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https://github.com/propensive/oubliette

Quickly launch new JVMs by remote control from Scala
https://github.com/propensive/oubliette

adoptium jdk jvm launcher programmatic scala

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Quickly launch new JVMs by remote control from Scala

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# Oubliette



__Launch new JVMs from Scala by remote control__



_Oubliette_ provides a convenient way to launch a new JVM instance by specifying the classpath, main method and

arguments to be invoked. Classes may be pre-loaded, providing near-instantaneous JVM startup time. This provides

similar functionality to invoking a main method through a classloader, but with significantly better isolation

from the initiating JVM.



## Features



- launch JVM instances by specifying command-line parameters

- achieve near-instantaneous startup times by preloading classes

- automatically download Adoptium JDKs before launching



## Availability



## Getting Started



_Oubliette_ can launch a new JVM, represented by an instance of `Jvm`, from a

particular installed version of a JDK, represented by an instance of `Jdk`.

This can either be done in a single command, `Jdk#launch`, or through a series

of steps, which may make the final invocation step faster in some cases.



The simplest invocation is,

```scala

val jvm: Jvm = jdk.launch(classpath, main, args)

```

where `classpath` is a `List` of paths, `main` is the name of the main class to

launch, and `args` is a `List` of arguments. The paths may be specified in any

type for which a `GenericPathReader` instanceexists, as defined in

[Anticipation](https://github.com/propensive/anticipation/), such as

`java.io.File`.



From a `Jvm` instance, methods such as `Jvm#stdout`, `Jvm#stderr` and

`Jvm#stdin` provide access to the JVM's input and output streams, through a

`LazyList[IArray[Byte]]` interface. Additionally, `Jvm#pid` will give the

running JVM's process ID, and `Jvm#abort` will abort execution.



But a JVM can be created without having it start execution. We can launch a new JVM with,

```scala

val jvm = jdk.init()

```

and provide it with the details it needs to run in steps, with:

- `Jvm#addClasspath` to add a path to the classpath,

- `Jvm#addArg` to add a single `Text` argument to the `main` method,

- `Jvm#setMain` to specify the `main` method, and,

- `Jvm#preload` to load the named classes early



Preloading classes offers the opportunity to prime the JVM instance to be as

ready as possible to invoke the specified `main` method when the time comes.

This results in near-instantaneous startup times, provided the classes can be

loaded long enough before the main method is invoked.



### Specifying a JDK



A `Jdk` instance can be created by specifying its version number, e.g. `17`,

and a path (in any path format) to its home directory, that is, the directory

which contains the `bin` directory in which the `java` executable resides. For

example:

```scala

val jdk = Jdk(14, java.io.File("/usr/lib/jdk"))

```



### Using Adoptium JVMs



[Adoptium](https://adoptium.net) provides prebuild OpenJDK binaries for

download, and Oubliette can automatically download and use them. This is as

simple as installing the Adoptium script to the filesystem with,

`Adoptium.install()`, and calling `get()` on the result, to fetch the most

recent version.



Other options (all with default values) for the `get` method include,

- `version`, the JDK version

- `jre`, should be `true` if a JRE is preferred over a full JDK

- `early`, should be `true` if early-access binaries should be considered

- `force`, to force download again, even if an existing installation exists



If an appropriate JDK can be found, then `get` will return a `Jdk` instance,

from which a `Jvm` can be launched.



## Status



Oubliette is classified as __embryonic__. For reference, Soundness projects are

categorized into one of the following five stability levels:



- _embryonic_: for experimental or demonstrative purposes only, without any guarantees of longevity

- _fledgling_: of proven utility, seeking contributions, but liable to significant redesigns

- _maturescent_: major design decisions broady settled, seeking probatory adoption and refinement

- _dependable_: production-ready, subject to controlled ongoing maintenance and enhancement; tagged as version `1.0.0` or later

- _adamantine_: proven, reliable and production-ready, with no further breaking changes ever anticipated



Projects at any stability level, even _embryonic_ projects, can still be used,

as long as caution is taken to avoid a mismatch between the project's stability

level and the required stability and maintainability of your own project.



Oubliette is designed to be _small_. Its entire source code currently consists

of 120 lines of code.



## Building



Oubliette will ultimately be built by Fury, when it is published. In the

meantime, two possibilities are offered, however they are acknowledged to be

fragile, inadequately tested, and unsuitable for anything more than

experimentation. They are provided only for the necessity of providing _some_

answer to the question, "how can I try Oubliette?".



1. *Copy the sources into your own project*

   

   Read the `fury` file in the repository root to understand Oubliette's build

   structure, dependencies and source location; the file format should be short

   and quite intuitive. Copy the sources into a source directory in your own

   project, then repeat (recursively) for each of the dependencies.



   The sources are compiled against the latest nightly release of Scala 3.

   There should be no problem to compile the project together with all of its

   dependencies in a single compilation.



2. *Build with [Wrath](https://github.com/propensive/wrath/)*



   Wrath is a bootstrapping script for building Oubliette and other projects in

   the absence of a fully-featured build tool. It is designed to read the `fury`

   file in the project directory, and produce a collection of JAR files which can

   be added to a classpath, by compiling the project and all of its dependencies,

   including the Scala compiler itself.

   

   Download the latest version of

   [`wrath`](https://github.com/propensive/wrath/releases/latest), make it

   executable, and add it to your path, for example by copying it to

   `/usr/local/bin/`.



   Clone this repository inside an empty directory, so that the build can

   safely make clones of repositories it depends on as _peers_ of `oubliette`.

   Run `wrath -F` in the repository root. This will download and compile the

   latest version of Scala, as well as all of Oubliette's dependencies.



   If the build was successful, the compiled JAR files can be found in the

   `.wrath/dist` directory.



## Contributing



Contributors to Oubliette are welcome and encouraged. New contributors may like

to look for issues marked

[beginner](https://github.com/propensive/oubliette/labels/beginner).



We suggest that all contributors read the [Contributing

Guide](/contributing.md) to make the process of contributing to Oubliette

easier.



Please __do not__ contact project maintainers privately with questions unless

there is a good reason to keep them private. While it can be tempting to

repsond to such questions, private answers cannot be shared with a wider

audience, and it can result in duplication of effort.



## Author



Oubliette was designed and developed by Jon Pretty, and commercial support and

training on all aspects of Scala 3 is available from [Propensive

OÜ](https://propensive.com/).



## Name



An _oubliette_ is a dungeon into which a prisonner could be condemned for a lifetime, no longer interacting with the outside world; metaphorically, a separate JVM instance.



### Pronunciation



`/ˌuːbliːˈet/`



In general, Soundness project names are always chosen with some rationale,

however it is usually frivolous. Each name is chosen for more for its

_uniqueness_ and _intrigue_ than its concision or catchiness, and there is no

bias towards names with positive or "nice" meanings—since many of the libraries

perform some quite unpleasant tasks.



Names should be English words, though many are obscure or archaic, and it

should be noted how willingly English adopts foreign words. Names are generally

of Greek or Latin origin, and have often arrived in English via a romance

language.



## Logo



The logo shows the trapdoor entrance to an _oubliette_ in a castle turret.



## License



Oubliette is copyright © 2025 Jon Pretty & Propensive OÜ, and

is made available under the [Apache 2.0 License](/license.md).