distbuild: Fix case where 'computing build graph' would hang forever

If there's no distbuild-helper process running on the controller then
the controller would hang forever. This situation is unlikely, but it's
important to give the user feedback instead of silently hanging forever.

2 files changed, 7 insertions, 1 deletions

diff --git a/distbuild/build_controller.py b/distbuild/build_controller.py
index cfa0e2e2..8dbbaef9 100644
--- a/distbuild/build_controller.py
+++ b/distbuild/build_controller.py
@@ -246,6 +246,9 @@ class BuildController(distbuild.StateMachine):
 
     def _request_command_execution(self, argv, request_id):
         '''Tell the controller's distbuild-helper to run a command.'''
+        if self.mainloop.n_state_machines_of_type(distbuild.HelperRouter) == 0:
+            self.fail('No distbuild-helper process running on controller!')
+
         msg = distbuild.message('exec-request',
             id=request_id,
             argv=argv,
diff --git a/distbuild/mainloop.py b/distbuild/mainloop.py
index f0e5eebc..8c46b2fb 100644
--- a/distbuild/mainloop.py
+++ b/distbuild/mainloop.py
@@ -56,7 +56,10 @@ class MainLoop(object):
     def remove_state_machine(self, machine):
         logging.debug('MainLoop.remove_state_machine: %s' % machine)
         self._machines.remove(machine)
-    
+
+    def n_state_machines_of_type(self, machine_type):
+        return len([m for m in self._machines if isinstance(m, machine_type)])
+
     def add_event_source(self, event_source):
         logging.debug('MainLoop.add_event_source: %s' % event_source)
         self._sources.append(event_source)