Re: [PATCH] ui/cocoa: Set UI information

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 16 Jun 2021 at 15:19, Akihiko Odaki <akihiko.odaki@gmail.com> wrote:
>
> Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
> ---
>  ui/cocoa.m | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 49 insertions(+)

Hi; I was looking at the cocoa.m code to see about maybe deleting the
unnecessary autorelease pools, and I ran into some code I was a bit
unsure about that was added in this patch.

In particular I'm wondering about the interactions across threads here.

> +- (void) updateUIInfo
> +{
> +    NSSize frameSize;
> +    QemuUIInfo info;
> +
> +    if (!qemu_console_is_graphic(dcl.con)) {
> +        return;
> +    }
> +
> +    if ([self window]) {
> +        NSDictionary *description = [[[self window] screen] deviceDescription];
> +        CGDirectDisplayID display = [[description objectForKey:@"NSScreenNumber"] unsignedIntValue];
> +        NSSize screenSize = [[[self window] screen] frame].size;
> +        CGSize screenPhysicalSize = CGDisplayScreenSize(display);
> +
> +        frameSize = isFullscreen ? screenSize : [self frame].size;
> +        info.width_mm = frameSize.width / screenSize.width * screenPhysicalSize.width;
> +        info.height_mm = frameSize.height / screenSize.height * screenPhysicalSize.height;
> +    } else {
> +        frameSize = [self frame].size;
> +        info.width_mm = 0;
> +        info.height_mm = 0;
> +    }
> +
> +    info.xoff = 0;
> +    info.yoff = 0;
> +    info.width = frameSize.width;
> +    info.height = frameSize.height;
> +
> +    dpy_set_ui_info(dcl.con, &info);

This function makes some cocoa calls, and it also calls a QEMU
UI layer function, dpy_set_ui_info().

> +- (void)windowDidChangeScreen:(NSNotification *)notification
> +{
> +    [cocoaView updateUIInfo];

We call it from the cocoa UI thread in callbacks like this.

>  /* Called when the user clicks on a window's close button */
>  - (BOOL)windowShouldClose:(id)sender
>  {
> @@ -1936,6 +1983,8 @@ static void cocoa_switch(DisplayChangeListener *dcl,
>
>      COCOA_DEBUG("qemu_cocoa: cocoa_switch\n");
>
> +    [cocoaView updateUIInfo];

We also call it from the QEMU thread, when the QEMU thread calls
this cocoa_switch callback function.

(1) A question for Akihiko:
Are all the cocoa calls we make in updateUIInfo safe to
make from a non-UI thread? Would it be preferable for this
call in cocoa_switch() to be moved inside the dispatch_async block?
(Moving it would mean that I wouldn't have to think about whether
any of the code in it needs to have an autorelease pool :-))

(2) A question for Gerd:
Is it safe to call dpy_set_ui_info() from a non-QEMU-main-thread?
It doesn't appear to do any locking that would protect against
multiple threads calling it simultaneously.

thanks
-- PMM