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#!/usr/bin/env PYTHONHASHSEED=1234 python3

# Copyright 2014-2019 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.

# Reproduce book environment

import random

random.seed(1234)

import logging

from pprint import pprint

from sys import stdout as STDOUT

# Write all output to a temporary directory

import atexit

import gc

import io

import os

import tempfile

TEST_DIR = tempfile.TemporaryDirectory()

atexit.register(TEST_DIR.cleanup)

# Make sure Windows processes exit cleanly

OLD_CWD = os.getcwd()

atexit.register(lambda: os.chdir(OLD_CWD))

os.chdir(TEST_DIR.name)

def close_open_files():

everything = gc.get_objects()

for obj in everything:

if isinstance(obj, io.IOBase):

obj.close()

atexit.register(close_open_files)

# Example 1

class Counter:

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

# Nothing actually happens here, but this is where

# the blocking I/O would go.

counter.increment(1)

# Example 3

from threading import Barrier

BARRIER = Barrier(5)

from threading import Thread

how_many = 10**5

counter = Counter()

threads = []

for i in range(5):

thread = Thread(target=worker,

args=(i, how_many, counter))

threads.append(thread)

thread.start()

for thread in threads:

thread.join()

expected = how_many * 5

found = counter.count

print(f'Counter should be {expected}, got {found}')

# Example 4

counter.count += 1

# Example 5

value = getattr(counter, 'count')

result = value + 1

setattr(counter, 'count', result)

# Example 6

# 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 7

from threading import Lock

class LockingCounter:

def __init__(self):

self.lock = Lock()

self.count = 0

def increment(self, offset):

with self.lock:

self.count += offset

# Example 8

BARRIER = Barrier(5)

counter = LockingCounter()

for i in range(5):

thread = Thread(target=worker,

args=(i, how_many, counter))

threads.append(thread)

thread.start()

for thread in threads:

thread.join()

expected = how_many * 5

found = counter.count

print(f'Counter should be {expected}, got {found}')