From 7f313d25e90f11d31a6098b904aefba9b213d370 Mon Sep 17 00:00:00 2001 From: Zhengyu Gu Date: Tue, 18 Aug 2026 13:51:22 +0000 Subject: [PATCH 1/2] Test case: for verifying main(String[]), run() method of Thread and its subclasses are marked entry frames --- .../datadoghq/profiler/ExternalLauncher.java | 85 +++++++++ .../com/datadoghq/profiler/JfrStackTrace.java | 5 +- .../profiler/jfr/EntryFrameTest.java | 175 ++++++++++++++++++ 3 files changed, 264 insertions(+), 1 deletion(-) create mode 100644 ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java diff --git a/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java b/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java index cb83816df5..e1132027a6 100644 --- a/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java +++ b/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java @@ -26,6 +26,10 @@ *
  • profiler-sequence [';'-delimited steps] - runs a sequence of start/stop calls in this * process; each step is either the literal {@code STOP} (calls {@link JavaProfiler#stop()}) * or a comma delimited profiler command list (calls {@link JavaProfiler#execute(String)})
    • + *
  • entry-frames [comma delimited profiler command list] - starts the profiler, then burns + * CPU concurrently on the main thread, on a plain {@code new Thread(Runnable)} and on a + * two-level {@link Thread} subclass, and stops the profiler again. The resulting recording + * holds samples rooted at each of the three thread entry points; see {@code EntryFrameTest}
    • * */ public class ExternalLauncher { @@ -41,6 +45,78 @@ private static Thread startVirtualThread(Runnable task) throws Exception { return (Thread) start.invoke(builder, task); } + /** How long each {@code entry-frames} thread burns CPU for. */ + private static final long ENTRY_FRAME_WORKLOAD_MILLIS = 1000; + + private static volatile long entryFrameSink; + + /** + * A {@link Thread} subclass that does not override {@code run()}, so that + * {@link EntryFrameThread} below sits two levels below {@link Thread} and its {@code run()} + * frame can only be recognised as a thread entry point by walking the whole superclass chain. + */ + private static class BaseEntryFrameThread extends Thread { + BaseEntryFrameThread(String name) { + super(name); + } + } + + private static final class EntryFrameThread extends BaseEntryFrameThread { + EntryFrameThread() { + super("entry-frame-subclass"); + } + + @Override + public void run() { + entryFrameWorkLevel1(ENTRY_FRAME_WORKLOAD_MILLIS); + } + } + + private static final class EntryFrameRunnable implements Runnable { + @Override + public void run() { + entryFrameWorkLevel1(ENTRY_FRAME_WORKLOAD_MILLIS); + } + } + + /** + * Burns CPU on the main thread and on the two worker threads at the same time, so that all + * three entry points ({@code ExternalLauncher.main(String[])}, {@code Thread.run()} for the + * {@link EntryFrameRunnable} thread and {@code EntryFrameThread.run()}) are the bottom frame + * of some samples. + */ + private static void runEntryFrameWorkload() throws InterruptedException { + Thread runnableThread = new Thread(new EntryFrameRunnable(), "entry-frame-runnable"); + Thread subclassThread = new EntryFrameThread(); + runnableThread.start(); + subclassThread.start(); + entryFrameWorkLevel1(ENTRY_FRAME_WORKLOAD_MILLIS); + runnableThread.join(); + subclassThread.join(); + } + + // entryFrameWorkLevel1/2 pad the call chain below every entry point, so that a recording + // taken with a small jstackdepth roots its samples inside the chain rather than at the + // entry frame itself - that is how EntryFrameTest gets its negative control. + private static void entryFrameWorkLevel1(long millis) { + entryFrameWorkLevel2(millis); + } + + private static void entryFrameWorkLevel2(long millis) { + entryFrameBurn(millis); + } + + private static void entryFrameBurn(long millis) { + long deadline = System.currentTimeMillis() + millis; + long acc = 0; + while (System.currentTimeMillis() < deadline) { + for (int i = 0; i < 100000; i++) { + acc += i * 31 + (acc >>> 3); + } + } + entryFrameSink = acc; + } + public static void main(String[] args) throws Exception { Thread worker = null; try { @@ -80,6 +156,15 @@ public static void main(String[] args) throws Exception { } } } + } else if (args[0].equals("entry-frames")) { + JavaProfiler instance = JavaProfiler.getInstance(); + if (args.length == 2 && !args[1].isEmpty()) { + instance.execute(args[1]); + } + runEntryFrameWorkload(); + // Stop explicitly rather than leaving it to JVM shutdown: the parent process + // starts reading the recording as soon as this process exits. + instance.stop(); } else if (args[0].startsWith("profiler-work:")) { long expectedCpuTime = Long.parseLong(args[0].substring("profiler-work:".length())); ThreadMXBean thrdBean = ManagementFactory.getThreadMXBean(); diff --git a/ddprof-test/src/test/java/com/datadoghq/profiler/JfrStackTrace.java b/ddprof-test/src/test/java/com/datadoghq/profiler/JfrStackTrace.java index 548230701c..bdb36edb04 100644 --- a/ddprof-test/src/test/java/com/datadoghq/profiler/JfrStackTrace.java +++ b/ddprof-test/src/test/java/com/datadoghq/profiler/JfrStackTrace.java @@ -54,7 +54,10 @@ static JfrStackTrace of(Object rawStackTrace) { return new JfrStackTrace(frames, truncated); } - /** This stack trace's frames, outermost (root) frame first. */ + /** + * This stack trace's frames in the order {@code Recording::writeStackTraces} wrote them: + * topmost (leaf) frame first, so the thread entry point is the last element. + */ public List frames() { return frames; } diff --git a/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java b/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java new file mode 100644 index 0000000000..2dba32cd7e --- /dev/null +++ b/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java @@ -0,0 +1,175 @@ +/* + * Copyright 2026, Datadog, Inc. + * SPDX-License-Identifier: Apache-2.0 + */ + +package com.datadoghq.profiler.jfr; + +import com.datadoghq.profiler.AbstractProcessProfilerTest; +import com.datadoghq.profiler.JfrEvent; +import com.datadoghq.profiler.JfrEvents; +import com.datadoghq.profiler.JfrFrame; +import com.datadoghq.profiler.JfrStackTrace; + +import org.junitpioneer.jupiter.RetryingTest; + +import java.nio.file.Files; +import java.nio.file.Path; +import java.nio.file.Paths; +import java.util.Collections; +import java.util.LinkedHashMap; +import java.util.Map; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertNotNull; +import static org.junit.jupiter.api.Assertions.assertTrue; + +/** + * Verifies which bottom-of-stack methods {@code Lookup::fillJavaMethodInfo} (flightRecorder.cpp) + * recognises as thread entry points: {@code void main(String[])}, {@code java.lang.Thread.run()} + * and the {@code void run()} override of any {@link Thread} subclass. + * + *

    Entry-point recognition is not exposed to Java directly. It surfaces in the recording as the + * {@code truncated} flag of {@code jdk.types.StackTrace}: {@code Recording::writeStackTraces} + * writes {@code truncated = !isEntry(bottomFrame)} whenever that bottom frame is a Java frame + * (the native-frame case falls back to the unwinder's own truncation flag instead). So a stack + * that bottoms out in a recognised entry point is reported as complete, and any other Java bottom + * frame is reported as truncated — the profiler cannot tell a stack that genuinely started there + * from one whose remaining frames were lost. + * + *

    The workload runs in a forked JVM ({@link #launch}) because {@code main(String[])} can only + * be the bottom frame of the process' primordial thread; inside the test JVM that frame belongs to + * the build tool's launcher, several dozen frames below the test method. + * + *

    The {@code cstack} mode is deliberately left at its default. Native frames are collected from + * the signal context down to the topmost Java frame only, so in every non-mixed mode the bottom + * frame of a Java thread's sample is still its Java entry point. Forcing a mode would only narrow + * the test: {@code cstack=vmx} appends the native frames below the Java stack and would + * route the bottom frame through the native branch instead, {@code cstack=vm} fails startup outside + * Linux/HotSpot, and {@code cstack=no} leaves {@code StackContext::sp} unset, which makes + * {@code HotspotSupport::getJavaTraceAsync} reject in-Java threads outright + * (AGCT_NATIVE_NO_JAVA_CONTEXT) and yields nothing but {@code no_Java_frame} samples. + */ +public class EntryFrameTest extends AbstractProcessProfilerTest { + + private static final String LAUNCHER = "com.datadoghq.profiler.ExternalLauncher"; + + /** {@code public static void main(String[] args)} of the forked JVM's main class. */ + private static final String MAIN_ROOT = LAUNCHER + ".main([Ljava/lang/String;)V"; + /** {@code new Thread(runnable)} bottoms out in {@code Thread}'s own {@code run()}. */ + private static final String THREAD_RUN_ROOT = "java.lang.Thread.run()V"; + /** A {@code run()} override two levels below {@link Thread}. */ + private static final String SUBCLASS_RUN_ROOT = LAUNCHER + "$EntryFrameThread.run()V"; + + /** Both engines are enabled, and both their event types read back, for sampling headroom. */ + private static final String PROFILER_COMMAND = "start,cpu=10ms,wall=10ms,jfr,file="; + + private static final String[] SAMPLE_EVENT_TYPES = { + "datadog.ExecutionSample", "datadog.MethodSample" + }; + + /** + * Every method the workload's padding call chain consists of. With a depth-limited recording + * these become bottom frames, and none of them is an entry point. + */ + private static final String[] NON_ENTRY_ROOTS = { + LAUNCHER + ".entryFrameWorkLevel1(J)V", + LAUNCHER + ".entryFrameWorkLevel2(J)V", + LAUNCHER + ".entryFrameBurn(J)V", + }; + + @RetryingTest(3) + void entryFramesAreNotMarkedTruncated() throws Exception { + Path recording = newRecordingPath(); + try { + runWorkload(recording, PROFILER_COMMAND + recording.toAbsolutePath()); + + Map roots = truncationCountsByRootFrame(recording); + for (String root : new String[] {MAIN_ROOT, THREAD_RUN_ROOT, SUBCLASS_RUN_ROOT}) { + long[] counts = roots.get(root); + assertNotNull(counts, root + " was never sampled as a bottom frame; bottom frames" + + " seen: " + roots.keySet()); + assertEquals(0L, counts[1], root + " is a thread entry point, but " + + counts[1] + " of its " + (counts[0] + counts[1]) + + " samples were marked truncated"); + } + } finally { + Files.deleteIfExists(recording); + } + } + + /** + * The counterpart of the assertions above: with {@code jstackdepth=2} the same workload's + * samples bottom out inside its padding call chain instead of at a thread entry point, and + * must then be marked truncated. Without this, a build in which nothing is ever recognised as + * an entry point — the {@code truncated} flag stuck at {@code false} — would still pass. + */ + @RetryingTest(3) + void nonEntryFramesAreMarkedTruncated() throws Exception { + Path recording = newRecordingPath(); + try { + runWorkload(recording, + PROFILER_COMMAND + recording.toAbsolutePath() + ",jstackdepth=2"); + + Map roots = truncationCountsByRootFrame(recording); + long notTruncated = 0; + long truncated = 0; + for (String root : NON_ENTRY_ROOTS) { + long[] counts = roots.get(root); + if (counts != null) { + notTruncated += counts[0]; + truncated += counts[1]; + } + } + assertTrue(truncated > 0, "no sample bottomed out inside the workload's call chain;" + + " bottom frames seen: " + roots.keySet()); + assertEquals(0L, notTruncated, notTruncated + " samples bottoming out inside the" + + " workload's call chain were reported as complete stacks"); + } finally { + Files.deleteIfExists(recording); + } + } + + private Path newRecordingPath() throws Exception { + Path rootDir = Paths.get("/tmp/recordings"); + Files.createDirectories(rootDir); + return Files.createTempFile(rootDir, "entry-frame-test", ".jfr"); + } + + private void runWorkload(Path recording, String commands) throws Exception { + LaunchResult result = launch("entry-frames", Collections.emptyList(), commands, + line -> LineConsumerResult.CONTINUE, line -> LineConsumerResult.CONTINUE); + assertTrue(result.inTime, "forked JVM did not exit in time"); + assertEquals(0, result.exitCode, "forked JVM exited with a non-zero code"); + assertTrue(Files.size(recording) > 0, "forked JVM wrote an empty recording"); + } + + /** + * Buckets every sample in {@code recording} by its bottom frame, counting how many of them + * were reported as complete (index 0) and how many as truncated (index 1). + * + *

    {@code Recording::writeStackTraces} emits the frames of a trace in the order the unwinder + * produced them - topmost frame first - so the entry point the {@code truncated} flag was + * derived from is the last frame of the list. + */ + private static Map truncationCountsByRootFrame(Path recording) throws Exception { + Map counts = new LinkedHashMap<>(); + for (String eventType : SAMPLE_EVENT_TYPES) { + for (JfrEvent sample : JfrEvents.load(recording, eventType)) { + JfrStackTrace stackTrace = sample.getStackTrace(); + if (stackTrace.isEmpty()) { + continue; + } + JfrFrame root = stackTrace.frames().get(stackTrace.frames().size() - 1); + String key = root.className() + "." + root.methodName() + root.methodDescriptor(); + long[] bucket = counts.get(key); + if (bucket == null) { + bucket = new long[2]; + counts.put(key, bucket); + } + bucket[stackTrace.isTruncated() ? 1 : 0]++; + } + } + return counts; + } +} From 570311d461fea74ae0b3285bbcb6be3a06357457 Mon Sep 17 00:00:00 2001 From: Zhengyu Gu Date: Tue, 18 Aug 2026 14:22:26 +0000 Subject: [PATCH 2/2] Fixes based on AI reviews --- .../datadoghq/profiler/ExternalLauncher.java | 19 +++++++++++++------ .../profiler/jfr/EntryFrameTest.java | 11 +++++++---- 2 files changed, 20 insertions(+), 10 deletions(-) diff --git a/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java b/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java index e1132027a6..2dbb429668 100644 --- a/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java +++ b/ddprof-test/src/test/java/com/datadoghq/profiler/ExternalLauncher.java @@ -26,7 +26,7 @@ *

  • profiler-sequence [';'-delimited steps] - runs a sequence of start/stop calls in this * process; each step is either the literal {@code STOP} (calls {@link JavaProfiler#stop()}) * or a comma delimited profiler command list (calls {@link JavaProfiler#execute(String)})
    • - *
  • entry-frames [comma delimited profiler command list] - starts the profiler, then burns + *
  • entry-frames <comma delimited profiler command list, required> - starts the profiler, then burns * CPU concurrently on the main thread, on a plain {@code new Thread(Runnable)} and on a * two-level {@link Thread} subclass, and stops the profiler again. The resulting recording * holds samples rooted at each of the three thread entry points; see {@code EntryFrameTest}
    • @@ -107,9 +107,11 @@ private static void entryFrameWorkLevel2(long millis) { } private static void entryFrameBurn(long millis) { - long deadline = System.currentTimeMillis() + millis; + // nanoTime() is monotonic: a wall-clock adjustment mid-burn cannot cut the workload short + // (which would starve the recording of samples) or stretch it past the launcher's timeout. + long deadline = System.nanoTime() + millis * 1_000_000L; long acc = 0; - while (System.currentTimeMillis() < deadline) { + while (System.nanoTime() - deadline < 0) { for (int i = 0; i < 100000; i++) { acc += i * 31 + (acc >>> 3); } @@ -157,10 +159,15 @@ public static void main(String[] args) throws Exception { } } } else if (args[0].equals("entry-frames")) { - JavaProfiler instance = JavaProfiler.getInstance(); - if (args.length == 2 && !args[1].isEmpty()) { - instance.execute(args[1]); + // Unlike the modes above, this one is only meaningful with a running profiler: + // silently skipping the start would leave the parent process parsing an empty + // recording and reporting a missing entry frame instead of a missing command. + if (args.length < 2 || args[1].isEmpty()) { + throw new IllegalArgumentException( + "entry-frames requires a profiler command list"); } + JavaProfiler instance = JavaProfiler.getInstance(); + instance.execute(args[1]); runEntryFrameWorkload(); // Stop explicitly rather than leaving it to JVM shutdown: the parent process // starts reading the recording as soon as this process exits. diff --git a/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java b/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java index 2dba32cd7e..76dc28e0b8 100644 --- a/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java +++ b/ddprof-test/src/test/java/com/datadoghq/profiler/jfr/EntryFrameTest.java @@ -15,7 +15,6 @@ import java.nio.file.Files; import java.nio.file.Path; -import java.nio.file.Paths; import java.util.Collections; import java.util.LinkedHashMap; import java.util.Map; @@ -130,10 +129,14 @@ void nonEntryFramesAreMarkedTruncated() throws Exception { } } + /** + * Allocates the recording in the JVM's own temp directory ({@code java.io.tmpdir}) rather than + * a hard-coded {@code /tmp/recordings}, so the test carries no assumption about a POSIX + * filesystem layout or about {@code /tmp} being writable. The {@code finally} blocks above + * delete it either way. + */ private Path newRecordingPath() throws Exception { - Path rootDir = Paths.get("/tmp/recordings"); - Files.createDirectories(rootDir); - return Files.createTempFile(rootDir, "entry-frame-test", ".jfr"); + return Files.createTempFile("entry-frame-test", ".jfr"); } private void runWorkload(Path recording, String commands) throws Exception {