1 files changed, 83 insertions, 0 deletions
diff --git a/pym/_emerge/SequentialTaskQueue.py b/pym/_emerge/SequentialTaskQueue.py
new file mode 100644
index 000000000..24fac0410
--- /dev/null
+++ b/pym/_emerge/SequentialTaskQueue.py
@@ -0,0 +1,83 @@
+from _emerge.SlotObject import SlotObject
+from collections import deque
+class SequentialTaskQueue(SlotObject):
+
+	__slots__ = ("max_jobs", "running_tasks") + \
+		("_dirty", "_scheduling", "_task_queue")
+
+	def __init__(self, **kwargs):
+		SlotObject.__init__(self, **kwargs)
+		self._task_queue = deque()
+		self.running_tasks = set()
+		if self.max_jobs is None:
+			self.max_jobs = 1
+		self._dirty = True
+
+	def add(self, task):
+		self._task_queue.append(task)
+		self._dirty = True
+
+	def addFront(self, task):
+		self._task_queue.appendleft(task)
+		self._dirty = True
+
+	def schedule(self):
+
+		if not self._dirty:
+			return False
+
+		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
+		state_changed = False
+
+		while task_queue and \
+			(max_jobs is True or len(running_tasks) < max_jobs):
+			task = task_queue.popleft()
+			cancelled = getattr(task, "cancelled", None)
+			if not cancelled:
+				running_tasks.add(task)
+				task.addExitListener(self._task_exit)
+				task.start()
+			state_changed = True
+
+		self._dirty = False
+		self._scheduling = False
+
+		return state_changed
+
+	def _task_exit(self, task):
+		"""
+		Since we can always rely on exit listeners being called, the set of
+ 		running tasks is always pruned automatically and there is never any need
+		to actively prune it.
+		"""
+		self.running_tasks.remove(task)
+		if self._task_queue:
+			self._dirty = True
+
+	def clear(self):
+		self._task_queue.clear()
+		running_tasks = self.running_tasks
+		while running_tasks:
+			task = running_tasks.pop()
+			task.removeExitListener(self._task_exit)
+			task.cancel()
+		self._dirty = False
+
+	def __nonzero__(self):
+		return bool(self._task_queue or self.running_tasks)
+
+	def __len__(self):
+		return len(self._task_queue) + len(self.running_tasks)
+