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Add alternative PollEvents() impl to prevent goroutine leaking #273

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Add alternative PollEvents() impl to prevent goroutine leaking #273

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18 changes: 18 additions & 0 deletions v3/events.go
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
package termui

import (
"context"
"fmt"

tb "github.com/nsf/termbox-go"
Expand Down Expand Up @@ -77,6 +78,23 @@ func PollEvents() <-chan Event {
return ch
}

// PollEventsWithContext same as PollEvents() prevents goroutine leaking using context.
func PollEventsWithContext(ctx context.Context) <-chan Event {
ch := make(chan Event)
go func() {
defer close(ch)
for {
select {
case <-ctx.Done():
return
default:
ch <- convertTermboxEvent(tb.PollEvent())
Comment on lines +90 to +91
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Suggested change
default:
ch <- convertTermboxEvent(tb.PollEvent())
case ch <- convertTermboxEvent(tb.PollEvent()):

is better, otherwise while you are waiting for ch input, cancelling the context is not efective.

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@maxatome The core problem is that tb.PollEvent() is blocking.
This suggestion would not fix that what you claim as it would just handle a cancel during the write on ch after an event has been blockingly read.

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@maxatome The core problem is that tb.PollEvent() is blocking.
This suggestion would not fix that what you claim as it would just handle a cancel during the write on ch after an event has been blockingly read.

Yes, I had this in mind.

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Do you have any suggestions how to make it better?

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@maxatome maxatome Nov 22, 2020 •
edited
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Good point @dolmen :)

What about a specific goroutine to handle this blocking function?

Something like that (not tested in termui context):

func PollEventsWithContext(ctx context.Context) <-chan Event {
	// tb.PollEvent() is a blocking function, so dedicate a goroutine for it
	tbEvent := make(chan Event)
	go func() {
		defer close(tbEvent)
		for {
			ev := tb.PollEvent()
			if ev.Type == tb.EventInterrupt {
				return
			}
			tbEvent <- convertTermboxEvent(ev)
		}
	}()

	ch := make(chan Event)
	go func() {
		defer close(ch)
		ctxDone := ctx.Done()
		for {
			select {
			case ctxDone:
				// interrupt tb.PollEvent(), this call blocks until the
				// PollEvent function has successfully been interrupted
				tb.Interrupt()
				ctxDone = nil
			case ev, ok := <-tbEvent:
				// Successfully interrupted
				if !ok {
					return
				}
				ch <- ev
			}
		}
	}()
	return ch
}

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Should works, however it looks like over usage of go-routines to me. I would like to suggest a simpler way to do it:

func PollEventsWithCancel() (<-chan Event, func()) {
	ch := make(chan Event)
	go func() {
		defer close(ch)
		for {
			ev := tb.PollEvent()
			if ev.Type == tb.EventInterrupt {
				return
			}
			ch <- convertTermboxEvent(ev)
		}
	}()
	return ch, func(){tb.Interrupt()}
}

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Another concern is that the method should be a singleton. In other way behavior is unpredictable and doesn't really make sense.

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Let me back to my pet proj after a while and see what can be done, any suggestions are welcome.

}
}
}()
return ch
}

var keyboardMap = map[tb.Key]string{
tb.KeyF1: "<F1>",
tb.KeyF2: "<F2>",
Expand Down