Cancel goroutine on new function call

Question

I need to cancel any previous goroutine on every function call. How would that be handled in Go? I've seen channels used but I can't quite wrap my head around the examples and whether a select statement is necessary.

The desired result would be that only the last request subtasks are ran.

package main

import (
    "fmt"
    "time"
)

func main() {
    for i := 0; i < 5; i++ {
        go handleRequest(i)
        time.Sleep(1 * time.Second) // Time between requests
    }
}

func handleRequest(incr int) {
    fmt.Println("New request registered: ", incr + 1)
    for i := 0; i <= 3; i++ {
        fmt.Println("Request: ", incr + 1, " | Sub-task: ", i + 1)
        time.Sleep(2 * time.Second) // Time processing
    }
    return
}

Answer 1

Goroutine cancellation can be done using a context. If you need to cancel a previous goroutine, start it with a context and cancel it when a new one starts. You have to write the goroutine to periodically check for the context:

   var ctx context.Context
   var cancel context.CancelFunc
   for i := 0; i < 5; i++ {
        if cancel!=nil {
             // cancel previous goroutine
             cancel()
        }
        ctx,cancel=context.WithCancel(context.Background())
        // start goroutine with a new context
        go handleRequest(ctx,i)
        time.Sleep(1 * time.Second) // Time between requests
    }  
    if cancel!=nil {
       cancel() 
    }

In your goroutine, you have to check for cancellation:

func handleRequest(ctx context.Context,incr int) {
    fmt.Println("New request registered: ", incr + 1)
    for i := 0; i <= 3; i++ {
        fmt.Println("Request: ", incr + 1, " | Sub-task: ", i + 1)
        time.Sleep(2 * time.Second) // Time processing
        select {
           case <-ctx.Done():
             // canceled
             return
           default:
             // not canceled
        }
    }
    return
}