Shared caches hold completed values

A Worker isolate can serve several requests. A request owns its unfinished I/O. Shared caches must contain completed values.¶

The cold-isolate 1101 failure in PR #64 crossed that boundary. ContentStore held pending asset reads in a shared cache. Another request could await work owned by the first request.¶

Effect.cached, Effect.cachedWithTTL, and Effect.cachedInvalidateWithTTL can share pending work. A successful result cache and a pending-work cache have different lifetimes.¶

Store the result after the read

ContentStore keeps an Option in a Ref. Each request reads that completed-value cache first.¶

A hit returns the completed value.¶
A miss reads assets within the current request.¶
A successful read stores its completed value.¶
A failed read leaves the cache empty.¶

Concurrent misses can repeat a read. They do not wait for another request’s unfinished read.¶

request A ── cache miss ── asset read ── completed value ── cache
request B ── cache miss ── asset read ── completed value ── cache
request C ── cache hit  ──────────────────────────────── value

The cache is a derived copy of generated content assets. The content build writes those assets; requests store only successfully decoded values.¶

Check the lifetime at construction

rat-stack-patterns/no-shared-pending-cache rejects these cache constructors in module, service, and Worker initialization effects. Keep request-local work inside its request handler.¶

A targeted exception must explain the cached value and its lifetime with a -- reason. CryptoKey derivation from a fixed secret needs separate review from request-bound asset reads.¶

The fixture tests plant the old ContentStore.make cache shape. The rule rejects it before it can reach a Worker.¶

See Worker init runs twice⁸ for the initialization boundary and the fence³⁹ for validation.¶

Sources

Cache completed content without shared request I/O. GitHub joelhooks/rat-stack. ContentStore replaces shared pending asset reads with completed-value caches. Accessed 2026-10-08.
Be explicit about lifetimes. GitHub just-be-dev. Assign each resource and mutable value to an explicit lifetime. Accessed 2026-10-08.
Request lifetime guardrail. GitHub just-be-dev. Keep request identity and instance locks within their owning lifetimes. Accessed 2026-10-08.

Last changed 2026-10-08 in ad718e1. Source on GitHub. Change log.

Linked from

Agent guide. An Effect stack so pure (aspirational) Kit Langton will blush.
Shared caches hold completed values — Keep pending request I/O out of isolate-scoped caches.
Change log. What changed in the files served here, newest first.
Shared caches hold completed values — new page: feat: fence shared pending caches and teach request lifetimes
Effect + Alchemy peer patterns. Source-grounded patterns from repos on nearby Effect and Alchemy pins.
rat-stack already adapts this guidance in cache completed values, UI tests, and opt-in tracing.
Full agent guide. An Effect stack so pure (aspirational) Kit Langton will blush.
profile-a-worker. Capture a CPU or heap profile of a deployed Cloudflare Worker or Durable Object and read it with pprof. Use when a Worker is slow, burns CPU, nears its memory limit, throws Exceeded Memory, or you need to know which function costs the most in production.
Link context
Common wins: compute a value once instead of per call, cache a completed value, stop building objects you throw away, remove code that a flag only half disables.¶
Rat Stack lore | rat-stack. Short, source-grounded notes on the ideas and decisions behind rat-stack.
Shared caches hold completed values — Keep pending request I/O out of isolate-scoped caches.
Source change history (log.md). The generated change log as Markdown.
Shared caches hold completed values — new page: feat: fence shared pending caches and teach request lifetimes