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Add two standalone modules: Stream Gatherers (JEP 485) and Scoped Values vs ThreadLocal (JEP 506)

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gatherers/: windowFixed, windowSliding, fold, scan, mapConcurrent, a custom
Gatherer (dedupeConsecutive, takeUntil), and a Collector-vs-Gatherer comparison.
Verified: windowSliding emits one short window on a too-short stream rather than
shrinking to empty like windowFixed; mapConcurrent waits for in-flight siblings
to finish (~901ms) rather than cancelling them when one mapper throws.

scoped-values/: ScopedValue API and rebinding, why plain threads (virtual or
platform) do not inherit a binding while a StructuredTaskScope subtask does,
and the memory cost vs InheritableThreadLocal measured two ways -- a noisy
heap-delta first pass, then a precise jcmd GC.class_histogram object census
(5 shared Carrier objects vs ~700,000 copied ThreadLocalMap/Entry objects for
100,000 threads).

Companion code for the ankurm.com posts "Java Stream Gatherers (JEP 485)" and
"Scoped Values vs ThreadLocal in Java 25: Migration Guide with Virtual Threads".

Co-Authored-By: Claude Sonnet 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01FtpJvZfg4nvLvtzgJTDWpB
This commit is contained in:
Claude
2026-09-24 04:27:12 +00:00
parent f59c1de96d
commit 6b5a918278
25 changed files with 1124 additions and 5 deletions
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docs/output/99-histogram-scopedvalue.txt
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$ jcmd <pid> GC.class_histogram (100000 subtasks parked, mode=sv, JDK 25)
1: 100000 115102880 jdk.internal.vm.StackChunk ([email protected])
2: 100000 16800000 java.lang.VirtualThread ([email protected])
9: 100000 2400000 java.util.concurrent.StructuredTaskScopeImpl$SubtaskImpl ([email protected])
128: 5 160 java.lang.ScopedValue$Carrier ([email protected])
175: 5 80 java.lang.InheritableThreadLocal ([email protected])
177: 5 80 java.lang.ScopedValue ([email protected])
203: 2 48 java.lang.ScopedValue$Snapshot ([email protected])
257: 1 32 java.util.concurrent.ThreadLocalRandom ([email protected])
281: 1 24 java.util.concurrent.StructuredTaskScopeImpl$SubtaskImpl$AltResult ([email protected])
292: 1 24 jdk.internal.vm.ScopedValueContainer$BindingsSnapshot ([email protected])
324: 1 16 java.lang.ThreadLocal ([email protected])
353: 1 16 java.util.concurrent.ThreadLocalRandom$Access$1 ([email protected])
Total 1133788 172079104