Difficulty Implementing Singleton Pattern in a Multithreaded Node.js Environment
I'm stuck on something that should probably be simple. I'm trying to implement the Singleton design pattern in a Node.js application to ensure that only one instance of a class is created, even in a multithreaded context. However, I'm running into issues when trying to access the singleton instance from multiple files, which results in unexpected behavior. The instance seems to be created multiple times, especially when I try to require the singleton module in different places. Here's the code that I'm working with: ```javascript // singleton.js class Singleton { constructor() { if (Singleton.instance) { return Singleton.instance; } this.data = {}; Singleton.instance = this; } getData() { return this.data; } setData(data) { this.data = data; } } module.exports = new Singleton(); ``` In another file, I have: ```javascript // app.js const singleton = require('./singleton'); singleton.setData({ key: 'value' }); console.log(singleton.getData()); // { key: 'value' } ``` And in a third file: ```javascript // anotherFile.js const singleton = require('./singleton'); console.log(singleton.getData()); // Should print { key: 'value' } ``` However, I sometimes see instances where the output does not reflect the changes made in `app.js`, and I get an empty object instead. I'm using Node.js version 16.0.0, and I'm not sure if this is related to how Node handles module caching or something else regarding my design. I've tried checking if the singleton instance is being created multiple times by adding debug logs, but the logs indicate that the same instance is being used. What could be causing this inconsistency, and how can I ensure that my singleton pattern works correctly in this setup? This is happening in both development and production on Windows 11. What are your experiences with this?