8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates #25429

AlanBateman · 2025-05-24T06:57:56Z

Updates the thread dump generated by HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file to include thread state and lock information. Also update the HotSpotDiagnosticMXBean.dumpThreads API description to link to a description of the JSON format dump as that format is intended to be parseable/read by tools.

This PR is dependent on pull/25425. As noted in that PR, the changes accumulated in the loom repo, and have been split up to make it easier to review.

The changes include some re-implementation of ThreadDumper. This is because it used PrintStream and didn't fail if there was an I/O error, e.g. file system full. Furthermore, the indentation to pretty print the json was fragile and hard to maintain so this is changed to use a supporting writer class to do this.

Test coverage is significantly expanded, including updating the test library that is used by several tests to parse the thread dump.

Testing: tier1-6

Progress

Change must be properly reviewed (1 review required, with at least 1 Reviewer)
Change must not contain extraneous whitespace
Commit message must refer to an issue
Change requires CSR request JDK-8356872 to be approved

Integration blocker

⚠️ Dependency #25425 must be integrated first

Issues

JDK-8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates (Enhancement - P3)
JDK-8356872: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates (CSR)

Reviewing

Using git

Checkout this PR locally:
$ git fetch https://git.openjdk.org/jdk.git pull/25429/head:pull/25429
$ git checkout pull/25429

Update a local copy of the PR:
$ git checkout pull/25429
$ git pull https://git.openjdk.org/jdk.git pull/25429/head

Using Skara CLI tools

Checkout this PR locally:
$ git pr checkout 25429

View PR using the GUI difftool:
$ git pr show -t 25429

Using diff file

Download this PR as a diff file:
https://git.openjdk.org/jdk/pull/25429.diff

Using Webrev

Link to Webrev Comment

bridgekeeper · 2025-05-24T06:58:39Z

👋 Welcome back alanb! A progress list of the required criteria for merging this PR into master will be added to the body of your pull request. There are additional pull request commands available for use with this pull request.

openjdk · 2025-05-24T06:58:49Z

❗ This change is not yet ready to be integrated.
See the Progress checklist in the description for automated requirements.

openjdk · 2025-05-24T06:59:21Z

@AlanBateman The following labels will be automatically applied to this pull request:

core-libs
hotspot
jmx
serviceability

When this pull request is ready to be reviewed, an "RFR" email will be sent to the corresponding mailing lists. If you would like to change these labels, use the /label pull request command.

AlanBateman · 2025-05-24T07:00:14Z

/label remove hotspot
/label remove core-libs
/label remove jmx

openjdk · 2025-05-24T07:00:48Z

@AlanBateman
The hotspot label was successfully removed.

openjdk · 2025-05-24T07:01:13Z

@AlanBateman
The core-libs label was successfully removed.

openjdk · 2025-05-24T07:01:38Z

@AlanBateman
The jmx label was successfully removed.

mlbridge · 2025-05-24T07:40:10Z

Webrevs

01: Full - Incremental (52bb3de7)
00: Full (52bb3de7)

src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java

wenshao · 2025-05-24T09:34:15Z

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java

- * text or JSON format.
+ * This class defines static methods to support the Thread.dump_to_file diagnostic command
+ * and the HotSpotDiagnosticMXBean.dumpThreads API. It defines methods to generate a
+ * thread dump to a file or byte array in plain text or JSON format.
 */
 public class ThreadDumper {


Suggested change

public class ThreadDumper {

public final class ThreadDumper {

wenshao · 2025-05-24T09:35:42Z

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java

-                        sb.append(String.format("\\u%04x", c));
-                    } else {
-                        sb.append(c);
+    private static class JsonWriter {


Suggested change

private static class JsonWriter {

private static final class JsonWriter {

private static final class Node {

wenshao · 2025-05-24T09:37:21Z

test/jdk/com/sun/management/HotSpotDiagnosticMXBean/DumpThreadsWithEliminatedLock.java

+                StringBuffer sb = new StringBuffer();
+                sb.append(System.currentTimeMillis());
+                String s = sb.toString();
+                ref.set(s);


Suggested change

StringBuffer sb = new StringBuffer();

sb.append(System.currentTimeMillis());

String s = sb.toString();

ref.set(s);

ref.set(

new StringBuffer()

.append(System.currentTimeMillis())

.toString());

wenshao · 2025-05-24T09:41:28Z

test/lib/jdk/test/lib/threaddump/ThreadDump.java

                sb.append(",");
                sb.append(name);


Suggested change

sb.append(",");

sb.append(name);

sb.append(",")

.append(name);

src/hotspot/share/classfile/javaClasses.cpp

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java

src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java

turbanoff · 2025-05-26T16:06:01Z

src/java.base/share/classes/jdk/internal/vm/ThreadDumper.java

+        Instant now = Instant.now();
+        Thread.State state = snapshot.threadState();
+        writer.println("#" + thread.threadId() + " \"" + snapshot.threadName()
+                +  "\" " + (thread.isVirtual() ? "virtual " : "") + state + " " + now);


Suggested change

+ "\" " + (thread.isVirtual() ? "virtual " : "") + state + " " + now);

+ "\" " + (thread.isVirtual() ? "virtual " : "") + state + " " + now);

Initial commit

52bb3de

openjdk bot added the csr Pull request needs approved CSR before integration label May 24, 2025

openjdk bot added serviceability [email protected] jmx [email protected] hotspot [email protected] core-libs [email protected] labels May 24, 2025

openjdk bot removed the hotspot [email protected] label May 24, 2025

openjdk bot removed the core-libs [email protected] label May 24, 2025

openjdk bot removed the jmx [email protected] label May 24, 2025

AlanBateman marked this pull request as ready for review May 24, 2025 07:36

openjdk bot added the rfr Pull request is ready for review label May 24, 2025

wenshao reviewed May 24, 2025

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src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java Outdated Show resolved Hide resolved

wenshao reviewed May 24, 2025

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src/java.base/share/classes/jdk/internal/vm/ThreadSnapshot.java Outdated Show resolved Hide resolved

wenshao reviewed May 24, 2025

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liach reviewed May 25, 2025

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AlanBateman changed the base branch from master to pr/25425 May 25, 2025 06:16

turbanoff reviewed May 26, 2025

View reviewed changes

	public class ThreadDumper {
	public final class ThreadDumper {

	private static class JsonWriter {
	private static final class JsonWriter {
	private static final class Node {

	+ "\" " + (thread.isVirtual() ? "virtual " : "") + state + " " + now);
	+ "\" " + (thread.isVirtual() ? "virtual " : "") + state + " " + now);

8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates #25429

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8356870: HotSpotDiagnosticMXBean.dumpThreads and jcmd Thread.dump_to_file updates #25429

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AlanBateman commented May 24, 2025 •

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