Port Agent

A RPC-like facility for making inter-thread function calls.

Introduction

Port Agent provides a simple and intuitive interface that makes inter-thread function calls easy. Please see the Usage or Examples for instructions on how to use Port Agent in your application.

Features

• Bi-directional inter-thread function calls.
• Port Agent will marshal the return value or Error from the other thread back to the caller.
• The other thread may be the main thread or a worker thread.
• Registered functions (i.e., agent.register) persist until deregistered (i.e., agent.deregister) .
• Late binding registrants will be called with previously awaited invocations.

Table of contents

• Concepts
• Usage
• Examples
• API
• Versioning
• Notes
• Support

Concepts

Agent

An instance of an Agent facilitates bi-directional communication between threads. The Agent can be used in order to register a function in one thread and call it from another thread. Calls may be made from the main thread to a worker thread, and conversely from a worker thread to the main thread.

Late binding registrants will be called with previously awaited invocations; thus preventing a race condition. This means that you may await a call to a function that has not yet been registered. Once the function is registered in the other thread it will be called and its return value or Error will be marshalled back to the caller.

Please see the Examples for variations on the Agent's usage.

Usage

How to create an Agent instance

Import the Agent class from Port Agent.

import { Agent } from "port_agent";

You can create a new Agent by passing a MessagePort or Worker instance to the Agent constructor.

In the main thread,

const worker = new Worker(fileURLToPath(import.meta.url));
const agent = new Agent(worker);

or, in a worker thread,

const agent = new Agent(worker_threads.parentPort);

How to use an Agent instance

You can register a function in the main thread or in a worker thread using the agent.register method.

agent.register(
  "hello_world",
  (value: string): string => `Hello, ${value} world!`
);

You can call a function registered in another thread (i.e., the main thread or a worker thread) using the agent.call method:

const greeting = await agent.call<string>("hello_world", "happy");
console.log(greeting); // Hello, happy world!

Examples

A simple example ^</Node.js>

Please see the simple example for a working implementation.

A comprehensive example ^{</TypeScript>}

Please see the comprehensive example for a working implementation.

API

The Agent class

new port_agent.Agent(port)

• port <threads.MessagePort> or <threads.Worker> The message port.

public agent.call<T>(name, ...args)

• name <string> The name of the registered function.
• ...args <Array<unknown>> Arguments to be passed to the registered function.

Returns: <Promise<T>>

Errors:

• If the registered function in the other thread throws an Error, the Error will be marshalled back from the other thread to this thread and the Promise will reject with the Error as its failure reason.
• If a worker thread throws an unhandled exception while a call is awaited, the Error will be marshalled back from the other thread to this thread and the Promise will reject with the unhandled exception as its failure reason.
• If a worker exits while a call is awaited, the Error will be marshalled back from the other thread to this thread and the Promise will reject with the exit code as its failure reason.

public agent.register(name, fn)

• name <string> The name of the registered function.
• fn <(...args: Array<any>) => any> The registered function.

Returns: <void>

public agent.deregister(name)

• name <string> The name of the registered function.

Returns: <void>

Versioning

The Port Agent package adheres to semantic versioning. Breaking changes to the public API will result in a turn of the major. Minor and patch changes will always be backward compatible.

Excerpted from Semantic Versioning 2.0.0:

Given a version number MAJOR.MINOR.PATCH, increment the:

1. MAJOR version when you make incompatible API changes
2. MINOR version when you add functionality in a backward compatible manner
3. PATCH version when you make backward compatible bug fixes

Additional labels for pre-release and build metadata are available as extensions to the MAJOR.MINOR.PATCH format.

Notes

Support for broadcastChannels

Port Agent supports one to one communication over a MessagePort. BroadcastChannels are not presently supported.

Support for other communication channels

Port Agent is strictly focused on efficient communication over MessagePorts. Port Agent will not support communication over other communication channels e.g., Sockets, IPC, etc.

Support

If you have a feature request or run into any issues, feel free to submit an issue or start a discussion. You’re also welcome to reach out directly to one of the authors.

• Adam Patterson