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Fan-Out/Fan-In Pipeline - Middle

Bound concurrency, propagate cancellation, and close output after every producer exits.

flowchart TD Input --> Pool[Fixed worker pool] Pool --> Out[Result channel] Group[Wait group] --> Close[Close after all workers] Error --> Cancel[Cancel whole pipeline]

For object-store validation, stream keys through a bounded channel, use errgroup workers, and attach the input sequence when ordered fan-in is required. Choose fail-fast, collect-all, or best-effort errors before implementation.

Test yourself

  1. Who closes the result channel?
  2. How does cancellation stop blocked workers?
  3. What does ordered fan-in cost?

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