Truffle served in a Holy Graal: Graal and Truffle for polyglot language interpretation on the JVM

03 Hotspot versus GraalVM

Reblogging from ZeroTurnaround’s Rebellab blog site

One of the most fascinating additions to Java 9 is the JVMCI: Java-Level JVM Compiler Interface, a Java based compiler interface which allows us to plug in a dynamic compiler into the JVM. One of the main inspirations for including it into Java 9 was due to project Graal — a dynamic state-of-the-art compiler written in Java.

In this post we look at the reasons Graal is such a fascinating project, its advantages, what are the general code optimization ideas, some performance comparisons, and why would you even bother with tinkering with a new compiler.

Like everyone else we were inspired by the vJUG session by Chris Seaton on Graal – it looks like a great tool and technology and so we decided to play with the technology and share it with the community.

…you can read the rest at ZeroTurnaround’s Rebellab blogs


In case, you are wondering what some of the ASCII-art images in one of the paragraphs is about, here’s a bit of explanation, hopefully it will clear up any doubts.

How does it actually work?

A typical flow would look like this:

02-a Program to machine code diagram (excludes expansion)
AST → Abstract Syntax Tree  (explicit data structures in memory)

We all know that a JIT is embedded inside HotSpot or the JVM. It’s old, complicated, written in C++ and assembly and is fairly hard to understand. It is a black box and there is no way to hook or link into the JIT.  All the JVM languages have to go through the same route:  

02-b Program to machine code diagram (via byte-code)

(ASM = assembly)

The flow or route when dealing with traditional compilers and VM would be:

02-c Program to machine code diagram (via JIT)
But with Graal, we get the below route or flow:

02-d Program to machine code diagram (via AST)
(notice Graal skips the steps that create byte-code by directly generating platform specific machine code)

Graal basically helps moving the control-flow from Code to the JIT bypassing the JVM (HotSpot, in our case). It means we will be running faster and more performant applications, on the JVM. These applications will not be interpreted anymore but compiled to machine code on fly or even natively.

I hope you enjoyed the read, please feel free to share any constructive feedback, so we can improve the material for the community as a whole. We learnt a lot while drafting this post and hope the same for you.

Original post by @theNeomatrix369 and  @shelajev !


Containers all the way through…

In this post I will attempt to cover fundamentals of Bare Metal Systems, Virtual Systems and Container Systems. And the purpose for doing so is to learn about these systems as they stand and also the differences between them, focusing on how they execute programs in their respective environments.

Bare metal systems

Let’s think of our Bare Metal Systems as desktops and laptops we use on a daily basis (or even servers in server rooms and data-centers), and we have the following components:

  • the hardware (outer physical layer)
  • the OS platform (running inside the hardware)
  • the programs running on the OS (as processes)

Programs are stored on the hard drive in the form of executable files (a format understandable by the OS) and loaded into memory via one or more processes. Programs interact with the kernel, which forms a core part of the OS architecture and the hardware. The OS coordinate communication between hardware i.e. CPU, I/O devices, Memory, etc… and the programs.


Bare Metal Systems

A more detailed explanation of what programs or executables are, how programs execute and where an Operating System come into play, can be found on this Stackoverflow page [2].

Virtual systems

On the other hand Virtual Systems, with the help of Virtual System controllers like, Virtual Box or VMWare or a hypervisor [1] run an operating system on a bare metal system. These systems emulate bare-metal hardware as software abstraction(s) inside which we run the real OS platform. Such systems can be made up of the following layers, and also referred to as a Virtual Machines (VM):

  • a software abstraction of the hardware (Virtual Machine)
  • the OS platform running inside the software abstraction (guest OS)
  • one or more programs running in the guest OS (processes)

It’s like running a computer (abstracted as software) inside another computer. And the rest of the fundamentals from the Bare Metal System applies to this abstraction layer as well. When a process is created inside the Virtual System, then the host OS which runs the Virtual System might also be spawning one or more processes.

Virtual Systems

Container systems

Now looking at Container Systems we can say the following:

  • they run on top of OS platforms running inside Bare Metal Systems or Virtual Systems
  • containers which allow isolating processes and sharing the kernel between each other (such isolation from other processes and resources are possible in some OSes like say Linux, due to OS kernel features like cgroups[3] and namespaces)[4]

A container creates an OS like environment, inside which one or more programs can be executed. Each of these executions could result in a one or more processes on the host OS. Container Systems are composed of these layers:

  • hardware (accessible via kernel features)
  • the OS platform (shared kernel)
  • one or more programs running inside the container (as processes)

Container Systems


Looking at these enclosures or rounded rectangles within each other, we can already see how it is containers all the way through.

Bare Metal Systems
Virtual SystemsContainer Systems

There is an increasing number of distinctions between Bare Metal Systems, Virtual Systems and Container Systems. While Virtual Systems encapsulate the Operating System inside a thick hardware virtualisation, Container Systems do something similar but with a much thinner virtualisation layer.

There are a number of pros and cons between these systems when we look at them individually, i.e. portability, performance, resource consumption, time to recreate such systems, maintenance, et al.

Word of thanks and stay in touch

Thank you for your time, feel free to send your queries and comments to @theNeomatrix369. Big thanks to my colleague, and  our DevOps craftsman  Robert Firek from Codurance for proof-reading my post and steering me in the right direction.