Commit 76094e37 authored by Michael Hanselmann's avatar Michael Hanselmann

Add generic worker pool implementation

Reviewed-by: ultrotter
parent 2cb687ad
......@@ -75,7 +75,8 @@ pkgpython_PYTHON = \
lib/serializer.py \
lib/ssconf.py \
lib/ssh.py \
lib/utils.py
lib/utils.py \
lib/workerpool.py
hypervisor_PYTHON = \
lib/hypervisor/__init__.py \
......@@ -172,6 +173,7 @@ dist_TESTS = \
test/ganeti.ssh_unittest.py \
test/ganeti.locking_unittest.py \
test/ganeti.serializer_unittest.py \
test/ganeti.workerpool_unittest.py \
test/ganeti.constants_unittest.py
nodist_TESTS =
......
#
#
# Copyright (C) 2008 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
"""Base classes for worker pools.
"""
import collections
import logging
import threading
from ganeti import errors
from ganeti import utils
class BaseWorker(threading.Thread, object):
"""Base worker class for worker pools.
Users of a worker pool must override RunTask in a subclass.
"""
def __init__(self, pool, worker_id):
"""Constructor for BaseWorker thread.
Args:
- pool: Parent worker pool
- worker_id: Identifier for this worker
"""
super(BaseWorker, self).__init__()
self.pool = pool
self.worker_id = worker_id
# Also used by WorkerPool
self._current_task = None
def ShouldTerminate(self):
"""Returns whether a worker should terminate.
"""
return self.pool.ShouldWorkerTerminate(self)
def run(self):
"""Main thread function.
Waits for new tasks to show up in the queue.
"""
pool = self.pool
assert self._current_task is None
while True:
try:
# We wait on lock to be told either terminate or do a task.
pool._lock.acquire()
try:
if pool._ShouldWorkerTerminateUnlocked(self):
break
# We only wait if there's no task for us.
if not pool._tasks:
# wait() releases the lock and sleeps until notified
pool._lock.wait()
# Were we woken up in order to terminate?
if pool._ShouldWorkerTerminateUnlocked(self):
break
if not pool._tasks:
# Spurious notification, ignore
continue
# Get task from queue and tell pool about it
try:
self._current_task = pool._tasks.popleft()
finally:
pool._lock.notifyAll()
finally:
pool._lock.release()
# Run the actual task
try:
self.RunTask(*self._current_task)
except:
logging.error("Worker %s: Caught unhandled exception",
self.worker_id, exc_info=True)
finally:
self._current_task = None
# Notify pool
pool._lock.acquire()
try:
pool._lock.notifyAll()
finally:
pool._lock.release()
def RunTask(self, *args):
"""Function called to start a task.
"""
raise NotImplementedError()
class WorkerPool(object):
"""Worker pool with a queue.
This class is thread-safe.
Tasks are guaranteed to be started in the order in which they're added to the
pool. Due to the nature of threading, they're not guaranteed to finish in the
same order.
"""
def __init__(self, num_workers, worker_class):
"""Constructor for worker pool.
Args:
- num_workers: Number of workers to be started (dynamic resizing is not
yet implemented)
- worker_class: Class to be instantiated for workers; should derive from
BaseWorker
"""
# Some of these variables are accessed by BaseWorker
self._lock = threading.Condition(threading.Lock())
self._worker_class = worker_class
self._last_worker_id = 0
self._workers = []
self._quiescing = False
# Terminating workers
self._termworkers = []
# Queued tasks
self._tasks = collections.deque()
# Start workers
self.Resize(num_workers)
# TODO: Implement dynamic resizing?
def AddTask(self, *args):
"""Adds a task to the queue.
Args:
- *args: Arguments passed to BaseWorker.RunTask
"""
self._lock.acquire()
try:
# Don't add new tasks while we're quiescing
while self._quiescing:
self._lock.wait()
# Add task to internal queue
self._tasks.append(args)
self._lock.notify()
finally:
self._lock.release()
def _ShouldWorkerTerminateUnlocked(self, worker):
"""Returns whether a worker should terminate.
"""
return (worker in self._termworkers)
def ShouldWorkerTerminate(self, worker):
"""Returns whether a worker should terminate.
"""
self._lock.acquire()
try:
return self._ShouldWorkerTerminateUnlocked(self)
finally:
self._lock.release()
def _HasRunningTasksUnlocked(self):
"""Checks whether there's a task running in a worker.
"""
for worker in self._workers + self._termworkers:
if worker._current_task is not None:
return True
return False
def Quiesce(self):
"""Waits until the task queue is empty.
"""
self._lock.acquire()
try:
self._quiescing = True
# Wait while there are tasks pending or running
while self._tasks or self._HasRunningTasksUnlocked():
self._lock.wait()
finally:
self._quiescing = False
# Make sure AddTasks continues in case it was waiting
self._lock.notifyAll()
self._lock.release()
def _NewWorkerIdUnlocked(self):
self._last_worker_id += 1
return self._last_worker_id
def _ResizeUnlocked(self, num_workers):
"""Changes the number of workers.
"""
assert num_workers >= 0, "num_workers must be >= 0"
logging.debug("Resizing to %s workers", num_workers)
current_count = len(self._workers)
if current_count == num_workers:
# Nothing to do
pass
elif current_count > num_workers:
if num_workers == 0:
# Create copy of list to iterate over while lock isn't held.
termworkers = self._workers[:]
del self._workers[:]
else:
# TODO: Implement partial downsizing
raise NotImplementedError()
#termworkers = ...
self._termworkers += termworkers
# Notify workers that something has changed
self._lock.notifyAll()
# Join all terminating workers
self._lock.release()
try:
for worker in termworkers:
worker.join()
finally:
self._lock.acquire()
# Remove terminated threads. This could be done in a more efficient way
# (del self._termworkers[:]), but checking worker.isAlive() makes sure we
# don't leave zombie threads around.
for worker in termworkers:
assert worker in self._termworkers, ("Worker not in list of"
" terminating workers")
if not worker.isAlive():
self._termworkers.remove(worker)
assert not self._termworkers, "Zombie worker detected"
elif current_count < num_workers:
# Create (num_workers - current_count) new workers
for i in xrange(num_workers - current_count):
worker = self._worker_class(self, self._NewWorkerIdUnlocked())
self._workers.append(worker)
worker.start()
def Resize(self, num_workers):
"""Changes the number of workers in the pool.
Args:
- num_workers: New number of workers
"""
self._lock.acquire()
try:
return self._ResizeUnlocked(num_workers)
finally:
self._lock.release()
def TerminateWorkers(self):
"""Terminate all worker threads.
Unstarted tasks will be ignored.
"""
logging.debug("Terminating all workers")
self._lock.acquire()
try:
self._ResizeUnlocked(0)
if self._tasks:
logging.debug("There are %s tasks left", len(self._tasks))
finally:
self._lock.release()
logging.debug("All workers terminated")
#!/usr/bin/python
#
# Copyright (C) 2008 Google Inc.
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
# General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
# 02110-1301, USA.
"""Script for unittesting the workerpool module"""
import unittest
import threading
import time
import sys
import zlib
from ganeti import workerpool
class DummyBaseWorker(workerpool.BaseWorker):
def RunTask(self, text):
pass
class ChecksumContext:
CHECKSUM_START = zlib.adler32("")
def __init__(self):
self.lock = threading.Condition(threading.Lock())
self.checksum = self.CHECKSUM_START
@staticmethod
def UpdateChecksum(current, value):
return zlib.adler32(str(value), current)
class ChecksumBaseWorker(workerpool.BaseWorker):
def RunTask(self, ctx, number):
ctx.lock.acquire()
try:
ctx.checksum = ctx.UpdateChecksum(ctx.checksum, number)
finally:
ctx.lock.release()
class TestWorkerpool(unittest.TestCase):
"""Workerpool tests"""
def testDummy(self):
wp = workerpool.WorkerPool(3, DummyBaseWorker)
try:
self._CheckWorkerCount(wp, 3)
for i in xrange(10):
wp.AddTask("Hello world %s" % i)
wp.Quiesce()
finally:
wp.TerminateWorkers()
self._CheckWorkerCount(wp, 0)
def testNoTasks(self):
wp = workerpool.WorkerPool(3, DummyBaseWorker)
try:
self._CheckWorkerCount(wp, 3)
self._CheckNoTasks(wp)
finally:
wp.TerminateWorkers()
self._CheckWorkerCount(wp, 0)
def testNoTasksQuiesce(self):
wp = workerpool.WorkerPool(3, DummyBaseWorker)
try:
self._CheckWorkerCount(wp, 3)
self._CheckNoTasks(wp)
wp.Quiesce()
self._CheckNoTasks(wp)
finally:
wp.TerminateWorkers()
self._CheckWorkerCount(wp, 0)
def testChecksum(self):
# Tests whether all tasks are run and, since we're only using a single
# thread, whether everything is started in order.
wp = workerpool.WorkerPool(1, ChecksumBaseWorker)
try:
self._CheckWorkerCount(wp, 1)
ctx = ChecksumContext()
checksum = ChecksumContext.CHECKSUM_START
for i in xrange(1, 100):
checksum = ChecksumContext.UpdateChecksum(checksum, i)
wp.AddTask(ctx, i)
wp.Quiesce()
self._CheckNoTasks(wp)
# Check sum
ctx.lock.acquire()
try:
self.assertEqual(checksum, ctx.checksum)
finally:
ctx.lock.release()
finally:
wp.TerminateWorkers()
self._CheckWorkerCount(wp, 0)
def _CheckNoTasks(self, wp):
wp._lock.acquire()
try:
# The task queue must be empty now
self.failUnless(not wp._tasks)
finally:
wp._lock.release()
def _CheckWorkerCount(self, wp, num_workers):
wp._lock.acquire()
try:
self.assertEqual(len(wp._workers), num_workers)
finally:
wp._lock.release()
if __name__ == '__main__':
unittest.main()
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