* Fix AsynchronousTask._wait_hook() to prevent potential recursive calls

  triggered when calling exit listeners.

* Make SequentialTaskQueue use exit listeners to trigger scheduling as
  soon as a task exits. This makes it possible for the queues to
  automatically schedule new tasks while scheduler remains in it's
  poll() loop.

svn path=/main/trunk/; revision=11008

diff --git a/pym/_emerge/__init__.py b/pym/_emerge/__init__.py
index a1a3d6fe7a080122c61105af33a7858bc1fa9c22..163e606a7921f6709ca756688abc2f01419df948 100644 (file)
--- a/pym/_emerge/__init__.py
+++ b/pym/_emerge/__init__.py
@@ -1545,7 +1545,14 @@ class AsynchronousTask(SlotObject):
                """
                if self.returncode is not None and \
                        self._exit_listeners is not None:
-                       for f in self._exit_listeners:
+
+                       # This prevents recursion, in case one of the
+                       # exit handlers triggers this method again by
+                       # calling wait().
+                       exit_listeners = self._exit_listeners
+                       self._exit_listeners = None
+
+                       for f in exit_listeners:
                                f(self)
                        self._exit_listeners = None
 
@@ -7604,7 +7611,7 @@ class PollSelectAdapter(PollConstants):
 
 class SequentialTaskQueue(SlotObject):
 
-       __slots__ = ("max_jobs", "running_tasks", "_task_queue")
+       __slots__ = ("max_jobs", "running_tasks", "_task_queue", "_scheduling")
 
        def __init__(self, **kwargs):
                SlotObject.__init__(self, **kwargs)
@@ -7624,6 +7631,13 @@ class SequentialTaskQueue(SlotObject):
                if not self:
                        return False
 
+               if self._scheduling:
+                       # Ignore any recursive schedule() calls triggered via
+                       # self._task_exit().
+                       return False
+
+               self._scheduling = True
+
                task_queue = self._task_queue
                running_tasks = self.running_tasks
                max_jobs = self.max_jobs
@@ -7640,12 +7654,18 @@ class SequentialTaskQueue(SlotObject):
                        task = task_queue.popleft()
                        cancelled = getattr(task, "cancelled", None)
                        if not cancelled:
+                               task.addExitListener(self._task_exit)
                                task.start()
                                running_tasks.add(task)
                        state_changed = True
 
+               self._scheduling = False
+
                return state_changed
 
+       def _task_exit(self, task):
+               self.schedule()
+
        def clear(self):
                self._task_queue.clear()
                running_tasks = self.running_tasks