Modules appear in Java 9 at last, but why? After all, OSGi has been around for more than 15 years and serves as the foundation of many desktop, server, and IoT applications. Its authors state that OSGi solves various dependency management problems in the most powerful way - at run time.
In this session, we will explore the problems that OSGi tries to solve, understand its approach, and identify its failures. Then we will figure out which of those problems the authors of Jigsaw ignored (and why), and which ones they solved (and how). Finally, we will talk about the challenges that Jigsaw brings with itself to the Java ecosystem and what we the developers have to do about them.
https://2017.javazone.no/program/83eb9ed50ba74946ad418a3abea0467a
JIT Versus AOT: Unity And Conflict of Dynamic and Static Compilers (JavaOne 2...Nikita Lipsky
Java has been constantly criticized for poor performance ever since its inception, but not as much in recent years. Thanks to optimizing dynamic native code compilers, Java performance today is very close to the performance of low-level languages such as C/C++. Along with dynamic compilers, static compilers for Java have been evolving as well, so there is still no clear winner between these two approaches. It is not a surprise that an AOT compiler is finally going to appear in Java 9 via JEP-295. This session’s speaker would like to dispel common myths about the old dispute over whether dynamic or static compilation is better, show that both approaches have their strengths and weaknesses, and explain why the future is the hybrid approach.
Ahead-Of-Time Compilation of Java ApplicationsNikita Lipsky
Geekout 2016 presentation.
Ahead-of-time (AOT) native compilation has been available for .NET for quite some time, whereas Java SE, while being older than .NET, still does not have a standard AOT compiler. Some people ask why, some people think that it could only work for certain limited types of Java applications, some people think that it is not needed.
The truth, however, is that a Java AOT compiler has been available for over a decade, as part of a compliant Java SE implementation called Excelsior JET, and it proved to be useful for many organizations around the world. In this session, I would like to dispel the common myths about Java AOT compilation and show where it has advantages over JIT compilation from the technical point of view.
An introduction to the Java Platform Module System (JPMS). This talk is from April 2017, before the Java SE 9 release, so the final details may be subtly different, particularly once a standard becomes established for module names.
Just a brief introduction I have given my team to get into the OSGi topic. Guess it is not the highest academic level, but should be enough to understand the fundamentals of OSGi.
In this core java training session, you will learn get introduction to Java. Topics covered in this session are:
• History of Java – A Programmer’s Perspective
• Salient Features of Java
• Major Java Editions
For more information about this course visit on this link: https://www.mindsmapped.com/courses/software-development/learn-java-fundamentals-hands-on-training-on-core-java-concepts/
JIT Versus AOT: Unity And Conflict of Dynamic and Static Compilers (JavaOne 2...Nikita Lipsky
Java has been constantly criticized for poor performance ever since its inception, but not as much in recent years. Thanks to optimizing dynamic native code compilers, Java performance today is very close to the performance of low-level languages such as C/C++. Along with dynamic compilers, static compilers for Java have been evolving as well, so there is still no clear winner between these two approaches. It is not a surprise that an AOT compiler is finally going to appear in Java 9 via JEP-295. This session’s speaker would like to dispel common myths about the old dispute over whether dynamic or static compilation is better, show that both approaches have their strengths and weaknesses, and explain why the future is the hybrid approach.
Ahead-Of-Time Compilation of Java ApplicationsNikita Lipsky
Geekout 2016 presentation.
Ahead-of-time (AOT) native compilation has been available for .NET for quite some time, whereas Java SE, while being older than .NET, still does not have a standard AOT compiler. Some people ask why, some people think that it could only work for certain limited types of Java applications, some people think that it is not needed.
The truth, however, is that a Java AOT compiler has been available for over a decade, as part of a compliant Java SE implementation called Excelsior JET, and it proved to be useful for many organizations around the world. In this session, I would like to dispel the common myths about Java AOT compilation and show where it has advantages over JIT compilation from the technical point of view.
An introduction to the Java Platform Module System (JPMS). This talk is from April 2017, before the Java SE 9 release, so the final details may be subtly different, particularly once a standard becomes established for module names.
Just a brief introduction I have given my team to get into the OSGi topic. Guess it is not the highest academic level, but should be enough to understand the fundamentals of OSGi.
In this core java training session, you will learn get introduction to Java. Topics covered in this session are:
• History of Java – A Programmer’s Perspective
• Salient Features of Java
• Major Java Editions
For more information about this course visit on this link: https://www.mindsmapped.com/courses/software-development/learn-java-fundamentals-hands-on-training-on-core-java-concepts/
Bytecode manipulation with Javassist for fun and profitJérôme Kehrli
Java bytecode is the form of instructions that the JVM executes.
A Java programmer, normally, does not need to be aware of how Java bytecode works.
Understanding the bytecode, however, is essential to the areas of tooling and program analysis, where the applications can modify the bytecode to adjust the behavior according to the application's domain. Profilers, mocking tools, AOP, ORM frameworks, IoC Containers, boilerplate code generators, etc. require to understand Java bytecode thoroughly and come up with means of manipulating it at runtime.
Each and every of these advanced features of what is nowadays standard approaches when programming with Java require a sound understanding of the Java bytecode, not to mention completely new languages running on the JVM such as Scala or Clojure.
Bytecode manipulation is not easy though ... except with Javassist.
Of all the libraries and tools providing advanced bytecode manipulation features, Javassist is the easiest to use and the quickest to master. It takes a few minutes to every initiated Java developer to understand and be able to use Javassist efficiently. And mastering bytecode manipulation, opens a whole new world of approaches and possibilities.
Once upon a time in the C++ century, the Great King of Sun said people need Duke, The PDA (a medieval version of a tablet). He picked his bravest knights – Naughton, Sheriden and Gosling – and entrusted them a secret mission to travel the universe in search for a perfect language that Duke can use.
After three years of a dangerous journey in a world of bits, bytes and memory leakages, on an Asian isle they found it. Java made of Oak has been discovered.
When they returned the King was not in power anymore. New world was ruled by a mysterious organisation, World Wide Web. Our brave knights honoured it with the glorious Java. And the world became perfect…
Mani and Rafal will take your through an exciting story of great programmers, multi-billion company wars, and - most importantly – language features. The history of Java, from its inception till just about today.
How to implement a simple dalvik virtual machineChun-Yu Wang
This slide is an introduction to Android Dalvik Virtual Machine on a short course.
We use two hand-made JVM and DVM which called Simple JVM and Simple DVM respectively, to tell student how they work. A Foo Class was provided as a target for verifying the execution results of those VM. We hope it will help student to understand JVM and DVM quickly.
Writing concurrent code that is also correct is unbelievably hard. Naturally, humanity has developed a number of approaches to handle concurrency in the code, starting from basic threads that follow the hardware way to do concurrency to higher level primitives like fibers and work-stealing solutions. But which approach is the best for you? In this session, we'll take a look at a simple concurrent problem and solve it using different ways to manage concurrency: threads, executors, actors, fibers, monadic code with completable futures. All these approaches are different from the simplicity, readability, configuration and management point of view. Some scenarios are better modelled with threads, while sometimes you're better off with actors. We'll discuss the benefits of each approach and figure out when it's worth pursuing in your project.
A quick introduction about everything that's new in Java 11. Includes API changes, language changes and new tools in the JDK.
Demo's for this presentation can be found here: https://github.com/MichelSchudel/java11demo
OSGi has gained popularity over the last two years. The platform has some very interesting features like versioning, dynamic updates and it's service oriented nature. These characteristics however come with a price. A firm understanding of how and why OSGi works how it works, is a necessity if you plan on getting into OSGi.
This talk will start with some basic principals on the java platform and will gradually move towards the OSGi infrastructure explaining the OSGi fundamentals. The following topics will be covered:
* Classloading in OSGi
* Lifecycle management of OSGi bundles
* OSGi Service, the service registry and service composition models
Afterwards, we will explain the generally accepted best practices and OSGi design patterns.
Escaping The Jar hell with Jigsaw LayersNikita Lipsky
Jigsaw modules are often criticized for the lack of versioning that exists in alternative module systems for Java, such as OSGi. One of the main purposes of versioning is to solve the so called Jar Hell problem that arises when your application depends on two different versions of the same library. While Jigsaw is able to detect this conflicting situation, it won’t allow you to load both versions that are placed on the module path. However, it is not always possible to eliminate all version conflicts from your application, because other versions of the same libraries can come to your application indirectly via dependencies that you do not control. Fortunately, there is a native solution for the problem in Jigsaw called Layers. In this session, I will show what problems Jigsaw could have introduced if it had explicit versions for modules, and how Jigsaw Layers in conjunction with Jigsaw Services help to solve the Jar Hell problem safely.
What is Java Technology (An introduction with comparision of .net coding)Shaharyar khan
A introductory slides for those who want to learn and know some basics of Java.Also for those persons who want to compare coding difference between Java and .net
Lecture 6 from the IAG0040 Java course in TTÜ.
See the accompanying source code written during the lectures: https://github.com/angryziber/java-course
Gives an overview how a software developer should organize their daily work, apart from technical skills.
Introduces Agile software development practices from XP and Scrum.
My goals have been:
- focusing on several project areas, where you can use jruby successfully
- share the experience that I made using ruby in the last years
- proove that things can be done easier as they are done in typical java projects
In this Java tutorial, we are going to learn about java evolution, development of Java language, java features, Java frameworks, and Java support systems. Java tutorial covers various development tools, classes in Java programming, and Java methods which comprises the Java environment. This tutorial on java will help you get a quick insight into the Java programming language and thus, help you learn java language.
Aim of this presentation is not to make you masters in Java 8 Concurrency, but to help you guide towards that goal. Sometimes it helps just to know that there is some API that might be suitable for a particular situation. Make use of the pointers given to search more and learn more on those topics. Refer to books, Java API Documentation, Blogs etc. to learn more. Examples and demos for all cases discussed will be added to my blog www.javajee.com.
Java9 Beyond Modularity - Java 9 más allá de la modularidadDavid Gómez García
These are the slides I used for my "Java 9 beyond modularity" at several different local meetups and conferences in Spain during 2017
Java 9 is about to reach its public release scheduled for September 2017. If we ask what are the new features that this new version will include, probably the first that comes to our head is modularity.
But java 9 brings with a lot of features beyound Jigsaw, JPMS or modularity. In this talk we will talk about at least 9 other new features that include this new version of Java that are interesting and maybe will end up being more used than the modularity itself for those who embrace the new version.
Those are changes that come to complement and improve even more the set of new tools (like Streams, Optionals, etc...) that Java 8 brought to us.
We'll take a look at small changes in language syntax (such as new ways of using try-with-resources), changes in Collections APIs and Streams, new tools like VarHandles, new APIs such as the Flow API, and As we allow the inclusion of reactive programming with Java.
Do you want to see in Java 9 beyond modularity? Do you want to have a more complete view of what you can provide? Let's take a look toghether!
Bytecode manipulation with Javassist for fun and profitJérôme Kehrli
Java bytecode is the form of instructions that the JVM executes.
A Java programmer, normally, does not need to be aware of how Java bytecode works.
Understanding the bytecode, however, is essential to the areas of tooling and program analysis, where the applications can modify the bytecode to adjust the behavior according to the application's domain. Profilers, mocking tools, AOP, ORM frameworks, IoC Containers, boilerplate code generators, etc. require to understand Java bytecode thoroughly and come up with means of manipulating it at runtime.
Each and every of these advanced features of what is nowadays standard approaches when programming with Java require a sound understanding of the Java bytecode, not to mention completely new languages running on the JVM such as Scala or Clojure.
Bytecode manipulation is not easy though ... except with Javassist.
Of all the libraries and tools providing advanced bytecode manipulation features, Javassist is the easiest to use and the quickest to master. It takes a few minutes to every initiated Java developer to understand and be able to use Javassist efficiently. And mastering bytecode manipulation, opens a whole new world of approaches and possibilities.
Once upon a time in the C++ century, the Great King of Sun said people need Duke, The PDA (a medieval version of a tablet). He picked his bravest knights – Naughton, Sheriden and Gosling – and entrusted them a secret mission to travel the universe in search for a perfect language that Duke can use.
After three years of a dangerous journey in a world of bits, bytes and memory leakages, on an Asian isle they found it. Java made of Oak has been discovered.
When they returned the King was not in power anymore. New world was ruled by a mysterious organisation, World Wide Web. Our brave knights honoured it with the glorious Java. And the world became perfect…
Mani and Rafal will take your through an exciting story of great programmers, multi-billion company wars, and - most importantly – language features. The history of Java, from its inception till just about today.
How to implement a simple dalvik virtual machineChun-Yu Wang
This slide is an introduction to Android Dalvik Virtual Machine on a short course.
We use two hand-made JVM and DVM which called Simple JVM and Simple DVM respectively, to tell student how they work. A Foo Class was provided as a target for verifying the execution results of those VM. We hope it will help student to understand JVM and DVM quickly.
Writing concurrent code that is also correct is unbelievably hard. Naturally, humanity has developed a number of approaches to handle concurrency in the code, starting from basic threads that follow the hardware way to do concurrency to higher level primitives like fibers and work-stealing solutions. But which approach is the best for you? In this session, we'll take a look at a simple concurrent problem and solve it using different ways to manage concurrency: threads, executors, actors, fibers, monadic code with completable futures. All these approaches are different from the simplicity, readability, configuration and management point of view. Some scenarios are better modelled with threads, while sometimes you're better off with actors. We'll discuss the benefits of each approach and figure out when it's worth pursuing in your project.
A quick introduction about everything that's new in Java 11. Includes API changes, language changes and new tools in the JDK.
Demo's for this presentation can be found here: https://github.com/MichelSchudel/java11demo
OSGi has gained popularity over the last two years. The platform has some very interesting features like versioning, dynamic updates and it's service oriented nature. These characteristics however come with a price. A firm understanding of how and why OSGi works how it works, is a necessity if you plan on getting into OSGi.
This talk will start with some basic principals on the java platform and will gradually move towards the OSGi infrastructure explaining the OSGi fundamentals. The following topics will be covered:
* Classloading in OSGi
* Lifecycle management of OSGi bundles
* OSGi Service, the service registry and service composition models
Afterwards, we will explain the generally accepted best practices and OSGi design patterns.
Escaping The Jar hell with Jigsaw LayersNikita Lipsky
Jigsaw modules are often criticized for the lack of versioning that exists in alternative module systems for Java, such as OSGi. One of the main purposes of versioning is to solve the so called Jar Hell problem that arises when your application depends on two different versions of the same library. While Jigsaw is able to detect this conflicting situation, it won’t allow you to load both versions that are placed on the module path. However, it is not always possible to eliminate all version conflicts from your application, because other versions of the same libraries can come to your application indirectly via dependencies that you do not control. Fortunately, there is a native solution for the problem in Jigsaw called Layers. In this session, I will show what problems Jigsaw could have introduced if it had explicit versions for modules, and how Jigsaw Layers in conjunction with Jigsaw Services help to solve the Jar Hell problem safely.
What is Java Technology (An introduction with comparision of .net coding)Shaharyar khan
A introductory slides for those who want to learn and know some basics of Java.Also for those persons who want to compare coding difference between Java and .net
Lecture 6 from the IAG0040 Java course in TTÜ.
See the accompanying source code written during the lectures: https://github.com/angryziber/java-course
Gives an overview how a software developer should organize their daily work, apart from technical skills.
Introduces Agile software development practices from XP and Scrum.
My goals have been:
- focusing on several project areas, where you can use jruby successfully
- share the experience that I made using ruby in the last years
- proove that things can be done easier as they are done in typical java projects
In this Java tutorial, we are going to learn about java evolution, development of Java language, java features, Java frameworks, and Java support systems. Java tutorial covers various development tools, classes in Java programming, and Java methods which comprises the Java environment. This tutorial on java will help you get a quick insight into the Java programming language and thus, help you learn java language.
Aim of this presentation is not to make you masters in Java 8 Concurrency, but to help you guide towards that goal. Sometimes it helps just to know that there is some API that might be suitable for a particular situation. Make use of the pointers given to search more and learn more on those topics. Refer to books, Java API Documentation, Blogs etc. to learn more. Examples and demos for all cases discussed will be added to my blog www.javajee.com.
Java9 Beyond Modularity - Java 9 más allá de la modularidadDavid Gómez García
These are the slides I used for my "Java 9 beyond modularity" at several different local meetups and conferences in Spain during 2017
Java 9 is about to reach its public release scheduled for September 2017. If we ask what are the new features that this new version will include, probably the first that comes to our head is modularity.
But java 9 brings with a lot of features beyound Jigsaw, JPMS or modularity. In this talk we will talk about at least 9 other new features that include this new version of Java that are interesting and maybe will end up being more used than the modularity itself for those who embrace the new version.
Those are changes that come to complement and improve even more the set of new tools (like Streams, Optionals, etc...) that Java 8 brought to us.
We'll take a look at small changes in language syntax (such as new ways of using try-with-resources), changes in Collections APIs and Streams, new tools like VarHandles, new APIs such as the Flow API, and As we allow the inclusion of reactive programming with Java.
Do you want to see in Java 9 beyond modularity? Do you want to have a more complete view of what you can provide? Let's take a look toghether!
Java 8 Stream API. A different way to process collections.David Gómez García
A look on one of the features of Java 8 hidden behind the lambdas. A different way to iterate Collections. You'll never see the Collecions the same way.
These are the slides I used on my talk at the "Tech Thursday" by Oracle in June in Madrid.
This is a beginner's guide to Java 8 Lambdas, accompnied with executable code examples which you can find at https://github.com/manvendrasinghkadam/java8streams. Java 8 Streams are based on Lambdas, so this presentation assumes you know Lambdas quite well. If don't then please let me know I'll create another presentation regarding it with code examples. Lambdas are relatively easy to use and with the power of stream api you can do functional programming in Java right from start. This is very cool to be a Java programmer now.
The slides from the talk I gave at Oracle III #JuevesTecnológicos in Madrid.
A review of how the ParallelStreams Work in Java 8 and some considerations we must know in order to get the better performance from the concurrent data processing in #Java8
Presentation was created after OSGi conference in Ludwigsburg : http://www.osgi.org/CommunityEvent2012/HomePage
Source code is available : https://stash-test.hybris.com/projects/PLAY/repos/osgi-presentation/browse
OSGi is on the core+ roadmap. This presentation introduces architecture, tools and design patterns used by OSGi.
It also shows the way how to refactor application to be really modular. Region cache will be example.
Modularity of the Java Platform (OSGi, Jigsaw and Penrose)Martin Toshev
Seminar "Modularity of the Java Platform" of the Bulgarian Java User Group.
Topics of the seminar:
Modularity 101
Modularity on top of the platform: OSGi
Modularity of the platform: Jigsaw
OSGi and Jigsaw interoperability: Penrose
OSGi & Java EE: A hybrid approach to Enterprise Java Application Development,...OpenBlend society
There's a considerable activity in the enterprise Java community about the use of OSGi in Java EE applications. We call such applications "hybrid applications." With hybrid applications, developers can continue to build standard and familiar enterprise application components, such as Java Servlets and EJBs, and take full advantage of:
* Features such as modularity/dependency management, service dynamism, and more provided by OSGi
* Infrastructure services such as transaction management, security, persistence, and more offered by Java EE
This session will present the current state of affairs, discuss the benefits of hybrid applications, and demonstrate development and deployment of such applications.
GlassFish will be used for demonstration.
Java 9 brings modules as a core concept to the platform, but it’s more than just a language feature. With modules in Java 9, we can improve the design of code to increase maintainability and extensibility. As with every design principle, modularity requires thought and trade-offs to really reap the benefits. This session covers design practices for making codebases more maintainable and extensible. You will also find out about trade-offs to help you make the best choices. Topics include hiding implementations, using services for extensibility, API modules, avoiding cycles, optional dependencies, and dynamically loading modules. Familiarity with modules is helpful but not required. The speakers are the authors of Java 9 Modularity (O’Reilly).
Also see https://javamodularity.com
The presentation slides used during WSO2Con 2011 tutorial session. The tutorial included hands on sessions as well. The slides named as 'demo' refers to hadns-on sessions/demos.
The Java platform is an unqualified success story. It’s used to develop applications
for everything from small mobile devices to massive enterprise endeavours.
But this success has come in spite of the fact that Java doesn’t have explicit support for building
modular systems beyond ordinary object-oriented data encapsulation
What does this mean to you? If Java is a success despite its lack of advanced modularization support, then you may wonder if that absence is a problem
Java Core | Java 8 and OSGi Modularisation | Tim Ellison & Neil BartlettJAX London
The talk will cover a bit of background first to set things up: what is a module, why do we need a module system, summary of Java's existing support for modularity. Then it will move on to give a comparison of OSGi's and Jigsaw's dependency models. Pros and cons of each model in different environments will be discussed. Finally, opportunities and challenges for interoperability: from the perspective of both application developers (who may need to integrate modules from both kinds) and from library module developers (who may need to target both module systems)
Moved to https://slidr.io/azzazzel/leveraging-osgi-to-create-extensible-plugi...Milen Dyankov
This slide deck will be removed from here in the future. It has been moved to : https://slidr.io/azzazzel/leveraging-osgi-to-create-extensible-plugins-for-liferay-6-2
Introduction to the Eclipse scripting tool Groovy Monkey. Groovy Monkey allows for you to engage in API exploration, Task Automation, Plugin prototyping and collaboration in a lightweight and simple way.
Here's our latest blog post, written by our Leonardo Veiga, FAE, Toradex Brasil, shows you how to use computer vision in embedded systems, by employing the OpenCV in Computer on Modules (CoMs) equipped with NXP i.MX 6 processors. Read on here: http://bit.ly/2Bf1jCS
В Java 9 с неизбежностью появятся модули. Кого-то это мало волнует, кого-то пугает, кто-то искренне недоумевает: зачем, ведь у нас уже больше 15 лет есть OSGi, который решает ровно те же проблемы, что и модули? Здесь мы попробуем разобраться, какие проблемы пытается решить OSGi, как он их решает и решает ли в действительности. Затем посмотрим, какие проблемы, которые пытается решить OSGi, Jigsaw совсем не решает и почему, а также какие проблемы решает и как. Ну и в конце, какие проблемы Jigsaw при этом привносит в экосистему Java и что с этим делать.
Языку Java присущ встроенный динамизм.
Reflection, динамическая загрузка — это то, без чего современные Java приложения просто не могут существовать, поэтому существует мнение, что AOT (статическая) компиляция вряд ли применима к Java в общем случае, а там где применима не может составить конкуренцию JIT (динамической) компиляции в плане прозводительности.
В этом докладе показывается почему это не (совсем) так, при этом рассматриваются случаи,
где у статических компиляторов действительно есть определенные сложности в обработке динамической семантики Java.
Также упоминается, где статическая компиляции для Java может быть полезна.
JIT vs. AOT: Unity And Conflict of Dynamic and Static Compilers Nikita Lipsky
Java had been constantly criticized for poor performance ever since its inception, but not so much in recent years. Thanks to optimizing dynamic native code compilers, Java performance today is very close to the performance of low level languages such as C/C++, and is even better on some classes of applications. Along with dynamic compilers, static compilers for Java have been evolving as well, so there is still no clear winner among these two approaches. It should then come as no surprise that an AOT compiler is finally going to appear even in the HotSpot JVM and OpenJDK via JEP-295, which is officially included in Java 9.
Her, I would like to dispel common myths around the old dispute on whether dynamic or static compilation is better, show that both approaches have their strengths and weaknesses, and explain why the future is the hybrid approach.
Верификация Java байткода: когда, как, а может отключить?Nikita Lipsky
Сегодня Java разработчики все чаще используют библиотеки для порождения Java байт-кода в рантайме. Делается это для эффективной реализации различных трюков, которые сложно или невозможно выразить на языке Javа. Когда используется Java, компилятор javac гарантирует, что на выходе получится корректный Java байт-код. Но, спускаясь на уровень непосредственно байт-кода, часто нужно самостоятельно следить за его корректностью. Иначе при загрузке порожденных классов на выходе будет j.l.VerifyError, потому что JVM посредством верификатора Java байт-кода строго следит за корректностью байт-кода, который она загружает. Таким образом, порождая байт-код, недостаточно просто знать семантику байт-кодных инструкций — нужно также знать, как работает Java byte-code верификатор, какой байт-код он считает корректным, а какой нет.
В этом докладе мы разберемся, какую миссию в JVM несет верификатор байт-кода, когда и как он работает, может ли повлиять на производительность вашего приложения и почему опасно его отключать.
Java SE 8 has brought lambdas, default methods, type annotations, compact profiles, etc. As a result, the Java SE platform specification was changed to reflect new features.
The session shows how the new Java 8 features have been implemented in Excelsior JET JVM, written from scratch, very different from the Oracle HotSpot JVM, but compatible with the Java SE specification.
As a result, an attendee will refresh his/her memory regarding new Java 8 features, will learn how they affected the JVM specification, how the lambda expressions are translated into Java bytecode and how they can be optimized at the JVM level.
JVM: краткий курс общей анатомии, JPoint 2016 Conference EditionNikita Lipsky
Говоря о Java, мы подразумеваем как минимум две вещи: JVM (виртуальную Java-машину) и Java-байткод, который исполняется на этой машине.
Внутреннее устройство JVM непростое, но очень важно понимать, из каких частей она состоит, какая часть за что отвечает и как это все вместе работает хотя бы в самых общих чертах. Эти знания помогут вам в понимании того, как работает ваша программа и как можно улучшить ее работу.
В этом докладе мы не будем лезть в кишки какой-то конкретной реализации JVM, однако мы покажем где у JVM кишки расположены, а также где находятся и для чего служат ее печень, сердце, почки, мозг и другие органы.
Доклад на конференциях JPoint 2016, JBreak 2016
Abstract: В Java SE 8 были добавлены лямбда-выражения, дефолтные методы, типовые аннотации, компактные профили и т.п., что привело к изменениям в спецификации Java SE платформы.
В этом докладе мы рассмотрим, как новые возможности, добавленные в Java 8, были реализованы в Excelsior JET JVM, полностью написанной с нуля, совершенно непохожей на Oracle HotSpot, но при этом совместимой со спецификацией Java SE.
В итоге, слушатель освежит в памяти, что появилось в Java 8, как это повлияло на спецификацию JVM, во что превращаются лямбда-выражения в Java байт-коде, как их можно статически оптимизировать, а также получит некоторое представление о внутреннем устройстве еще одной JVM.
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7. Why Jigsaw is not OSGi?
Mark Reinhold (the Chief Architect of the Java Platform Group):
“…As it (OSGi) stands, moreover, it’s useful for
library and application modules but, since it’s
built strictly on top of the Java SE Platform, it
can’t be used to modularize the Platform itself”
7
8. Why Jigsaw is not OSGi?
Question: why the presence of j.l.Object in Java
Language Specification, implemented in Java in
turn, does not lead to a bootstrap problem?
Факт: Существует реализация Java SE, где
OSGi поддерживается на уровне JVM (на
уровне платформы).
8
9. Why Jigsaw is not OSGi?
Question: why the presence of j.l.Object in Java
Language Specification, implemented in Java in
turn, does not lead to a bootstrap problem?
Fact: There is a Java SE implementation that
supports OSGi at the JVM level (at the platform
level).
9
10. Nikita Lipsky
• 20+ years in software development
• Excelsior JET project initiator
– 16+ years of contributions
– compiler engineer
– team lead
– product lead
– etc.
• Twitter: @pjBooms
10
11. Excelsior JET?
• AOT-centric Java SE implementation
– certified as Java Compatible since 2005
• AOT compiler + Java Runtime
– mixed compilation: AOT + JIT
– AOT support for custom classloaders (Eclipse RCP, Tomcat)
• Toolkit
– Startup Optimizer
– Deployment
11
12. Agenda
• Why OSGi
• How OSGi does it
• Why NOT OSGi
• Why Jigsaw is not OSGi
• Jigsaw mantra
• Jigsaw problems
12
13. Where OSGi?
Standardized by OSGi Alliance (IBM, Adobe, Bosch,
Huawei, NTT, Oraсle)
Implementations:
• Equinox
– Eclipse IDE, Eclipse RCP, IBM Websphere
• Apache Felix
– Oracle WebLogic, Glassfish, Netbeans
13
17. OSGi Module System
OSGi module – Bundle:
• Jar or directory
• Import/export is defined in META-INF/MANIFEST.MF:
Manifest-Version: 1.0 Bundle-ManifestVersion: 2
Bundle-SymbolicName: B
Bundle-Version: 1
Bundle-Name: B Bundle
Export-Package: org.bar
Import-Package: org.foo;version=“[1,2)”
17
18. OSGi Module System
• OSGi bundle imports/exports
– packages (Import-Package/Export-Package)
– services (Import-Service/Export-Service).
• May import other bundles directly
– Require-Bundle directive
– However it is not the best practice (less flexible)
18
19. OSGi Module System
19
Bundle A
Class A
Bundle B
Class B
Bundle C
Class C
Export-Package: packageC
Import-Package: packageA
Export-Package: packageA
I
Import-Package: packageA,
packageC
20. OSGi Runtime
• Resolves Import/Export of OSGi bundles
(wiring)
• Defines bundle life cycle
– May start (activate) bundles lazily
– Enables on-the-fly bundle updates without system
restart (aka hot redeploy).
20
22. Versioning in OSGi
• OSGI resolves JAR hell:
– import/export is qualified by version
– If two bundles require a library bundle of two
different versions, both versions will be loaded
22
23. Why OSGi?
So, OSGi promises:
• Modularity
– explicit dependencies
– encapsulation
• JAR Hell problem resolution
– via versioning
• Hot ReDeploy
– via ability to update a separate bundle dynamically
23
24. Why OSGi?
So, OSGi promises:
• Modularity
– explicit dependencies
– encapsulation
• JAR Hell problem resolution
– via versioning
• Hot ReDeploy
– via ability to update a separate bundle dynamically
24
25. Why OSGi?
So, OSGi promises:
• Modularity
– explicit dependencies
– encapsulation
• JAR Hell problem resolution
– via versioning
• Hot ReDeploy
– via ability to update a separate bundle dynamically
25
26. Why OSGi?
So, OSGi promises:
• Modularity
– explicit dependencies
– encapsulation
• JAR Hell problem resolution
– via versioning
• Hot ReDeploy
– via ability to update a separate bundle dynamically
26
29. Versioning in OSGi
Question: How to implement versioning?
Task: For given A module importing Lib (v1)
library, and B module importing Lib (v2), it is
required that both versions of Lib working
without conflicts.
Solution: load the versions of the library by
different classloaders.
29
30. Versioning in OSGi
Question: How to implement versioning?
Task: For a given module A importing library Lib
(v1), and module B importing Lib (v2), it is
required that both versions of Lib work without
conflicts.
Solution: load the versions of the library by
different classloaders.
30
31. Versioning in OSGi
Question: How to implement versioning?
Task: For a given module A importing library Lib
(v1), and module B importing Lib (v2), it is
required that both versions of Lib work without
conflicts.
Solution: load versions of the library by different
classloaders.
31
32. Versioning in OSGi
Thus each OSGi bundle is loaded by its own
classloader:
• Subtype of java.lang.ClassLoader
• Unique class namespace
• No conflicts with classes of other bundles
32
35. Encapsulation in OSGi
src/com/foo/exported/A.java:
package com.foo.exported;
import com.foo.internal.B;
public class A {
B useB;
}
src/com/foo/internal/B.java:
package com.foo.internal;
public class B {
}
How to make the class B inaccessible from outside?
35
37. Encapsulation in OSGi
Question: how to make an internal class of a
module declared public inaccessible outside?
Answer: classloaders (!) may hide internal
classes.
37
39. Dynamic Updates
Task: update one (!) changed bundle in a
running program without stopping it
Solution: CLASSLOADERS!
(unload old bundle, load new bundle by a new
classloader)
39
41. Lazy start
Start of bundles in OSGi is implemented via the
bundle activators feature:
• Each bundle may have an activator
– Bundle-Activator manifest directive
– Implementation of an interface with methods
start(), stop()
– Static class initializer analogue for bundles
41
42. Lazy start
Start of bundles in OSGi is implemented via the
bundle activators feature:
public interface BundleActivator {
void start(BundleContext context) throws Exception;
void stop(BundleContext context) throws Exception;
}
42
43. Lazy start
• Bundle start can be defined by OSGi
configuration
• Otherwise the bundle starts when it is
required by other started bundles
43
44. Lazy start
Task: start (load) bundles only when they
become needed for program execution
44
45. Lazy start
Solution: CLASSLOADERS (again!) in OSGi invoke
the start()method of the bundle activator
right before loading of the first class of a bundle
Since classloading in the JVM is lazy, bundle
activation becomes lazy AUTOMATICALLY
45
46. Lazy start
Solution: CLASSLOADERS (again!) in OSGi invoke
the start()method of the bundle activator
right before loading of the first class of a bundle
Since classloading in the JVM is lazy, bundle
activation becomes lazy AUTOMATICALLY
46
47. Lazy start
Solution: CLASSLOADERS (again!) in OSGi invoke
the start()method of the bundle activator
right before loading of the first class of a bundle
Since classloading in the JVM is lazy, bundle
activation becomes lazy AUTOMATICALLY
47
71. Symbolic references resolution
• A class references other classes and their
fields/methods symbolically
• JVM resolves those symbolic references with
real values at runtime
71
72. Symbolic references resolution
• A class references other classes and their
fields/methods symbolically
• JVM resolves those symbolic references with
real values at runtime
• Once a reference is resolved, the value of the
reference is never changed!
72
73. On the fly updates?
• If a reference from a class B to a class A is
resolved then the class А cannot be unloaded
from the JVM without unloading the class B
73
74. On the fly updates?
• If a reference from a class B to a class A is
resolved then the class А cannot be unloaded
from the JVM without unloading the class B
• Hence if a bundle В imports a bundle А then
the bundle А cannot be unloaded without
also unloading the bundle B
74
75. On the fly updates?
Bundle ABundle B
Let’s update bundle A
75
81. On the fly updates?
• On the fly updates in OSGi work, more or less,
only for leaf bundles that are not imported by
other bundles – plugins
81
82. On the fly updates?
• On the fly updates in OSGi work, more or less,
only for leaf bundles that are not imported by
other bundles – plugins
• There are much simpler ways than OSGi to
implement plugins
82
83. On the fly updates?
Even leaf bundles are not so easy to unload from
the JVM:
• The classes from leaf bundles can live in the
JVM after their unloading
– Known problem: Classloaders Memory Leak
83
84. One does not simply
unload a class from the JVM 84
97. Loading constraints
• Loading constraints prohibit two classes with
the same fully qualified name to appear in the
namespace of another class
97
98. Loading constraints
B.java:
class B {
T1 f1 = A.f;
int f2 = A.m(t2);
}
A.java:
class A {
static T1 f;
static int m(T2 t)
If B is loaded by L1 classloader and A is loaded by L2 then the
JVM will check that (T1, L1) = (T1, L2) and (T2, L1) = (T2, L2)
==
98
100. Versioning?
• JVM throws java.lang.LinkageError on loading
constraints violation
• OSGi DOES NOT help developers to avoid
loading constraints violation
– Just google for “OSGI” and “LinkageError” to
estimate the scale of the problem
100
101. Versioning?
There are bundles in the latest Eclipse versions
with potential loading constraints violations and
nobody cares!
101
105. Reflection – universal countermeasure
against encapsulation in Java
Encapsulation?
setAccessible(true)
105
106. Encapsulation?
Question: well, at least the encapsulation
problem is solved by OSGi, right?
Answer: OSGi does not protect from
unauthorized access via Reflection
106
110. Lazy start?
Bundle activation order in OSGi depends on
classloading order directly
– A bundle is started from loadClass() of the
bundle classloader
110
111. Lazy start?
Bundle activation order in OSGi depends on
classloading order directly
– A bundle is started from loadClass() of the
bundle classloader
However, class loading order is not defined by
the JVM specification!
111
112. Symbolic references resolution
A class may reference other classes and their
fields/methods symbolically. A JVM may resolve
references:
• Lazily
– Each reference is resolved on first access
• Eagerly
– All references are resolved at the time of class loading
112
113. Lazy start?
The classloading order depends on the class
reference resolution scheme in the given JVM
implementation: lazy, less lazy, eager.
113
114. Lazy start?
Bundle B activator:
class B implements BundleActivator {
public void start() {
assert A.f!= null;
}
Bundle A activator:
class A implements BundleActivator {
static T f;
public void start() {
f = new T();
}
Typical case: В thinks that А is already activated, but in fact
А can be activated after B, so assertion fails
114
115. Lazy start?
• Bundle activation scheme in OSGi is a time
bomb:
– If the JVM starts to resolve class references less
lazily, practically all OSGi applications will stop
working
115
116. Why NOT OSGi?
• Modularity with cycles
• Hot Redeploy works for leaf bundles only
• No protection from loading constraints violation
• No protection of implementation details from
reflective access
• Bundle activation order depends substantially
on class reference resolution scheme
116
119. Jigsaw vs. OSGi
OSGi is dynamic essentially
– modules appear at run time only
119
120. Jigsaw vs. OSGi
Jigsaw was thought up as static from the beginning.
Practically all JDK tools know about modules:
– javac: respects modules visibility rules
– jdeps: analyses dependencies
– jar, jmod: pack modules
– jlink: prepares final image for deployment
– java: there are modules in runtime as well
120
129. Jigsaw and classloaders
Backward compatibility problem:
According to the specification
getClassloader() == null
for core platform classes.то противоречит
That precludes splitting of the platform into
modules, with each module loaded by its loader
129
130. Jigsaw and classloaders
Backward compatibility problem:
According to the specification
getClassloader() == null
for core platform classes.то противоречит
That precludes splitting of the platform into
modules, with each module loaded by its loader
130
132. Versioning
Another detail: import in early Jigsaw versions
(as in OSGi) was qualified by not a single version
but by а version range:
– A module may declare that it can work with a
dependency of “from” version to “to” version
132
133. Versioning
Problem 3: Resolving dependencies (wiring
modules) from version ranges is an NP-complete
problem!
– Reduced to 3-SAT
133
142. Reliable Configuration
Reliable configuration:
• All module dependencies are resolved
• No cyclic dependencies
• No modules containing the same packages
(split packages)
These properties are checked at startup (wiring)
142
144. Strong Encapsulation
Java 9 modules are first class citizens
• Define visibility access rules
– via declared export
• There is no access to non-exported functionality
outside of the module even via reflection
– Even setAccessible(true) does not work
144
145. Strong Encapsulation
Java 9 modules are first class citizens
• Define visibility access rules
– via declared export
• There is no access to non-exported functionality
outside of the module even via reflection
– Even setAccessible(true) does not work
145
146. Strong Encapsulation
Java 9 modules are first class citizens
• Define visibility access rules
– via declared export
• There is no access to non-exported functionality
outside of the module even via reflection
– Even setAccessible(true) does not work
146
149. Reliable Configuration?
• Reflective access was prohibited between
modules without explicit dependencies in
early Jigsaw drafts
• However it had to be relaxed when
classloaders had gone from JPMS
– because Class.forName() has to work
backward compatible
149
150. Reliable Configuration?
• Reflective access was prohibited between
modules without explicit dependencies in
early Jigsaw drafts
• Had to be relaxed when classloaders had gone
from JPMS
– because Class.forName() had to remain
backward compatible
150
151. Reliable Configuration?
However if you may have reflective
dependencies that are not explicitly declared,
where is the guarantee that the resulting
configuration is reliable?
151
153. Jigsaw Layers *
To solve the application containers problem
Layers feature was introduced in JPMS:
• Local module system for each application in a
container
• Two modules containing the same package
have to belong to different layers
153
154. Jigsaw Layers *
* The picture is from Alex Buckley’s presentation: Project Jigsaw Under the hood
154
157. Strong Encapsulation?
The platform is split into modules:
• Which means that private APIs become really
private
• But what about
sun.misc.Unsafe ?
157
160. Strong Encapsulation?
DI frameworks essentially depend on:
• reflective access to the code in
which they inject dependencies
• including non-exported code
160
165. Strong Encapsulation?
Open modules were introduced to solve the DI
frameworks problem:
• An open module allows reflective access to its
non-exported functionality
165
168. Jigsaw benefits
If all your dependencies are on the classpath now,
migrating to the modulepath would improve the
architecture of your application by eliminating:
• cycles in the dependencies
• split packages (jar hell)
• unsound access into implementation details of
other modules
• dependencies to JDK private API
168
169. Jigsaw benefits
If all your dependencies are on the classpath now,
migrating to the modulepath would improve the
architecture of your application by eliminating:
• cycles in the dependency graph
• split packages (jar hell)
• unsound access into implementation details of
other modules
• dependencies to JDK private API
169
170. Jigsaw benefits
If all your dependencies are on the classpath now,
migrating to the modulepath would improve the
architecture of your application by eliminating:
• cycles in the dependency graph
• split packages (jar hell)
• unsound access into implementation details of
other modules
• dependencies to JDK private API
170
171. Jigsaw benefits
If all your dependencies are on the classpath now,
migrating to the modulepath would improve the
architecture of your application by eliminating:
• cycles in the dependency graph
• split packages (jar hell)
• unsound reliance upon implementation details of
other modules
• dependencies to JDK private API
171
172. Jigsaw benefits
If all your dependencies are on the classpath now,
migrating to the modulepath would improve the
architecture of your application by eliminating:
• cycles in the dependency graph
• split packages (jar hell)
• unsound reliance upon implementation details of
other modules
• dependencies on JDK private APIs
172
173. Jigsaw benefits
Jigsaw introduces a migration path to the
modulepath:
• Old classpath forms Unnamed Modulе
• Jars from classpath may be temporally moved as
is to modulepath as Auto Modules
• Module declaration can be added to auto
modules later
173
174. Jigsaw benefits
Jigsaw introduces a migration path to the
modulepath:
• Old classpath forms Unnamed Module
• Jars from classpath may be temporally moved as
is to modulepath as Auto Modules
• Module declaration can be added to auto
modules later
174
175. Jigsaw benefits
Jigsaw introduces a migration path to the
modulepath:
• Old classpath forms Unnamed Modulе
• Jars from classpath may be temporarily moved
“as-is” to modulepath as Auto Modules
• Module declaration can be added to auto
modules later
175
176. Jigsaw benefits
Jigsaw introduces a migration path to the
modulepath:
• Old classpath forms Unnamed Modulе
• Jars from classpath may be temporarily moved
“as-is” to modulepath as Auto Modules
• Module declaration can be added to auto
modules later
176
177. Jigsaw benefits
Unfortunately, most Java developers won’t benefit
from JPMS immediately:
• Java EE standards do not define how they will
interoperate with JPMS yet
• Even servlet containers standard knows nothing
about modules so far
– Dependencies in war файлах are essentially old plain
classpath!
177
178. Jigsaw benefits
Unfortunately, most Java developers won’t benefit
from JPMS immediately:
• Java EE standards do not define how they will
interoperate with JPMS yet
• Even the servlet container standard knows
nothing about modules so far
– Dependencies in war files are old plain classpath in
fact!
178
180. Conclusion
• OSGi is a nice attempt to give modules to Java
developers
– but OSGi has many problems unfortunately
– including fundamental
• Jigsaw is a carefully designed system without
visible fundamental problems
– but with a system of checks and balances
– there are community acceptance problems
180