feat(trace-utils)!: change buffer implementation#2055
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Add the main ChangeBufferState<T> struct and its full implementation: span creation/pooling, change buffer interpretation (opcodes), deferred tag resolution, span header materialization, flush logic, and string table management. This is the core state machine that processes batched span mutations from JS/WASM via a shared memory buffer. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
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| let num: u32 = self.change_buffer.read_unchecked(index); | ||
| self.string_table | ||
| .get_unchecked(num as usize) | ||
| .clone() | ||
| .unwrap_unchecked() |
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When a cached non-create operation such as SetName or SetServiceName is decoded from the shared FFI buffer, the caller reaches this helper without validating either that the string id is still present in string_table or that the argument bytes are in bounds. An out-of-sync/evicted string id that used to produce ChangeBufferError::StringNotFound now hits unwrap_unchecked(), which is undefined behavior across the FFI-facing change-buffer path rather than a recoverable error.
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Codecov Report❌ Patch coverage is Additional details and impacted files@@ Coverage Diff @@
## yannham/change-buffer-foundation #2055 +/- ##
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- Coverage 73.03% 72.47% -0.56%
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Files 465 465
Lines 76881 77436 +555
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- Hits 56147 56122 -25
- Misses 20734 21314 +580
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What does this PR do?
This PR backports the change buffer implementation required for dd-trace-js adoption of native spans. Follow-up of #2046.
The change buffer is a contiguous region of memory where span operations are encoded from the JS runtime, similar to a byte code. The implementation decode all those span events and reconstruct the corresponding span objects.
Motivation
Required to land native spans dd-trace-js.
How to test the change?
tests included.