When exactly does the switching between different goroutines occur in a program?

Switching between goroutines in Go occurs when the current goroutine is blocked or voluntarily yields control. This can happen:

• When calling blocking operations, such as waiting on a channel (read or write operations), system calls, or synchronization.
• When using the keyword runtime.Gosched(), which explicitly hands over control to the scheduler.
• When a goroutine finishes.

The Go scheduler manages goroutine switching by scheduling their execution on available system threads (M). The switching occurs at the runtime level, and programmers typically do not control it directly.

Thus, switching is a reaction of the scheduler to blocks or explicit yields, ensuring concurrent execution of multiple goroutines.