# Copyright 2014 Brett Slatkin, Pearson Education Inc.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# Preamble to mimick book environment
import logging
from pprint import pprint
from sys import stdout as STDOUT
# Example 1
class Counter(object):
def __init__(self):
self.count = 0
def increment(self, offset):
self.count += offset
# Example 2
def worker(sensor_index, how_many, counter):
# I have a barrier in here so the workers synchronize
# when they start counting, otherwise it's hard to get a race
# because the overhead of starting a thread is high.
BARRIER.wait()
for _ in range(how_many):
# Read from the sensor
counter.increment(1)
# Example 3
from threading import Barrier, Thread
BARRIER = Barrier(5)
def run_threads(func, how_many, counter):
threads = []
for i in range(5):
args = (i, how_many, counter)
thread = Thread(target=func, args=args)
threads.append(thread)
thread.start()
for thread in threads:
thread.join()
# Example 4
how_many = 10**5
counter = Counter()
run_threads(worker, how_many, counter)
print('Counter should be %d, found %d' %
(5 * how_many, counter.count))
Counter should be 500000, found 202643
# Example 5
offset = 5
counter.count += offset
# Example 6
value = getattr(counter, 'count')
result = value + offset
setattr(counter, 'count', result)
# Example 7
# Running in Thread A
value_a = getattr(counter, 'count')
# Context switch to Thread B
value_b = getattr(counter, 'count')
result_b = value_b + 1
setattr(counter, 'count', result_b)
# Context switch back to Thread A
result_a = value_a + 1
setattr(counter, 'count', result_a)
# Example 8
from threading import Lock
class LockingCounter(object):
def __init__(self):
self.lock = Lock()
self.count = 0
def increment(self, offset):
with self.lock:
self.count += offset
# Example 9
BARRIER = Barrier(5)
counter = LockingCounter()
run_threads(worker, how_many, counter)
print('Counter should be %d, found %d' %
(5 * how_many, counter.count))
Counter should be 500000, found 500000