Workaround deadlock in ipython

shutdown_hook is called after all non-daemon threads exit, but it is needed for 
them to exit. Thus I had to use daemon threads in ipython or find some hack to 
make .shutdown be called earlier.

powerline/__init__.py

@@ -36,7 +36,7 @@ def load_json_config(config_file_path, load=json.load, open_file=open_file):
 
 
 class PowerlineState(object):
-	def __init__(self, logger, environ, getcwd, home):
+	def __init__(self, use_daemon_threads, logger, environ, getcwd, home):
 		self.environ = environ
 		self.getcwd = getcwd
 		self.home = home or environ.get('HOME', None)
@@ -103,6 +103,7 @@ class Powerline(object):
 				renderer_module=None,
 				run_once=False,
 				logger=None,
+				use_daemon_threads = False,
 				environ=os.environ,
 				getcwd=getattr(os, 'getcwdu', os.getcwd),
 				home=None):
@@ -114,6 +115,7 @@ class Powerline(object):
 		self.environ = environ
 		self.getcwd = getcwd
 		self.home = home
+		self.use_daemon_threads = use_daemon_threads
 
 		self.config_paths = self.get_config_paths()
 
@@ -174,7 +176,7 @@ class Powerline(object):
 					self.logger.setLevel(level)
 					self.logger.addHandler(handler)
 
-				self.pl = PowerlineState(logger=self.logger, environ=self.environ, getcwd=self.getcwd, home=self.home)
+				self.pl = PowerlineState(self.use_daemon_threads, self.logger, self.environ, self.getcwd, self.home)
 
 				self.renderer_options = {
 					'term_truecolor': self.common_config.get('term_truecolor', False),
@@ -234,6 +236,8 @@ class Powerline(object):
 										**self.renderer_options)
 				except Exception as e:
 					self.pl.exception('Failed to construct renderer object: {0}', str(e))
+					if not hasattr(self, 'renderer'):
+						raise
 				else:
 					self.renderer = renderer
 
@@ -351,6 +355,8 @@ class Powerline(object):
 		'''Lock renderer from modifications and run its ``.shutdown()`` method.
 		'''
 		self.shutdown_event.set()
+		if self.use_daemon_threads and self.is_alive():
+			self.thread.join()
 		with self.renderer_lock:
 			self.renderer.shutdown()
 
@@ -359,6 +365,8 @@ class Powerline(object):
 
 	def start(self):
 		self.thread = Thread(target=self.run)
+		if self.use_daemon_threads:
+			self.thread.daemon = True
 		self.thread.start()
 
 	def run(self):

powerline/ipython.py

@@ -6,7 +6,7 @@ from powerline.lib import mergedicts
 
 class IpythonPowerline(Powerline):
 	def __init__(self):
-		super(IpythonPowerline, self).__init__('ipython')
+		super(IpythonPowerline, self).__init__('ipython', use_daemon_threads=True)
 
 	def get_config_paths(self):
 		if self.path:

powerline/lib/threaded.py

@@ -11,6 +11,7 @@ class ThreadedSegment(object):
 	min_sleep_time = 0.1
 	update_first = True
 	interval = 1
+	daemon = False
 
 	def __init__(self):
 		super(ThreadedSegment, self).__init__()
@@ -49,6 +50,7 @@ class ThreadedSegment(object):
 	def start(self):
 		self.shutdown_event.clear()
 		self.thread = Thread(target=self.run)
+		self.thread.daemon = self.daemon
 		self.thread.start()
 
 	def run(self):
@@ -65,6 +67,8 @@ class ThreadedSegment(object):
 
 	def shutdown(self):
 		self.shutdown_event.set()
+		if self.daemon and self.is_alive():
+			self.thread.join()
 
 	def set_interval(self, interval=None):
 		# Allowing “interval” keyword in configuration.
@@ -81,6 +85,7 @@ class ThreadedSegment(object):
 	def startup(self, pl, **kwargs):
 		self.run_once = False
 		self.pl = pl
+		self.daemon = pl.use_daemon_threads
 
 		self.set_state(**kwargs)