Merge pull request #1609 from minrk/sigterm

exit notebook cleanly on SIGINT, SIGTERM, and add a safety (text) dialog to ask for exit confirmation.  This prevents an accidental Ctrl-C in the wrong window from destroying a user's potentially large set of notebooks that could have taken a long time to create.

Closes #1601

IPython/frontend/html/notebook/notebookapp.py

@@ -20,10 +20,13 @@ Authors:
 import errno
 import logging
 import os
+import re
+import select
 import signal
 import socket
 import sys
 import threading
+import time
 import webbrowser
 
 # Third party
@@ -449,11 +452,73 @@ class NotebookApp(BaseIPythonApplication):
                 self.port = port
                 break
     
+    def init_signal(self):
+        # FIXME: remove this check when pyzmq dependency is >= 2.1.11
+        # safely extract zmq version info:
+        try:
+            zmq_v = zmq.pyzmq_version_info()
+        except AttributeError:
+            zmq_v = [ int(n) for n in re.findall(r'\d+', zmq.__version__) ]
+            if 'dev' in zmq.__version__:
+                zmq_v.append(999)
+            zmq_v = tuple(zmq_v)
+        if zmq_v >= (2,1,9):
+            # This won't work with 2.1.7 and
+            # 2.1.9-10 will log ugly 'Interrupted system call' messages,
+            # but it will work
+            signal.signal(signal.SIGINT, self._handle_sigint)
+        signal.signal(signal.SIGTERM, self._signal_stop)
+    
+    def _handle_sigint(self, sig, frame):
+        """SIGINT handler spawns confirmation dialog"""
+        # register more forceful signal handler for ^C^C case
+        signal.signal(signal.SIGINT, self._signal_stop)
+        # request confirmation dialog in bg thread, to avoid
+        # blocking the App
+        thread = threading.Thread(target=self._confirm_exit)
+        thread.daemon = True
+        thread.start()
+    
+    def _restore_sigint_handler(self):
+        """callback for restoring original SIGINT handler"""
+        signal.signal(signal.SIGINT, self._handle_sigint)
+    
+    def _confirm_exit(self):
+        """confirm shutdown on ^C
+        
+        A second ^C, or answering 'y' within 5s will cause shutdown,
+        otherwise original SIGINT handler will be restored.
+        """
+        # FIXME: remove this delay when pyzmq dependency is >= 2.1.11
+        time.sleep(0.1)
+        sys.stdout.write("Shutdown Notebook Server (y/[n])? ")
+        sys.stdout.flush()
+        r,w,x = select.select([sys.stdin], [], [], 5)
+        if r:
+            line = sys.stdin.readline()
+            if line.lower().startswith('y'):
+                self.log.critical("Shutdown confirmed")
+                ioloop.IOLoop.instance().stop()
+                return
+        else:
+            print "No answer for 5s:",
+        print "resuming operation..."
+        # no answer, or answer is no:
+        # set it back to original SIGINT handler
+        # use IOLoop.add_callback because signal.signal must be called
+        # from main thread
+        ioloop.IOLoop.instance().add_callback(self._restore_sigint_handler)
+    
+    def _signal_stop(self, sig, frame):
+        self.log.critical("received signal %s, stopping", sig)
+        ioloop.IOLoop.instance().stop()
+    
     @catch_config_error
     def initialize(self, argv=None):
         super(NotebookApp, self).initialize(argv)
         self.init_configurables()
         self.init_webapp()
+        self.init_signal()
 
     def cleanup_kernels(self):
         """shutdown all kernels