What is a goroutine? How does it differ from an OS thread? Who manages goroutines?

A goroutine is a lightweight thread of execution in the Go language, managed by the Go runtime rather than the operating system. Unlike OS threads, goroutines use much less memory (usually a few kilobytes of stack, which can grow and shrink dynamically), and their creation and switching are much cheaper in terms of resources.

Main differences from OS threads:

• Goroutines are scheduled and managed by the Go runtime, not the OS.
• There can be thousands or even tens of thousands of goroutines in a single process without significant load.
• Context switching between goroutines is faster because it does not require kernel switching.

Goroutine management is handled by the Go runtime, which contains its own scheduler (M:N scheduler), mapping many goroutines (G) onto fewer OS threads (M). This allows efficient use of system resources and simplifies parallel programming.