Frequently Asked Questions

What is TruffleRuby?

TruffleRuby is a high-performance implementation of the Ruby programming language built on GraalVM using the Truffle language implementation framework and the GraalVM compiler. TruffleRuby is one part of GraalVM, a platform for high-performance polyglot programming.

What is Truffle?

The Truffle language implementation framework is a Java framework for writing AST interpreters. To implement a language using Truffle, you write an AST for your language and add methods to interpret – perform the action of – each node.

Truffle also incorporates the concept of specialization. In most AST interpreters the nodes are megamorphic – they handle all possible types and other possible conditions. In the Truffle framework you write several different nodes for the same semantic action, but for different types and conditions. As runtime conditions change, you switch which nodes you are using. After the program has warmed up you should end up with an AST that is precisely tailored for the types and conditions that you are actually using. If these conditions change, you can just switch nodes again.

What is the GraalVM compiler?

The GraalVM compiler is a new implementation of a just-in-time compiler (JIT compiler, or we’d normally say dynamic compiler) in the OpenJDK Java Virtual Machine. Unlike the current compilers, Graal is written in Java, and exposes a Java API to the running program. This means that instead of emitting bytecode, a JVM language can directly control the compiler. However this is complicated, so normally the Truffle framework uses the GraalVM compiler on your behalf to partially evaluate your AST interpreter into machine code.

What is GraalVM?

GraalVM is the platform on which TruffleRuby runs. It is a system for high-performance polyglot programming.

More concretely, GraalVM is a JDK (Java Development Kit) with extra components like the GraalVM compiler and GraalVM Native Image. The GraalVM compiler and GraalVM Native Image are then used by Truffle languages like TruffleRuby.

How do I get TruffleRuby?

There are multiple ways to install TruffleRuby, see Getting Started.

Why is TruffleRuby slow on a standard JVM?

The expected way to run TruffleRuby is using the GraalVM compiler. TruffleRuby isn’t designed to be efficient on a JVM without this.

Why is TruffleRuby faster on the GraalVM?

When running with the GraalVM compiler, the Truffle framework can use the API exposed by the GraalVM compiler. The Truffle framework gets the bytecode representation of all of the AST interpreter methods involved in running your Ruby method, combines them into something like a single Java method, optimizes them together, and emits a single machine code function. The Truffle framework also provides wrappers for JVM functionality not normally available to Java applications, such as code deoptimization. TruffleRuby uses this to provide a dramatically simpler and faster implementation of Ruby.

Where did this code come from?

Chris Seaton wrote an implementation of Ruby on Truffle and Graal as part of an internship at Oracle Labs in the first half of 2013. The code was merged into JRuby in early 2014. Benoit Daloze and Kevin Menard joined as researchers in the second half of 2014, then Petr Chalupa in 2015, Brandon Fish in 2016, and Duncan MacGregor in 2017. Since then we have also accepted contributions from people outside Oracle Labs. In 2017 the code was forked back out of JRuby after it had matured.

Who do I ask about TruffleRuby?

See the Contact section of this README page.

How do I know if I’m using TruffleRuby?

RUBY_ENGINE will be 'truffleruby'.

How do I know if I’m using a VM that has the GraalVM compiler?

ruby --version will report GraalVM CE or Oracle GraalVM. TruffleRuby versions before 23.0 report GraalVM EE instead of Oracle GraalVM.

Also, TruffleRuby.jit? will tell you if you are running with the GraalVM compiler.

What is Oracle GraalVM?

Oracle GraalVM is the GraalVM distribution from Oracle available under the GraalVM Free Terms and Conditions. Oracle GraalVM provides the best TruffleRuby experience: it is significantly faster and more memory-efficient than GraalVM Community Edition.

How do I know that I’m using the Community Edition of GraalVM?

ruby --version will report GraalVM CE.

How do I know that I’m using Oracle GraalVM?

ruby --version will report Oracle GraalVM. TruffleRuby versions before 23.0 report GraalVM EE instead.

How do I know that I’m using the native version of TruffleRuby?

ruby --version will report Native.

TruffleRuby.native? will return true.

How can I see the GraalVM compiler is working?

Put this program into test.rb:

loop do
  14 + 2
end

We’ll use the --engine.TraceCompilation to ask the Truffle framework to tell us when it compiles something using the GraalVM compiler.

ruby --engine.TraceCompilation test.rb
[truffle] opt done         block in <main> test.rb:1 <opt> <split-3a9ffa1b>         |ASTSize       8/    8 |Time   103(  99+4   )ms |DirectCallNodes I    0/D    0 |GraalNodes    24/    3 |CodeSize           69 |CodeAddress 0x11245cf50 |Source   ../test.rb:1

Here you can see that Truffle has decided to use the GraalVM compiler to compile the block of 127 - the loop to machine code - just 69 bytes of machine code in all.

Why doesn’t TruffleRuby perform well for my benchmark?

Benchmarks that we haven’t looked at yet may require new code paths to be specialized. Currently we’ve added specialization for the code paths in the benchmarks and applications that we’ve been using. Adding them is generally not complicated and over time we will have specializations to cover a broad range of applications.

Make sure that you are using Oracle GraalVM for the best performance.

How is this related to `invokedynamic`?

TruffleRuby doesn’t use invokedynamic, as it doesn’t emit bytecode. However it does have an optimizing method dispatch mechanism that achieves a similar result.

Why doesn’t JRuby switch to Truffle as well?

JRuby is taking a different approach to optimizing and adding new functionality to Ruby. Both JRuby and TruffleRuby are important projects.

Why did you fork from JRuby?

We merged into JRuby in order to be able to use large parts of their Java implementation code. We forked back out of JRuby when we had reached the point where the code that we were using needed to be modified for our purposes and we no longer had any dependency on the core part of JRuby. Forking also allowed us to simplify our code base.