On Wed, 13 Nov 2024 at 19:16, BALATON Zoltan <bala...@eik.bme.hu> wrote:
> On Wed, 13 Nov 2024, Phil Dennis-Jordan wrote:
> > macOS's Cocoa event handling must be done on the initial (main) thread
> > of the process. Furthermore, if library or application code uses
> > libdispatch, the main dispatch queue must be handling events on the main
> > thread as well.
> >
> > So far, this has affected Qemu in both the Cocoa and SDL UIs, although
> > in different ways: the Cocoa UI replaces the default qemu_main function
> > with one that spins Qemu's internal main event loop off onto a
> > background thread. SDL (which uses Cocoa internally) on the other hand
> > uses a polling approach within Qemu's main event loop. Events are
> > polled during the SDL UI's dpy_refresh callback, which happens to run
> > on the main thread by default.
> >
> > As UIs are mutually exclusive, this works OK as long as nothing else
> > needs platform-native event handling. In the next patch, a new device is
> > introduced based on the ParavirtualizedGraphics.framework in macOS.
> > This uses libdispatch internally, and only works when events are being
> > handled on the main runloop. With the current system, it works when
> > using either the Cocoa or the SDL UI. However, it does not when running
> > headless. Moreover, any attempt to install a similar scheme to the
> > Cocoa UI's main thread replacement fails when combined with the SDL
> > UI.
> >
> > This change tidies up main thread management to be more flexible.
> >
> > * The qemu_main global function pointer is a custom function for the
> > main thread, and it may now be NULL. When it is, the main thread
> > runs the main Qemu loop. This represents the traditional setup.
> > * When non-null, spawning the main Qemu event loop on a separate
> > thread is now done centrally rather than inside the Cocoa UI code.
> > * For most platforms, qemu_main is indeed NULL by default, but on
> > Darwin, it defaults to a function that runs the CFRunLoop.
> > * The Cocoa UI sets qemu_main to a function which runs the
> > NSApplication event handling runloop, as is usual for a Cocoa app.
> > * The SDL UI overrides the qemu_main function to NULL, thus
> > specifying that Qemu's main loop must run on the main
> > thread.
> > * The GTK UI also overrides the qemu_main function to NULL.
> > * For other UIs, or in the absence of UIs, the platform's default
> > behaviour is followed.
> >
> > This means that on macOS, the platform's runloop events are always
> > handled, regardless of chosen UI. The new PV graphics device will
> > thus work in all configurations. There is no functional change on other
> > operating systems.
> >
> > Signed-off-by: Phil Dennis-Jordan <p...@philjordan.eu>
> > Reviewed-by: Akihiko Odaki <akihiko.od...@daynix.com>
> > ---
> >
> > v5:
> >
> > * Simplified the way of setting/clearing the main loop by going back
> > to setting qemu_main directly, but narrowing the scope of what it
> > needs to do, and it can now be NULL.
> >
> > v6:
> >
> > * Folded function qemu_run_default_main_on_new_thread's code into
> > main()
> > * Removed whitespace changes left over on lines near code removed
> > between v4 and v5
> >
> > v9:
> >
> > * Set qemu_main to NULL for GTK UI as well.
> >
> > v10:
> >
> > * Added comments clarifying the functionality and purpose of qemu_main.
> >
> > include/qemu-main.h | 21 ++++++++++++++--
> > include/qemu/typedefs.h | 1 +
> > system/main.c | 50 ++++++++++++++++++++++++++++++++++----
> > ui/cocoa.m | 54 ++++++++++-------------------------------
> > ui/gtk.c | 8 ++++++
> > ui/sdl2.c | 4 +++
> > 6 files changed, 90 insertions(+), 48 deletions(-)
> >
> > diff --git a/include/qemu-main.h b/include/qemu-main.h
> > index 940960a7dbc..fc70681c8b5 100644
> > --- a/include/qemu-main.h
> > +++ b/include/qemu-main.h
> > @@ -5,7 +5,24 @@
> > #ifndef QEMU_MAIN_H
> > #define QEMU_MAIN_H
> >
> > -int qemu_default_main(void);
> > -extern int (*qemu_main)(void);
> > +/*
> > + * The function to run on the main (initial) thread of the process.
> > + * NULL means QEMU's main event loop.
> > + * When non-NULL, QEMU's main event loop will run on a purposely created
> > + * thread, after which the provided function pointer will be invoked on
> > + * the initial thread.
> > + * This is useful on platforms which treat the main thread as special
> > + * (macOS/Darwin) and/or require all UI API calls to occur from a
> > + * specific thread.
> > + * Implementing this via a global function pointer variable is a bit
> > + * ugly, but it's probably worth investigating the existing UI thread
> rule
> > + * violations in the SDL (e.g. #2537) and GTK+ back-ends. Fixing those
> > + * issues might precipitate requirements similar but not identical to
> those
> > + * of the Cocoa UI; hopefully we'll see some kind of pattern emerge,
> which
> > + * can then be used as a basis for an overhaul. (In fact, it may turn
> > + * out to be simplest to split the UI/native platform event thread from
> the
> > + * QEMU main event loop on all platforms, with any UI or even none at
> all.)
> > + */
> > +extern qemu_main_fn qemu_main;
>
> qemu_main_fn is defined in typdefefs.h but not included here. Also coding
> style says typedefs should be CamelCase but maybe it's just not worth to
> define a type for this and you can just leave the existing line here only
> removing the qemu_default_main declaration and adding the comment.
>
> > #endif /* QEMU_MAIN_H */
> > diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> > index 3d84efcac47..b02cfe1f328 100644
> > --- a/include/qemu/typedefs.h
> > +++ b/include/qemu/typedefs.h
> > @@ -131,5 +131,6 @@ typedef struct IRQState *qemu_irq;
> > * Function types
> > */
> > typedef void (*qemu_irq_handler)(void *opaque, int n, int level);
> > +typedef int (*qemu_main_fn)(void);
>
> Then drop this change...
>
> > #endif /* QEMU_TYPEDEFS_H */
> > diff --git a/system/main.c b/system/main.c
> > index 9b91d21ea8c..d9397a6d5d0 100644
> > --- a/system/main.c
> > +++ b/system/main.c
> > @@ -24,13 +24,14 @@
> >
> > #include "qemu/osdep.h"
> > #include "qemu-main.h"
> > +#include "qemu/main-loop.h"
> > #include "sysemu/sysemu.h"
> >
> > -#ifdef CONFIG_SDL
> > -#include <SDL.h>
> > +#ifdef CONFIG_DARWIN
> > +#include <CoreFoundation/CoreFoundation.h>
> > #endif
> >
> > -int qemu_default_main(void)
> > +static int qemu_default_main(void)
> > {
> > int status;
> >
> > @@ -40,10 +41,49 @@ int qemu_default_main(void)
> > return status;
> > }
> >
> > -int (*qemu_main)(void) = qemu_default_main;
>
> ...and leave this line here without init to define the global variable and
> only put assigning the init value in the #ifdef if you don't want to
> repeat the function pointer definition twice (but that wouldn't be a
> problem either in my opinion to do it in the #ifdef this way).
>
> > +/*
> > + * Various macOS system libraries, including the Cocoa UI and anything
> using
> > + * libdispatch, such as ParavirtualizedGraphics.framework, requires
> that the
> > + * main runloop, on the main (initial) thread be running or at least
> regularly
> > + * polled for events. A special mode is therefore supported, where the
> QEMU
> > + * main loop runs on a separate thread and the main thread handles the
> > + * CF/Cocoa runloop.
> > + */
> > +
> > +static void *call_qemu_default_main(void *opaque)
> > +{
> > + int status;
> > +
> > + bql_lock();
> > + status = qemu_default_main();
> > + bql_unlock();
> > +
> > + exit(status);
> > +}
> > +
> > +#ifdef CONFIG_DARWIN
> > +static int os_darwin_cfrunloop_main(void)
> > +{
> > + CFRunLoopRun();
> > + abort();
>
> Is it better to use g_assert_not_reached() here?
>
> > +}
> > +
> > +qemu_main_fn qemu_main = os_darwin_cfrunloop_main;
> > +#else
> > +qemu_main_fn qemu_main;
> > +#endif
> >
> > 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?
>
> Regards,
> BALATON Zoltan
>
>
Alright, I've gone ahead and worked through that, and it does indeed make
things simpler. This is what I have for include/qemu-main.h and
system/main.c now:
diff --git a/include/qemu-main.h b/include/qemu-main.h
index 940960a7dbc..e1041fe99b4 100644
--- a/include/qemu-main.h
+++ b/include/qemu-main.h
@@ -5,7 +5,29 @@
#ifndef QEMU_MAIN_H
#define QEMU_MAIN_H
-int qemu_default_main(void);
+/*
+ * The function to run on the main (initial) thread of the process.
+ * NULL means QEMU's main event loop.
+ * When non-NULL, QEMU's main event loop will run on a purposely created
+ * thread, after which the provided function pointer will be invoked on
+ * the initial thread.
+ * This is useful on platforms which treat the main thread as special
+ * (macOS/Darwin) and/or require all UI API calls to occur from a
+ * specific thread.
+ * In practice, this means that on macOS, it is initialised to a function
+ * that runs the Core Foundation runloop. The Cocoa UI "upgrades" this
+ * to the NSApplication-specific event processing variant. Other platforms
+ * currently leave it at NULL; the SDL and GTK UIs reset it to NULL even
+ * on macOS as they directly poll the runloop.
+ * Implementing this via a global function pointer variable is a bit
+ * ugly, but it's probably worth investigating the existing UI thread rule
+ * violations in the SDL (e.g. #2537) and GTK+ back-ends. Fixing those
+ * issues might precipitate requirements similar but not identical to those
+ * of the Cocoa UI; hopefully we'll see some kind of pattern emerge, which
+ * can then be used as a basis for an overhaul. (In fact, it may turn
+ * out to be simplest to split the UI/native platform event thread from the
+ * QEMU main event loop on all platforms, with any UI or even none at all.)
+ */
extern int (*qemu_main)(void);
#endif /* QEMU_MAIN_H */
diff --git a/system/main.c b/system/main.c
index 9b91d21ea8c..2d9d144ed46 100644
--- a/system/main.c
+++ b/system/main.c
@@ -24,26 +24,48 @@
#include "qemu/osdep.h"
#include "qemu-main.h"
+#include "qemu/main-loop.h"
#include "sysemu/sysemu.h"
-#ifdef CONFIG_SDL
-#include <SDL.h>
+#ifdef CONFIG_DARWIN
+#include <CoreFoundation/CoreFoundation.h>
#endif
-int qemu_default_main(void)
+static void *qemu_default_main(void *opaque)
{
int status;
+ bql_lock();
status = qemu_main_loop();
qemu_cleanup(status);
+ bql_unlock();
- return status;
+ exit(status);
}
-int (*qemu_main)(void) = qemu_default_main;
+#ifdef CONFIG_DARWIN
+static int os_darwin_cfrunloop_main(void)
+{
+ CFRunLoopRun();
+ g_assert_not_reached();
+}
+
+int (*qemu_main)(void) = os_darwin_cfrunloop_main;
+#else
+int (*qemu_main)(void);
+#endif
int main(int argc, char **argv)
{
+ QemuThread main_loop_thread;
+
qemu_init(argc, argv);
- return qemu_main();
+ bql_unlock();
+ if (qemu_main) {
+ qemu_thread_create(&main_loop_thread, "qemu_main",
+ qemu_default_main, NULL, QEMU_THREAD_DETACHED);
+ return qemu_main();
+ } else {
+ qemu_default_main(NULL);
+ }
}
