_PATH, \
         BUS_DAEMON_IFACE
@@ -187,28 +189,36 @@ class SignalMatch(object):
             return False
 
         #logger.debug('%r: yes, I want to handle that signal', self)
-        # minor optimization: if we already extracted the args with the right
-        # calling convention to do the args match, don't bother doing so again
-        if args is None or not self._utf8_strings or not self._byte_arrays:
-            args = message.get_args_list(utf8_strings=self._utf8_strings,
-                                         byte_arrays=self._byte_arrays)
-        #logger.debug('%r: extracted signal arguments', self)
-        kwargs = {}
-        if self._sender_keyword is not None:
-            kwargs[self._sender_keyword] = message.get_sender()
-        if self._destination_keyword is not None:
-            kwargs[self._destination_keyword] = message.get_destination()
-        if self._path_keyword is not None:
-            kwargs[self._path_keyword] = message.get_path()
-        if self._member_keyword is not None:
-            kwargs[self._member_keyword] = message.get_member()
-        if self._interface_keyword is not None:
-            kwargs[self._interface_keyword] = message.get_interface()
-        if self._message_keyword is not None:
-            kwargs[self._message_keyword] = message
-        #logger.debug('%r: calling handler with %r and %r', self, args, kwargs)
-        self._handler(*args, **kwargs)
-        #logger.debug('%r: signal handled', self)
+
+        try:
+            # minor optimization: if we already extracted the args with the right
+            # calling convention to do the args match, don't bother doing so again
+            if args is None or not self._utf8_strings or not self._byte_arrays:
+                args = message.get_args_list(utf8_strings=self._utf8_strings,
+                                             byte_arrays=self._byte_arrays)
+            #logger.debug('%r: extracted signal arguments', self)
+            kwargs = {}
+            if self._sender_keyword is not None:
+                kwargs[self._sender_keyword] = message.get_sender()
+            if self._destination_keyword is not None:
+                kwargs[self._destination_keyword] = message.get_destination()
+            if self._path_keyword is not None:
+                kwargs[self._path_keyword] = message.get_path()
+            if self._member_keyword is not None:
+                kwargs[self._member_keyword] = message.get_member()
+            if self._interface_keyword is not None:
+                kwargs[self._interface_keyword] = message.get_interface()
+            if self._message_keyword is not None:
+                kwargs[self._message_keyword] = message
+            #logger.debug('%r: calling handler with %r and %r', self, args, kwargs)
+            self._handler(*args, **kwargs)
+            #logger.debug('%r: signal handled', self)
+        except:
+            # FIXME: need to decide whether dbus-python uses logging, or
+            # stderr, or what, and make it consistent
+            sys.stderr.write('Exception in handler for D-Bus signal:\n')
+            print_exc()
+
         return True
 
     def remove(self):
-- 
1.4.4.4