blog/Structured Concurrency

Series · 9 parts

Structured Concurrency

Nine posts written through a fan-out service rollout. Cancellation, timeouts, and what to do when a subtask outlives the request.

Start with part 1: What structured scopes actually catch

parts9

first post2026-03-22

latest2026-05-17

total read~97 min

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9 parts

newest first

012026-05-17
Migrating our fan-out service from Java 21 to Java 25
ShutdownOnFailure became a Joiner and throwIfFailed disappeared. The two non-mechanical parts of our Java 25 migration.
11 min
022026-05-10
Four operational checks we run on every StructuredTaskScope
Outcome counters per scope, propagated deadlines, bulkheads, and JFR pinning watch: four checks before trusting fan-out.
11 min
032026-05-04
Three structured-concurrency patterns we run in a fan-out service
Quorum aggregation, per-tenant bulkheads, and a deadline shape that survives a slow upstream. Cancellation comes first.
11 min
042026-04-26
Composing resilience policies as separable layers
Each resilience policy stays a separable layer that fires visibly in logs, or you rebuild the complexity you removed.
10 min
052026-04-19
Why downstream capacity is the real ceiling on fan-out
Downstream capacity caps fan-out, not thread count. One semaphore per dependency stops a hot path draining the pool.
11 min
062026-04-12
Two workflow shapes that show up after fork-and-wait
Streaming results as subtasks finish suits user-facing flows; nested scopes mirror the service tree. What each costs.
12 min
072026-04-06
Cancelling siblings before they burn capacity
Throwing inside a subtask cancels siblings before they waste capacity, and sometimes that is wrong. Where it backfires.
11 min
082026-03-30
What a missed deadline should do, and what it should not
Should a missed deadline fail the request or return what made it back in time? Three timeout shapes and where each fits.
9 min
092026-03-22
What structured scopes actually catch
Most concurrency bugs come from missing lifecycle, not missing parallelism. A scope makes task lifetime visible in code.
11 min