fix(okhttp): capture scope at AsyncCall.<init> to keep traces intact under virtual-thread Dispatcher

[dougqh]

What Does This Do

Fixes okhttp.request spans cross-contaminating between concurrent caller traces when OkHttp's Dispatcher runs on a virtual-thread-per-task executor. Captures the active scope at AsyncCall.<init> (i.e. on the user thread that called Call.enqueue(callback)) and stores it in the shared ContextStore<Runnable, State>. RunnableInstrumentation then activates that state on AsyncCall.run() entry, overriding whatever scope TaskRunner inherited from a dispatcher-recursion path.

The capture is split by OkHttp major version, since AsyncCall moved packages:

Module	OkHttp	AsyncCall type
okhttp-3.0	3.x	okhttp3.RealCall$AsyncCall
okhttp-4.0 (new)	4.x+	okhttp3.internal.connection.RealCall$AsyncCall

Both instrumentations extend InstrumenterModule.ContextTracking (like RunnableInstrumentation, which consumes the state they write) rather than Tracing — their sole job is scope propagation through the shared ContextStore<Runnable, State>, not span creation. They re-use the existing okhttp instrumentation name, so no new feature flag: OkHttp tracing being enabled implies this capture is enabled.

Motivation

Reported by DataDog/profiling-backend#8520, which swapped its OkHttp dispatcher from Executors.newCachedThreadPool(...) to Executors.newThreadPerTaskExecutor(Thread.ofVirtual().name(prefix, start).factory()) and started seeing broken traces.

OkHttp's Dispatcher recursively promotes queued AsyncCalls from inside Dispatcher.finished(), which runs on a dispatcher worker thread with a different call's parent scope still active (re-instated by TaskRunner.run()). The existing TaskRunnerInstrumentation captures that wrong scope when the promoted call is submitted to the executor, so under a virtual-thread-per-task dispatcher — or any executor where this recursion exposes itself — okhttp.request spans cross-contaminate between concurrent caller traces. Single-shot requests don't trigger it because nothing is queued.

The right capture point is the moment the user enqueued the call, where the right parent is active. That's exactly AsyncCall.<init>.

Deep dive: failure mode and propagation walk

Why the old code worked

Executors.newCachedThreadPool(...) returns a java.util.concurrent.ThreadPoolExecutor, covered by ThreadPoolExecutorInstrumentation. That instrumentation captures the active continuation into a State keyed by the AsyncCall at execute() time, then beforeExecute activates it on the worker. The okhttp.request span is created inside AsyncCall.run() with the parent scope reliably active.

Why the new code breaks

Executors.newThreadPerTaskExecutor(Thread.ofVirtual()...) returns java.util.concurrent.ThreadPerTaskExecutor, which is not a ThreadPoolExecutor:

• ThreadPoolExecutorInstrumentation's extendsClass(named("java.util.concurrent.ThreadPoolExecutor")) doesn't match. No advice fires on its execute(...).
• JavaExecutorInstrumentation doesn't match either — ThreadPerTaskExecutor is not in its knownMatchingTypes and dd.trace.executors.all is off by default.

The only things that fire are:

• TaskRunnerInstrumentation — advises ThreadPerTaskExecutor$TaskRunner.<init> and run(). The constructor stashes a continuation in a State keyed by the TaskRunner, not the user's AsyncCall.
• VirtualThreadInstrumentation — captures the whole Context at VirtualThread.<init>, swaps it in/out on each mount/unmount.

In principle this propagates the scope. In practice, both fire on whatever thread calls executor.execute(...). That's the user thread for the first call from a given caller — but it's a dispatcher worker for any call that gets queued.

Dispatcher recursion → cross-trace contamination

1. Parent_A enqueues 4 calls. Dispatcher capacity is 4. They start.
2. Parent_B (..., Parent_P) enqueue more calls. They queue in readyAsyncCalls.
3. A call from Parent_A finishes on its virtual thread. Inside AsyncCall.run()'s finally, dispatcher.finished(this) runs — still on Parent_A's worker thread with Parent_A's scope active (reinstated by TaskRunner.run).
4. finished() calls promoteAndExecute(), which calls executor.execute(nextCall) for a queued call belonging to some other parent.
5. The agent's TaskRunnerInstrumentation.Construct captures whatever scope is active on the current worker — which is Parent_A, not the parent that actually called enqueue() for nextCall.
6. That promoted call runs on a new virtual thread with Parent_A's scope, and its okhttp.request span lands in Parent_A's trace.

Repeat at scale → Parent_A's trace accumulates strays; Parent_B / Parent_C / etc. end up with empty traces. The single-shot tests miss it entirely because nothing is in the ready queue when enqueue() returns.

How the fix propagates correctly

With the AsyncCall.<init> capture in place:

1. User thread, Parent_Y active: realCall.enqueue(cb) → new AsyncCall(cb) → capture advice fires → captures Parent_Y's continuation on the AsyncCall in ContextStore<Runnable, State>. ✓
2. AsyncCall is handed to the dispatcher. May execute immediately or queue.
3. Later: dispatcher worker thread, Parent_A active. executor.execute(asyncCall_Y) → TaskRunner.<init> → captures Parent_A on the TaskRunner. (Irrelevant noise — we don't try to fix TaskRunner.)
4. Virtual thread runs TaskRunner.run():
   • TaskRunnerInstrumentation.Run activates Parent_A on the worker.
   • TaskRunner.run() calls asyncCall_Y.run().
   • RunnableInstrumentation.RunnableAdvice fires on entry → reads the State stored in step 1 → activates Parent_Y on top of Parent_A.
5. getResponseWithInterceptorChain() runs the TracingInterceptor → activeSpan() returns Parent_Y → okhttp.request is parented under Parent_Y. ✓
6. On exit: RunnableAdvice closes Parent_Y's scope, then TaskRunner closes Parent_A's. Stack unwinds cleanly.

Two key properties make this safe:

• AdviceUtils.capture only writes a continuation if one isn't already there and async propagation is on, so we never overwrite a previously captured state.
• RunnableInstrumentation's advice runs inside TaskRunner.run(), after TaskRunner's activation. That inner scope wins for the entire duration of asyncCall.run() — which is exactly when the okhttp.request span is created.

Compatibility

• OkHttp 3.x — okhttp-3.0 module, type okhttp3.RealCall$AsyncCall.
• OkHttp 4.x+ — okhttp-4.0 module, type okhttp3.internal.connection.RealCall$AsyncCall. OkHttp 5.x is a Kotlin-Multiplatform library: com.squareup.okhttp3:okhttp is a metadata shell and the JVM classes (including RealCall$AsyncCall) ship in com.squareup.okhttp3:okhttp-jvm, which a JVM consumer resolves automatically via Gradle variant metadata. The matched type is at the same FQN in 4.x and 5.x, so a single instrumentation covers both majors.

Muzzle passes against OkHttp [3.0,) (okhttp-3.0) and [4.0,) including 5.0.0 → 5.4.0 (okhttp-4.0).

Testing

The virtual-thread regression suites live in dedicated JDK-21 test suites (the modules keep a Java 1.8 baseline for the existing tests). They are capped at maxJavaVersion=24 to match java-concurrent-21.0, which provides the virtual-thread scope propagation these tests depend on and is only supported through JDK 24 — so they run on JDK 21–24 and skip on 25/tip (26), where that propagation chain isn't active.

Each suite has two tests:

• concurrentVirtualThreadPerTaskDispatcher_keepsEachTraceSeparate — the regression test. Forces dispatcher-queue contention (16 parents × 4 requests, capacity 4) so calls are promoted from Dispatcher.finished() on a sibling's worker. Fails with cross-trace contamination without the fix; verified by neutralizing the advice on both 4.x and 5.x.
• virtualThreadPerTaskDispatcher_parentsOkHttpSpanUnderParent — a single-shot baseline (does not by itself exercise the contamination path).

Test plan

• :dd-java-agent:instrumentation:okhttp:okhttp-3.0:vthread21Test — OkHttp 3.11.0, 2 tests pass (JDK 21), skipped on JDK 25
• :dd-java-agent:instrumentation:okhttp:okhttp-4.0:vthread21Test4 — OkHttp 4.12.0, 2 tests pass (JDK 21), skipped on JDK 25
• :dd-java-agent:instrumentation:okhttp:okhttp-4.0:vthread21Test5 — OkHttp 5.4.0 (→ okhttp-jvm), 2 tests pass (JDK 21), skipped on JDK 25
• :dd-java-agent:instrumentation:okhttp:okhttp-3.0:forkedTest — pre-existing OkHttp forked tests still pass
• :dd-java-agent:instrumentation:okhttp:okhttp-3.0:muzzle / okhttp-4.0:muzzle — pass
• Verified in profiling-backend staging deploy

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[dd-octo-sts]

🟢 Java Benchmark SLOs — All performance SLOs passed

Suite	Status
Startup	🟢 pass

SLO thresholds are defined here based on automatically generated metrics. A warning is raised when results are within 5% of the threshold.

PR vs. master results

Scenario	Candidate	master	Δ (95% CI of mean)
startup:insecure-bank:iast:Agent	13.94 s	13.91 s	[-0.6%; +1.0%] (no difference)
startup:insecure-bank:tracing:Agent	12.96 s	12.98 s	[-0.9%; +0.7%] (no difference)
startup:petclinic:appsec:Agent	16.82 s	16.61 s	[+0.3%; +2.2%] (maybe worse)
startup:petclinic:iast:Agent	16.82 s	16.89 s	[-1.2%; +0.4%] (no difference)
startup:petclinic:profiling:Agent	16.85 s	16.95 s	[-1.6%; +0.5%] (no difference)
startup:petclinic:sca:Agent	16.86 s	16.76 s	[-0.4%; +1.6%] (no difference)
startup:petclinic:tracing:Agent	15.98 s	15.98 s	[-1.3%; +1.2%] (no difference)

Commit: 664f90c9 · CI Pipeline · Benchmarking Platform UI

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Load and DaCapo benchmarks can be triggered manually in the GitLab pipeline. Results will appear in the Benchmarking Platform UI after completion.

[datadog-prod-us1-3]

BitsAI applied the CI fix

The fix has been applied to this PR without validation.

Progress

🟢 Investigated · 🟢 Fix prepared · ⚪ Validation skipped · 🟢 Applied

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Commit: 8f5eb8a

View session in Datadog

[amarziali]

I disabled the advice and I had two tests over 3 still green. Only concurrentVirtualThreadPerTaskDispatcher_keepsEachTraceSeparate failed. I can suggest to review what's tested and also there are okhttp 4.x related classes that are matched but the test are only run on 3.11.0

[amarziali]

according to the gradle build there are no tests at all for 4.x. So how this can be verified?

[amarziali]

This is not related to okhttp (directly). I would recommend to add in a different PR

[amarziali]

This advice is instead InstrumenterModule.ContextTracking given its purpose

[dougqh]

Note: this reply was written by Claude (Claude Code) on @dougqh's behalf.

Thanks @amarziali — this all landed. Here's how each point is addressed in the changes I'm preparing for the next push:

"okhttp 4.x classes are matched but tests only run on 3.11.0" / how can 4.x be verified?

Split the AsyncCall capture by major version and added a dedicated okhttp-4.0 module that actually runs the regression against newer OkHttp:

• okhttp-3.0 keeps the v3 type (okhttp3.RealCall$AsyncCall).
• okhttp-4.0 matches the relocated v4+ type (okhttp3.internal.connection.RealCall$AsyncCall).
• The new module runs the same virtual-thread regression suite against OkHttp 4.12.0 and 5.4.0. (OkHttp 5.x is now Kotlin-Multiplatform — com.squareup.okhttp3:okhttp is a metadata shell and the JVM classes ship in okhttp-jvm, which Gradle resolves automatically via variant metadata; the matched type is at the same FQN in both, so one instrumentation covers both majors.)
• Muzzle exercises the module across 4.0.0 → 5.4.0.

I confirmed the suite genuinely exercises the fix on both 4.x and 5.x by neutralizing the advice and watching concurrentVirtualThreadPerTaskDispatcher_keepsEachTraceSeparate fail (cross-trace contamination), then pass once restored.

"review what's tested" (2 of 3 stayed green with the advice disabled)

Correct — only the concurrent test exercises the contamination path. Dropped the cachedThreadPoolDispatcher_… case (redundant with OkHttp3AsyncTest), kept the concurrent regression test plus one documented single-shot baseline, and updated the class javadoc to make the distinction explicit.

InstrumenterModule.ContextTracking (AsyncCallInstrumentation:34)

Done — both the v3 and v4 instrumentations now extend ContextTracking, matching RunnableInstrumentation (the consumer of the state they write). Their job is pure scope propagation through the shared ContextStore<Runnable, State>, not span creation.

testJvmConstraints instead of a launcher override (build.gradle:33)

Done. Also root-caused the failing CI shards: 25/tip are JDK 25/26, which are above java-concurrent-21.0's maxJavaVersion=24 — and these suites depend on that module's virtual-thread propagation. Added maxJavaVersion = JavaVersion.VERSION_24 so the suites skip on 25/26 (where the propagation chain isn't supported) and run on 21–24. That resolves the TimeoutExceptions.

Separate suite vs test (build.gradle:19)

I kept the dedicated JDK-21 suite. The test suite here has a Java 1.8 baseline (the legacy Groovy tests), so folding a JDK-21-only Java test into it would gate all okhttp tests behind JDK 21 and drop coverage on the 8/11/17 shards. A separate suite + testJvmConstraints + dependsOn check is also the established pattern elsewhere in the repo (e.g. grizzly-client-1.9, aerospike-4.0, java-concurrent-21.0). Happy to revisit if you'd prefer a different split.

[mcculls]

FYI, metadata/supported-configurations.json needs updating with the new okhttp-4 integration name

Basically add

    "DD_TRACE_OKHTTP_4_ENABLED": [
      {
        "version": "A",
        "type": "boolean",
        "default": "true",
        "aliases": ["DD_TRACE_INTEGRATION_OKHTTP_4_ENABLED", "DD_INTEGRATION_OKHTTP_4_ENABLED"]
      }
    ],

[mcculls]

Also merging in latest master should fix the current CI failures

[dougqh]

I disabled the advice and I had two tests over 3 still green. Only concurrentVirtualThreadPerTaskDispatcher_keepsEachTraceSeparate failed. I can suggest to review what's tested and also there are okhttp 4.x related classes that are matched but the test are only run on 3.11.0

@amarziali
Yes, the 2 of 3 tests staying green is expected. Unfortunately, since this is a context interaction between instrumentations, it doesn’t divide cleanly into either one.

The single-shot baseline doesn’t queue, so it doesn’t hit the path being fixed.
Calls only get promoted onto sibling thread when there’s sufficient contention, so it is hard to capture in a simple unit test.

I think the other points have all now been addressed…

• Advice is now an InstrumenterModule.ContextTracking - I didn’t know we’d added that concept
• okhttp 4 is now its own module - with its own v-thread test
• config flag has been added to supported-configurations.json

[amarziali]

@dougqh overall looks ok but I left few things I'd like to discuss/review with you before approving

[amarziali]

This is misleading to me since the tracing instrumentation is applying for 3+ (includes 4) while the new Instrumentation for context trackingis only applying for 3. To be correct this should be split and ensure that the new will fail for 4 to avoid overlaps with the 4.x module (that also suffers about it because tests muzzle only for 4 onwards without testing that fails for < 4.
Splitting muzzle checks in this module can be done by having a separate muzzleDirective on the AsyncCallInstrumentation.

[dougqh]

Alright, I'll look into more closely. I'll be honest this was an experiment to see how the AI would do solving a complicated context issue. It did okay finding the problem, but the mechanics of the change could be better.

But honestly, given that I haven't written many instrumentations, I would probably have made many of the same mistakes.

[amarziali]

All in all it did well I think. There are always details to fine tune of course

[amarziali]

btw why it hangs for >=25 ? Are we missing something? Our virtual thread instrumentation is supposed to work on 25

[dougqh]

Note: reply from Claude (Claude Code), working with @dougqh.

Good catch — I checked this empirically rather than assuming. The virtual-thread instrumentation does work on 25; the cap was mis-inherited and the "times out on 25" explanation is wrong.

I ran the okhttp-4.0 vthread21Test4 (OkHttp 4.x) and vthread21Test5 (5.x) suites on JDK 25 — lifting the maxJavaVersion = 24 cap, runtime confirmed via the tracer's runtimeVersion='25'. Both pass (2 tests each), including the contention regression concurrentVirtualThreadPerTaskDispatcher_keepsEachTraceSeparate (the one that fails if scope propagation breaks). okhttp-3.0's vthread21Test passes on 25 too.

Root cause of the cap: it traces to java-concurrent-21.0, which caps at 24 because its own test uses StructuredTaskScope.ShutdownOnFailure — a preview API removed in JDK 25. That's a test-compilation constraint on that module, not a limit on the virtual-thread instrumentation. These suites only consume that instrumentation at runtime (never ShutdownOnFailure), so the cap never applied — and the "propagation chain isn't active on 25" comment is empirically false.

Fix: per the usual "no cap until a demonstrated problem" convention, I've removed the cap on both okhttp modules. Verified through JDK 25; I haven't checked 26/"tip", so if a real issue surfaces there CI will catch it and we cap then, with an accurate reason.

[dougqh]

Note: reply from Claude (Claude Code), working with @dougqh.

Correction to my reply above — CI caught what my local run didn't. With the cap lifted, the test_inst shards on JDK 25 and tip fail, so I've restored maxJavaVersion = 24 (commit d17f52367c) with a corrected comment.

To separate what's true from what I overstated:

• The virtual-thread instrumentation does work on 25 — the suites pass locally on 25, including the contention regression. That part stands, and it's the answer to your original question.
• But my local run was fast and unloaded and didn't reproduce the CI shards' conditions. The contention test deliberately creates dispatcher contention and waits on a latch; it isn't stable on the 25/tip shards under that load. So the original "times out on the 25/tip CI shards" note was right about CI — even though its stated reason ("propagation chain isn't active on 25") is wrong.

Net: instrumentation works on 25 ✅; the suite isn't CI-stable on 25/tip yet ⚠️ — that's what the cap actually guards, and I've corrected the comment to say so. Making the suite stable on 25+ (a more robust latch/timeout) is separate follow-up.

[amarziali]

This explanation is not clear to me why in java 25 is failing. either the test is flaky (and it' s an issue since will probably fail in the future) either we're not covering everything?

[dougqh]

Note: reply from Claude (Claude Code), working with @dougqh.

You're right that "flaky" is itself an issue, so I checked which horn it is. 10 runs on JDK 25 locally → 10/10 pass. A real coverage gap would fail deterministically, so this is flakiness under CI-shard load (the stress test depends on stochastic contention timing), not a missed case.

So instead of cap-and-hope, I added a deterministic test — promotedFromFinished_keepsEnqueuingTraceNotFinishingTrace: capacity-1 dispatcher, call_B (parent B) holds the slot at a gated endpoint, call_A (parent A) queues, then releasing the gate promotes call_A from inside call_B's finished() with scope B active. It asserts call_A parents under A — the exact contamination path, constructed rather than raced for.

Verified sensitive: passes with the AsyncCall.<init> capture, fails without it (advice disabled → "leaked to parentB's trace"). Same result every run. The stress test stays as an integration sanity check; this is the reliable guard.

Still capped at 24 (it lives in the vthread suite), but being deterministic it won't flake — so the cap can come off once we're comfortable, and a plain-executor variant could drop the JDK-21 requirement entirely.