bootstrap-vz/base/tasklist.py

from common.exceptions import TaskListError
import logging
log = logging.getLogger(__name__)


class TaskList(object):

	def __init__(self):
		self.tasks = set()
		self.tasks_completed = []

	def add(self, *args):
		self.tasks.update(args)

	def remove(self, *args):
		for task in args:
			self.tasks.discard(task)

	def run(self, bootstrap_info):
		task_list = self.create_list(self.tasks)
		log.debug('Tasklist:\n\t{list}'.format(list='\n\t'.join(repr(task) for task in task_list)))

		for task_type in task_list:
			task = task_type()
			if hasattr(task, 'description'):
				log.info(task.description)
			else:
				log.info('Running {task}'.format(task=task))
			task.run(bootstrap_info)
			self.tasks_completed.append(task)

	def create_list(self, tasks):
		from common.phases import order
		graph = {}
		for task in tasks:
			self.check_ordering(task)
			successors = set()
			successors.update(task.before)
			successors.update(filter(lambda succ: task in succ.after, tasks))
			succeeding_phases = order[order.index(task.phase) + 1:]
			successors.update(filter(lambda succ: succ.phase in succeeding_phases, tasks))
			graph[task] = filter(lambda succ: succ in tasks, successors)

		components = self.strongly_connected_components(graph)
		cycles_found = 0
		for component in components:
			if len(component) > 1:
				cycles_found += 1
				log.debug('Cycle: {list}\n'.format(list=', '.join(repr(task) for task in component)))
		if cycles_found > 0:
			msg = ('{0} cycles were found in the tasklist, '
			       'consult the logfile for more information.'.format(cycles_found))
			raise TaskListError(msg)

		sorted_tasks = self.topological_sort(graph)

		return sorted_tasks

	def check_ordering(self, task):
		for successor in task.before:
			if successor.phase > successor.phase:
				msg = ("The task {task} is specified as running before {other}, "
				       "but its phase '{phase}' lies after the phase '{other_phase}'"
				       .format(task=task, other=successor, phase=task.phase, other_phase=successor.phase))
				raise TaskListError(msg)
		for predecessor in task.after:
			if task.phase < predecessor.phase:
				msg = ("The task {task} is specified as running after {other}, "
				       "but its phase '{phase}' lies before the phase '{other_phase}'"
				       .format(task=task, other=predecessor, phase=task.phase, other_phase=predecessor.phase))
				raise TaskListError(msg)

	def strongly_connected_components(self, graph):
		# Source: http://www.logarithmic.net/pfh-files/blog/01208083168/sort.py
		# Find the strongly connected components in a graph using Tarjan's algorithm.
		# graph should be a dictionary mapping node names to lists of successor nodes.

		result = []
		stack = []
		low = {}

		def visit(node):
			if node in low:
				return

			num = len(low)
			low[node] = num
			stack_pos = len(stack)
			stack.append(node)

			for successor in graph[node]:
				visit(successor)
				low[node] = min(low[node], low[successor])

			if num == low[node]:
				component = tuple(stack[stack_pos:])
				del stack[stack_pos:]
				result.append(component)
				for item in component:
					low[item] = len(graph)

		for node in graph:
			visit(node)

		return result

	def topological_sort(self, graph):
		# Source: http://www.logarithmic.net/pfh-files/blog/01208083168/sort.py
		count = {}
		for node in graph:
			count[node] = 0
		for node in graph:
			for successor in graph[node]:
				count[successor] += 1

		ready = [node for node in graph if count[node] == 0]

		result = []
		while ready:
			node = ready.pop(-1)
			result.append(node)

			for successor in graph[node]:
				count[successor] -= 1
				if count[successor] == 0:
					ready.append(successor)

		return result