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item_63.py
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executable file
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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
import asyncio
# On Windows, a ProactorEventLoop can't be created within
# threads because it tries to register signal handlers. This
# is a work-around to always use the SelectorEventLoop policy
# instead. See: https://bugs.python.org/issue33792
policy = asyncio.get_event_loop_policy()
policy._loop_factory = asyncio.SelectorEventLoop
async def run_tasks(handles, interval, output_path):
with open(output_path, 'wb') as output:
async def write_async(data):
output.write(data)
tasks = []
for handle in handles:
coro = tail_async(handle, interval, write_async)
task = asyncio.create_task(coro)
tasks.append(task)
await asyncio.gather(*tasks)
# Example 2
import time
async def slow_coroutine():
time.sleep(0.5) # Simulating slow I/O
asyncio.run(slow_coroutine(), debug=True)
# Example 3
from threading import Thread
class WriteThread(Thread):
def __init__(self, output_path):
super().__init__()
self.output_path = output_path
self.output = None
self.loop = asyncio.new_event_loop()
def run(self):
asyncio.set_event_loop(self.loop)
with open(self.output_path, 'wb') as self.output:
self.loop.run_forever()
# Run one final round of callbacks so the await on
# stop() in another event loop will be resolved.
self.loop.run_until_complete(asyncio.sleep(0))
# Example 4
async def real_write(self, data):
self.output.write(data)
async def write(self, data):
coro = self.real_write(data)
future = asyncio.run_coroutine_threadsafe(
coro, self.loop)
await asyncio.wrap_future(future)
# Example 5
async def real_stop(self):
self.loop.stop()
async def stop(self):
coro = self.real_stop()
future = asyncio.run_coroutine_threadsafe(
coro, self.loop)
await asyncio.wrap_future(future)
# Example 6
async def __aenter__(self):
loop = asyncio.get_event_loop()
await loop.run_in_executor(None, self.start)
return self
async def __aexit__(self, *_):
await self.stop()
# Example 7
class NoNewData(Exception):
pass
def readline(handle):
offset = handle.tell()
handle.seek(0, 2)
length = handle.tell()
if length == offset:
raise NoNewData
handle.seek(offset, 0)
return handle.readline()
async def tail_async(handle, interval, write_func):
loop = asyncio.get_event_loop()
while not handle.closed:
try:
line = await loop.run_in_executor(
None, readline, handle)
except NoNewData:
await asyncio.sleep(interval)
else:
await write_func(line)
async def run_fully_async(handles, interval, output_path):
async with WriteThread(output_path) as output:
tasks = []
for handle in handles:
coro = tail_async(handle, interval, output.write)
task = asyncio.create_task(coro)
tasks.append(task)
await asyncio.gather(*tasks)
# Example 8
# This is all code to simulate the writers to the handles
import collections
import os
import random
import string
from tempfile import TemporaryDirectory
def write_random_data(path, write_count, interval):
with open(path, 'wb') as f:
for i in range(write_count):
time.sleep(random.random() * interval)
letters = random.choices(
string.ascii_lowercase, k=10)
data = f'{path}-{i:02}-{"".join(letters)}\n'
f.write(data.encode())
f.flush()
def start_write_threads(directory, file_count):
paths = []
for i in range(file_count):
path = os.path.join(directory, str(i))
with open(path, 'w'):
# Make sure the file at this path will exist when
# the reading thread tries to poll it.
pass
paths.append(path)
args = (path, 10, 0.1)
thread = Thread(target=write_random_data, args=args)
thread.start()
return paths
def close_all(handles):
time.sleep(1)
for handle in handles:
handle.close()
def setup():
tmpdir = TemporaryDirectory()
input_paths = start_write_threads(tmpdir.name, 5)
handles = []
for path in input_paths:
handle = open(path, 'rb')
handles.append(handle)
Thread(target=close_all, args=(handles,)).start()
output_path = os.path.join(tmpdir.name, 'merged')
return tmpdir, input_paths, handles, output_path
# Example 9
def confirm_merge(input_paths, output_path):
found = collections.defaultdict(list)
with open(output_path, 'rb') as f:
for line in f:
for path in input_paths:
if line.find(path.encode()) == 0:
found[path].append(line)
expected = collections.defaultdict(list)
for path in input_paths:
with open(path, 'rb') as f:
expected[path].extend(f.readlines())
for key, expected_lines in expected.items():
found_lines = found[key]
assert expected_lines == found_lines
input_paths = ...
handles = ...
output_path = ...
tmpdir, input_paths, handles, output_path = setup()
asyncio.run(run_fully_async(handles, 0.1, output_path))
confirm_merge(input_paths, output_path)
tmpdir.cleanup()