JAVA-6155 add thread dumps to evergreen logs on failed test cases by strogiyotec · Pull Request #1932 · mongodb/mongo-java-driver

strogiyotec · 2026-04-01T18:21:56Z

JAVA-6155
This PR adds thread dumps whenever test fails
The motivation behind this PR was a failing test case poolClearedExceptionMustBeRetryable
Claude identified a deadlock that I wasn't able to reproduce locally
With this PR develop could easily see thread dumps of all the threads directly in evergreen and locally

Here is an example of a patch that deliberately makes a test case fail and it's output

Copilot

Pull request overview

This PR introduces a JUnit 5 TestWatcher extension that emits a full JVM thread dump to the test logs whenever a test fails, making deadlocks and hung-thread scenarios easier to diagnose in Evergreen and locally.

Changes:

Add ThreadDumpOnFailureExtension (JUnit Jupiter TestWatcher) that logs a thread dump on test failure.
Register the extension via META-INF/services/... and enable JUnit Jupiter extension autodetection via junit-platform.properties.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java	Adds the failure hook and thread-dump collection logic.
driver-core/src/test/resources/META-INF/services/org.junit.jupiter.api.extension.Extension	Registers the extension for ServiceLoader-based autodetection.
driver-core/src/test/resources/junit-platform.properties	Enables JUnit Jupiter extension autodetection so the extension is picked up automatically.

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Copilot · 2026-04-01T18:26:56Z

driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java

+    public void testFailed(final ExtensionContext context, final Throwable cause) {
+        String testName = context.getDisplayName();
+        String threadDump = getAllThreadsDump();
+        LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump);


testFailed ignores the provided cause, so the log entry won’t include the exception/stack trace that triggered the failure. Logging the throwable (e.g., using the error(String, Throwable) overload) would keep the failure reason adjacent to the thread dump in Evergreen/local logs.

Suggested change

LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump);

LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump, cause);

the cause will already be provided on assertion fail I don't think duplicating it for thread dumps makes sense

Copilot · 2026-04-01T18:26:57Z

driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java

+    public void testFailed(final ExtensionContext context, final Throwable cause) {
+        String testName = context.getDisplayName();
+        String threadDump = getAllThreadsDump();
+        LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump);
+    }
+
+    private static String getAllThreadsDump() {
+        final ThreadMXBean threadMXBean = ManagementFactory.getThreadMXBean();
+        ThreadInfo[] threadInfos = threadMXBean.dumpAllThreads(
+                threadMXBean.isObjectMonitorUsageSupported(),
+                threadMXBean.isSynchronizerUsageSupported()
+        );


getAllThreadsDump() (via ThreadMXBean.dumpAllThreads) can throw at runtime (e.g., SecurityException). If this happens inside testFailed, the extension itself may error and you’ll lose the diagnostic output. Consider wrapping thread-dump generation in a try/catch and logging a clear fallback message so the original test failure reporting isn’t impacted.

good point, wrapped it with try catch

Copilot · 2026-04-01T18:26:57Z

driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java

+ */
+public final class ThreadDumpOnFailureExtension implements TestWatcher {
+
+    private static final Logger LOGGER = Loggers.getLogger(ThreadDumpOnFailureExtension.class.getName());


Logger naming is inconsistent with other driver-core tests: most use a short suffix like ClassName.class.getSimpleName() (e.g., ConnectionPoolTest / ConnectionPoolAsyncTest). Passing class.getName() here yields a very long logger name (org.mongodb.driver.com.mongodb...) that’s harder to filter/read in logs; consider switching to getSimpleName() or a conventional test logger suffix.

Suggested change

private static final Logger LOGGER = Loggers.getLogger(ThreadDumpOnFailureExtension.class.getName());

private static final Logger LOGGER = Loggers.getLogger(ThreadDumpOnFailureExtension.class.getSimpleName());

replaced to use simple name

Copilot

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

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Copilot · 2026-04-01T19:07:43Z

driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java

+import java.lang.management.ManagementFactory;
+import java.lang.management.ThreadInfo;
+import java.lang.management.ThreadMXBean;
+
+
+import com.mongodb.internal.diagnostics.logging.Logger;
+import com.mongodb.internal.diagnostics.logging.Loggers;
+
+import org.junit.jupiter.api.extension.ExtensionContext;
+import org.junit.jupiter.api.extension.TestWatcher;
+
+


Import order/grouping here is inconsistent with the repo’s established convention (typically project com.mongodb.* imports first, then org.*, then java.*, e.g. driver-core/src/test/unit/com/mongodb/internal/connection/ConnectionPoolTest.java:19-28). Reorder the imports to match the surrounding codebase style to keep diffs consistent and reduce merge noise.

Suggested change

import java.lang.management.ManagementFactory;

import java.lang.management.ThreadInfo;

import java.lang.management.ThreadMXBean;

import com.mongodb.internal.diagnostics.logging.Logger;

import com.mongodb.internal.diagnostics.logging.Loggers;

import org.junit.jupiter.api.extension.ExtensionContext;

import org.junit.jupiter.api.extension.TestWatcher;

import com.mongodb.internal.diagnostics.logging.Logger;

import com.mongodb.internal.diagnostics.logging.Loggers;

import org.junit.jupiter.api.extension.ExtensionContext;

import org.junit.jupiter.api.extension.TestWatcher;

import java.lang.management.ManagementFactory;

import java.lang.management.ThreadInfo;

import java.lang.management.ThreadMXBean;

Copilot · 2026-04-01T19:07:43Z

driver-core/src/test/unit/com/mongodb/internal/diagnostics/ThreadDumpOnFailureExtension.java

+    public void testFailed(final ExtensionContext context, final Throwable cause) {
+        String testName = context.getDisplayName();
+        String threadDump = getAllThreadsDump();
+        LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump);
+    }


This logs a full JVM thread dump on every failed test. When failures cascade (e.g., environment outage causing many tests to fail), this can produce very large Evergreen logs and make the original failures harder to find. Consider throttling (e.g., only dump once per JVM via an AtomicBoolean, or once per test class) and/or adding a clear header/footer delimiter so each dump is easy to locate in the log stream.

Copilot · 2026-04-01T19:07:44Z

driver-core/src/test/resources/junit-platform.properties

@@ -0,0 +1 @@
+junit.jupiter.extensions.autodetection.enabled=true


junit-platform.properties is included in driver-core’s testArtifacts JAR (see buildSrc/src/main/kotlin/conventions/test-artifacts.gradle.kts:26-29), and several other modules depend on :driver-core:testArtifacts for their tests (e.g., driver-sync/build.gradle.kts:37-39). That means this setting may unintentionally enable JUnit Jupiter extension autodetection beyond driver-core depending on classpath resource resolution. If the intent is to scope this behavior to a specific module/test task, consider enabling it via the Gradle Test task/system property instead, or placing a shared properties file in a deliberately shared test-resources location.

Suggested change

junit.jupiter.extensions.autodetection.enabled=true

# NOTE:

# This file is included in driver-core's testArtifacts JAR and is therefore

# visible on the test classpath of other modules that depend on :driver-core:testArtifacts.

# Enabling JUnit Jupiter extension autodetection here would unintentionally

# turn it on for those modules as well.

#

# If you need autodetection, configure it in the specific module or Gradle

# Test task instead (e.g. via system property junit.jupiter.extensions.autodetection.enabled=true),

# or in a module-local junit-platform.properties that is not shared via testArtifacts.

#

# Example (do NOT uncomment here unless you really want it shared globally):

# junit.jupiter.extensions.autodetection.enabled=true

JAVA-6155 add thread dumps to failed test cases

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strogiyotec requested a review from a team as a code owner April 1, 2026 18:21

strogiyotec requested review from Copilot and nhachicha and removed request for nhachicha April 1, 2026 18:21

Copilot started reviewing on behalf of strogiyotec April 1, 2026 18:22 View session

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strogiyotec requested a review from Copilot April 1, 2026 19:02

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JAVA-6155 add thread dumps to evergreen logs on failed test cases#1932

JAVA-6155 add thread dumps to evergreen logs on failed test cases#1932
strogiyotec wants to merge 2 commits intomongodb:mainfrom
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	LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump);
	LOGGER.error("Test failed: " + testName + "\nThread dump:\n" + threadDump, cause);

	private static final Logger LOGGER = Loggers.getLogger(ThreadDumpOnFailureExtension.class.getName());
	private static final Logger LOGGER = Loggers.getLogger(ThreadDumpOnFailureExtension.class.getSimpleName());

		@@ -0,0 +1 @@
		junit.jupiter.extensions.autodetection.enabled=true

-junit.jupiter.extensions.autodetection.enabled=true
+# NOTE:
+# This file is included in driver-core's testArtifacts JAR and is therefore
+# visible on the test classpath of other modules that depend on :driver-core:testArtifacts.
+# Enabling JUnit Jupiter extension autodetection here would unintentionally
+# turn it on for those modules as well.
+#
+# If you need autodetection, configure it in the specific module or Gradle
+# Test task instead (e.g. via system property junit.jupiter.extensions.autodetection.enabled=true),
+# or in a module-local junit-platform.properties that is not shared via testArtifacts.
+#
+# Example (do NOT uncomment here unless you really want it shared globally):
+# junit.jupiter.extensions.autodetection.enabled=true

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strogiyotec commented Apr 1, 2026 •

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