fix(registry): add large-thread-count feature to raise slab MAX_THREADS#4
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Maxence Caron (mc-ditto) wants to merge 8 commits intodeprecate-macros-for-ditto-loggingfrom
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fix(registry): add large-thread-count feature to raise slab MAX_THREADS#4Maxence Caron (mc-ditto) wants to merge 8 commits intodeprecate-macros-for-ditto-loggingfrom
Maxence Caron (mc-ditto) wants to merge 8 commits intodeprecate-macros-for-ditto-loggingfrom
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Adds a `large-thread-count` feature (off by default) that raises the sharded-slab MAX_THREADS limit from 4 096 to 131 072. This prevents tracing_subscriber from panicking on high-core nodes where large numbers of native threads are spawned (e.g. by the Ditto SDK in load-gen pods). When the feature is disabled the upstream default of 4 096 is used via the Config trait's default impl, so there is no behaviour change for existing consumers. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
… enabled Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…l init Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…gate The large-thread-count Cargo feature caused complex activation problems across multiple workspace boundaries in the Ditto monorepo. Since this fork is always used with Ditto builds, raise MAX_THREADS = 131_072 unconditionally — no feature flag required. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Make MAX_THREADS = 131_072 conditional on the `large-thread-count` feature flag rather than unconditional. The feature was previously removed to work around a cross-workspace patch issue in the ditto monorepo (now fixed by updating .cargo/config.toml patches). Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
On 32-bit targets (e.g. wasm32-unknown-unknown), MAX_THREADS = 131 072 requires 17 bits for thread IDs, which exhausts sharded-slab's bit-packing budget (total usize width = 32 bits) and causes a compile-time overflow in slot::Generation::LEN. Guard the raised constant behind `target_pointer_width = "64"` so wasm32 and other 32-bit targets fall back to the sharded-slab default of 4 096. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Madeleine Mortensen (maddiemort)
previously requested changes
Apr 17, 2026
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Madeleine Mortensen (maddiemort)
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The logic is fine, but I'd prefer my comments to be addressed before we start using this.
Madeleine Mortensen (maddiemort)
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their stale review
My top concern was addressed
Madeleine Mortensen (maddiemort)
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Apr 17, 2026
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| // Confirm the Registry pool is actually parameterised on SlabConfig — | ||
| // this is a compile-time check: if `Registry::spans` ever changes to a | ||
| // different Config type, the type annotation below will fail to compile. | ||
| let registry = Registry::default(); | ||
| let _: &Pool<DataInner, SlabConfig> = ®istry.spans; |
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Nice, that should do the trick - thanks
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Summary
large-thread-countfeature flag (off by default) totracing-subscriberSlabConfigraisesMAX_THREADSfrom 4 096 to 131 072, preventing panics when large numbers of native threads are spawned on high-core nodessharded-slabfork or workspace-level[patch.crates-io]overrideTest plan
cargo test -p tracing-subscriber --features large-thread-count— all tests passcargo test -p tracing-subscriber— all tests pass without the feature🤖 Generated with Claude Code