We are trying to proceed multiprocessing in Django, but it never works.
To have a simple example, we started an empty Django-project and created the app mp. Then, we added the following code:
views.py:
from django.http import HttpResponse
from .mp import MultiProcess
def DoubleIt(number):
print("haha")
a = number * 2
return a
def mp_view(request):
mylist = [111,222,333]
with MultiProcess() as mp:
mp.map(DoubleIt, mylist)
results = mp.results()
return HttpResponse("Test")
urls.py
from django.conf.urls import url
from django.contrib import admin
from mp.views import *
urlpatterns = [
url(r'^mp/', mp_view, name="mp_view"),
]
mp.py from https://engineering.talentpair.com/django-multiprocessing-153dbcf51dab:
from __future__ import print_function, absolute_import, unicode_literals
import time
try:
from Queue import Empty
except ImportError:
from queue import Empty
from multiprocessing import Process, cpu_count, Manager
import logging
import traceback
from django import db
from django.conf import settings
from django.core.cache import caches
from elasticsearch_dsl import connections
loggly = logging.getLogger('loggly')
class Timer(object):
""" Simple class for timing code blocks
"""
def __init__(self):
self.start_time = time.time()
def done(self):
end_time = time.time()
return int(end_time - self.start_time)
def close_service_connections():
""" Close all connections before we spawn our processes
This function should only be used when writing multithreaded scripts where connections need to manually
opened and closed so that threads don't reuse the same connection
https://stackoverflow.com/questions/8242837/django-multiprocessing-and-database-connections
"""
# close db connections, they will be recreated automatically
db.connections.close_all()
# close ES connection, needs to be manually recreated
# connections.connections.remove_connection("default")
# close redis connections, will be recreated automatcially
for k in settings.CACHES.keys():
caches[k].close()
def recreate_service_connections():
""" All this happens automatically when django starts up, this function should only be used when writing
multithreaded scripts where connections need to manually opened and closed so that threads don't reuse
the same connection
"""
# ES is the only one that needs to be recreated explicitly
# connections.connections.create_connection(hosts=[settings.ELASTIC_FULL_URL], timeout=20)
def threadwrapper(some_function, catch_exceptions=True):
""" This wrapper should only be used when a function is being called in a multiprocessing context
"""
def wrapper(queue, items):
recreate_service_connections()
for i in items:
try:
rv = some_function(i)
except Exception:
rv = None
if catch_exceptions:
loggly.error("threadwrapper caught an error, continuing - %s" % traceback.format_exc())
else:
raise
queue.put(rv, block=False)
close_service_connections()
return wrapper
class MultiProcess(object):
""" Nicely abstracts away some of the challenges when doing multiprocessing with Django
Unfortunately, falls over when running tests so its not really tested
We implement this as a context manager so we dont have to worry about garbage collection calling __del__
"""
queue = None
item_count = 1
workers = []
def __init__(self, num_workers=None, max_workers=None, debug_print=False, status_interval=20):
if num_workers is None:
# always use at least one threads and leave one cpu available for other stuff
# but 1 is the minumum
self.num_workers = cpu_count() - 1
if self.num_workers < 2:
self.num_workers = 1
if max_workers and self.num_workers > max_workers:
self.num_workers = max_workers
else:
self.num_workers = num_workers
self.debug_print = debug_print
self.status_interval = status_interval
if debug_print:
print("Using %s workers" % self.num_workers)
def __enter__(self):
close_service_connections()
return self
def map(self, func, iterable):
self.queue = Manager().Queue()
self.item_count = len(iterable) or 1
for worker_idx in range(self.num_workers):
items = []
for idx, item in enumerate(iterable):
if idx % self.num_workers == worker_idx:
items.append(item)
if self.debug_print:
print("Working on %s uids of %s in worker %s" % (len(items), len(iterable), worker_idx))
p = Process(target=threadwrapper(func), args=[self.queue, items])
p.start()
self.workers.append(p)
self._wait()
def _wait(self):
""" Wait for all workers to finish and wakes up peridocially to print out how much work has happened
"""
total_time = Timer()
while [p for p in self.workers if p.is_alive()]:
tpt = Timer()
for p in self.workers:
p.join(timeout=self.status_interval)
interval_secs = tpt.done() // 1000
# if we've timed out on the status interval, print it out and reset the counter
if self.debug_print and interval_secs >= self.status_interval:
tpt = Timer()
total_secs = total_time.done() // 1000
percent = (self.queue.qsize() * 100) // self.item_count
print("--------- {}% done ({}s elapsed) ---------".format(percent, total_secs))
def results(self):
rv = []
try:
while True:
rv.append(self.queue.get(block=False))
except Empty:
return rv
def __exit__(self, type, value, traceback):
# recreate the connections so we can do more stuff
recreate_service_connections()
We received the following error message:
Environment:
Request Method: GET Request URL: http://127.0.0.1:8000/mp/
Django Version: 1.11.14 Python Version: 3.6.1 Installed Applications: ['django.contrib.admin', 'django.contrib.auth', 'django.contrib.contenttypes', 'django.contrib.sessions', 'django.contrib.messages', 'django.contrib.staticfiles'] Installed Middleware: ['django.middleware.security.SecurityMiddleware', 'django.contrib.sessions.middleware.SessionMiddleware', 'django.middleware.common.CommonMiddleware', 'django.middleware.csrf.CsrfViewMiddleware', 'django.contrib.auth.middleware.AuthenticationMiddleware', 'django.contrib.messages.middleware.MessageMiddleware', 'django.middleware.clickjacking.XFrameOptionsMiddleware']
Traceback:
File "C:\django-env\lib\site-packages\django\core\handlers\exception.py" in inner 41. response = get_response(request)
File "C:\django-env\lib\site-packages\django\core\handlers\base.py" in _get_response 187. response = self.process_exception_by_middleware(e, request)
File "C:\django-env\lib\site-packages\django\core\handlers\base.py" in _get_response 185. response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "C:/multiprocessing_example\mp\views.py" in mp_view 18. mp.map(DoubleIt, mylist)
File "C:/multiprocessing_example\mp\mp.py" in map 141. p.start()
File "c:\users\robert\anaconda3\Lib\multiprocessing\process.py" in start 105. self._popen = self._Popen(self)
File "c:\users\robert\anaconda3\Lib\multiprocessing\context.py" in _Popen 223. return _default_context.get_context().Process._Popen(process_obj)
File "c:\users\robert\anaconda3\Lib\multiprocessing\context.py" in _Popen 322. return Popen(process_obj)
File "c:\users\robert\anaconda3\Lib\multiprocessing\popen_spawn_win32.py" in init 65. reduction.dump(process_obj, to_child)
File "c:\users\robert\anaconda3\Lib\multiprocessing\reduction.py" in dump 60. ForkingPickler(file, protocol).dump(obj)
Exception Type: AttributeError at /mp/ Exception Value: Can't pickle local object 'threadwrapper..wrapper'
Any idea how to fix that in Django?
