When does cooperative (non-preemptive) goroutine switching occur?

In Go, cooperative goroutine switching (non-preemptive switching) occurs in the following cases:

• When a goroutine performs operations that explicitly invoke the scheduler, such as calling runtime.Gosched(). This allows the current goroutine to yield control to other goroutines.
• During blocking operations, such as waiting on a channel, input/output, or synchronization, the goroutine is suspended, and the scheduler switches to another.

Thus, cooperative switching happens when a goroutine voluntarily yields control, unlike preemptive switching, where the scheduler forcibly switches context.

Example:

func main() {
    go func() {
        for i := 0; i < 5; i++ {
            fmt.Println("Goroutine 1", i)
            runtime.Gosched() // yield control
        }
    }()

    for i := 0; i < 5; i++ {
        fmt.Println("Main goroutine", i)
        runtime.Gosched()
    }
}