I have found several other questions that touch on this topic but none that are quite like my situation.
I have several very large text files (3+ gigabytes in size).
I would like to process them (say 2 documents) in parallel using multiprocessing. As part of my processing (within a single process) I need to make an API call and because of this would like to have each process have it's own threads to run asynchronously.
I have came up with a simplified example ( I have commented the code to try to explain what I think it should be doing):
import multiprocessing
from threading import Thread
import threading
from queue import Queue
import time
def process_huge_file(*, file_, batch_size=250, num_threads=4):
# create APICaller instance for each process that has it's own Queue
api_call = APICaller()
batch = []
# create threads that will run asynchronously to make API calls
# I expect these to immediately block since there is nothing in the Queue (which is was
# the api_call.run depends on to make a call
threads = []
for i in range(num_threads):
thread = Thread(target=api_call.run)
threads.append(thread)
thread.start()
for thread in threads:
thread.join()
####
# start processing the file line by line
for line in file_:
# if we are at our batch size, add the batch to the api_call to to let the threads do
# their api calling
if i % batch_size == 0:
api_call.queue.put(batch)
else:
# add fake line to batch
batch.append(fake_line)
class APICaller:
def __init__(self):
# thread safe queue to feed the threads which point at instances
of these APICaller objects
self.queue = Queue()
def run(self):
print("waiting for something to do")
self.queue.get()
print("processing item in queue")
time.sleep(0.1)
print("finished processing item in queue")
if __name__ == "__main__":
# fake docs
fake_line = "this is a fake line of some text"
# two fake docs with line length == 1000
fake_docs = [[fake_line] * 1000 for i in range(2)]
####
num_processes = 2
procs = []
for idx, doc in enumerate(fake_docs):
proc = multiprocessing.Process(target=process_huge_file, kwargs=dict(file_=doc))
proc.start()
procs.append(proc)
for proc in procs:
proc.join()
As the code is now, "waiting for something to do" prints 8 times (makes sense 4 threads per process) and then it stops or "deadlocks" which is not what I expect - I expect it to start sharing time with the threads as soon as I start putting items in the Queue but the code does not appear to make it this far. I ordinarily would step through to find a hang up but I still don't have a solid understanding of how to best debug using Threads (another topic for another day).
In the meantime, can someone help me figure out why my code is not doing what it should be doing?
I have made a few adjustments and additions and the code appears to do what it is supposed to now. The main adjustments are: adding a CloseableQueue class (from Brett Slatkins Effective Python Item 55), and ensuring that I call close and join on the queue so that the threads properly exit. Full code with these changes below:
import multiprocessing
from threading import Thread
import threading
from queue import Queue
import time
from concurrency_utils import CloseableQueue
def sync_process_huge_file(*, file_, batch_size=250):
batch = []
for idx, line in enumerate(file_):
# do processing on the text
if idx % batch_size == 0:
time.sleep(0.1)
batch = []
# api_call.queue.put(batch)
else:
computation = 0
for i in range(100000):
computation += i
batch.append(line)
def process_huge_file(*, file_, batch_size=250, num_threads=4):
api_call = APICaller()
batch = []
# api call threads
threads = []
for i in range(num_threads):
thread = Thread(target=api_call.run)
threads.append(thread)
thread.start()
for idx, line in enumerate(file_):
# do processing on the text
if idx % batch_size == 0:
api_call.queue.put(batch)
else:
computation = 0
for i in range(100000):
computation += i
batch.append(line)
for _ in threads:
api_call.queue.close()
api_call.queue.join()
for thread in threads:
thread.join()
class APICaller:
def __init__(self):
self.queue = CloseableQueue()
def run(self):
for item in self.queue:
print("waiting for something to do")
pass
print("processing item in queue")
time.sleep(0.1)
print("finished processing item in queue")
print("exiting run")
if __name__ == "__main__":
# fake docs
fake_line = "this is a fake line of some text"
# two fake docs with line length == 1000
fake_docs = [[fake_line] * 10000 for i in range(2)]
####
time_s = time.time()
num_processes = 2
procs = []
for idx, doc in enumerate(fake_docs):
proc = multiprocessing.Process(target=process_huge_file, kwargs=dict(file_=doc))
proc.start()
procs.append(proc)
for proc in procs:
proc.join()
time_e = time.time()
print(f"took {time_e-time_s} ")
class CloseableQueue(Queue):
SENTINEL = object()
def __init__(self, **kwargs):
super().__init__(**kwargs)
def close(self):
self.put(self.SENTINEL)
def __iter__(self):
while True:
item = self.get()
try:
if item is self.SENTINEL:
return # exit thread
yield item
finally:
self.task_done()
As expected this is a great speedup from running synchronously - 120 seconds vs 50 seconds.
Related
Using below code I start to thread processes, write_process writes to a queue and read_process reads from a queue :
import time
from multiprocessing import Process, Queue, Pool
class QueueFun():
def writing_queue(self, work_tasks):
while True:
print("Writing to queue")
work_tasks.put(1)
time.sleep(1)
def read_queue(self, work_tasks):
while True:
print('Reading from queue')
work_tasks.get()
time.sleep(2)
if __name__ == '__main__':
q = QueueFun()
work_tasks = Queue()
write_process = Process(target=q.writing_queue,
args=(work_tasks,))
write_process.start()
read_process = Process(target=q.read_queue,
args=(work_tasks,))
read_process.start()
write_process.join()
read_process.join()
Running above code prints:
Writing to queue
Reading from queue
Writing to queue
Reading from queue
Writing to queue
Writing to queue
Reading from queue
Writing to queue
How to start N processes to read from the queue?
I tried starting 3 processes using below code but just 1 process is started, this is because the .join() prevents the second process from starting?:
for i in range(0 , 3):
read_process = Process(target=q.read_queue,
args=(work_tasks,))
print('Starting read_process' , i)
read_process.start()
read_process.join()
I also considered using a Pool as described in https://docs.python.org/2/library/multiprocessing.html but this seems just relevant for transforming an existing collection :
print pool.map(f, range(10))
How to start n threads where each thread processes a shared queue?
You can just put it to list, and join it outside of creation loop:
if __name__ == '__main__':
q = QueueFun()
work_tasks = Queue()
write_process = Process(target=q.writing_queue,
args=(work_tasks,))
write_process.start()
processes = []
for i in range(0, 5):
processes.append(Process(target=q.read_queue,
args=(work_tasks,)))
for p in processes:
p.start()
write_process.join()
for p in processes:
p.join()
I'm trying to implement basic multiprocessing and I've run into an issue. The python script is attached below.
import time, sys, random, threading
from multiprocessing import Process
from Queue import Queue
from FrequencyAnalysis import FrequencyStore, AnalyzeFrequency
append_queue = Queue(10)
database = FrequencyStore()
def add_to_append_queue(_list):
append_queue.put(_list)
def process_append_queue():
while True:
item = append_queue.get()
database.append(item)
print("Appended to database in %.4f seconds" % database.append_time)
append_queue.task_done()
return
def main():
database.load_db()
print("Database loaded in %.4f seconds" % database.load_time)
append_queue_process = Process(target=process_append_queue)
append_queue_process.daemon = True
append_queue_process.start()
#t = threading.Thread(target=process_append_queue)
#t.daemon = True
#t.start()
while True:
path = raw_input("file: ")
if path == "exit":
break
a = AnalyzeFrequency(path)
a.analyze()
print("Analyzed file in %.4f seconds" % a._time)
add_to_append_queue(a.get_results())
append_queue.join()
#append_queue_process.join()
database.save_db()
print("Database saved in %.4f seconds" % database.save_time)
sys.exit(0)
if __name__=="__main__":
main()
The AnalyzeFrequency analyzes the frequencies of words in a file and get_results() returns a sorted list of said words and frequencies. The list is very large, perhaps 10000 items.
This list is then passed to the add_to_append_queue method which adds it to a queue. The process_append_queue takes the items one by one and adds the frequencies to a "database". This operation takes a bit longer than the actual analysis in main() so I am trying to use a seperate process for this method. When I try and do this with the threading module, everything works perfectly fine, no errors. When I try and use Process, the script hangs at item = append_queue.get().
Could someone please explain what is happening here, and perhaps direct me toward a fix?
All answers appreciated!
UPDATE
The pickle error was my fault, it was just a typo. Now I am using the Queue class within multiprocessing but the append_queue.get() method still hangs.
NEW CODE
import time, sys, random
from multiprocessing import Process, Queue
from FrequencyAnalysis import FrequencyStore, AnalyzeFrequency
append_queue = Queue()
database = FrequencyStore()
def add_to_append_queue(_list):
append_queue.put(_list)
def process_append_queue():
while True:
database.append(append_queue.get())
print("Appended to database in %.4f seconds" % database.append_time)
return
def main():
database.load_db()
print("Database loaded in %.4f seconds" % database.load_time)
append_queue_process = Process(target=process_append_queue)
append_queue_process.daemon = True
append_queue_process.start()
#t = threading.Thread(target=process_append_queue)
#t.daemon = True
#t.start()
while True:
path = raw_input("file: ")
if path == "exit":
break
a = AnalyzeFrequency(path)
a.analyze()
print("Analyzed file in %.4f seconds" % a._time)
add_to_append_queue(a.get_results())
#append_queue.join()
#append_queue_process.join()
print str(append_queue.qsize())
database.save_db()
print("Database saved in %.4f seconds" % database.save_time)
sys.exit(0)
if __name__=="__main__":
main()
UPDATE 2
This is the database code:
class FrequencyStore:
def __init__(self):
self.sorter = Sorter()
self.db = {}
self.load_time = -1
self.save_time = -1
self.append_time = -1
self.sort_time = -1
def load_db(self):
start_time = time.time()
try:
file = open("results.txt", 'r')
except:
raise IOError
self.db = {}
for line in file:
word, count = line.strip("\n").split("=")
self.db[word] = int(count)
file.close()
self.load_time = time.time() - start_time
def save_db(self):
start_time = time.time()
_db = []
for key in self.db:
_db.append([key, self.db[key]])
_db = self.sort(_db)
try:
file = open("results.txt", 'w')
except:
raise IOError
file.truncate(0)
for x in _db:
file.write(x[0] + "=" + str(x[1]) + "\n")
file.close()
self.save_time = time.time() - start_time
def create_sorted_db(self):
_temp_db = []
for key in self.db:
_temp_db.append([key, self.db[key]])
_temp_db = self.sort(_temp_db)
_temp_db.reverse()
return _temp_db
def get_db(self):
return self.db
def sort(self, _list):
start_time = time.time()
_list = self.sorter.mergesort(_list)
_list.reverse()
self.sort_time = time.time() - start_time
return _list
def append(self, _list):
start_time = time.time()
for x in _list:
if x[0] not in self.db:
self.db[x[0]] = x[1]
else:
self.db[x[0]] += x[1]
self.append_time = time.time() - start_time
Comments suggest you're trying to run this on Windows. As I said in a comment,
If you're running this on Windows, it can't work - Windows doesn't
have fork(), so each process gets its own Queue and they have nothing
to do with each other. The entire module is imported "from scratch" by
each process on Windows. You'll need to create the Queue in main(),
and pass it as an argument to the worker function.
Here's fleshing out what you need to do to make it portable, although I removed all the database stuff because it's irrelevant to the problems you've described so far. I also removed the daemon fiddling, because that's usually just a lazy way to avoid shutting down things cleanly, and often as not will come back to bite you later:
def process_append_queue(append_queue):
while True:
x = append_queue.get()
if x is None:
break
print("processed %d" % x)
print("worker done")
def main():
import multiprocessing as mp
append_queue = mp.Queue(10)
append_queue_process = mp.Process(target=process_append_queue, args=(append_queue,))
append_queue_process.start()
for i in range(100):
append_queue.put(i)
append_queue.put(None) # tell worker we're done
append_queue_process.join()
if __name__=="__main__":
main()
The output is the "obvious" stuff:
processed 0
processed 1
processed 2
processed 3
processed 4
...
processed 96
processed 97
processed 98
processed 99
worker done
Note: because Windows doesn't (can't) fork(), it's impossible for worker processes to inherit any Python object on Windows. Each process runs the entire program from its start. That's why your original program couldn't work: each process created its own Queue, wholly unrelated to the Queue in the other process. In the approach shown above, only the main process creates a Queue, and the main process passes it (as an argument) to the worker process.
queue.Queue is thread-safe, but doesn't work across processes. This is quite easy to fix, though. Instead of:
from multiprocessing import Process
from Queue import Queue
You want:
from multiprocessing import Process, Queue
I have a Python application where I use processes for computing classification. For communication processes use Queues. Everything works fine except that after all sub-processes are done the main process does not get control back. So, as I understand, the sub-processes did not terminated. But, why?
#!/usr/bin/python
from wraper import *
from multiprocessing import Process, Lock,Queue
def start_threads(data,counter,threads_num,reporter):
threads = []
d_lock = Lock()
c_lock = Lock()
r_lock = Lock()
dq = Queue()
rq = Queue()
cq = Queue()
dq.put(data)
rq.put(reporter)
cq.put(counter)
for i in range(threads_num):
t = Process(target=mule, args=(dq,cq,rq,d_lock,c_lock,r_lock))
threads.append(t)
for t in threads:
t.start()
for t in threads:
t.join()
return rq.get()
def mule(dq,cq,rq,d_lock,c_lock,r_lock):
c_lock.acquire()
counter = cq.get()
can_continue = counter.next_ok()
idx = counter.get_features_indeces()
cq.put(counter)
c_lock.release()
while can_continue:
d_lock.acquire()
data = dq.get()
labels, features = data.get_features(idx)
dq.put(data)
d_lock.release()
accuracy = test_classifier(labels, features)
r_lock.acquire()
reporter = rq.get()
reporter.add_result(accuracy[0],idx)
rq.put(reporter)
r_lock.release()
c_lock.acquire()
counter = cq.get()
can_continue = counter.next_ok()
idx = counter.get_features_indeces()
cq.put(counter)
c_lock.release()
print('done' )
It writes for each process that it did it's job and that's it...
I try to write a script in python to convert url into its corresponding ip. Since the url file is huge (nearly 10GB), so I'm trying to use multiprocessing lib.
I create one process to write output to file and a set of processes to convert url.
Here is my code:
import multiprocessing as mp
import socket
import time
num_processes = mp.cpu_count()
sentinel = None
def url2ip(inqueue, output):
v_url = inqueue.get()
print 'v_url '+v_url
try:
v_ip = socket.gethostbyname(v_url)
output_string = v_url+'|||'+v_ip+'\n'
except:
output_string = v_url+'|||-1'+'\n'
print 'output_string '+output_string
output.put(output_string)
print output.full()
def handle_output(output):
f_ip = open("outputfile", "a")
while True:
output_v = output.get()
if output_v:
print 'output_v '+output_v
f_ip.write(output_v)
else:
break
f_ip.close()
if __name__ == '__main__':
output = mp.Queue()
inqueue = mp.Queue()
jobs = []
proc = mp.Process(target=handle_output, args=(output, ))
proc.start()
print 'run in %d processes' % num_processes
for i in range(num_processes):
p = mp.Process(target=url2ip, args=(inqueue, output))
jobs.append(p)
p.start()
for line in open('inputfile','r'):
print 'ori '+line.strip()
inqueue.put(line.strip())
for i in range(num_processes):
# Send the sentinal to tell Simulation to end
inqueue.put(sentinel)
for p in jobs:
p.join()
output.put(None)
proc.join()
However, it did not work. It did produce several outputs (4 out of 10 urls in the test file) but it just suddenly stops while queues are not empty (I did check queue.empty())
Could anyone suggest what's wrong?Thanks
You're workers exit after processing a single url each, they need to loop internally until they get the sentinel. However, you should probably just look at multiprocessing.pool instead, as that does the bookkeeping for you.
The purpose of my program is to download files with threads. I define the unit, and using len/unit threads, the len is the length of the file which is going to be downloaded.
Using my program, the file can be downloaded, but the threads are not stopping. I can't find the reason why.
This is my code...
#! /usr/bin/python
import urllib2
import threading
import os
from time import ctime
class MyThread(threading.Thread):
def __init__(self,func,args,name=''):
threading.Thread.__init__(self);
self.func = func;
self.args = args;
self.name = name;
def run(self):
apply(self.func,self.args);
url = 'http://ubuntuone.com/1SHQeCAQWgIjUP2945hkZF';
request = urllib2.Request(url);
response = urllib2.urlopen(request);
meta = response.info();
response.close();
unit = 1000000;
flen = int(meta.getheaders('Content-Length')[0]);
print flen;
if flen%unit == 0:
bs = flen/unit;
else :
bs = flen/unit+1;
blocks = range(bs);
cnt = {};
for i in blocks:
cnt[i]=i;
def getStr(i):
try:
print 'Thread %d start.'%(i,);
fout = open('a.zip','wb');
fout.seek(i*unit,0);
if (i+1)*unit > flen:
request.add_header('Range','bytes=%d-%d'%(i*unit,flen-1));
else :
request.add_header('Range','bytes=%d-%d'%(i*unit,(i+1)*unit-1));
#opener = urllib2.build_opener();
#buf = opener.open(request).read();
resp = urllib2.urlopen(request);
buf = resp.read();
fout.write(buf);
except BaseException:
print 'Error';
finally :
#opener.close();
fout.flush();
fout.close();
del cnt[i];
# filelen = os.path.getsize('a.zip');
print 'Thread %d ended.'%(i),
print cnt;
# print 'progress : %4.2f'%(filelen*100.0/flen,),'%';
def main():
print 'download at:',ctime();
threads = [];
for i in blocks:
t = MyThread(getStr,(blocks[i],),getStr.__name__);
threads.append(t);
for i in blocks:
threads[i].start();
for i in blocks:
# print 'this is the %d thread;'%(i,);
threads[i].join();
#print 'size:',os.path.getsize('a.zip');
print 'download done at:',ctime();
if __name__=='__main__':
main();
Could someone please help me understand why the threads aren't stopping.
I can't really address your code example because it is quite messy and hard to follow, but a potential reason you are seeing the threads not end is that a request will stall out and never finish. urllib2 allows you to specify timeouts for how long you will allow the request to take.
What I would recommend for your own code is that you split your work up into a queue, start a fixed number of thread (instead of a variable number), and let the worker threads pick up work until it is done. Make the http requests have a timeout. If the timeout expires, try again or put the work back into the queue.
Here is a generic example of how to use a queue, a fixed number of workers and a sync primitive between them:
import threading
import time
from Queue import Queue
def worker(queue, results, lock):
local_results = []
while True:
val = queue.get()
if val is None:
break
# pretend to do work
time.sleep(.1)
local_results.append(val)
with lock:
results.extend(local_results)
print threading.current_thread().name, "Done!"
num_workers = 4
threads = []
queue = Queue()
lock = threading.Lock()
results = []
for i in xrange(100):
queue.put(i)
for _ in xrange(num_workers):
# Use None as a sentinel to signal the threads to end
queue.put(None)
t = threading.Thread(target=worker, args=(queue,results,lock))
t.start()
threads.append(t)
for t in threads:
t.join()
print sorted(results)
print "All done"