OpenJ9

Last updated
Eclipse OpenJ9
Original author(s) IBM
Developer(s) Eclipse Foundation
Stable release
0.45.0 [1]   OOjs UI icon edit-ltr-progressive.svg / 21 May 2024;45 days ago (21 May 2024)
Repository
Written in C, C++, Java, assembly
Operating system Linux, AIX, Windows, macOS, z/OS, IBM i
Type Java virtual machine
License Apache License 2.0

Eclipse Public License 2.0

GNU General Public License, version 2 with the GNU Classpath Exception

Contents

GNU General Public License, version 2 with the OpenJDK Assembly Exception [2]
Website www.eclipse.org/openj9/   OOjs UI icon edit-ltr-progressive.svg

Eclipse OpenJ9 (previously known as IBM J9) is a high performance, scalable, Java virtual machine (JVM) implementation that is fully compliant with the Java Virtual Machine Specification. [3]

OpenJ9 can be built from source, or can be used with pre-built binaries available at the IBM Semeru Runtimes project for a number of platforms including Linux, Windows [4] and macOS. OpenJ9 is also a core component of the IBM developer kit, which is embedded in many IBM middleware products, including WebSphere Application Server and Websphere Liberty. OpenJ9 is also a component of Open Liberty. [5]

Extensive configuration options ensure that the JVM can be tuned to satisfy the requirements of a wide range of Java applications, from complex enterprise applications that run on mainframe hardware to short-lived applications that run on container-based cloud services.

History

OpenJ9 can trace its roots back to the ENVY/Smalltalk product developed by Object Technology International (OTI). IBM purchased OTI in 1996 for their Smalltalk expertise and products. However, when the Java language emerged as a leading language for the enterprise market, the existing Smalltalk VM was adapted to process Java bytecodes instead. The name J9 evolved from the naming convention for the Smalltalk source code, K8. K→J (a backward step) because the developers believed that Smalltalk was better than Java, but 8→9 (a forward step) because the new VM would be better than before. [6]

The J9 JVM became the runtime engine for many of IBM's enterprise middleware products, where it has built its reputation for high performance, scalability, and reliability.

In 2017, J9 became an Eclipse Foundation project under the name Eclipse OpenJ9. IBM continue to be actively involved in the project and continue to put this Java VM at the core of many software offerings. At the Eclipse Foundation, OpenJ9 is classified as an incubator project, with the first release, v0.8.0, delivered in 2018.

Features

The Eclipse OpenJ9 JVM is fully compliant with the Java JVM specification. The same version of the JVM can be used in OpenJDK 8 and later releases, which means that many features and improvements can be exploited by applications that run on different versions of Java. Compared to Oracle's HotSpot VM, OpenJ9 touts higher start-up performance and lower memory consumption at a similar overall throughput. [7]

Eclipse OpenJ9 embeds Eclipse OMR , which provides core runtime components that can be used to build runtime environments for different programming languages. At the OpenJ9 project, an extra layer of code adds the language semantics to provide a runtime environment for Java applications. [8]

The components that make up Eclipse OpenJ9 are described in the following sections:

JIT compiler

The Just-In-Time (JIT) improves the performance of Java applications by compiling platform-neutral Java bytecode into native machine code at run time. Not every method that gets called by an application is compiled. Instead, OpenJ9 records the number of times a method is called and triggers JIT compilation at a predefined threshold. The JIT compiler compiles methods at different optimization levels: cold, warm, hot, very hot (with profiling), or scorching. The hotter the optimization level, the better the expected performance, but the higher the cost in terms of CPU and memory. The higher optimization levels use special techniques such as escape analysis and partial redundancy elimination, or loop through certain optimization sequences more times. Although these techniques use more CPU and memory, the improved performance that is delivered by the optimizations can make the trade-off worthwhile.

AOT compiler

Ahead of Time (AOT) compilation is a mechanism for improving start up performance. Methods are dynamically compiled into AOT code at runtime, which enables the JVM to start an application faster. AOT is enabled automatically when class data sharing is used (-Xshareclasses) and doesn't require any special tuning. OpenJ9 automatically chooses which methods to compile based on heuristics that identify the start-up phase of large applications. For small or short running applications, the -Xtune:virtualized option should be added to get the most out of AOT-compiled code.

Class data sharing

Sharing class data between JVMs has two main benefits:

  1. Start up performance is improved by placing classes that an application needs when initializing into a shared classes cache.
  2. Memory footprint is reduced by sharing common classes between applications that run in separate Java VMs.

Unlike other class data sharing (CDS) implementations, enabling the feature in OpenJ9 requires only one step: setting -Xshareclasses on the command line when you start your application. When specified, OpenJ9 creates a memory mapped file to store and share the classes in memory. By default, OpenJ9 always shares both the bootstrap and application classes that are loaded by the default system class loader. Another benefit of the OpenJ9 CDS implementation is that the cache is updated dynamically. So when an application loads new classes, the JVM automatically stores them in the cache without any user intervention. [9]

OpenJ9 also provides a public Helper API for integrating class sharing support into custom class loaders, plus several utilities for managing active caches.

Garbage collector

To prevent applications running out of memory, objects in the Java heap that are no longer required must be reclaimed. This process is known as garbage collection (GC). OpenJ9 provides a number of garbage collection policies that are designed around different types of applications and workloads. Choosing the right policy depends on usage and performance goals. By default, OpenJ9 uses the Generational Concurrent (-Xgcpolicy:gencon) policy, which is best suited to transactional applications that have many short lived objects. Alternative policies are available, including those that cater for applications with large Java heaps (-Xgcpolicy:balanced), applications that are sensitive to response-time (-Xgcpolicy:metronome), or applications that require high application throughput (-Xgcpolicy:optthruput).

An "idle tuning" option (-XX:+IdleTuningGcOnIdle) triggers garbage collection in OpenJ9 when the application is idle. Doing this reduces memory footprint, meaningful for some virtual hosting billing plans. [7]

JIT server

In January 2020, OpenJ9 delivered an experimental feature to JIT compile code outside JVM and remotely on a server.

Diagnostic component

OpenJ9 contains extensive trace and debugging utilities to help identify, isolate and solve runtime problems. Different types of diagnostic data are automatically produced by default when certain events occur, but can also be triggered from the command line. Types of data include:

Java dumps
These are produced when the JVM ends unexpectedly because of an operating system signal, OutOfMemoryError exception, or a user initiated keystroke combination. Java dumps summarize the state of the JVM when the event occurs, with most of the information relating to components of the JVM.
Heap dumps
Heap dumps show all the live objects on the Java heap when the JVM ends because of an OutOfMemoryError exception or when requested by a user. The information includes object address, type or class name, size, and references to other objects. Analyzing heap dumps might tell you which objects are using large amounts of memory on the Java heap and why these are not being garbage collected.
System dumps
Often known as core dumps, these are platform-specific and contain a raw binary dump of the process memory. This dump has a complete copy of the Java heap, including the contents of all Java objects in the application. OpenJ9 tools are available to process the system dump into a readable format for analysis.
Garbage collection data
To analyze garbage collection problems you can enable verbose logging, which provides data on all garbage collection operations including initialization, stop-the-world processing, finalization, reference processing, and allocation failures. For even more detailed analysis, you can turn on garbage collection tracing.
Trace data
The OpenJ9 trace facility can be used to trace applications, Java methods, or internal JVM operations with minimal impact on performance.
JIT data
If a general protection fault or abort event takes place, the JIT produces a small binary dump that can be analyzed by OpenJ9 developers to help determine the root cause.
Shared classes data
The shared classes data component provides some verbose options that can be used at runtime to show cache activity. The printStats and printAllStats utilities allow you to analyze the contents of a shared class cache.

The diagnostic component also includes the DTFJ application programming interface, which can be used to build diagnostic tools. DTFJ works with data from a system dump or a Java dump.

Adoption

See also

Related Research Articles

<span class="mw-page-title-main">Java (programming language)</span> Object-oriented programming language

Java is a high-level, class-based, object-oriented programming language that is designed to have as few implementation dependencies as possible. It is a general-purpose programming language intended to let programmers write once, run anywhere (WORA), meaning that compiled Java code can run on all platforms that support Java without the need to recompile. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of the underlying computer architecture. Although its syntax is similar to that of C and C++, the Java language has fewer low-level facilities than either of them. The Java runtime provides dynamic capabilities that are typically not available in traditional compiled languages.

<span class="mw-page-title-main">Java virtual machine</span> Virtual machine that runs Java programs

A Java virtual machine (JVM) is a virtual machine that enables a computer to run Java programs as well as programs written in other languages that are also compiled to Java bytecode. The JVM is detailed by a specification that formally describes what is required in a JVM implementation. Having a specification ensures interoperability of Java programs across different implementations so that program authors using the Java Development Kit (JDK) need not worry about idiosyncrasies of the underlying hardware platform.

Java and C++ are two prominent object-oriented programming languages. By many language popularity metrics, the two languages have dominated object-oriented and high-performance software development for much of the 21st century, and are often directly compared and contrasted. Java's syntax was based on C/C++.

In computing, just-in-time (JIT) compilation is compilation during execution of a program rather than before execution. This may consist of source code translation but is more commonly bytecode translation to machine code, which is then executed directly. A system implementing a JIT compiler typically continuously analyses the code being executed and identifies parts of the code where the speedup gained from compilation or recompilation would outweigh the overhead of compiling that code.

HotSpot, released as Java HotSpot Performance Engine, is a Java virtual machine for desktop and server computers, developed by Sun Microsystems which was purchased by and became a division of Oracle Corporation in 2010. Its features improved performance via methods such as just-in-time compilation and adaptive optimization. It is the de facto Java Virtual Machine, serving as the reference implementation of the Java programming language.

Jikes Research Virtual Machine is a mature virtual machine that runs programs written for the Java platform. Unlike most other Java virtual machines (JVMs), it is written in the programming language Java, in a style of implementation termed meta-circular. It is free and open source software released under an Eclipse Public License.

Application virtualization software refers to both application virtual machines and software responsible for implementing them. Application virtual machines are typically used to allow application bytecode to run portably on many different computer architectures and operating systems. The application is usually run on the computer using an interpreter or just-in-time compilation (JIT). There are often several implementations of a given virtual machine, each covering a different set of functions.

<span class="mw-page-title-main">Java (software platform)</span> Set of computer software and specifications

Java is a set of computer software and specifications that provides a software platform for developing application software and deploying it in a cross-platform computing environment. Java is used in a wide variety of computing platforms from embedded devices and mobile phones to enterprise servers and supercomputers. Java applets, which are less common than standalone Java applications, were commonly run in secure, sandboxed environments to provide many features of native applications through being embedded in HTML pages.

OpenJDK is a free and open-source implementation of the Java Platform, Standard Edition. It is the result of an effort Sun Microsystems began in 2006. The implementation is licensed under the GPL-2.0-only with a linking exception. Were it not for the GPL linking exception, components that linked to the Java Class Library would be subject to the terms of the GPL license. OpenJDK is the official reference implementation of Java SE since version 7.

In software development, the programming language Java was historically considered slower than the fastest third-generation typed languages such as C and C++. In contrast to those languages, Java compiles by default to a Java Virtual Machine (JVM) with operations distinct from those of the actual computer hardware. Early JVM implementations were interpreters; they simulated the virtual operations one-by-one rather than translating them into machine code for direct hardware execution.

<span class="mw-page-title-main">Azul Systems</span> Computer manufacturer of appliances for executing Java-based applications

Azul Systems, Inc. develops runtimes for executing Java-based applications. Azul Systems, founded in March 2002, Azul Systems has headquarters in Sunnyvale, California.

<span class="mw-page-title-main">Da Vinci Machine</span> Sun Microsystems project

The Da Vinci Machine, also called the Multi Language Virtual Machine, was a Sun Microsystems project aiming to prototype the extension of the Java Virtual Machine (JVM) to add support for dynamic languages.

VisualVM is a tool that provides a visual interface for viewing detailed information about Java applications while they are running on a Java Virtual Machine (JVM). VisualVM organizes JVM data that is retrieved by the Java Development Kit (JDK) tools and presents the information in a way that allows data on multiple Java applications to be quickly viewed—both local applications and applications that are running on remote hosts. Programmers can also capture data about the JVM software and save the data to the local system, and then view the data later or share it with others. VisualVM is built on the NetBeans Platform; its architecture is modular and easy to extend with plugins.

The Java Development Kit (JDK) is a distribution of Java technology by Oracle Corporation. It implements the Java Language Specification (JLS) and the Java Virtual Machine Specification (JVMS) and provides the Standard Edition (SE) of the Java Application Programming Interface (API). It is derivative of the community driven OpenJDK which Oracle stewards. It provides software for working with Java applications. Examples of included software are the Java virtual machine, a compiler, performance monitoring tools, a debugger, and other utilities that Oracle considers useful for Java programmers.

Excelsior JET is a now-defunct proprietary Java SE technology implementation built around an ahead-of-time (AOT) Java to native code compiler. The compiler transforms the portable Java bytecode into optimized executables for the desired hardware and operating system (OS). Also included are a Java runtime featuring a just-in-time (JIT) compiler for handling classes that were not precompiled for whatever reason, the complete Java SE API implementation licensed from Oracle, and a toolkit to aid deployment of the optimized applications. Excelsior JET was developed by Excelsior LLC, headquartered in Novosibirsk, Russia.

<span class="mw-page-title-main">GraalVM</span> Virtual machine software

GraalVM is a Java Development Kit (JDK) written in Java. The open-source distribution of GraalVM is based on OpenJDK, and the enterprise distribution is based on Oracle JDK. As well as just-in-time (JIT) compilation, GraalVM can compile a Java application ahead of time. This allows for faster initialization, greater runtime performance, and decreased resource consumption, but the resulting executable can only run on the platform it was compiled for.

Android Runtime (ART) is an application runtime environment used by the Android operating system. Replacing Dalvik, the process virtual machine originally used by Android, ART performs the translation of the application's bytecode into native instructions that are later executed by the device's runtime environment.

Quarkus is a Java framework tailored for deployment on Kubernetes. Key technology components surrounding it are OpenJDK HotSpot and GraalVM. The goal of Quarkus is to make Java a leading platform in Kubernetes and serverless environments while offering developers a unified reactive and imperative programming model to optimally address a wider range of distributed application architectures.

References

  1. ↑ "Eclipse OpenJ9 v0.45.0". 21 May 2024. Retrieved 22 May 2024.
  2. ↑ "openj9/LICENSE at openj9-0.24.0 · eclipse/openj9". GitHub . Retrieved 6 March 2021.
  3. ↑ Leonardo Zanivan (7 February 2018). "New Open Source JVM optimized for Cloud and Microservices". medium.
  4. ↑ Holger Voormann (14 March 2018). "Hello OpenJ9 on Windows, I Didn't Expect You So Soon!". DZone.
  5. ↑ David Rubinstein (20 September 2017). "IBM releases WebSphere Liberty code to open source". SD Times.
  6. ↑ Ronald Servant (18 September 2017). "How did the J9 in OpenJ9 get its name". medium.
  7. 1 2 Dan Heidinga (6 June 2018). "Eclipse OpenJ9; not just any Java Virtual Machine". JAXenter.
  8. ↑ Monica Beckwith (1 March 2018). "Eclipse OpenJ9 - an Open Source Java Virtual Machine Based on the Eclipse OMR Project". InfoQ.
  9. ↑ Corrie, Ben; Shao, Hang (6 June 2018). "Class sharing in Eclipse OpenJ9". IBM developerWorks.
  10. ↑ IBM (18 August 2023). "Introducing the no-cost IBM Semeru Runtimes to develop and run Java applications". IBM Developer.
  11. ↑ Parameswaran Selvam (9 March 2018). "Apache OpenWhisk Java actions on Eclipse OpenJ9 Runtime". medium.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.