COMP/PKGTOOLS/scheduler.py

from Queue import Queue
from threading import Thread
from time import sleep
import threading
import sys
import traceback
from StringIO import StringIO

# Helper class to avoid conflict between result
# codes and quit state transition.
class _SchedulerQuitCommand(object):
  pass

def transition(what, fromList, toList):
  try:
    fromList.remove(what)
  except ValueError, e:
    print what + " not in source list"
    raise e
  toList.append(what)

class Scheduler(object):
  # A simple job scheduler.
  # Workers queue is to specify to threads what to do. Results
  # queue is whatched by the master thread to wait for results
  # of workers computations.
  # All worker threads begin trying to fetch from the command queue (and are
  # therefore blocked).
  # Master thread does the scheduling and then sits waiting for results.
  # Scheduling implies iterating on the list of jobs and creates an entry
  # in the parallel queue for all the jobs which does not have any dependency
  # which is not done.
  # If a job has dependencies which did not build, move it do the failed queue.
  # Post an appropriate build command for all the new jobs which got added.
  # If there are jobs still to be done, post a reschedule job on the command queue
  # if there are no jobs left, post the "kill worker" task.
  def __init__(self, parallelThreads, logDelegate=None):
    self.workersQueue = Queue()
    self.resultsQueue = Queue()
    self.jobs = {}
    self.pendingJobs = []
    self.runningJobs = []
    self.doneJobs = []
    self.brokenJobs = []
    self.parallelThreads = parallelThreads
    self.logDelegate = logDelegate
    self.errors = {}
    if not logDelegate:
      self.logDelegate = self.__doLog 

  def run(self):
    for i in xrange(self.parallelThreads):
      t = Thread(target=self.__createWorker())
      t.daemon = True
      t.start()
    
    self.notifyMaster(self.__rescheduleParallel)
    # Wait until all the workers are done.
    while self.parallelThreads:
      try:
        who, item = self.resultsQueue.get()
        #print who, item
        item[0](*item[1:])
        sleep(0.1)
      except KeyboardInterrupt:
        print "Ctrl-c received, waiting for workers to finish"
        while self.workersQueue.full():
          self.workersQueue.get(False)
        self.shout(self.quit)
    
    # Prune the queue.
    while self.resultsQueue.full():
      item = self.resultsQueue.get() 
      item[0](*item[1:])
    return

  # Create a worker.
  def __createWorker(self):
    def worker():
      while True:
        taskId, item = self.workersQueue.get()
        try:
          result = item[0](*item[1:])
        except Exception, e:
          s = StringIO()
          traceback.print_exc(file=s)
          result = s.getvalue()
          
        if type(result) == _SchedulerQuitCommand:
          self.notifyMaster(self.__releaseWorker)
          return
        self.log(str(item) + " done")
        self.notifyMaster(self.__updateJobStatus, taskId, result)
        self.notifyMaster(self.__rescheduleParallel)
        # Only in 2.5: self.workersQueue.task_done()
    return worker
  
  def __releaseWorker(self):
    self.parallelThreads -= 1

  def parallel(self, taskId, deps, *spec):
    if taskId in self.pendingJobs:
      self.log("Double task %s" % taskId)
    self.jobs[taskId] = {"scheduler": "parallel", "deps": deps, "spec":spec}
    self.pendingJobs.append(taskId)

  # Does the rescheduling of tasks. Derived class should call it.
  def __rescheduleParallel(self):
    parallelJobs = [j for j in self.pendingJobs if self.jobs[j]["scheduler"] == "parallel"]
    # First of all clean up the pending parallel jobs from all those
    # which have broken dependencies.
    for taskId in parallelJobs:
      brokenDeps = [dep for dep in self.jobs[taskId]["deps"] if dep in self.brokenJobs]
      if not brokenDeps:
        continue
      transition(taskId, self.pendingJobs, self.brokenJobs)
      self.errors[taskId] = "The following dependencies could not complete:\n%s" % "\n".join(brokenDeps)

    # If no tasks left, quit. Notice we need to check also for serial jobs
    # since they might queue more parallel payloads.
    if not self.pendingJobs:
      self.shout(self.quit)
      self.notifyMaster(self.quit)
      return

    # Otherwise do another round of scheduling of all the tasks. In this
    # case we only queue parallel jobs to the parallel queue.
    for taskId in parallelJobs:
      pendingDeps = [dep for dep in self.jobs[taskId]["deps"] if not dep in self.doneJobs]
      if pendingDeps:
        continue
      # No broken dependencies and no pending ones. we can continue.
      transition(taskId, self.pendingJobs, self.runningJobs)
      self.__scheduleParallel(taskId, self.jobs[taskId]["spec"])

  # Update the job with the result of running.
  def __updateJobStatus(self, taskId, error):
    if not error:
      transition(taskId, self.runningJobs, self.doneJobs)
      return
    transition(taskId, self.runningJobs, self.brokenJobs)
    self.errors[taskId] = error
  
  # One task at the time.
  def __scheduleParallel(self, taskId, commandSpec):
    self.workersQueue.put((taskId, commandSpec))

  # Helper to enqueue commands for all the threads.
  def shout(self, *commandSpec):
    for x in xrange(self.parallelThreads):
      self.__scheduleParallel("quit-" + str(x), commandSpec)

  # Helper to enqueu replies to the master thread.
  def notifyMaster(self, *commandSpec):
    self.resultsQueue.put((threading.current_thread(), commandSpec))

  def serial(self, taskId, deps, *commandSpec):
    spec = [self.doSerial, taskId, deps] + list(commandSpec)
    self.resultsQueue.put((threading.current_thread(), spec))
    self.jobs[taskId] = {"scheduler": "serial", "deps": deps, "spec": spec}
    self.pendingJobs.append(taskId)

  def doSerial(self, taskId, deps, *commandSpec):
    brokenDeps = [dep for dep in deps if dep in self.brokenJobs]
    if brokenDeps:
      transition(taskId, self.pendingJobs, self.brokenJobs)
      self.errors[taskId] = "The following dependencies could not complete:\n%s" % "\n".join(brokenDeps)
      # Remember to do the scheduling again!
      self.notifyMaster(self.__rescheduleParallel)
      return
    
    # Put back the task on the queue, since it has pending dependencies.
    pendingDeps = [dep for dep in deps if not dep in self.doneJobs]
    if pendingDeps:
      self.resultsQueue.put((threading.current_thread(), [self.doSerial, taskId, deps] + list(commandSpec)))
      return
    # No broken dependencies and no pending ones. Run the job.
    transition(taskId, self.pendingJobs, self.runningJobs)
    try:
      result = commandSpec[0](*commandSpec[1:])
    except Exception, e:
      s = StringIO()
      traceback.print_exc(file=s)
      result = s.getvalue()
    self.__updateJobStatus(taskId, result)
    # Remember to do the scheduling again!
    self.notifyMaster(self.__rescheduleParallel)
  
  # Helper method to do logging:
  def log(self, s):
    self.notifyMaster(self.logDelegate, s)

  # Task which forces a worker to quit.
  def quit(self):
    self.log("Requested to quit.")
    return _SchedulerQuitCommand()

  # Helper for printouts.
  def __doLog(self, s):
    print s

  def reschedule(self):
    self.notifyMaster(self.__rescheduleParallel)

def dummyTask():
  sleep(0.1)

def dummyTaskLong():
  sleep(1)

def errorTask():
  return "This will always have an error"

def exceptionTask():
  raise Exception("foo")

# Mimics cmsBuild workflow.
def scheduleMore(scheduler):
  scheduler.parallel("download", [], dummyTask)
  scheduler.parallel("build", ["download"], dummyTask)
  scheduler.serial("install", ["build"], dummyTask)

if __name__ == "__main__":
  scheduler = Scheduler(10)
  scheduler.run()

  scheduler = Scheduler(1)
  scheduler.run()
  
  scheduler = Scheduler(10)
  scheduler.parallel("test", [], scheduler.log, "This is england");
  scheduler.run()

  scheduler = Scheduler(10)
  for x in xrange(50):
    scheduler.parallel("test" + str(x), [], dummyTask)
  scheduler.run()
  assert(len(scheduler.brokenJobs) == 0)
  assert(len(scheduler.jobs) == 50)
  
  scheduler = Scheduler(1)
  scheduler.parallel("test", [], errorTask)
  scheduler.run()
  assert(len(scheduler.brokenJobs) == 1)
  assert(len(scheduler.runningJobs) == 0)
  assert(len(scheduler.doneJobs) == 0)
  
  # Check dependency actually works.
  scheduler = Scheduler(10)
  scheduler.parallel("test2", ["test1"], dummyTask)
  scheduler.parallel("test1", [], dummyTaskLong) 
  scheduler.run()
  assert(scheduler.doneJobs == ["test1", "test2"])

  # Check dependency actually works.
  scheduler = Scheduler(10)
  scheduler.parallel("test3", ["test2"], dummyTask)
  scheduler.parallel("test2", ["test1"], errorTask)
  scheduler.parallel("test1", [], dummyTaskLong) 
  scheduler.run()
  assert(scheduler.doneJobs == ["test1"])
  assert(scheduler.brokenJobs == ["test2", "test3"])

  # Check ctrl-C will exit properly.
  scheduler = Scheduler(2)
  for x in xrange(250):
    scheduler.parallel("test" + str(x), [], dummyTask)
  print "Print Control-C to continue"
  scheduler.run()

  # Handle tasks with exceptions.
  scheduler = Scheduler(2)
  scheduler.parallel("test", [], exceptionTask)
  scheduler.run()
  assert(scheduler.errors["test"])

  # Handle tasks which depend on tasks with exceptions.
  scheduler = Scheduler(2)
  scheduler.parallel("test0", [], dummyTask)
  scheduler.parallel("test1", [], exceptionTask)
  scheduler.parallel("test2", ["test1"], dummyTask)
  scheduler.run()
  assert(scheduler.errors["test1"])
  assert(scheduler.errors["test2"])

  # Handle serial execution tasks.
  scheduler = Scheduler(2)
  scheduler.serial("test0", [], dummyTask)
  scheduler.run()
  assert(scheduler.doneJobs == ["test0"])

  # Handle serial execution tasks, one depends from
  # the previous one.
  scheduler = Scheduler(2)
  scheduler.serial("test0", [], dummyTask)
  scheduler.serial("test1", ["test0"], dummyTask)
  scheduler.run()
  assert(scheduler.doneJobs == ["test0", "test1"])

  # Serial tasks depending on one another.
  scheduler = Scheduler(2)
  scheduler.serial("test1", ["test0"], dummyTask)
  scheduler.serial("test0", [], dummyTask)
  scheduler.run()
  assert(scheduler.doneJobs == ["test0", "test1"])

  # Serial and parallel tasks being scheduled at the same time.
  scheduler = Scheduler(2)
  scheduler.serial("test1", ["test0"], dummyTask)
  scheduler.serial("test0", [], dummyTask)
  scheduler.parallel("test2", [], dummyTask)
  scheduler.parallel("test3", [], dummyTask)
  scheduler.run()
  scheduler.doneJobs.sort()
  assert(scheduler.doneJobs == ["test0", "test1", "test2", "test3"])

  # Serial and parallel tasks. Parallel depends on serial.
  scheduler = Scheduler(2)
  scheduler.serial("test1", ["test0"], dummyTask)
  scheduler.serial("test0", [], dummyTask)
  scheduler.parallel("test2", ["test1"], dummyTask)
  scheduler.parallel("test3", ["test2"], dummyTask)
  scheduler.run()
  assert(scheduler.doneJobs == ["test0", "test1", "test2", "test3"])

  # Serial task scheduling two parallel task and another dependent
  # serial task. This is actually what needs to be done for building 
  # packages. I.e.
  # The first serial task is responsible for checking if a package is already there,
  # then it queues a parallel download sources task, a subsequent build sources
  # one and finally the install built package one.
  scheduler = Scheduler(3)
  scheduler.serial("check-pkg", [], scheduleMore, scheduler)
  scheduler.run()
  assert(scheduler.doneJobs == ["check-pkg", "download", "build", "install"])
Revision:	1.5
Committed:	Sun Jan 8 22:27:25 2012 UTC (13 years, 3 months ago) by eulisse
Content type:	text/x-python
Branch:	MAIN
Changes since 1.4:	+17 -4 lines
Log Message:	Better errors when an exception is raised.
#	User	Rev	Content
1	eulisse	1.1	from Queue import Queue
2			from threading import Thread
3			from time import sleep
4			import threading
5	eulisse	1.5	import sys
6			import traceback
7			from StringIO import StringIO
8	eulisse	1.1
9			# Helper class to avoid conflict between result
10			# codes and quit state transition.
11			class _SchedulerQuitCommand(object):
12			pass
13
14			def transition(what, fromList, toList):
15			try:
16			fromList.remove(what)
17			except ValueError, e:
18			print what + " not in source list"
19			raise e
20			toList.append(what)
21
22			class Scheduler(object):
23			# A simple job scheduler.
24			# Workers queue is to specify to threads what to do. Results
25			# queue is whatched by the master thread to wait for results
26			# of workers computations.
27			# All worker threads begin trying to fetch from the command queue (and are
28			# therefore blocked).
29			# Master thread does the scheduling and then sits waiting for results.
30			# Scheduling implies iterating on the list of jobs and creates an entry
31			# in the parallel queue for all the jobs which does not have any dependency
32			# which is not done.
33			# If a job has dependencies which did not build, move it do the failed queue.
34			# Post an appropriate build command for all the new jobs which got added.
35			# If there are jobs still to be done, post a reschedule job on the command queue
36			# if there are no jobs left, post the "kill worker" task.
37			def __init__(self, parallelThreads, logDelegate=None):
38			self.workersQueue = Queue()
39			self.resultsQueue = Queue()
40			self.jobs = {}
41			self.pendingJobs = []
42			self.runningJobs = []
43			self.doneJobs = []
44			self.brokenJobs = []
45			self.parallelThreads = parallelThreads
46			self.logDelegate = logDelegate
47	eulisse	1.2	self.errors = {}
48	eulisse	1.1	if not logDelegate:
49			self.logDelegate = self.__doLog
50
51			def run(self):
52			for i in xrange(self.parallelThreads):
53	eulisse	1.3	t = Thread(target=self.__createWorker())
54	eulisse	1.1	t.daemon = True
55			t.start()
56
57	eulisse	1.3	self.notifyMaster(self.__rescheduleParallel)
58	eulisse	1.1	# Wait until all the workers are done.
59			while self.parallelThreads:
60			try:
61			who, item = self.resultsQueue.get()
62	eulisse	1.5	#print who, item
63	eulisse	1.1	item[0](*item[1:])
64	eulisse	1.5	sleep(0.1)
65	eulisse	1.1	except KeyboardInterrupt:
66			print "Ctrl-c received, waiting for workers to finish"
67	eulisse	1.5	while self.workersQueue.full():
68			self.workersQueue.get(False)
69	eulisse	1.1	self.shout(self.quit)
70
71			# Prune the queue.
72			while self.resultsQueue.full():
73			item = self.resultsQueue.get()
74			item[0](*item[1:])
75			return
76
77			# Create a worker.
78	eulisse	1.3	def __createWorker(self):
79	eulisse	1.1	def worker():
80			while True:
81			taskId, item = self.workersQueue.get()
82	eulisse	1.2	try:
83			result = item[0](*item[1:])
84			except Exception, e:
85	eulisse	1.5	s = StringIO()
86			traceback.print_exc(file=s)
87			result = s.getvalue()
88	eulisse	1.2
89	eulisse	1.1	if type(result) == _SchedulerQuitCommand:
90	eulisse	1.3	self.notifyMaster(self.__releaseWorker)
91	eulisse	1.1	return
92			self.log(str(item) + " done")
93			self.notifyMaster(self.__updateJobStatus, taskId, result)
94	eulisse	1.3	self.notifyMaster(self.__rescheduleParallel)
95	eulisse	1.1	# Only in 2.5: self.workersQueue.task_done()
96			return worker
97
98	eulisse	1.3	def __releaseWorker(self):
99	eulisse	1.1	self.parallelThreads -= 1
100
101	eulisse	1.3	def parallel(self, taskId, deps, *spec):
102	eulisse	1.1	if taskId in self.pendingJobs:
103			self.log("Double task %s" % taskId)
104	eulisse	1.3	self.jobs[taskId] = {"scheduler": "parallel", "deps": deps, "spec":spec}
105	eulisse	1.1	self.pendingJobs.append(taskId)
106
107			# Does the rescheduling of tasks. Derived class should call it.
108	eulisse	1.3	def __rescheduleParallel(self):
109			parallelJobs = [j for j in self.pendingJobs if self.jobs[j]["scheduler"] == "parallel"]
110			# First of all clean up the pending parallel jobs from all those
111	eulisse	1.1	# which have broken dependencies.
112	eulisse	1.3	for taskId in parallelJobs:
113	eulisse	1.1	brokenDeps = [dep for dep in self.jobs[taskId]["deps"] if dep in self.brokenJobs]
114			if not brokenDeps:
115			continue
116			transition(taskId, self.pendingJobs, self.brokenJobs)
117	eulisse	1.2	self.errors[taskId] = "The following dependencies could not complete:\n%s" % "\n".join(brokenDeps)
118	eulisse	1.1
119	eulisse	1.3	# If no tasks left, quit. Notice we need to check also for serial jobs
120			# since they might queue more parallel payloads.
121	eulisse	1.1	if not self.pendingJobs:
122			self.shout(self.quit)
123			self.notifyMaster(self.quit)
124	eulisse	1.3	return
125	eulisse	1.1
126	eulisse	1.3	# Otherwise do another round of scheduling of all the tasks. In this
127			# case we only queue parallel jobs to the parallel queue.
128			for taskId in parallelJobs:
129	eulisse	1.1	pendingDeps = [dep for dep in self.jobs[taskId]["deps"] if not dep in self.doneJobs]
130			if pendingDeps:
131			continue
132			# No broken dependencies and no pending ones. we can continue.
133			transition(taskId, self.pendingJobs, self.runningJobs)
134	eulisse	1.3	self.__scheduleParallel(taskId, self.jobs[taskId]["spec"])
135	eulisse	1.1
136			# Update the job with the result of running.
137			def __updateJobStatus(self, taskId, error):
138			if not error:
139			transition(taskId, self.runningJobs, self.doneJobs)
140			return
141			transition(taskId, self.runningJobs, self.brokenJobs)
142	eulisse	1.2	self.errors[taskId] = error
143	eulisse	1.1
144			# One task at the time.
145	eulisse	1.3	def __scheduleParallel(self, taskId, commandSpec):
146	eulisse	1.1	self.workersQueue.put((taskId, commandSpec))
147
148			# Helper to enqueue commands for all the threads.
149			def shout(self, *commandSpec):
150			for x in xrange(self.parallelThreads):
151	eulisse	1.3	self.__scheduleParallel("quit-" + str(x), commandSpec)
152	eulisse	1.1
153			# Helper to enqueu replies to the master thread.
154			def notifyMaster(self, *commandSpec):
155			self.resultsQueue.put((threading.current_thread(), commandSpec))
156	eulisse	1.3
157			def serial(self, taskId, deps, *commandSpec):
158			spec = [self.doSerial, taskId, deps] + list(commandSpec)
159			self.resultsQueue.put((threading.current_thread(), spec))
160			self.jobs[taskId] = {"scheduler": "serial", "deps": deps, "spec": spec}
161			self.pendingJobs.append(taskId)
162
163			def doSerial(self, taskId, deps, *commandSpec):
164			brokenDeps = [dep for dep in deps if dep in self.brokenJobs]
165			if brokenDeps:
166			transition(taskId, self.pendingJobs, self.brokenJobs)
167			self.errors[taskId] = "The following dependencies could not complete:\n%s" % "\n".join(brokenDeps)
168			# Remember to do the scheduling again!
169			self.notifyMaster(self.__rescheduleParallel)
170			return
171
172			# Put back the task on the queue, since it has pending dependencies.
173			pendingDeps = [dep for dep in deps if not dep in self.doneJobs]
174			if pendingDeps:
175			self.resultsQueue.put((threading.current_thread(), [self.doSerial, taskId, deps] + list(commandSpec)))
176			return
177			# No broken dependencies and no pending ones. Run the job.
178			transition(taskId, self.pendingJobs, self.runningJobs)
179			try:
180			result = commandSpec[0](*commandSpec[1:])
181			except Exception, e:
182	eulisse	1.5	s = StringIO()
183			traceback.print_exc(file=s)
184			result = s.getvalue()
185	eulisse	1.3	self.__updateJobStatus(taskId, result)
186			# Remember to do the scheduling again!
187			self.notifyMaster(self.__rescheduleParallel)
188	eulisse	1.1
189			# Helper method to do logging:
190			def log(self, s):
191			self.notifyMaster(self.logDelegate, s)
192
193			# Task which forces a worker to quit.
194			def quit(self):
195			self.log("Requested to quit.")
196			return _SchedulerQuitCommand()
197
198			# Helper for printouts.
199			def __doLog(self, s):
200			print s
201
202	eulisse	1.5	def reschedule(self):
203			self.notifyMaster(self.__rescheduleParallel)
204
205	eulisse	1.1	def dummyTask():
206			sleep(0.1)
207
208			def dummyTaskLong():
209			sleep(1)
210
211			def errorTask():
212			return "This will always have an error"
213
214	eulisse	1.2	def exceptionTask():
215			raise Exception("foo")
216
217	eulisse	1.4	# Mimics cmsBuild workflow.
218			def scheduleMore(scheduler):
219			scheduler.parallel("download", [], dummyTask)
220			scheduler.parallel("build", ["download"], dummyTask)
221			scheduler.serial("install", ["build"], dummyTask)
222
223	eulisse	1.1	if __name__ == "__main__":
224			scheduler = Scheduler(10)
225			scheduler.run()
226
227			scheduler = Scheduler(1)
228			scheduler.run()
229
230			scheduler = Scheduler(10)
231	eulisse	1.3	scheduler.parallel("test", [], scheduler.log, "This is england");
232	eulisse	1.1	scheduler.run()
233
234			scheduler = Scheduler(10)
235			for x in xrange(50):
236	eulisse	1.3	scheduler.parallel("test" + str(x), [], dummyTask)
237	eulisse	1.1	scheduler.run()
238			assert(len(scheduler.brokenJobs) == 0)
239			assert(len(scheduler.jobs) == 50)
240
241			scheduler = Scheduler(1)
242	eulisse	1.3	scheduler.parallel("test", [], errorTask)
243	eulisse	1.1	scheduler.run()
244			assert(len(scheduler.brokenJobs) == 1)
245			assert(len(scheduler.runningJobs) == 0)
246			assert(len(scheduler.doneJobs) == 0)
247
248			# Check dependency actually works.
249			scheduler = Scheduler(10)
250	eulisse	1.3	scheduler.parallel("test2", ["test1"], dummyTask)
251			scheduler.parallel("test1", [], dummyTaskLong)
252	eulisse	1.1	scheduler.run()
253			assert(scheduler.doneJobs == ["test1", "test2"])
254
255			# Check dependency actually works.
256			scheduler = Scheduler(10)
257	eulisse	1.3	scheduler.parallel("test3", ["test2"], dummyTask)
258			scheduler.parallel("test2", ["test1"], errorTask)
259			scheduler.parallel("test1", [], dummyTaskLong)
260	eulisse	1.1	scheduler.run()
261			assert(scheduler.doneJobs == ["test1"])
262			assert(scheduler.brokenJobs == ["test2", "test3"])
263
264			# Check ctrl-C will exit properly.
265			scheduler = Scheduler(2)
266			for x in xrange(250):
267	eulisse	1.3	scheduler.parallel("test" + str(x), [], dummyTask)
268	eulisse	1.1	print "Print Control-C to continue"
269	eulisse	1.2	scheduler.run()
270
271			# Handle tasks with exceptions.
272			scheduler = Scheduler(2)
273	eulisse	1.3	scheduler.parallel("test", [], exceptionTask)
274	eulisse	1.2	scheduler.run()
275	eulisse	1.5	assert(scheduler.errors["test"])
276	eulisse	1.2
277			# Handle tasks which depend on tasks with exceptions.
278			scheduler = Scheduler(2)
279	eulisse	1.3	scheduler.parallel("test0", [], dummyTask)
280			scheduler.parallel("test1", [], exceptionTask)
281			scheduler.parallel("test2", ["test1"], dummyTask)
282	eulisse	1.2	scheduler.run()
283			assert(scheduler.errors["test1"])
284			assert(scheduler.errors["test2"])
285	eulisse	1.3
286			# Handle serial execution tasks.
287			scheduler = Scheduler(2)
288			scheduler.serial("test0", [], dummyTask)
289			scheduler.run()
290			assert(scheduler.doneJobs == ["test0"])
291
292			# Handle serial execution tasks, one depends from
293			# the previous one.
294			scheduler = Scheduler(2)
295			scheduler.serial("test0", [], dummyTask)
296			scheduler.serial("test1", ["test0"], dummyTask)
297			scheduler.run()
298			assert(scheduler.doneJobs == ["test0", "test1"])
299
300			# Serial tasks depending on one another.
301			scheduler = Scheduler(2)
302			scheduler.serial("test1", ["test0"], dummyTask)
303			scheduler.serial("test0", [], dummyTask)
304			scheduler.run()
305			assert(scheduler.doneJobs == ["test0", "test1"])
306
307			# Serial and parallel tasks being scheduled at the same time.
308			scheduler = Scheduler(2)
309			scheduler.serial("test1", ["test0"], dummyTask)
310			scheduler.serial("test0", [], dummyTask)
311			scheduler.parallel("test2", [], dummyTask)
312			scheduler.parallel("test3", [], dummyTask)
313			scheduler.run()
314			scheduler.doneJobs.sort()
315			assert(scheduler.doneJobs == ["test0", "test1", "test2", "test3"])
316
317			# Serial and parallel tasks. Parallel depends on serial.
318			scheduler = Scheduler(2)
319			scheduler.serial("test1", ["test0"], dummyTask)
320			scheduler.serial("test0", [], dummyTask)
321			scheduler.parallel("test2", ["test1"], dummyTask)
322			scheduler.parallel("test3", ["test2"], dummyTask)
323			scheduler.run()
324			assert(scheduler.doneJobs == ["test0", "test1", "test2", "test3"])
325	eulisse	1.4
326			# Serial task scheduling two parallel task and another dependent
327			# serial task. This is actually what needs to be done for building
328			# packages. I.e.
329			# The first serial task is responsible for checking if a package is already there,
330			# then it queues a parallel download sources task, a subsequent build sources
331			# one and finally the install built package one.
332			scheduler = Scheduler(3)
333			scheduler.serial("check-pkg", [], scheduleMore, scheduler)
334			scheduler.run()
335			assert(scheduler.doneJobs == ["check-pkg", "download", "build", "install"])