Re: [PATCH v10 01/15] ui & main loop: Redesign of system-specific main thread event handling

[Paolo Bonzini]

On Wed, Nov 13, 2024 at 7:16 PM BALATON Zoltan <balaton@eik.bme.hu> wrote:
> > int main(int argc, char **argv)
> > {
> > +    QemuThread main_loop_thread;
> > +
> >     qemu_init(argc, argv);
> > -    return qemu_main();
> > +    if (qemu_main) {
> > +        qemu_thread_create(&main_loop_thread, "qemu_main",
> > +                           call_qemu_default_main, NULL, 
> > QEMU_THREAD_DETACHED);
> > +        bql_unlock();
> > +        return qemu_main();
> > +    } else {
> > +        qemu_default_main();
>
> I think you need 'return qemu_default_main()' here but I'm a bit confused
> by all this wrapping of qemu_default_main in call_qemu_default_main. I see
> that may be needed because qemu_thread_create takes a different function
> but now that qemu_default main is static and not replaced externally could
> that be changed to the right type and avoid this confusion and simplify
> this a bit?

Note that qemu_default_main() expects the BQL to be locked, whereas
qemu_main() and call_qemu_default_main() do not (because they run in a
separate thread).

But you're right, we could push bql_lock()/bql_unlock() into
qemu_default_main(), and do

     bql_unlock();
     if (qemu_main) {
        qemu_thread_create(&main_loop_thread, "qemu_main",
                           call_qemu_default_main, NULL, QEMU_THREAD_DETACHED);
        return qemu_main();
    } else {
        return qemu_default_main();
    }

Paolo

> Regards,
> BALATON Zoltan
>
> > +    }
> > }
> > diff --git a/ui/cocoa.m b/ui/cocoa.m
> > index 4c2dd335323..30b8920d929 100644
> > --- a/ui/cocoa.m
> > +++ b/ui/cocoa.m
> > @@ -73,6 +73,8 @@
> >     int height;
> > } QEMUScreen;
> >
> > +@class QemuCocoaPasteboardTypeOwner;
> > +
> > static void cocoa_update(DisplayChangeListener *dcl,
> >                          int x, int y, int w, int h);
> >
> > @@ -107,6 +109,7 @@ static void cocoa_switch(DisplayChangeListener *dcl,
> > static NSInteger cbchangecount = -1;
> > static QemuClipboardInfo *cbinfo;
> > static QemuEvent cbevent;
> > +static QemuCocoaPasteboardTypeOwner *cbowner;
> >
> > // Utility functions to run specified code block with the BQL held
> > typedef void (^CodeBlock)(void);
> > @@ -1321,8 +1324,10 @@ - (void) dealloc
> > {
> >     COCOA_DEBUG("QemuCocoaAppController: dealloc\n");
> >
> > -    if (cocoaView)
> > -        [cocoaView release];
> > +    [cocoaView release];
> > +    [cbowner release];
> > +    cbowner = nil;
> > +
> >     [super dealloc];
> > }
> >
> > @@ -1938,8 +1943,6 @@ - (void)pasteboard:(NSPasteboard *)sender 
> > provideDataForType:(NSPasteboardType)t
> >
> > @end
> >
> > -static QemuCocoaPasteboardTypeOwner *cbowner;
> > -
> > static void cocoa_clipboard_notify(Notifier *notifier, void *data);
> > static void cocoa_clipboard_request(QemuClipboardInfo *info,
> >                                     QemuClipboardType type);
> > @@ -2002,43 +2005,8 @@ static void 
> > cocoa_clipboard_request(QemuClipboardInfo *info,
> >     }
> > }
> >
> > -/*
> > - * The startup process for the OSX/Cocoa UI is complicated, because
> > - * OSX insists that the UI runs on the initial main thread, and so we
> > - * need to start a second thread which runs the qemu_default_main():
> > - * in main():
> > - *  in cocoa_display_init():
> > - *   assign cocoa_main to qemu_main
> > - *   create application, menus, etc
> > - *  in cocoa_main():
> > - *   create qemu-main thread
> > - *   enter OSX run loop
> > - */
> > -
> > -static void *call_qemu_main(void *opaque)
> > -{
> > -    int status;
> > -
> > -    COCOA_DEBUG("Second thread: calling qemu_default_main()\n");
> > -    bql_lock();
> > -    status = qemu_default_main();
> > -    bql_unlock();
> > -    COCOA_DEBUG("Second thread: qemu_default_main() returned, exiting\n");
> > -    [cbowner release];
> > -    exit(status);
> > -}
> > -
> > static int cocoa_main(void)
> > {
> > -    QemuThread thread;
> > -
> > -    COCOA_DEBUG("Entered %s()\n", __func__);
> > -
> > -    bql_unlock();
> > -    qemu_thread_create(&thread, "qemu_main", call_qemu_main,
> > -                       NULL, QEMU_THREAD_DETACHED);
> > -
> > -    // Start the main event loop
> >     COCOA_DEBUG("Main thread: entering OSX run loop\n");
> >     [NSApp run];
> >     COCOA_DEBUG("Main thread: left OSX run loop, which should never 
> > happen\n");
> > @@ -2120,8 +2088,6 @@ static void cocoa_display_init(DisplayState *ds, 
> > DisplayOptions *opts)
> >
> >     COCOA_DEBUG("qemu_cocoa: cocoa_display_init\n");
> >
> > -    qemu_main = cocoa_main;
> > -
> >     // Pull this console process up to being a fully-fledged graphical
> >     // app with a menubar and Dock icon
> >     ProcessSerialNumber psn = { 0, kCurrentProcess };
> > @@ -2185,6 +2151,12 @@ static void cocoa_display_init(DisplayState *ds, 
> > DisplayOptions *opts)
> >     qemu_clipboard_peer_register(&cbpeer);
> >
> >     [pool release];
> > +
> > +    /*
> > +     * The Cocoa UI will run the NSApplication runloop on the main thread
> > +     * rather than the default Core Foundation one.
> > +     */
> > +    qemu_main = cocoa_main;
> > }
> >
> > static QemuDisplay qemu_display_cocoa = {
> > diff --git a/ui/gtk.c b/ui/gtk.c
> > index bf9d3dd679a..fbf20161f36 100644
> > --- a/ui/gtk.c
> > +++ b/ui/gtk.c
> > @@ -38,6 +38,7 @@
> > #include "qemu/cutils.h"
> > #include "qemu/error-report.h"
> > #include "qemu/main-loop.h"
> > +#include "qemu-main.h"
> >
> > #include "ui/console.h"
> > #include "ui/gtk.h"
> > @@ -2485,6 +2486,13 @@ static void gtk_display_init(DisplayState *ds, 
> > DisplayOptions *opts)
> > #ifdef CONFIG_GTK_CLIPBOARD
> >     gd_clipboard_init(s);
> > #endif /* CONFIG_GTK_CLIPBOARD */
> > +
> > +    /*
> > +     * GTK+ calls must happen on the main thread at least on some 
> > platforms,
> > +     * and on macOS the main runloop is polled via GTK+'s event handling.
> > +     * Don't allow QEMU's event loop to be moved off the main thread.
> > +     */
> > +    qemu_main = NULL;
> > }
> >
> > static void early_gtk_display_init(DisplayOptions *opts)
> > diff --git a/ui/sdl2.c b/ui/sdl2.c
> > index bd4f5a9da14..44ab2762262 100644
> > --- a/ui/sdl2.c
> > +++ b/ui/sdl2.c
> > @@ -34,6 +34,7 @@
> > #include "sysemu/sysemu.h"
> > #include "ui/win32-kbd-hook.h"
> > #include "qemu/log.h"
> > +#include "qemu-main.h"
> >
> > static int sdl2_num_outputs;
> > static struct sdl2_console *sdl2_console;
> > @@ -965,6 +966,9 @@ static void sdl2_display_init(DisplayState *ds, 
> > DisplayOptions *o)
> >     }
> >
> >     atexit(sdl_cleanup);
> > +
> > +    /* SDL's event polling (in dpy_refresh) must happen on the main 
> > thread. */
> > +    qemu_main = NULL;
> > }
> >
> > static QemuDisplay qemu_display_sdl2 = {
> >
>