How Graalvm Native Image is Changing Java

Since its release three years ago, GraalVM has sparked a revolution in the Java developer community. Native Image, which uses Ahead-of-Time (AOT) compilation, is one of the most talked-about GraalVM features. It enables the native application performance profile at runtime while maintaining the usual Java developer productivity and tools.

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Classical Java Application Runtime

The execution of code by the Java Virtual Machine (JVM) is one of the most fascinating and powerful features of the Java platform, allowing for high peak performance.

The virtual machine (VM) analyses your program's code and gathers profiling data throughout the first run. The JVM interpreter is quick, but it cannot compete with the speed of compiled code. For this reason, the Oracle JVM (HotSpot) has just-in-time (JIT) compilers, which convert your application's source code to machine code while your programme runs. The C1 JIT compiler will generate machine code for your code if it "warms up," or is often run.

Then, if its execution frequency and thresholds are high enough, the best JIT compiler is used to create an optimised version (C2 or the Graal compiler). The profiling data is utilised by the best compiler to optimise the code based on things like how often loops are used and what types are used in polymorphic code.

The compiler will sometimes make optimizations based on speculation. With the profiling data it gathers, the JVM may create a compiled, optimized version of a function, for instance. Nevertheless, due to the dynamic nature of the JVM's code execution, if the JVM subsequently discovers that its initial assumptions were incorrect, it will deoptimize, meaning that it will no longer utilize the compiled code and instead run in the interpreted mode.

The JVM's strength lies in its adaptability, which allows it to quickly begin running code, take advantage of optimizing compilers for frequently performed code, and apply even more stringent optimizations based on speculation.

This method seems like the best way to execute the program at first glance. Like with any strategy, though, there are drawbacks to this one as well. Complex calculations are performed by the JVM when it conducts its activities (such as code verification, class loading, dynamic compilation, and profiling information collection). The JVM also takes a significant amount of time and memory to boot up, and a large amount of memory is needed to store profiling information.

At a startup stage, and memory directly impact the cost of deploying an application, those expenses become more important as more businesses move their apps to the cloud. Is it possible to maintain the same level of Java productivity, libraries, and tools while decreasing startup time and memory usage? Indeed, and that's exactly what GraalVM Native Image does.

GraalVM Comes Out on Top

GraalVM was first developed as a study at Oracle Laboratories a decade ago. Programming languages and virtual machines, machine learning and security, graph processing, and other fields are being investigated by Oracle Labs, the company's R&D division. GraalVM is a fantastic case study for Oracle Labs since it is founded on years of study and more than a hundred scholarly articles.

The Graal compiler, a brand new, highly-optimizing, contemporary compiler, is the backbone of the project. As a result of several sophisticated optimizations, the resulting code often outperforms that produced by the C2 compiler. Partial escape analysis is one such optimization; by using scalar replacement, it eliminates heap object allocations when an object does not escape the compilation unit, and the Graal compiler makes sure an object is allocated on the heap when an object does escape.

As fewer objects are maintained on the heap using this method, the application's memory usage is reduced. Furthermore, less trash has to be collected, which means less work for the CPU. Also, by taking use of dynamic runtime feedback, GraalVM's sophisticated speculations generate speedier machine code. The GraalVM compiler improves the code's efficiency by guessing which sections of the program won't be used during execution.

The Graal compiler is surprisingly written almost entirely in Java. If you look at the main GraalVM repository on GitHub, you'll discover that more than 90% of the code is written in Java, which is another testament to the language's flexibility and strength.

Native Image Functioning

Being an AOT compiler, the Graal compiler may generate native executables ahead of time. Considering the dynamic nature of Java, could you please explain?

In AOT mode, the compiler does all compiles at build time, before to execution, as opposed to JIT mode, when compilation and execution occur simultaneously. The key concept is to do all the "hard lifting," or costly calculations, during build time so that they only need to be done once, and then at runtime the resulting executables may start quickly and be fully operational right away since everything has already been calculated and built.

Java bytecode is read by the GraalVM 'native-image' function, which then produces a native executable. The tool does this by a static analysis of the bytecode using the notion of a closed environment. When doing the analysis, the tool will seek out and remove any unused lines of code from your program.

How Native Images are Created

Evidence-based discussion. GraalVM Native Image will only compile the native executable if it has all the methods, and fields that are accessible at runtime. In a points-to analysis, the starting point is always the primary entrance point. Any code paths that may be accessible through transitive closure are repeatedly processed until a stopping point is reached. This includes not just the main program, but also any required libraries or JDK classes. Only then can the application be packaged as a standalone binary.

Construction-time initializations. Class initialization at runtime is the default in GraalVM Native Image. Nonetheless, Native Image will start these classes during construction if you can demonstrate that it is safe to do so. These boost speed by eliminating the need for initialization and checks to be performed during runtime.

Take a picture of a heap. An in-depth look at the fascinating idea of taking heap snapshots in Native Image. Java objects allocated using static initializers, along with all other accessible objects, are written to the image heap during the build process. With the heap already full, your app will launch much more quickly.

The snapshotting that creates the image heap may make additional ways accessible for the points-to-analysis, which is an intriguing property of both techniques.

Graal then compiles all the access codes into a native executable tailored to the analyzed platform. The executable can operate without the JVM and has complete functionality on its own. In the end, you'll have a native executable version of your Java software that's just as fast and efficient as the original, but which has just the bare minimum of code and external libraries.

Who, however, manages the native executable's memory and schedules its threads? Native Image's Substrate VM is a lightweight virtual machine that provides essential runtime features including a garbage collector and a thread scheduler. GraalVM Native Image AOT compiles the Java source code of Substrate VM, which is built in Java, into native code.

Native Image allows a new performance profile for your Java programs by using AOT compilation and memory snapshotting.

An online Java course can be helpful to get a better understanding of this subject.