Sub Msg is lost when a subscription triggers twice rapidly

[dancras]

I have written a module to keep track of the state of the keyboard arrow keys using the Keyboard.ups and Keyboard.downs subscriptions. The problem is when two "keyup" events occur rapidly, the second Msg does not make it to the update function.

The function mapping the subscription data (keyCode) to a Msg is run for both occurrences, but somewhere between this and the update function the second "keyup" event's Msg is lost.

I've tagged my project at a point where the issue is easy to reproduce with some debug logging. Holding down the left and right arrow key, then quickly releasing both will result in the one of the arrow keys getting stuck in the down state due to the lost Msg.

Main.elm:835 lstate: KeyDown
Main.elm:835 update: LeftKeyChange KeyDown
Main.elm:835 rstate: KeyDown
Main.elm:835 update: RightKeyChange KeyDown
-- repeated events from holding right key removed
Main.elm:835 rstate: KeyUp
Main.elm:835 lstate: KeyUp
Main.elm:835 update: RightKeyChange KeyUp

https://github.com/dancras/eggdude-elm/tree/debug-skipped-messages
https://github.com/dancras/eggdude-elm/blob/debug-skipped-messages/src/ArrowKeys.elm

I'm using OS X Chrome Version 50.0.2661.94 (64-bit)

[evancz]

Thanks for the example and fix! Should be fixed by elm-lang@cce1dc5 and coming out soon.

[evancz]

Thanks for the example and fix! Should be fixed by elm-lang@cce1dc5 and coming out soon.