JDK Mission Control: Where We Are, Where We Are Going [Code One 2019]

The following is intended to outline our general product direction. It is intended for information purposes
only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code,
or functionality, and should not be relied upon in making purchasing decisions. The development,
release, timing, and pricing of any features or functionality described for Oracle’s products may change
and remains at the sole discretion of Oracle Corporation.
Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and
prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed
discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and
Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q
under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website
at http://www.oracle.com/investor. All information in this presentation is current as of September 2019
and Oracle undertakes no duty to update any statement in light of new information or future events.
Safe Harbor

JDK Mission Control:
Where We Are, Where We Are Going
Principal Member of Technical Staff
Java Platform Group
September 16, 2019
David Buck

JVM Sustaining Engineer
OpenJDK 8 Update Project
Maintainer
JavaOne Rock Star
Co-author of Oracle WebLogic
Server 11g 構築・運用ガイド
@DavidBuckJP
https://blogs.oracle.com/buck/
Who am I? David Buck (left)

• Background / History
• Building
• Demo
• Takaways
Agenda

Introduction to JDK Mission Control and JDK Flight Recorder [DEV2316]
Marcus Hirt and Klara Ward
Monday 16:00 Moscone South Room 202
Improving Observability in Your Application with JFR and JMC [DEV3460]
Marcus Hirt and Mario Torre
Tuesday 11:30 Moscone South Room 201
Java Flight Recorder: Black Box of Java Applications[DEV3957]
Poonam Parhar
Wednesday 12:30 Moscone South Room 203
Robotics on JDK 11? With Modules? Are You… [DEV2329]
Marcus Hirt, Miro Wengner, and Robert Savage
Wednesday 16:00 Moscone South Room 313
Four Productive Ways to Use Open Source JFR and JMC Revisited [DEV3118]
Sven Reimers and Martin Klähn
Thursday 11:15 Moscone South Room 304
Enhanced Java Flight Recorder at Alibaba [DEV3667]
Sanhong Li, Fangxi Yin, and Guangyu Zhu
Performance Monitoring with Java Flight Recorder on OpenJDK [DEV2406]
Hirofumi Iwasaki and Hiroaki Nakada

Several Closely Related Technologies
(JRockit / Java / JDK) Mission Control
Flight Recording
Oracle JDK: JDK 7
OpenJDK: JDK 11
JEP 167: Event-Based JVM Tracing (JDK 7)
JEP 328: Flight Recorder (JDK 11)

Flight Recorder
Technology to generate and persist JVM event data
Low-overhead
Intended for use in production
Viable for “always on” use-case

Mission Control
Eclipse-based (RCP) GUI tool
Visualization of Flight Recording data
Automated Flight Recording analysis
JMX console for real-time monitoring (and control) of target
Plug-in framework for additional functionality
Support for integration into Eclipse IDE

Our Story Begins in Sweden
By Holger.Ellgaard - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=5623391

JRockit
Developed by Stockholm-based
Appeal Virtual Systems
JIT-only JVM (no interpreter)
Heavily focused on Intel (x86 /
AMD64 / IA64) performance

Value Add
JRockit was originally sold as a “Virtual Machine for Java”
Sun required each Java licensee to have a “value add”
“Superior performance” didn’t go over well...
JRockit’s monitoring and management tools were presented as its
value add to differentiate itself from Sun’s offerings

Alex Flury at English Wikipedia [Public domain]

By VARA - Beeld- en Geluidwiki, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=49198465

Appeal Virtual Machines
BEA Systems

A Combined Legacy
JRockit’s best features ported over to HotSpot
Diagnostic commands (JDK 7)
Compiler control (JDK 9)
Native memory tracking (JDK 7)
Flight Recorder (JDK 7)
Build system (behind the scenes) (JDK 8)
JRockit Mission Control -> Java Mission Control

JRockit Runtime Analyzer
Based on experience gained while consulting
“Cast a big net” to avoid multiple support iterations
Most data collection piggy-backed onto internal JVM operations
(low overhead)
Data persisted at zipped XML

JRockit Mission Control 4
Post Oracle acquisition (JRockit R28)
Flight Recorder replaces JRockit Runtime Analyzer
XML data -> binary data
Much lower overhead to collect and persist data

Flight Recorder in HotSpot
Flight Recorder support added in 7u40
JMC 5 bundled with JDK

JDK 7 JMC 5
JDK 8 JMC 5.5
JDK 9 JMC 6
JDK 10 JMC 6

JDK Mission Control 7
Open source
No longer bundled with JDK (as of JDK 11)
Flight Recorder implementation open sourced (as of JDK 11)

Universal Permissive License
Clear patent protection
Clear & simplified relicensing
Reduced overhead in source files
It can be used as a contributor agreement
See FAQ (link at end of slide deck) for details

Oracle Contributor Agreement
Must be signed and sent to Oracle to contribute code to Mission
Control
Same requirement as other OpenJDK projects
Only needs to be done once

“...you're doing an awesome job in building a real community and a
*very* open source project.“
- Red Hat Contributor to Marcus Hirt
jmc-dev alias, November 8, 2018

Compatibility
Flight Recording format changes between JDK versions
Mission Control has always been backwards compatible with flight
recordings from older HotSpot releases.
JDK 11 requires JMC 7
JMC 7 is currently the only version that supports all HotSpot based
flight recordings

Requirements
Mercurial (hg)
Maven
JDK 8

OpenJDK JMC repositories
jmc Mainline Development Branch
jmc-graphics images / branding resources
jmc7 JMC 7.0 branch

GitHub Mirror
Only mainline development branch
Not in full sync at the moment
Recommend using hg until project Skara migration *
* Maybe...

A Tale of Two Shells...
Shell 1
cd releng/third-party
mvn p2:site
mvn jetty:run
Shell 2
cd core
mvn install
cd ..
mvn clean package

A Tale of Two Shells...
Equinox p2: provisioning platform for OSGi artifacts and meta-data
Shell 1 sets up a p2 repository that hosts dependencies needed by
the build process run in shell 2

Cross Compilation?!
Regardless of build platform, binaries for all three target platforms
are generated
Platform-dependent bits are downloaded as dependencies

Building
Quick and easy to do
Builds virtually out of the box on most Linux distros
Build platform does not need to match target platform

Safepoints
Stop-the-World implementation
Guarantees Java state of thread is known
All threads executing Java code must stop
JNI code can continue
Cooperative suspension
Polling based
By YPLeroux at English Wikipedia, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid=17734859

Safepoint Polling
Interpreter can stop instantly
template dispatch table replaced
“polling” is essentially free
Explicit poll inserted into C1/C2 JIT output
Global safepoint polling page in address space
Poll implemented by attempted read of this address
Safepoint triggered by change in page permissions

JIT Safepoint Polling
On return from method call
Backend branches in most loops
Any transition to native code (JVM / JNI)

Collatz Conjecture
Simple rules:
If number is even, divide by 2
If number is odd, multiply by 3 and add 1
Conjecture: Start with any positive integer, and you’ll eventually
end up at 1
An open problem in math

Collatz Conjecture Examples
2 1
3 10 5 16 8 4 2 1
4 2 1
5 16 8 4 2 1
6 3 10 5 16 8 4 2 1
7 22 11 34 17 52 26 13 40 20 10 5 16 8...

Collatz Conjecture
By Kunashmilovich - Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=48786325

Let’s test the Collatz Conjecture...

Let’s test the Collatz Conjecture...
the stupidest way imaginable!

Testing the Collatz Conjecture
private static long next(long num) {
return (num%2 == 0) ? num / 2 : 3 * num + 1;
}

Testing the Collatz Conjecture
public static void main(String[] args) {
long num;
for (int i=2; i < Integer.MAX_VALUE; i++) {
num = i;
for (int j=0; j < Integer.MAX_VALUE; j++) {
num = next(num);
if (num == 1) break;
}
if (num != 1) {
System.out.println(i + " did not end at 1.");
System.exit(-1);
} else if (i % 1000000 == 0) {
System.out.println("done with " + i);
}
}
}

Counted Loop
Loop that increments / decrements an int index
Worst case scenario, we loop 4 billion times (very short)
HotSpot may not bother adding a safepoint pool to the loop

Profiler Types
Sampling Profiler
Process sampled periodically
Invocation count is not exact
Observer effect should be
negligible
Invocation Counter Profiler
Code is instrumented
Exact number of invocations
Observer effect often distorts
results

Traditional Sampler
JVMTI / Bytecode instrumentation can only stop thread at a
safepoint poll
What happens between safpoint polls is invisible to the profiler

Flight Recording
Can asynchronously stop execution thread at any time
No dependence on safe points for profiling
HotSpot internal API (AsyncGetCallTrace)
Honest Profiler
Oracle Developer Studio

Flight Recorder
Mission Control

What happened?
Safepoints have corresponding metadata
Byte Code Index (bci)
Liveness data (what stack positions point to Java heap)

What happened?
By default, metadata is normally only generated for safepoints
DebugNonSafepoints flag forces metadata generation for all code
(obvious performance cost)

Takeaways
Open sourcing of JMC has been a great success
JMC 7 and higher are the ideal MC to use regardless of JDK version
Binary builds from Oracle should be available in the near future
JMC is simple to build on your own today
Flight Recording’s AsyncGetCallTrace-based profiling can provide a
level of accuracy unachievable by most other tools.

References
Marcus Hirt’s Blog
http://hirt.se/blog/
The Universal Permissive License (UPL)
https://oss.oracle.com/licenses/upl/

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The preceding is intended to outline our general product direction. It is intended for information purposes
only, and may not be incorporated into any contract. It is not a commitment to deliver any material, code,
or functionality, and should not be relied upon in making purchasing decisions. The development,
release, timing, and pricing of any features or functionality described for Oracle’s products may change
and remains at the sole discretion of Oracle Corporation.
Statements in this presentation relating to Oracle’s future plans, expectations, beliefs, intentions and
prospects are “forward-looking statements” and are subject to material risks and uncertainties. A detailed
discussion of these factors and other risks that affect our business is contained in Oracle’s Securities and
Exchange Commission (SEC) filings, including our most recent reports on Form 10-K and Form 10-Q
under the heading “Risk Factors.” These filings are available on the SEC’s website or on Oracle’s website
at http://www.oracle.com/investor. All information in this presentation is current as of September 2019
and Oracle undertakes no duty to update any statement in light of new information or future events.
Safe Harbor

JDK Mission Control: Where We Are, Where We Are Going [Code One 2019]

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