exp/shiny: windriver: AccessDenied for DestroyWindow

[ktye]

What version of Go are you using (go version)?

go version go1.9.2 windows/amd64

Does this issue reproduce with the latest release?

That should be the case.

What operating system and processor architecture are you using (go env)?

windows/amd64

What did you do?

Trying to close a window programmatically by sending a lifecycle event.
I'll send a comment with a link to an example program.

What did you expect to see?

The window to disappear.

What did you see instead?

For the main window this works, but client windows are not destroyed.

Description

This is a follow up to CL 115515.
It's a similar topic but an independent problem.

I tracked it down to shiny/driver/internal/win32/win32.go:121
Release calls DestroyWindow on the handle.
Adding a Printf shows that it returns AccessDenied.
I am not sure about the reason, it might be related to "running on the same thread".

Proposed fix

shiny/driver/internal/win32/win32.go:121
Replace _DestroyWindow(hwnd) with SendMessage(hwnd, _WM_CLOSE, 0, 0)
It works for me.

If you agree that this is the right fix, I'll send a CL.
Should I also remove the TODO's from @andlabs around it? I'm not sure if they are appropriate anymore.

[ktye]

To run the example I promised:
go get github.com/ktye/goissues/25671

[andlabs]

Is Release being called from another OS thread? DestroyWindow isn't allowed to destroy windows from another OS thread. Sadly it's been too long since I wrote that code, so I have no idea how Shiny works now (I'm surprised it has activity again!) or what the thread structure of your code is. But yes, you can use WM_CLOSE to do this; you can either accept the behavior of DefWindowProc or do it yourself and the TODOs can go away too.

Maybe I should peek back in...

[ktye]

@andlabs: it might be.
I create the client window in a goroutine, as it should have it's own event loop:
https://github.com/ktye/goissues/blob/master/25671/main.go#L104

I haven't seen any other shiny examples where multiple windows are handled.
Maybe there are none, as this (and my last fix) have not been reported before.
I came across these issues implementing a shiny backend for mjl-/duit.

[ianlancetaylor]

CC @nigeltao

[alexbrainman]

I will debug this on weekend.

Alex

[alexbrainman]

Release calls DestroyWindow on the handle.
Adding a Printf shows that it returns AccessDenied.

That error was there all the time.

I am not sure about the reason, it might be related to "running on the same thread".

I am certain you get that error because DestroyWindows is called on a different thread from the message pump thread. I added GetCurrentThreadId to check.

Replace _DestroyWindow(hwnd) with SendMessage(hwnd, _WM_CLOSE, 0, 0)
It works for me.

Sounds good to me.

If you agree that this is the right fix, I'll send a CL.

Please, do.

Should I also remove the TODO's from @andlabs around it? I'm not sure if they are appropriate anymore.

Please, remove whatever TODOs you think are inappropriate. We will make final decision once we review your CL.

Thank you.

Alex

[gopherbot]

Change https://golang.org/cl/115998 mentions this issue: shiny/driver/internal/win32: send WM_CLOSE on Release