collatz

README

Collatz

This directory contains a Service Weaver application that explores the Collatz conjecture. Given a positive integer x, the Collatz process is the process of repeatedly executing the following operation:

• If x is even, set x to x/2.
• If x is odd, set x to 3x+1.

For example, if we execute the Collatz process on x = 10, then we get the sequence of numbers 10, 5, 16, 8, 4, 2, 1. This sequence of numbers is called the hailstone sequence of 10. The Collatz conjecture states that the hailstone sequence of every positive number reaches 1. Nobody knows if the Collatz conjecture is true; it is one of the most famous unsolved problems in mathematics.

This Service Weaver application implements a service that executes the Collatz process. You can send the service a positive number, and the server replies with that number's hailstone sequence.

Components

This Service Weaver application has three components: main, Odd and Even. Given a positive number x, main repeatedly calls Odd (if x is odd) or Even (if x is even) to receive the next number in the hailstone sequence.

This application highlights the benefits of colocation. The performance of the application improves significantly when main, Odd, and Even are colocated in the same OS process.

Running Locally

To run this app locally, run go run .. In a separate terminal, curl the service (which defaults to localhost:9000):

$ go run .                  # In one terminal.
$ curl localhost:9000?x=27  # In a different terminal.

To run the app across multiple processes, use weaver multi deploy. The weaver.toml config file runs every component in a separate process, and the colocated.toml config file colocates all three components.

$ weaver multi deploy weaver.toml     # not colocated
$ weaver multi deploy colocated.toml # colocated

Running on GKE

To run the app on GKE, use weaver gke deploy:

$ weaver gke deploy weaver.toml

Documentation

Overview

Package main implements a service that explores the Collatz conjecture.

Given a positive integer x, the Collatz process is the process of repeatedly executing the following operation:

• If x is even, set x to x/2.
• If x is odd, set x to 3x+1.

For example, if we execute the Collatz process on x = 10, then we get the sequence of numbers 10, 5, 16, 8, 4, 2, 1. This sequence of numbers is called the hailstone sequence of 10. The Collatz conjecture states that the hailstone sequence of every positive number reaches 1. Nobody knows if the Collatz conjecture is true; it is one of the most famous unsolved problems in mathematics.

Package main implements a service that executes the Collatz process. You can send the service a positive number, and the server replies with that number's hailstone sequence.

The service is implemented as an HTTP server that uses two Service Weaver components: Odd and Even. Odd has a method Do that takes in an odd number x and returns 3x+1. Even has a method Do that takes in an even number x and return x/2. When the HTTP server receives a number x, it repeatedly sends x to either Odd or Even---depending on whether x is odd or even---until x equals 1. It then sends back the hailstone sequence.

This Service Weaver application is interesting because it demonstrates the benefits of colocation. Colocating the main component with the Odd and Even components improves performance considerably.