Python Concurrency with asyncio 1st Edition by Matthew Fowler 1638357080 9781638357087

1 Getting to know asyncio

1.1 What is asyncio?

1.2 What is I/O-bound and what is CPU-bound?

1.3 Understanding concurrency, parallelism, and multitasking

1.3.1 Concurrency

1.3.2 Parallelism

1.3.3 The difference between concurrency and parallelism

1.3.4 What is multitasking?

1.3.5 The benefits of cooperative multitasking

1.4 Understanding processes, threads, multithreading, and multiprocessing

1.4.1 Process

1.4.2 Thread

1.5 Understanding the global interpreter lock

1.5.1 Is the GIL ever released?

1.5.2 asyncio and the GIL

1.6 How single-threaded concurrency works

1.6.1 What is a socket?

1.7 How an event loop works

Summary

2 asyncio basics

2.1 Introducing coroutines

2.1.1 Creating coroutines with the async keyword

2.1.2 Pausing execution with the await keyword

2.2 Introducing long-running coroutines with sleep

2.3 Running concurrently with tasks

2.3.1 The basics of creating tasks

2.3.2 Running multiple tasks concurrently

2.4 Canceling tasks and setting timeouts

2.4.1 Canceling tasks

2.4.2 Setting a timeout and canceling with wait_for

2.5 Tasks, coroutines, futures, and awaitables

2.5.1 Introducing futures

2.5.2 The relationship between futures, tasks, and coroutines

2.6 Measuring coroutine execution time with decorators

2.7 The pitfalls of coroutines and tasks

2.7.1 Running CPU-bound code

2.7.2 Running blocking APIs

2.8 Accessing and manually managing the event loop

2.8.1 Creating an event loop manually

2.8.2 Accessing the event loop

2.9 Using debug mode

2.9.1 Using asyncio.run

2.9.2 Using command-line arguments

2.9.3 Using environment variables

Summary

3 A first asyncio application

3.1 Working with blocking sockets

3.2 Connecting to a server with Telnet

3.2.1 Reading and writing data to and from a socket

3.2.2 Allowing multiple connections and the dangers of blocking

3.3 Working with non-blocking sockets

3.4 Using the selectors module to build a socket event loop

3.5 An echo server on the asyncio event loop

3.5.1 Event loop coroutines for sockets

3.5.2 Designing an asyncio echo server

3.5.3 Handling errors in tasks

3.6 Shutting down gracefully

3.6.1 Listening for signals

3.6.2 Waiting for pending tasks to finish

Summary

4 Concurrent web requests

4.1 Introducing aiohttp

4.2 Asynchronous context managers

4.2.1 Making a web request with aiohttp

4.2.2 Setting timeouts with aiohttp

4.3 Running tasks concurrently, revisited

4.4 Running requests concurrently with gather

4.4.1 Handling exceptions with gather

4.5 Processing requests as they complete

4.5.1 Timeouts with as_completed

4.6 Finer-grained control with wait

4.6.1 Waiting for all tasks to complete

4.6.2 Watching for exceptions

4.6.3 Processing results as they complete

4.6.4 Handling timeouts

4.6.5 Why wrap everything in a task?

Summary

5 Non-blocking database drivers

5.1 Introducing asyncpg

5.2 Connecting to a Postgres database

5.3 Defining a database schema

5.4 Executing queries with asyncpg

5.5 Executing queries concurrently with connection pools

5.5.1 Inserting random SKUs into the product database

5.5.2 Creating a connection pool to run queries concurrently

5.6 Managing transactions with asyncpg

5.6.1 Nested transactions

5.6.2 Manually managing transactions

5.7 Asynchronous generators and streaming result sets

5.7.1 Introducing asynchronous generators

5.7.2 Using asynchronous generators with a streaming cursor

Summary

6 Handling CPU-bound work

6.1 Introducing the multiprocessing library

6.2 Using process pools

6.2.1 Using asynchronous results

6.3 Using process pool executors with asyncio

6.3.1 Introducing process pool executors

6.3.2 Process pool executors with the asyncio event loop

6.4 Solving a problem with MapReduce using asyncio

6.4.1 A simple MapReduce example

6.4.2 The Google Books Ngram dataset

6.4.3 Mapping and reducing with asyncio

6.5 Shared data and locks

6.5.1 Sharing data and race conditions

6.5.2 Synchronizing with locks

6.5.3 Sharing data with process pools

6.6 Multiple processes, multiple event loops

Summary

7 Handling blockingwork with threads

7.1 Introducing the threading module

7.2 Using threads with asyncio

7.2.1 Introducing the requests library

7.2.2 Introducing thread pool executors

7.2.3 Thread pool executors with asyncio

7.2.4 Default executors

7.3 Locks, shared data, and deadlocks

7.3.1 Reentrant locks

7.3.2 Deadlocks

7.4 Event loops in separate threads

7.4.1 Introducing Tkinter

7.4.2 Building a responsive UI with asyncio and threads

7.5 Using threads for CPU-bound work

7.5.1 Multithreading with hashlib

7.5.2 Multithreading with NumPy

Summary

8 Streams

8.1 Introducing streams

8.2 Transports and protocols

8.3 Stream readers and stream writers

8.4 Non-blocking command-line input

8.4.1 Terminal raw mode and the read coroutine

8.5 Creating servers

8.6 Creating a chat server and client

Summary

9 Web applications

9.1 Creating a REST API with aiohttp

9.1.1 What is REST?

9.1.2 aiohttp server basics

9.1.3 Connecting to a database and returning results

9.1.4 Comparing aiohttp with Flask

9.2 The asynchronous server gateway interface

9.2.1 How does ASGI compare to WSGI?

9.3 ASGI with Starlette

9.3.1 A REST endpoint with Starlette

9.3.2 WebSockets with Starlette

9.4 Django asynchronous views

9.4.1 Running blocking work in an asynchronous view

9.4.2 Using async code in synchronous views

Summary

10 Microservices

10.1 Why microservices?

10.1.1 Complexity of code

10.1.2 Scalability

10.1.3 Team and stack independence

10.1.4 How can asyncio help?

10.2 Introducing the backend-for-frontend pattern

10.3 Implementing the product listing API

10.3.1 User favorite service

10.3.2 Implementing the base services

10.3.3 Implementing the backend-for-frontend service

10.3.4 Retrying failed requests

10.3.5 The circuit breaker pattern

Summary

11 Synchronization

11.1 Understanding single-threaded concurrency bugs

11.2 Locks

11.3 Limiting concurrency with semaphores

11.3.1 Bounded semaphores

11.4 Notifying tasks with events

11.5 Conditions

Summary

12 Asynchronous queues

12.1 Asynchronous queue basics

12.1.1 Queues in web applications

12.1.2 A web crawler queue

12.2 Priority queues

12.3 LIFO queues

Summary

13 Managing subprocesses

13.1 Creating a subprocess

13.1.1 Controlling standard output

13.1.2 Running subprocesses concurrently

13.2 Communicating with subprocesses

Summary

14 Advanced asyncio

14.1 APIs with coroutines and functions

14.2 Context variables

14.3 Forcing an event loop iteration

14.4 Using different event loop implementations

14.5 Creating a custom event loop

14.5.1 Coroutines and generators

14.5.2 Generator-based coroutines are deprecated

14.5.3 Custom awaitables

14.5.4 Using sockets with futures

14.5.5 A task implementation

14.5.6 Implementing an event loop

14.5.7 Implementing a server with a custom event loop

Summary

index

inside back cover