🦀 Nested `async/await` in Rust — What Happens Under the Hood

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When one async fn calls another, Rust builds nested state machines to manage suspension and resumption. The outer future holds the inner one in its environment, and each .await becomes a state transition in a generated jump table.

The article below provides a detailed walkthrough of this transformation, illustrating how high-level async code compiles into low-level control flow and data structures. It covers:

  • How each async fn becomes a Future with explicit states and a poll loop
  • How nested awaits create layered state machines with captured environments
  • How loops translate into back-edges in the generated jump table
  • What the resulting assembly looks like, with comments on how the executor interacts with it
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