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# Copyright 2011 Lars Wirzenius
#
# 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 3 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, see <http://www.gnu.org/licenses/>.
import multiprocessing
import Queue
import time
def worker(func, requests, results): # pragma: no cover
while True:
item = requests.get()
if item is None:
break
request = item[0]
result = func(request)
results.put(result)
class BackgroundProcessing(object):
'''Manage background processing queues.'''
def __init__(self, func, numprocs=None):
self._pending_requests = 0
self.requests = multiprocessing.Queue()
self.results = multiprocessing.Queue()
args = (func, self.requests, self.results)
n = numprocs or multiprocessing.cpu_count()
self.processes = [multiprocessing.Process(target=worker, args=args)
for i in range(n)]
for p in self.processes:
p.start()
def enqueue_request(self, request):
'''Put a request into queue, to be processed by workers whenever.'''
self._pending_requests += 1
self.requests.put((request,))
def close_requests(self):
'''Signal workers that they can retire.
All pending requests will be processed, but after the queue
is empty, the workers will finish. No more requests may be
enqueued.
'''
for p in self.processes:
self.requests.put(None)
def finish(self):
'''Wait until all children have finished.'''
for p in self.processes:
p.join()
def get_results(self, block=False):
'''Return currently available results.
If 'block' is True, then wait until there is at least one
result.
'''
if block and self._pending_requests == 0:
return []
items = []
while True:
try:
item = self.results.get(block)
except Queue.Empty:
break
else:
self._pending_requests -= 1
items.append(item)
block = False
return items
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