Race condition on pylibmc

pylibmc_concurrency_test.py

import argparse
import multiprocessing
import threading

from pylibmc.test import make_test_client
import random

NUM_THREADS = 2
NUM_PROCS = 4
NUM_SETS = 10000


def inner_set_values(client):
    key, val = str(random.randrange(1, 5)), str(random.randrange(1, 10))
    operation = random.choice(['set', 'delete'])
    for i in range(NUM_SETS):
        if operation in ('delete'):
            client.delete(key)
        else:
            client.set(key, val)


def set_values():
    client = make_test_client(binary=True)
    threads = []
    for _ in range(NUM_THREADS):
        th = threading.Thread(target=inner_set_values, args=(client, ))
        th.daemon = False
        th.start()
        threads.append(th)

    for t in threads:
        t.join(None)
    client.disconnect_all()


def parse_arguments():
    parser = argparse.ArgumentParser(description='Stress test pylibmc set')
    parser.add_argument('-p', '--procs', default=NUM_PROCS, type=int)
    parser.add_argument('-t', '--threads', default=NUM_THREADS, type=int)
    parser.add_argument('-s', '--sets', default=NUM_SETS, type=int)

    return parser.parse_args()


def main():
    ns = parse_arguments()
    global NUM_PROCS, NUM_SETS, NUM_THREADS
    NUM_PROCS = ns.procs
    NUM_THREADS = ns.threads
    NUM_SETS = ns.sets

    procs = [multiprocessing.Process(target=set_values) for _ in range(NUM_PROCS)]
    for proc in procs:
        proc.start()

    for proc in procs:
        proc.join()


if __name__ == '__main__':
    main()

Running this will create a strange error:

Traceback (most recent call last):
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 810, in __bootstrap_inner
    self.run()
  File "/opt/local/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/threading.py", line 763, in run
    self.__target(*self.__args, **self.__kwargs)
  File "./performance/pylibmc_stress_test.py", line 21, in inner_set_values
    client.set(key, val)
NotFound: error 16 from memcached_set: SUCCESS

Basically a NotFound exception on a memcached set operation.