What are threads in General ? and explain Different Threads in ReactNative with Use of Each ?

Threads are a way for a program to divide itself into two or more simultaneously (or pseudo-simultaneously) running tasks. Threads are lighter than processes, and share the same memory space, which means they can communicate with each other more easily than if they were separate processes.

In the context of React Native, there are three main threads:

1. JavaScript Thread: This is where your JavaScript code is run. All your React Native components, logic, and console logs are executed in this thread. This thread is also responsible for the JSON messages sent to the native side.

2. Native UI Thread: This is where the UI is drawn. If you're making an animation, for example, regardless of where this animation is initiated, the UI thread is responsible for executing it.

3. Native Modules Thread: Sometimes, you might want to offload some heavy work to a background thread to keep the UI thread free. This is where the native modules thread comes in. Any native code that you write will be executed in this thread.

Each of these threads has a specific role and they all work together to ensure that your React Native app runs smoothly. The JavaScript thread communicates with the native threads using a batched async message system, which means that it sends a bunch of changes to the native side at once, instead of sending one change at a time. This is one of the ways React Native optimizes for performance.