Feudalism

Controlled borrowing of mutable values for safe concurrency.

A mutex is a data structure designed for safe reading and writing to a mutable variable in a concurrent environment. Specifically, a mutex variable may be mutated (that is, its old value read and transformed into a new value) so long as no other threads are reading or writing to the mutex at the same time. However, any number of threads may read the mutex variable concurrently.

Feudalism implements a generic Mutex type which guarantees these constraints.

Features

• implements a basic, generic mutex
• provides fast and safe concurrent access to a variable
• especially performant on Java 21 with virtual threads

Availability Plan

Feudalism has not yet been published. The medium-term plan is to build Feudalism with Fury and to publish it as a source build on Vent. This will enable ordinary users to write and build software which depends on Feudalism.

Subsequently, Feudalism will also be made available as a binary in the Maven Central repository. This will enable users of other build tools to use it.

For the overeager, curious and impatient, see building.

Getting Started

Creating a new Mutex

A new mutex, an instance of type Mutex[ValueType] for some choice of ValueTyp, can be constructed by supplying its initial value to the Mutex factory method, like so:

val count: Mutex[Int] = Mutex(32)

This represents a mutex variable, which is set to 32. Any thread which has a reference to count may read or modify this variable, but only in delimited blocks.

We can read the value only through a lambda applied to the read method of Mutex, which provides a reference for accessing the value.

Status

Feudalism is classified as fledgling. 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.

Feudalism is designed to be small. Its entire source code currently consists of 100 lines of code.

Building

Feudalism 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 Feudalism?".

1. Copy the sources into your own project

   Read the fury file in the repository root to understand Feudalism'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

   Wrath is a bootstrapping script for building Feudalism 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, 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 feudalism. Run wrath -F in the repository root. This will download and compile the latest version of Scala, as well as all of Feudalism's dependencies.

   If the build was successful, the compiled JAR files can be found in the .wrath/dist directory.

Contributing

Contributors to Feudalism are welcome and encouraged. New contributors may like to look for issues marked beginner.

We suggest that all contributors read the Contributing Guide to make the process of contributing to Feudalism 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

Feudalism was designed and developed by Jon Pretty, and commercial support and training on all aspects of Scala 3 is available from Propensive OÜ.

Name

Feudalism was the predominant social system in Medieval times, whereby wealthy landowners would divide their land into strips, and lease it to tenants to work. This is vaguely analogous, on some level, to the controlled access a mutex provides to readers and writers of its variable.

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 a ring, split into two halves representing read-access and write-access; in the read-access half, the ring splits into multiple threads, while in the write-access half, the ring is just a single thread.

License

Feudalism is copyright © 2024 Jon Pretty & Propensive OÜ, and is made available under the Apache 2.0 License.