potential problem with pkg/gate package

[johncming]

There's a potential problem with pkg/gate package.

prometheus/promql/engine.go

Lines 387 to 390 in ead0933

	if err := ng.gate.Start(ctx); err != nil {
	return nil, nil, contextErr(err, "query queue")
	}
	defer ng.gate.Done()

The current gate implementation can easily panic if length is 0.

prometheus/pkg/gate/gate.go

Line 44 in 4c52400

case <-g.ch:

If capacity 0, Start return because timeout.

Two proposals:

1. Close channel when Start timeout returns
2. Create a Gate interface, channelGate is just an implementation. Add other implementations later

[roidelapluie]

Do you have a way to reproduce this?

[roidelapluie]

Friendly ping @johncming

[johncming]

Friendly ping @johncming

I try it but not find a way to reproduce. I find this issue when reading code.

[beorn7]

Hello from the bug scrub.

We assume that the case raised in this issue can never happen. Closing, but please feel free to follow up with more evidence.