feat: nested-scope context save/restore via ScopeStack#496
feat: nested-scope context save/restore via ScopeStack#496
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Pull request overview
Restores ContextSetter snapshot/restore support needed by dd-trace-java profiling scopes by reintroducing a read-back API for custom context attributes and optimizing the read path to avoid allocations after writes.
Changes:
- Add
ContextSetter.readContextValue(int)/readContextValue(String)for reading current thread’s attribute values. - Add
JavaProfiler.readContextAttribute(int)bridge and implement a per-slot value cache inThreadContextto make reads allocation-free on the warm path. - Add
TagContextTest.testSnapshotRestore()covering set/read/overwrite/restore and clear cycles.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds a unit test validating snapshot/restore behavior via the new read API. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Introduces indexedValueCache and updates readContextAttribute to use it for warm-path reads. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Adds package-private bridge readContextAttribute(int) delegating to TLS ThreadContext. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds public read-back methods symmetric with existing setContextValue overloads. |
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CI Test ResultsRun: #24889214046 | Commit:
Status Overview
Legend: ✅ passed | ❌ failed | ⚪ skipped | 🚫 cancelled Summary: Total: 32 | Passed: 32 | Failed: 0 Updated: 2026-04-24 12:56:01 UTC |
- Return null when valid=0 (after clearContext, attrs_data_size is intentionally stale — scanning it would return cleared attributes) - Cache cold-path result in indexedValueCache to avoid repeated scans after resetThreadContext() Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Pull request overview
Restores snapshot/restore support for custom profiling context attributes by adding allocation-free readback APIs, enabling dd-trace-java ProfilingScope to correctly restore prior context values when nested scopes close.
Changes:
- Add
ContextSetter.readContextValue(int)/readContextValue(String)for snapshotting current custom attribute values. - Introduce a per-slot
indexedValueCacheinThreadContextand use it inreadContextAttribute()to avoid scanning/allocations on the warm path. - Add
testSnapshotRestore()inTagContextTestto validate snapshot/overwrite/restore behavior and name-based reads.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds snapshot/restore unit test coverage for the new readback API. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Adds per-slot readback caching and enhances readContextAttribute() to support snapshot/restore. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Exposes package-level readContextAttribute(int) delegating to thread-local ThreadContext. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds public readContextValue(...) APIs used by nested scope snapshot/restore logic. |
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Co-Authored-By: muse <muse@noreply>
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Pull request overview
Restores snapshot/restore support for custom profiling context attributes by introducing allocation-free read-back of attribute values from thread-local profiling context, enabling nested scope closures (e.g., ProfilingScope.close()) to correctly restore previous values.
Changes:
- Add
ContextSetter.readContextValue(int)andContextSetter.readContextValue(String)to read current custom attribute values for snapshot/restore. - Introduce a per-slot
indexedValueCacheinThreadContextand updatereadContextAttribute()to use it (warm-path allocation-free; cold-path scansattrs_dataonce and caches results, including “absent”). - Add
JavaProfiler.readContextAttribute(int)and a newTagContextTest.testSnapshotRestore()to validate snapshot/restore behavior.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds snapshot/restore test coverage for readContextValue() behavior. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Adds per-slot read-back cache and updates read path to support snapshot/restore efficiently. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Exposes package-private readContextAttribute(int) delegating to thread-local ThreadContext. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds readContextValue(...) API for callers to snapshot/restore custom attributes. |
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Co-Authored-By: muse <muse@noreply>
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Pull request overview
Restores context snapshot/restore support for custom profiling context attributes by adding allocation-free readback of the current attribute value from thread-local context, enabling nested scope close to correctly restore prior values.
Changes:
- Add
ContextSetter.readContextValue(int)andreadContextValue(String)to support snapshot/restore semantics. - Add a per-slot
indexedValueCacheinThreadContext(withABSENTsentinel) to makereadContextAttribute()warm-path allocation-free and avoid repeatedattrs_datascans. - Expose
JavaProfiler.readContextAttribute(int)as a package-private bridge to thread-localThreadContext.readContextAttribute().
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds testSnapshotRestore() validating snapshot/overwrite/restore and null/clear behavior. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Introduces per-slot readback cache and updates clear/write paths + readContextAttribute() logic. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Adds readContextAttribute(int) to read TLS ThreadContext attribute values. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds public readContextValue(...) APIs for restoring context values on scope close. |
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…irect Co-Authored-By: muse <muse@noreply>
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Pull request overview
Restores snapshot/restore support for custom profiling context attributes by adding string read-back APIs in ContextSetter, backed by a per-slot cache in ThreadContext to keep readContextAttribute() allocation-free on the warm path. This enables dd-trace-java’s ProfilingScope to correctly restore prior attribute values when nested scopes close.
Changes:
- Add
ContextSetter.readContextValue(int)andreadContextValue(String)to enable snapshot/restore of custom attributes. - Add a per-slot
indexedValueCache(withABSENTsentinel) inThreadContext.readContextAttribute()to avoid rescanningattrs_dataand allocating on repeated reads. - Add
TagContextTest.testSnapshotRestore()to cover null/set/overwrite/restore/clear cycles and the String-key overload.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds a focused snapshot/restore regression test for custom context attributes. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Implements per-slot read-back caching for custom attribute reads and keeps it in sync across set/clear/reset paths. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Exposes a package-private TLS read helper delegating to ThreadContext.readContextAttribute(). |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds public read APIs used for snapshot/restore within nested profiling scopes. |
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- Add Javadoc to JavaProfiler.readContextAttribute and ContextSetter.readContextValue(String) - Document valid=0 invariant and ABSENT ClassLoader-singleton requirement in ThreadContext - Expand readContextAttribute Javadoc (warm/cold path, allocation contract) - Document orphan Dictionary encoding in setContextAttribute Javadoc - Add tests: cold-path scan, attrs_data overflow, put() cache clear, cross-slot isolation - Fix raw-offset assumption in testSnapshotRestore (use offsetOf instead of hardcoded 0) Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Pull request overview
Restores snapshot/restore support for custom profiling context attributes by adding read-back APIs to ContextSetter, backed by an allocation-free warm-path cache in ThreadContext. This enables dd-trace-java nested ProfilingScope instances to correctly restore prior attribute values when scopes close.
Changes:
- Add
ContextSetter.readContextValue(int)/readContextValue(String)to read the current attribute value from same-thread TLS. - Add
ThreadContext.indexedValueCache+ABSENTsentinel and implementThreadContext.readContextAttribute(int)with warm-path O(1) reads and cold-pathattrs_datascan. - Add
JavaProfiler.readContextAttribute(int)TLS delegate and expandTagContextTestwith snapshot/restore + cold-path + overflow + isolation coverage.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds targeted tests for snapshot/restore behavior and cache/cold-path correctness. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Introduces per-slot string cache and read-back API, keeping sidecar/OTEP views consistent on overflow/clear. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Adds TLS delegate to expose ThreadContext.readContextAttribute() within the package. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds read APIs to support snapshot/restore patterns for nested scopes. |
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…ries On musl (no JVM fork) the per-thread attrCacheKeys persists across @RetryingTest retries. Once "0"-"9" are cached in the native Dictionary and the Java cache, subsequent retries hit the cache, skip registerConstant0(), and leave dictionary_context_keys=0. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Pull request overview
Restores snapshot/restore support for custom profiling context attributes by adding read-back APIs in ContextSetter and an allocation-free warm-path cache in ThreadContext, ensuring nested scopes can correctly restore prior attribute values.
Changes:
- Add
ContextSetter.readContextValue(int)/readContextValue(String)to enable snapshot/restore patterns in callers (e.g., nested scopes). - Add
ThreadContext.indexedValueCachewith anABSENTsentinel and cold-path scan caching to make same-thread reads O(1) on the warm path. - Expand
TagContextTestwith targeted tests for snapshot/restore, cold-path scan behavior, overflow handling, and cache-clearing semantics.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds/adjusts tests to validate snapshot/restore behavior and cache semantics across warm/cold/overflow paths. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Introduces per-slot read-back cache and updates write/clear paths to keep it consistent; enhances readContextAttribute() with warm/cold behavior. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Exposes TLS-delegated readContextAttribute(int) for same-thread read-back. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds read-back APIs (readContextValue) to support snapshot/restore patterns for nested scopes. |
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Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
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Pull request overview
Restores same-thread snapshot/restore for custom context attributes (needed by dd-trace-java ProfilingScope) by adding read-back APIs to ContextSetter, backed by an allocation-free warm-path cache in ThreadContext.
Changes:
- Add
ContextSetter.readContextValue(int)andContextSetter.readContextValue(String)for snapshot/restore of custom attribute values. - Add
ThreadContext.indexedValueCache(with anABSENTsentinel) and implement warm/cold read-back inThreadContext.readContextAttribute(int). - Expand
TagContextTestwith new tests covering snapshot/restore behavior, cold-path scanning, attrs_data overflow handling, cache clearing onsetContext, and cross-slot isolation; adjust the existing retrying test to use session-unique strings.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds targeted tests for snapshot/restore and cache behaviors; makes retry attempts register fresh dictionary values. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Introduces per-slot value cache + sentinel and uses it to provide warm-path, allocation-free read-back (with cold-path scan fallback). |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Adds TLS-delegating readContextAttribute(int) entry point for ContextSetter. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Exposes public read APIs (readContextValue) to support snapshot/restore in nested scopes. |
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Adds a 688-byte DirectByteBuffer aliasing record+sidecar for one-memcpy save/restore of nested scope state. New ScopeStack provides tiered scratch (6-slot eager + lazy 12-slot chunks) for allocation-free per-thread use. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Pull request overview
This PR restores same-thread snapshot/restore support for custom context attributes by adding read-back APIs on ContextSetter, plus introduces allocation-free warm-path reads in ThreadContext via a per-slot string cache. It also adds an optional bulk snapshot/restore mechanism (ThreadContext.snapshot/restore + ScopeStack) to efficiently save/restore full context state for nested scopes.
Changes:
- Add
ContextSetter.readContextValue(int)/readContextValue(String)to support restoring previous custom attribute values when nested scopes close. - Add
ThreadContext.indexedValueCache+ warm/cold read logic to make read-back O(1) and allocation-free on the warm path, with tests covering snapshot/restore, cold-path scan, overflow, and cache clearing. - Extend TLS initialization to return a third DirectByteBuffer (“combined” record+sidecar) and add
ThreadContext.snapshot/restore+ newScopeStackfor bulk memcpy-based scope transitions.
Reviewed changes
Copilot reviewed 7 out of 7 changed files in this pull request and generated 3 comments.
Show a summary per file
| File | Description |
|---|---|
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds tests for snapshot/restore read-back behavior, cold-path scan, overflow handling, cache clearing, and cross-slot isolation; also makes retry attempts register unique dictionary values. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Adds per-slot string cache and read-back API, plus new bulk snapshot/restore support over a combined buffer. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ScopeStack.java | Introduces a per-thread snapshot stack for nested-scope bulk save/restore. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Adds TLS read-back delegate and updates TLS initialization to construct ThreadContext from 3 buffers. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds public read-back methods (readContextValue) for restoring prior attribute values. |
| ddprof-lib/src/main/cpp/thread.h | Documents/enforces contiguous layout expectations for combined buffer usage. |
| ddprof-lib/src/main/cpp/javaApi.cpp | Updates JNI to return 3 DirectByteBuffers and creates the combined contiguous buffer view. |
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Java readers of custom attrs are test-only — the profiler signal handler uses sidecar encodings and OTEL eBPF reads attrs_data directly. Drop the per-slot String cache and scan attrs_data on the test-only read path. Reject values whose UTF-8 encoding exceeds 255 bytes at setContextAttribute to keep the OTEP view consistent and avoid orphan Dictionary entries. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
- Drop dead Math.min truncation in replaceOtepAttribute (unreachable after up-front rejection); document the caller contract - Fix stale "via cache" assertion message in testAttrsDataOverflow - Refresh MAX_VALUE_BYTES comment to match the new enforcement point - Move ScopeStackTest to com.datadoghq.profiler so it can reference ThreadContext.SNAPSHOT_SIZE / OTEL_MAX_RECORD_SIZE instead of duplicating layout constants Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
…ffer initializeContextTLS0 returns a single 688-byte DirectByteBuffer; metadata[5] is the absolute LRS offset in that buffer. Tag-encoding writes use TAG_ENCODINGS_OFFSET (=OTEL_MAX_RECORD_SIZE). One less JNI call per thread, one less field per ThreadContext, identical memory layout. Also fixes Java 8 CI: cast ByteBuffer to Buffer before calling position(int) so bytecode targets the Java 8 Buffer method signature rather than the JDK 9+ covariant ByteBuffer override. Update doc/architecture/TLSContext.md to match the unified-buffer API. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
snapshot() used to unconditionally re-attach after the bulk read. If the record was intentionally left unpublished (valid=0 after the all-zero clear path in setContextDirect), snapshot would flip valid=1 over stale attrs_data. Now both snapshot and restore consult the pre-snapshot valid byte (stored in scratch[validOffset]) and only re-publish when the captured state was valid. Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
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Pull request overview
Restores nested-scope snapshot/restore of custom context attributes by adding read APIs to ContextSetter and enabling bulk save/restore of the per-thread OTEP record + DD sidecar state (now exposed as a single contiguous DirectByteBuffer).
Changes:
- Switch TLS context initialization to return one unified 688B
DirectByteBuffer(record + tag encodings + LRS) and update Java/C++ plumbing accordingly. - Add
ThreadContext.snapshot()/restore()and introduceScopeStack+ a pure-Java unit test for stack behavior. - Add
ContextSetter.readContextValue(...)and expand tests around snapshot/restore and attrs_data overflow behavior.
Reviewed changes
Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.
Show a summary per file
| File | Description |
|---|---|
| doc/architecture/TLSContext.md | Updates architecture docs to reflect unified ctxBuffer layout and snapshot/restore semantics. |
| ddprof-test/src/test/java/com/datadoghq/profiler/context/TagContextTest.java | Adds snapshot/restore, overflow, and isolation tests for context attributes. |
| ddprof-test/src/test/java/com/datadoghq/profiler/ScopeStackTest.java | New pure-Java unit tests for ScopeStack behavior (no native lib required). |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ThreadContext.java | Unifies buffers, adds bulk snapshot/restore, enforces value size limit, and adjusts attrs_data write paths. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ScopeStack.java | New per-thread stack for nested-scope snapshot/restore storage. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/JavaProfiler.java | Updates JNI contract to single buffer + adds TLS-delegated attribute read method. |
| ddprof-lib/src/main/java/com/datadoghq/profiler/ContextSetter.java | Adds readContextValue(int) / readContextValue(String) to support snapshot/restore patterns. |
| ddprof-lib/src/main/cpp/thread.h | Enforces/clarifies contiguity and gating invariants for unified TLS context layout. |
| ddprof-lib/src/main/cpp/javaApi.cpp | Returns a single contiguous DirectByteBuffer and updates metadata offsets accordingly. |
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- ScopeStackTest: drop unused assertNull import (3137117966) - ThreadContext.readContextAttribute: replace stale "test-only path" Javadoc with accurate description — method now backs ContextSetter.readContextValue used for scope snapshot/restore (3137117980) Co-Authored-By: muse <muse@noreply>
Previous Javadoc revision suggested it was reachable from production scope snapshot/restore; in fact ContextSetter.readContextValue is only used from tests. Mark the method test-only, state that allocation is acceptable, and caution against adding a readback cache without a real production consumer. Co-Authored-By: muse <muse@noreply>
dd-trace-java will not call readContextValue — the only caller chain was TagContextTest -> ContextSetter.readContextValue -> JavaProfiler .readContextAttribute -> ThreadContext.readContextAttribute. Drop the two middle hops and let the test reach ThreadContext directly via JavaProfiler.getThreadContext(), mirroring OtelContextStorageModeTest. - Remove ContextSetter.readContextValue(int) / (String) - Remove JavaProfiler.readContextAttribute(int) - TagContextTest uses a local readTag helper that goes through profiler.getThreadContext().readContextAttribute(offset) - Strengthen ThreadContext.readContextAttribute Javadoc to reflect that the sole caller is now a test Co-Authored-By: muse <muse@noreply>
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| if (utf8.length > MAX_VALUE_BYTES) { | ||
| return false; |
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When this slot already has a value and a caller tries to replace it with a string whose UTF-8 encoding exceeds 255 bytes, this early return leaves the old sidecar encoding and attrs_data entry published. The method reports failure, but subsequent samples still carry the previous tag value; the other failure paths below clear the slot, so this size check should do the same before returning false.
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What does this PR do?:
Adds a bulk save/restore path for the per-thread profiling context, so
dd-trace-java'sProfilingScopecan propagate trace/span/LRS + custom-attribute state across nested scopes with one memcpy per transition.ScopeStack— per-thread stack of context snapshots, with a contiguous fast-path buffer for the first 6 depths and lazily allocated 12-slot chunks beyond.ThreadContext.snapshot(byte[], int)/restore(byte[], int)— bulk memcpy over the full record + sidecar, gated by detach/attach so concurrent signal handlers never observe partial state. Preserves the pre-snapshotvalidbyte: a cleared (valid=0) record stays unpublished across save/restore.ctxBufferthatjavaApi.cppnow returns to Java. Used for both per-field access and bulk memcpy.Dictionary, so the write-onlyDictionarynever gets orphan entries.Motivation:
In 1.41.0,
setContextValue(int, int)andencode(String)were removed (correctly — the int-only path left OTEPattrs_datastale). That also removed the restore path thatProfilingScope.close()relied on, so profiling samples after a nested scope closed were attributed to stale context values from the finished scope.Additional Notes:
ThreadContext.readContextAttributeis retained purely as a test-only read path exercised byTagContextTest. Its Javadoc calls this out; do not add a readback cache unless a production consumer appears.setContextValue(int, int)is still not restored — the int-only path was the original inconsistency source.How to test the change?:
ScopeStackTest(new, pure Java — no native lib required): depth accounting, underflow, fast-path and chunked-path round-trips, reuse after full unwind, and the clear-doesn't-republish regression.TagContextTest.testSnapshotRestore/testAttrsDataOverflow/testPutClearsCustomSlots/testCrossSlotIsolation: native-backed coverage of set/clear/overwrite cycles and attrs_data overflow behavior.TagContextTest.test()exercises the full profiling path with custom attributes.For Datadog employees:
@DataDog/security-design-and-guidance.Unsure? Have a question? Request a review!