> On 8 Jan 2021, at 1:59 pm, Robert Engels <reng...@ix.netcom.com> wrote:
>
> You need to pass the context to the expensive work a periodically check if it
> has been cancelled.
Thanks. I was thinking how to implement this. Is this a nice way to do it?
func clientDisconnected(ctx context.Context, done chan bool) bool {
select {
case <-done:
return false
case <-ctx.Done():
log.Printf("api: client disconnected.")
return true
}
}
func apiHandlerFunction(w http.ResponseWriter, r *http.Request) {
done := make(chan bool)
go func() {
log.Println("First expensive operation")
time.Sleep(5 * time.Second)
done <- true
}()
if clientDisconnected(r.Context(), done) {
return
}
go func() {
log.Println("Second expensive operation")
time.Sleep(5 * time.Second)
done <- true
}()
if clientDisconnected(r.Context(), done) {
return
}
fmt.Fprintf(w, "All operations done")
}
>
>> On Jan 7, 2021, at 8:55 PM, Amit Saha <amitsaha...@gmail.com> wrote:
>>
>> Hi all, I want to confirm whether my understanding related to handling
>> HTTP client disconnections is correct or not.
>>
>> Consider this:
>>
>> func longRunningProcessing(ctx context.Context, w http.ResponseWriter) {
>> done := make(chan bool)
>> go func() {
>> expensiveWork() # This is a blocking expensive processing call
>> done <- true
>> }()
>> select {
>> case <-ctx.Done():
>> log.Printf("Client disconnected. Cancelling expensive operation.")
>> return
>> case <- done:
>> fmt.Fprintf(w, "Done!")
>> }
>> }
>>
>> func apiHandler(w http.ResponseWriter, r *http.Request) {
>> ctx := r.Context()
>> longRunningProcessing(ctx)
>> }
>>
>> When a client connection close is detected, the Done() call in select
>> unblocks and the call goes out of the longRunningProcessing()
>> function.
>> However, the goroutine with the expensiveWork() is actually still running?
>>
>> It seems like there is *no* way there is *not* going to be a goroutine
>> leak (and resources associated with it) in a pattern like the above
>> unless
>> I have control over expensiveWork() and can instrument it with a child
>> context. I am also thinking if there is a way to obtain the behavior
>> similar to exec.CommandContext() command
>> which does a hard kill of the external process when the context is cancelled.
>>
>> Thanks for any insights and clarifications.
>>
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>
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