Add faulthandler module support for debugging hangs/segfaults

- No-op if not present

doc/dev/debugging.rst

@@ -63,6 +63,12 @@ On Linux/OSX:
 
 TODO: Windows
 
+Viewing stack traces when Exaile hangs
+--------------------------------------
+
+If you have the `faulthandler <https://github.com/haypo/faulthandler>`_ module
+installed, on Linux/OSX if you send SIGUSR2 to Exaile it will dump stacktraces
+of all current Python threads to stderr.
 
 GStreamer Debugging Techniques
 ------------------------------

xl/logger_setup.py

@@ -176,6 +176,20 @@ def log_unhandled_exception(*args):
             logger.error("Unhandled exception", exc_info=args)
 
         sys.excepthook = log_unhandled_exception
+
+    # Strictly speaking, this isn't logging, but it's useful for debugging
+    # when Exaile hangs. Requires the 'faulthandler' module to be installed
+    # from pip on python2, comes with python 3.3+
+    try:
+        import faulthandler
+    except ImportError:
+        pass
+    else:
+        # Windows doesn't allow custom fault handler registration
+        if hasattr(faulthandler, 'register'):
+            import signal
+            faulthandler.register(signal.SIGUSR2)
+        faulthandler.enable()
 
 def stop_logging():
     logging.shutdown()