cleanup restart logic

should actually be right, now

IPython/kernel/ioloop/restarter.py

@@ -49,14 +49,11 b' class IOLoopKernelRestarter(KernelRestarter):'
             self._pcallback = ioloop.PeriodicCallback(
                 self.poll, 1000*self.time_to_dead, self.loop
             )
-        self._pcallback.start()
+            self._pcallback.start()
 
     def stop(self):
         """Stop the kernel polling."""
         if self._pcallback is not None:
             self._pcallback.stop()
+            self._pcallback = None
 
-    def clear(self):
-        """Clear the underlying PeriodicCallback."""
-        self.stop()
-        self._pcallback = None

IPython/kernel/restarter.py

@@ -89,8 +89,13 b' class KernelRestarter(LoggingConfigurable):'
                 self.log.warn("KernelRestarter: restart failed")
                 self._fire_callbacks('dead')
                 self._restarting = False
+                self.stop()
             else:
                 self.log.info('KernelRestarter: restarting kernel')
                 self._fire_callbacks('restart')
                 self.kernel_manager.restart_kernel(now=True)
                 self._restarting = True
+        else:
+            if self._restarting:
+                self.log.debug("KernelRestarter: restart apparently succeeded")
+            self._restarting = False