Thread SpanPrototype through span construction (parked until dense store)#11834
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Thread SpanPrototype through span construction (parked until dense store)#11834dougqh wants to merge 1 commit into
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…bing) Threads a spanPrototype through the span builder exactly like tagLedger — field + startImpl + both startSpan overloads + buildSpan + buildSpanContext + reset — and applies it at buildSpanContext right after defaultSpanTags (before the per-span ledger, so per-span tags override the prototype's constants). Adds CoreSpanBuilder.withSpanPrototype(...) as the setter. Additive: defaults to SpanPrototype.NONE at every site, so the applied branch is skipped and every existing span-creation path is byte-for-byte unchanged. CoreSpanBuilderTest (25) + CoreTracerTest2 (15) green. Next: public startSpan/buildSpan(SpanPrototype, ...) entry points + the old-vs-new SpanStartBenchmark (which exercises the seeding end-to-end). Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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Draft — PARKED. Stacked on #11828. Do not merge before the dense store.
Increment 2a of the SpanPrototype work: threads a
spanPrototypethroughCoreSpanBuilder(mirroringtagLedger— field,startImpl, bothstartSpanoverloads,buildSpan,buildSpanContext,reset) and applies it atbuildSpanContextright afterdefaultSpanTags(before the per-span ledger, so per-span tags override the prototype's constants). AddsCoreSpanBuilder.withSpanPrototype(...).Why parked
The construction-seed's payoff is a copy-down, which only beats per-span N-
setwhen the copy is cheap. On today's bucketedOptimizedTagMapit isn't — the per-mechanism micro (on #11828) showedcopy()of a 4-entry map losing to 4set(cachedEntry)(≈295M/243M vs 417M ops/s), with identical 104 B/op across all arms. The win is dense-store-gated: a contiguous positional layout makes copy-down anarraycopy, and drops the alloc.So this lands with/after the dense store, where touching the critical span-creation path arrives with a demonstrable win rather than a flat change. Because SpanPrototype rides the existing
TagMap.copy/setAllTagsAPI (not dense internals), the wiring auto-cashes-in when the dense store lands — no surface change, no penalty to holding.Safety
Additive:
SpanPrototype.NONEdefault at every threaded site → the applied branch is skipped and every existing span-creation path is byte-for-byte unchanged.CoreSpanBuilderTest(25) +CoreTracerTest2(15) green.Remaining (when unparked)
startSpan/buildSpan(SpanPrototype, …)entry points (additive overloads, delegate existing →NONE).SpanStartBenchmark({startSpan, buildSpan}×{old afterStart, new prototype}) to characterize the dispatch-level delta on the dense store.🤖 Generated with Claude Code