How Can Goroutine Starvation Be Avoided in Go's Cooperative Scheduling?

Goroutines and Cooperative Scheduling

Goroutines, the lightweight concurrent processes in Go, utilize cooperative scheduling, meaning they rely on voluntarily yielding execution to other goroutines. However, concerns have been raised that this approach may lead to starvation of other goroutines if one goroutine continuously loops without yielding.

Code Example

Consider the following code snippet, where multiple goroutines are used to perform a looping operation:

// sum function repeatedly adds numbers up to a specified limit
func sum(x int) {
    sum := 0
    for i := 0; i < x; i++ {
        sum += i
    }
    fmt.Println(sum)
}

// Start four goroutines, each performing the sum operation with different inputs
func main() {
    go sum(100)
    go sum(200)
    go sum(300)
    go sum(400)
}

Starvation Scenario

If only a single thread is available, as suggested in the question, it is possible that one of the goroutines enters an infinite loop, preventing other goroutines from executing. This situation is known as starvation.

Cooperatively Yielding in Goroutines

Goroutine starvation can be addressed through cooperative yielding, where goroutines explicitly cede execution to other goroutines through mechanisms such as channel operations or blocking on primitives in the sync package.

In the context of the code example, printing the sum using fmt.Println(sum) within the sum function triggers a function call, which invokes the runtime scheduler. This scheduler may choose to switch to another goroutine, introducing an opportunity for other goroutines to execute.

Alternative Scheduling Approach

Recently, proposals have been made within the Go runtime to automatically insert scheduler calls within tight loops or other situations where goroutine starvation may occur. This approach would further mitigate starvation concerns.

Conclusion

Cooperative scheduling in goroutines requires the explicit yielding of execution to prevent starvation. Function calls and specific operations provide opportunities for the runtime scheduler to switch between goroutines. Future developments in the runtime may automate this process even further.

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