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# Copyright 1999-2009 Gentoo Foundation
# Distributed under the terms of the GNU General Public License v2
# $Id$
from portage import os
from _emerge.CompositeTask import CompositeTask
from _emerge.AsynchronousTask import AsynchronousTask
from collections import deque
class TaskSequence(CompositeTask):
"""
A collection of tasks that executes sequentially. Each task
must have a addExitListener() method that can be used as
a means to trigger movement from one task to the next.
"""
__slots__ = ("_task_queue",)
def __init__(self, **kwargs):
AsynchronousTask.__init__(self, **kwargs)
self._task_queue = deque()
def add(self, task):
self._task_queue.append(task)
def _start(self):
self._start_next_task()
def cancel(self):
self._task_queue.clear()
CompositeTask.cancel(self)
def _start_next_task(self):
self._start_task(self._task_queue.popleft(),
self._task_exit_handler)
def _task_exit_handler(self, task):
if self._default_exit(task) != os.EX_OK:
self.wait()
elif self._task_queue:
self._start_next_task()
else:
self._final_exit(task)
self.wait()
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