Volker Simonis

CRaC (Coordinated Restore at Checkpoint) is an OpenJDK project for the coordination of Java applications at checkpoints which leverages the CRIU (Checkpoint/Restore In Userspace) library for process snapshotting. This talk will briefly introduce Firecracker, an open source virtualization technology based on KVM, explain how CRaC can be used with it and compare it with CRIU.

The second part of the talk will introduce some new tools based on Userfaultfd and DAMON which allow fine grained analysis of of the JVM's memory access patterns during restore and end with a discussion on how the JVM could be optimized to improve them.

Rumble in the Java Jungle

OracleJDK, OpenJDK, AdoptOpenJDK, OpenJ9, Zulu, IcedTea, Liberica, SapMachine, GraalVM, SubstrateVM. 8, 9, 10, 11, 12, 18.3, 18.9, short-term, mid-term, long-term support release, security updates. GPLv2, Classpath Exception, Oracle Binary Code License, Technology Network License Agreement. Field of use restriction, private and commercial use, reference implementation, substantially derived, TCK/JCK, Oracle Contribution Agreement, OpenJDK Community TCK License Agreement (OCTLA), Java Community Process (JCP), Java Specification Request (JSR), Java Enhancement Proposal (JEP), Preview Features, Incubator Modules, Java (TM), Java SE compatibility, OpenJDK trademark notice.

Confused? Come and hear from Java and OpenJDK veteran Volker Simonis how the Java world has been radically turned inside out in the last year and how this impacts you as a Java user or developer. After the talk you'll have a clear understanding what's going on in the Java ecosystem and you'll be ready to plan your or your companies future Java strategy.

Class Data Sharing (CDS) is a feature that was introduced in Java 5 to improve startup performance and reduce the memory footprint of the JVM by sharing the metadata of system classes between virtual machines running on the same host. During the last years, this feature has been constantly improved. In OpenJDK 10 CDS will be extended by AppCDS which additionally allows the sharing of application classes between VM instances (see JEP 310: Application Class-Data Sharing [1]).

In this talk I will briefly introduce CDS and AppCDS. After demonstrating its various use cases, I will do a short deep-dive into the implementation details and challenges. Finally I will briefly describe how Strings and Symbols can be stored in the CDS archive and shared across VM as well since OpenJDK 9.

After the talk, the audience should have a better understand of the CDS/AppCDS feature and be able to decide whether it makes sense to use it for their own applications.

[1] http://openjdk.java.net/jeps/310

The HotSpot JIT compilers use a lot of sophisticated optimization techniques to speed up your Java code. Sometimes, these advanced optimizations are so aggressive that they may eliminate required checks by mistake and therefore suppress expected program errors.

In this talk, I'll briefly introduce Escape Analysis and Intrinsics, two commonly used HotSpot optimization techniques. I'll show how a combination of these two features can optimize away IndexOutOfBoundsExceptions in some corner cases where they are required by the standard and how I fixed this error in recent versions of the OpenJDK.

One of the not so well-known tools of the HotSpot VM is its Whitebox-Testing API. Introduced in Java 7 it has been significantly improved and extended in Java 8 and 9. It can be used to query or change HotSpot internals which are not otherwise exposed to Java-land. While its features make it an indispensable tool for writing good HotSpot regression tests, it can also be used for experiments or for the mere fun of peeking into the VM.

This talk will give an overview of the Whitebox-Testing API, it will show you how to build and use it and finally it will explain how the API can be easily extend to fit your own needs.

Debugging Java applications is comfortable and simple, but if you want to look beyond the Java horizon, you need special knowledge and and different tools.

This interactive session shows you how to debug a running VM or analyze a VM core file with a native debugger like gdb. You will also learn how to use some of the more than 1,200 VM options to trace or modify the VM behavior. This knowledge can greatly help you identify, isolate and reproduce the root cause of hard VM crashes, and it can also be pure fun to see which actual machine instruction the CPU is executing for your Java code.

Java is often criticized for its lack of supporting C-style structs. This makes it hard to efficiently implement certain type of data structures (like for example arrays of small objects) in Java.

However, recently there have been several different approaches which try to address this problem. My talk will briefly introduce "Packed Objects", an extension available in IBM's Java SDK 8, "Object Layout", a layout-optimized Java data structure package proposed by Azul Systems and Value Types [3][4], an OpenJDK proposal for immutable, reference-free value objects.

I will describe the commonalities and differences of the three approaches and explain how they can improve the memory overhead and locality of Java objects.

The PowerPC/AIX porting project currently driven by IBM and SAP is a good example how the OpenJDK fosters the cooperation of different players in the Java ecosystem in an open environment. At last years' FOSDEM, we presented our JCK-certified JDK7 port. This year, we will showcase our JDK8 port. But more importantly, we will describe the lengthy process of integrating the port into the main OpenJDK repository, thus making it a first class citizen in the OpenJDK environment.

The PowerPC/AIX porting project currently driven by IBM and SAP is a good example how the OpenJDK fosters the cooperation of different players in the Java ecosystem in an open environment.

At last years FOSDEM, we presented our JCK-certified JDK7 port. This year, we will showcase our JDK8 port. But more importantly, we will describe the lengthy process of integrating the port into the main OpenJDK repository, thus making it a first class citizen in the OpenJDK environment. This process includes the creation of a JDK Enhancement Proposals, the agreement on a detailed Integration Plan between all parties, the thorough review of all changes by OpenJDK reviewers, the integration into the main development repositories and finally the downport into a released version.

Of course we will also highlight the general improvements in the OpenJDK code base which are the result of our port. Finally, we will be happy to answer any kind of technical questions regarding a JDK port to a new CPU and OS platform.

The PowerPC/AIX porting project currently driven by IBM and SAP is a good example how the OpenJDK fosters the cooperation of different players in the Java ecosystem in an open environment.

The project was initially started in June 2012 with the goal to provide a full-featured and certifiable version of OpenJDK on the Linux and AIX PowerPC platforms. By now the PowerPC/AIX port can successfully run a couple of different standard benchmarks in mixed mode (C++ interpreter plus C2 "server" JIT compiler) and passes the JCK test on both platforms.

This talk will describe what we've done to reach the current state and what still needs to be done until we can integrate our port into the main JDK8 code line which is the ultimate goal of the project.