Evidence label: deterministic synthetic teaching model. This browser page executes a small JavaScript model of the stated policy. It does not run Java, access a JVM, create actual worker threads or contact a tool. Use it to understand the boundary and compare assumptions before running the separate Java example.
Predict the boundary before running the model
Predict whether copying only the outer object protects a reader's nested token list. Then compare outer copying, nested copying and sharing the original object.
Write a prediction for the terminal outcome, then use Run model. The summary reports the calculated end-state for the current inputs. The trace begins at its first event so you can inspect how that outcome is reached. Next event advances one row; Show complete trace exposes every row. Restart trace changes only the viewing position, not the selected inputs.
Run and inspect the synthetic experiment
Expected outcomes and useful counterexamples
Copying both levels keeps the captured reader at version one with the seed token. Reusing the nested list changes the reader's tokens even when its version stays one. Sharing the whole object changes both.
Change one input, rerun and compare the exact values in the table. A boundary that still holds under the changed inputs is more informative than an attractive animation. Trace rows and text labels carry the result; the visual colors are supplementary. The model recalculates only after Run model, so an edited input does not silently replace the trace you are inspecting.
What this lab cannot establish
This is an explicit aliasing/interleaving model, not a Java Memory Model simulator. It does not demonstrate atomic-reference ordering, compare-and-set retries, disk persistence or distributed ownership. The Java fixture checks a separate in-memory CAS example.
The controls have intentionally small finite ranges. They are not operational recommendations. No output here demonstrates production capacity, a recommended heap size, successful cancellation of a remote effect or a GC performance improvement. Use the downloadable Java fixture and then a representative integration test to investigate those separate questions. Keep the runtime version and the measurement method with any real results.
Continue with the Java implementation
Publish Stable Java Harness Checkpoints Without Sharing Mutable State contains the original Java fixture, the failure analysis and its primary references. Continue with Budget JVM Memory Beyond the Heap Before Increasing Concurrency to examine the next ownership boundary. The examples have synthetic non-personal inputs and do not require an account, API key or external service.
All six guides and labs · Lab catalog.
- AtomicReference memory effects
- Map.copyOf and unmodifiable maps
- Concurrent utilities and memory consistency
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