Guard rethrowIfBlockingException call against unexpected failures by dougqh · Pull Request #12240 · DataDog/dd-trace-java

dougqh · 2026-08-19T17:41:51Z

What Does This Do

Moves the BlockingExceptionHandler.rethrowIfBlockingException(t) call generated by ExceptionHandlers inside the existing try/catch that guards the rest of the instrumentation exception handler, and has the catch handler instanceof-check the caught Throwable before rethrowing — only a genuine BlockingException propagates; everything else is swallowed like any other instrumentation error.

Motivation

rethrowIfBlockingException (added in #7516 so BlockingException could escape the swallow-and-log) was previously called outside the try/catch. That meant any Throwable from that call — not just a genuine BlockingException — would escape uncaught, replacing the original swallowed exception and potentially crashing the instrumented method's caller (e.g. a NoClassDefFoundError from a classloader that can't see the appsec module).

Found while investigating a top-volume error-tracking issue whose "Failed to handle exception in instrumentation for ..." log samples traced back to this handler.

Additional Notes

None.

Test plan

:dd-java-agent:agent-tooling:forkedTest — ExceptionHandlerForkedTest, ExceptionHandlerExitOnFailureForkedTest, AppSecDisabledExceptionHandlerForkedTest (covers the "blocking exception is rethrown" case) all pass
./gradlew spotlessApply — no additional changes

🤖 Generated with Claude Code

BlockingExceptionHandler.rethrowIfBlockingException was invoked outside the try/catch that guards the rest of the instrumentation exception handler, so any unexpected Throwable from that call itself (e.g. a NoClassDefFoundError from a classloader that can't see the appsec module) would escape uncaught, replacing the original swallowed exception and crashing the instrumented method's caller instead of being logged. Move the call inside the try/catch and only rethrow when the caught exception is actually a BlockingException. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

datadog-official · 2026-08-19T17:56:21Z

🎯 Code Coverage (details)
• Patch Coverage: 0.00%
• Overall Coverage: 62.66% (+3.99%)

_{This comment will be updated automatically if new data arrives.

🔗 Commit SHA: 2261d3f | Docs | View more details | Give us feedback!}

dd-octo-sts · 2026-08-19T18:23:39Z

🟢 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	14.00 s	13.93 s	[-0.2%; +1.2%] (no difference)
startup:insecure-bank:tracing:Agent	12.92 s	12.97 s	[-1.4%; +0.5%] (no difference)
startup:petclinic:appsec:Agent	17.63 s	17.38 s	[+0.4%; +2.4%] (maybe worse)
startup:petclinic:iast:Agent	17.59 s	17.60 s	[-0.7%; +0.6%] (no difference)
startup:petclinic:profiling:Agent	17.56 s	17.34 s	[+0.1%; +2.4%] (maybe worse)
startup:petclinic:sca:Agent	17.54 s	17.41 s	[-0.3%; +1.8%] (no difference)
startup:petclinic:tracing:Agent	16.65 s	16.63 s	[-1.1%; +1.3%] (no difference)

Commit: 2261d3f8 · CI Pipeline · Benchmarking Platform UI

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

dd-octo-sts · 2026-08-21T13:29:22Z

Hi! 👋 Thanks for your pull request! 🎉

To help us review it, please make sure to:

Add at least one type, and one component or instrumentation label to the pull request

If you need help, please check our contributing guidelines.

chatgpt-codex-connector

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 209973c00a

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

Open a pull request for review
Mark a draft as ready
Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

datadog-official

The new catch handler loads BlockingException after it catches a linkage failure. An isolated class loader can throw another NoClassDefFoundError from this check, so the instrumentation error can still reach application code.

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 209973c · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

…ception handler Documents the gap flagged by codex on PR #12240: the eatException catch block's own `instanceof BlockingException` check resolves the class via the instrumented class's own classloader, so a classloader that can't see the appsec module gets a NoClassDefFoundError instead of the original exception. Left failing intentionally; not pushed until a fix is decided. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Replace the INSTANCEOF check with a class-name comparison so the catch handler no longer forces resolution of BlockingException via the instrumented class's own classloader - the same NoClassDefFoundError risk the try/catch exists to guard against. Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

…ption-escape

chatgpt-codex-connector

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 2261d3f847

ℹ️ About Codex in GitHub

Codex has been enabled to automatically review pull requests in this repo. Reviews are triggered when you

Open a pull request for review
Mark a draft as ready
Comment "@codex review".

If Codex has suggestions, it will comment; otherwise it will react with 👍.

When you sign up for Codex through ChatGPT, Codex can also answer questions or update the PR, like "@codex address that feedback".

chatgpt-codex-connector · 2026-08-21T16:17:36Z

+                false);
+            mv.visitMethodInsn(
+                Opcodes.INVOKEVIRTUAL, "java/lang/Class", "getName", "()Ljava/lang/String;", false);
+            mv.visitLdcInsn("datadog.appsec.api.blocking.BlockingException");


Preserve blocking for BlockingException subclasses

When advice throws a subclass of the public, non-final BlockingException, BlockingExceptionHandler.rethrowIfBlockingException recognizes it via instanceof and throws the same object, but this exact runtime-name comparison returns false and the subsequent POP swallows it. The instrumented operation then continues instead of enforcing the AppSec block; preserve the helper's subtype semantics without resolving BlockingException through the instrumented classloader, for example by inspecting superclass names.

Useful? React with 👍 / 👎.

datadog-official

The new exact class-name check swallows a BlockingException subclass. The existing helper rethrows this subclass.

_{Open Bits AI session}

_{🤖 Datadog Autotest · Commit 2261d3f · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

datadog-official · 2026-08-21T16:20:25Z

+                false);
+            mv.visitMethodInsn(
+                Opcodes.INVOKEVIRTUAL, "java/lang/Class", "getName", "()Ljava/lang/String;", false);
+            mv.visitLdcInsn("datadog.appsec.api.blocking.BlockingException");


Preserve BlockingException subclass propagation

An AppSec or RASP block that uses a BlockingException subclass can fail, so the request can continue.

Assertion details

Input: Enabled AppSec instrumentation advice throws a subclass of the public, non-final BlockingException class.

Expected: The handler must rethrow BlockingException and its subclasses, as rethrowIfBlockingException does with an instanceof check.

Actual: The catch handler compares the thrown object's exact class name with BlockingException. It discards a subclass because its class name differs.

Was this helpful? React 👍 or 👎
_{🤖 Datadog Autotest · What is Autotest? · @DataDog review to ask questions · Any feedback? Reach out in #autotest}

dougqh marked this pull request as ready for review August 21, 2026 13:29

dougqh requested a review from a team as a code owner August 21, 2026 13:29

dougqh requested review from mtoffl01 and removed request for a team August 21, 2026 13:29

dd-octo-sts Bot added the tag: ai generated Largely based on code generated by an AI or LLM label Aug 21, 2026

chatgpt-codex-connector Bot reviewed Aug 21, 2026

View reviewed changes

Comment thread ...ent/agent-tooling/src/main/java/datadog/trace/agent/tooling/bytebuddy/ExceptionHandlers.java Outdated

dougqh marked this pull request as draft August 21, 2026 14:09

datadog-official Bot reviewed Aug 21, 2026

View reviewed changes

Comment thread ...ent/agent-tooling/src/main/java/datadog/trace/agent/tooling/bytebuddy/ExceptionHandlers.java Outdated

dougqh and others added 3 commits August 21, 2026 10:24

Merge branch 'master' into dougqh/fix-exception-handler-blocking-exce…

2261d3f

…ption-escape

dougqh marked this pull request as ready for review August 21, 2026 16:13

chatgpt-codex-connector Bot reviewed Aug 21, 2026

View reviewed changes

datadog-official Bot reviewed Aug 21, 2026

View reviewed changes

dougqh added comp: tooling Build & Tooling type: bug fix Bug fix labels Aug 21, 2026

Navigation Menu

Uh oh!

Guard rethrowIfBlockingException call against unexpected failures - #12240

Guard rethrowIfBlockingException call against unexpected failures#12240
dougqh wants to merge 4 commits into
masterfrom
dougqh/fix-exception-handler-blocking-exception-escape

dougqh commented Aug 19, 2026 •

edited

Loading

Uh oh!

datadog-official Bot commented Aug 19, 2026 •

edited by datadog-prod-us1-5 Bot

Loading

Uh oh!

dd-octo-sts Bot commented Aug 19, 2026 •

edited

Loading

Uh oh!

dd-octo-sts Bot commented Aug 21, 2026

Uh oh!

chatgpt-codex-connector Bot left a comment

Uh oh!

Uh oh!

datadog-official Bot left a comment

Uh oh!

Uh oh!

chatgpt-codex-connector Bot left a comment

Uh oh!

chatgpt-codex-connector Bot Aug 21, 2026

Uh oh!

datadog-official Bot left a comment

Uh oh!

datadog-official Bot Aug 21, 2026

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

Uh oh!

Conversation

dougqh commented Aug 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

What Does This Do

Motivation

Additional Notes

Test plan

Uh oh!

datadog-official Bot commented Aug 19, 2026 • edited by datadog-prod-us1-5 Bot Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

dd-octo-sts Bot commented Aug 19, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

🟢 Java Benchmark SLOs — All performance SLOs passed

Uh oh!

dd-octo-sts Bot commented Aug 21, 2026

Uh oh!

chatgpt-codex-connector Bot left a comment

Choose a reason for hiding this comment

💡 Codex Review

Uh oh!

Uh oh!

datadog-official Bot left a comment

Choose a reason for hiding this comment

Uh oh!

Uh oh!

chatgpt-codex-connector Bot left a comment

Choose a reason for hiding this comment

💡 Codex Review

Uh oh!

chatgpt-codex-connector Bot Aug 21, 2026

Choose a reason for hiding this comment

Uh oh!

datadog-official Bot left a comment

Choose a reason for hiding this comment

Uh oh!

datadog-official Bot Aug 21, 2026

Choose a reason for hiding this comment

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

1 participant

dougqh commented Aug 19, 2026 •

edited

Loading

datadog-official Bot commented Aug 19, 2026 •

edited by datadog-prod-us1-5 Bot

Loading

dd-octo-sts Bot commented Aug 19, 2026 •

edited

Loading