Notes on structured concurrency, or: Go statement considered harmful

3 hours ago

Concurrency APIs have traditionally used go statements (thread spawning, callbacks, futures) that allow background tasks to run independently, similar to goto statements in control flow.
Go statements break abstraction by making functions non-black-box (they may spawn tasks without caller knowledge), disrupt automatic resource cleanup, and hinder proper error propagation.
Trio introduces nurseries as a structured alternative, where tasks are started within a nursery block and the parent task waits for all child tasks to finish before exiting, ensuring control flow follows the 'black box' rule.
Nurseries preserve function abstraction, support dynamic task spawning, allow explicit passing of nursery objects for flexibility, enable custom nursery-like types, and integrate automatic error propagation and cancellation.
Removing go statements enables new features like reliable cancellation and proper control-C handling in Python, and nurseries encourage clearer, more robust concurrent programming, as demonstrated by simplified implementations like Happy Eyeballs in Trio.

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