Gleam OTP

A Gleam library for building fault tolerant multi-core programs using the actor model. It is compatible with Erlang’s OTP framework.

Gleam’s actor system is built with a few primary goals:

• Full type safety of actors and messages.
• Be compatible with Erlang’s OTP actor framework.
• Provide fault tolerance and self-healing through supervisors.
• Have equivalent performance to Erlang’s OTP.

This library documents its abstractions and functionality, but you may also wish to read the documentation or other material on Erlang’s OTP framework to get a fuller understanding of OTP, the problems it solves, and and the motivations for its design.

Not all Erlang/OTP functionality is included in this library. Some is not possible to represent in a type safe way, so it is not included. Other features are still in development, such as further process supervision strategies.

Usage

Add this library to your Gleam project.

gleam add gleam_otp

Actor hierarchy

This library provides several different types of actor that can be used in Gleam programs.

Process

The process is the lowest level building block of OTP, all other actors are built on top of processes either directly or indirectly. Typically this abstraction would not be used very often in Gleam applications, favour other actor types that provide more functionality.

Gleam’s process module is defined in the gleam_erlang library.

Actor

The actor is the most commonly used process type in Gleam and serves as a good building block for other abstractions. Like Erlang’s gen_server it handles OTP’s system messages automatically to enable OTP’s debugging and tracing functionality.

Documentation

Task

A task is a kind of process that computes a value and then sends the result back to its parent. Commonly multiple tasks are used to compute multiple things at once.

• gleam/otp/task documentation.

Supervisor

Supervisors is a process that starts and then supervises a group of processes, restarting them if they crash. Supervisors can start other supervisors, resulting in a hierarchical process structure called a supervision tree, providing fault tolerance to a Gleam application.

• gleam/otp/static_supervisor documentation.
• gleam/otp/supervisor documentation.

Limitations and known issues

This library does not currently replicate all of the Erlang/OTP functionality. Some limitations include:

• There is no support for named processes. They are untyped global mutable variables which may be uninitialized, more research is needed to find a suitable type safe alternative.
• There are relatively few actor abstractions provided by this library. More will be added in the future.
• Actors do not yet support all OTP system messages. Unsupported messages are dropped.
• Supervisors do not yet support different shutdown periods per child. In practice this means that children that are supervisors do not get an unlimited amount of time to shut down, as is expected in Erlang or Elixir.
• This library has not seen much testing compared to the Erlang OTP libraries, both in terms of unit tests and real world testing in applications.