I have a basic question about scheduling "cancellable" goroutines.
I want to schedule a function execution, every 3 seconds.
The function can take up to 5 seconds.
In case it takes more than 2999ms I want to stop/terminate it, to avoid overlapping w/ the next one.
I'm doing it wrong:
func main() {
fmt.Println("startProcessing")
go startProcessing()
time.Sleep(time.Second * 60)
fmt.Println("endProcessing after 60s")
}
func startProcessing() {
ticker := time.NewTicker(3 * time.Second)
for _ = range ticker.C {
ctx, _ := context.WithTimeout(context.Background(), (time.Second*3)-time.Millisecond)
fmt.Println("start doSomething")
doSomething(ctx)
}
}
func doSomething(ctx context.Context) {
executionTime := time.Duration(rand.Intn(5) 1) * time.Second
for {
select {
case <-ctx.Done():
fmt.Printf("timed out after %s\n", executionTime)
return
default:
time.Sleep(executionTime)
fmt.Printf("did something in %s\n", executionTime)
return
}
}
}
This is my output now:
startProcessing
start doSomething
did something in 2s
start doSomething
did something in 3s
start doSomething
did something in 3s
start doSomething
did something in 5s
start doSomething
did something in 2s
...
I want to read timed out after 5s
instead of did something in 5s
.
CodePudding user response:
You just need to put the time.Sleep(executionTime)
outside the select
and there is no need for the for
loop. I think this is somehow what you want but beware that it's not good practice. So take a look at the warning below.
func doSomething(ctx context.Context) {
executionTime := time.Duration(rand.Intn(5) 1) * time.Second
processed := make(chan int)
go func() {
time.Sleep(executionTime)
processed <- 1
}()
select {
case <-ctx.Done():
fmt.Printf("timed out after %s\n", executionTime)
case <-processed:
fmt.Printf("did something in %s\n", executionTime)
}
}
Obs: I changed the original answer a bit. We can not interrupt a goroutine in the middle of its execution. We could delegate the long-running task to another goroutine and receive the result through a dedicated channel.
Warning: I wouldn't recommend that if you expect the processing time to exceed the deadline because now you will have a leaking goroutine.