concurrentfutures

concurrent.futures is a Python standard library module that provides a high-level interface for asynchronously executing callables using pools of worker threads or processes. It offers two executor implementations: ThreadPoolExecutor for concurrent threads and ProcessPoolExecutor for concurrent processes, enabling simple parallelism without directly managing threads or processes.

The central abstraction is the Future object, which represents the result of an asynchronous computation. Work is submitted with executor.submit(fn, *args, **kwargs) and returns a Future. Future methods include result(timeout=None) to retrieve the result, exception() to fetch any raised exception, done() to check completion, and add_done_callback(callback) to register a callback. The map function applies a callable to an iterable of inputs and returns results in input order. The as_completed function yields futures as they complete, enabling processing of results as they become available. The wait function blocks until a set of futures reaches a specified state. The executor can be shut down with shutdown(wait=True).

Usage considerations: ThreadPoolExecutor is well suited for IO-bound tasks, such as network or file I/O, while ProcessPoolExecutor is better for CPU-bound tasks but incurs higher overhead and requires that functions and data be picklable to transfer between processes. The module mitigates some of the complexity of threading and multiprocessing by providing a consistent API. When using ProcessPoolExecutor, care must be taken to avoid shared state and to serialize inputs and outputs.

History and scope: Introduced in Python 3.2, concurrent.futures remains a core part of the standard library for parallel execution. A backport named futures existed to provide similar functionality for older Python versions. The module is designed to be a lightweight, cross-platform way to perform parallel computations without low-level thread or process management.