[RFC PATCH-for-7.0 v2] cocoa: run qemu_init in the main thread

[Philippe Mathieu-Daudé]

From: Paolo Bonzini <pbonzini@redhat.com>

Simplify the initialization dance by running qemu_init() in the main
thread before the Cocoa event loop starts.  The cocoa_display_init()
code that is post-applicationDidFinishLaunching: moves to the
application delegate itself, and the secondary thread only runs
the rest of qemu_main(), namely qemu_main_loop() and qemu_cleanup().

This fixes a case where addRemovableDevicesMenuItems() calls
qmp_query_block() while expecting the main thread to still hold
the BQL.  The newly-introduced assertions in the block layer
complain about this.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20220307151004.578069-1-pbonzini@redhat.com>
[PMD: Fixed trivial build failures & rebased]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
---
Cc: Akihiko Odaki <akihiko.odaki@gmail.com>
Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: Emanuele Giuseppe Esposito <eesposit@redhat.com>

v1: 
20220307151004.578069-1-pbonzini@redhat.com/">https://lore.kernel.org/qemu-devel/20220307151004.578069-1-pbonzini@redhat.com/
---
 softmmu/main.c |  12 ++--
 ui/cocoa.m     | 153 ++++++++++++++++++++++---------------------------
 2 files changed, 74 insertions(+), 91 deletions(-)

diff --git a/softmmu/main.c b/softmmu/main.c
index 639c67ff48..0c4384e980 100644
--- a/softmmu/main.c
+++ b/softmmu/main.c
@@ -39,16 +39,18 @@ int main(int argc, char **argv)
 #endif
 #endif /* CONFIG_SDL */
 
-#ifdef CONFIG_COCOA
-#undef main
-#define main qemu_main
-#endif /* CONFIG_COCOA */
-
+#ifndef CONFIG_COCOA
 int main(int argc, char **argv, char **envp)
 {
+    /*
+     * ui/cocoa.m relies on this being the exact content of main(),
+     * because it has to run everything after qemu_init in a secondary
+     * thread.
+     */
     qemu_init(argc, argv, envp);
     qemu_main_loop();
     qemu_cleanup();
 
     return 0;
 }
+#endif /* CONFIG_COCOA */
diff --git a/ui/cocoa.m b/ui/cocoa.m
index cb6e7c41dc..e69ce97f44 100644
--- a/ui/cocoa.m
+++ b/ui/cocoa.m
@@ -75,6 +75,9 @@ typedef struct {
     int height;
 } QEMUScreen;
 
+@interface QemuCocoaPasteboardTypeOwner : NSObject<NSPasteboardTypeOwner>
+@end
+
 static void cocoa_update(DisplayChangeListener *dcl,
                          int x, int y, int w, int h);
 
@@ -97,20 +100,23 @@ static int last_buttons;
 static int cursor_hide = 1;
 static int left_command_key_enabled = 1;
 static bool swap_opt_cmd;
+static bool full_screen;
+static bool full_grab;
+static bool have_cocoa_ui;
 
-static int gArgc;
-static char **gArgv;
 static bool stretch_video;
 static NSTextField *pauseLabel;
 
-static QemuSemaphore display_init_sem;
-static QemuSemaphore app_started_sem;
 static bool allow_events;
 
 static NSInteger cbchangecount = -1;
 static QemuClipboardInfo *cbinfo;
 static QemuEvent cbevent;
 
+static QemuCocoaPasteboardTypeOwner *cbowner;
+static QemuClipboardPeer cbpeer;
+static QemuThread main_thread;
+
 // Utility functions to run specified code block with iothread lock held
 typedef void (^CodeBlock)(void);
 typedef bool (^BoolCodeBlock)(void);
@@ -142,6 +148,33 @@ static bool bool_with_iothread_lock(BoolCodeBlock block)
     return val;
 }
 
+/*
+ * 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 qemu_main_loop():
+ *
+ * Initial thread:                    2nd thread:
+ * in main():
+ *  qemu_init()
+ *  create application, menus, etc
+ *  enter OSX run loop
+ * in applicationDidFinishLaunching:
+ *  fullscreen if needed
+ *  create main loop thread
+ *                                    call qemu_main_loop()
+ */
+
+static void *call_qemu_main_loop(void *opaque)
+{
+    COCOA_DEBUG("Second thread: calling qemu_main()\n");
+    qemu_mutex_lock_iothread();
+    qemu_main_loop();
+    COCOA_DEBUG("Second thread: qemu_main_loop() returned, exiting\n");
+    qemu_cleanup();
+    [cbowner release];
+    exit(0);
+}
+
 // Mac to QKeyCode conversion
 static const int mac_to_qkeycode_map[] = {
     [kVK_ANSI_A] = Q_KEY_CODE_A,
@@ -780,9 +813,7 @@ static CGEventRef handleTapEvent(CGEventTapProxy proxy, 
CGEventType type, CGEven
         /*
          * Just let OSX have all events that arrive before
          * applicationDidFinishLaunching.
-         * This avoids a deadlock on the iothread lock, which 
cocoa_display_init()
-         * will not drop until after the app_started_sem is posted. (In theory
-         * there should not be any such events, but OSX Catalina now emits 
some.)
+         * This may not be needed anymore?
          */
         return false;
     }
@@ -1280,8 +1311,22 @@ static CGEventRef handleTapEvent(CGEventTapProxy proxy, 
CGEventType type, CGEven
 {
     COCOA_DEBUG("QemuCocoaAppController: applicationDidFinishLaunching\n");
     allow_events = true;
-    /* Tell cocoa_display_init to proceed */
-    qemu_sem_post(&app_started_sem);
+
+    // register vga output callbacks
+    register_displaychangelistener(&dcl);
+
+    qemu_clipboard_peer_register(&cbpeer);
+    qemu_mutex_unlock_iothread();
+    qemu_thread_create(&main_thread, "qemu_main_loop", call_qemu_main_loop,
+                       NULL, QEMU_THREAD_DETACHED);
+
+    if (full_screen) {
+        [NSApp activateIgnoringOtherApps: YES];
+        [self toggleFullScreen: nil];
+    }
+    if (full_grab) {
+        [self setFullGrab: nil];
+    }
 }
 
 - (void)applicationWillTerminate:(NSNotification *)aNotification
@@ -1804,9 +1849,6 @@ static void addRemovableDevicesMenuItems(void)
     qapi_free_BlockInfoList(pointerToFree);
 }
 
-@interface QemuCocoaPasteboardTypeOwner : NSObject<NSPasteboardTypeOwner>
-@end
-
 @implementation QemuCocoaPasteboardTypeOwner
 
 - (void)pasteboard:(NSPasteboard *)sender 
provideDataForType:(NSPasteboardType)type
@@ -1841,8 +1883,6 @@ static void addRemovableDevicesMenuItems(void)
 
 @end
 
-static QemuCocoaPasteboardTypeOwner *cbowner;
-
 static void cocoa_clipboard_notify(Notifier *notifier, void *data);
 static void cocoa_clipboard_request(QemuClipboardInfo *info,
                                     QemuClipboardType type);
@@ -1903,60 +1943,18 @@ 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 vl.c qemu_main():
- *
- * Initial thread:                    2nd thread:
- * in main():
- *  create qemu-main thread
- *  wait on display_init semaphore
- *                                    call qemu_main()
- *                                    ...
- *                                    in cocoa_display_init():
- *                                     post the display_init semaphore
- *                                     wait on app_started semaphore
- *  create application, menus, etc
- *  enter OSX run loop
- * in applicationDidFinishLaunching:
- *  post app_started semaphore
- *                                     tell main thread to fullscreen if needed
- *                                    [...]
- *                                    run qemu main-loop
- *
- * We do this in two stages so that we don't do the creation of the
- * GUI application menus and so on for command line options like --help
- * where we want to just print text to stdout and exit immediately.
- */
-
-static void *call_qemu_main(void *opaque)
+int main(int argc, char **argv, char **envp)
 {
-    int status;
-
-    COCOA_DEBUG("Second thread: calling qemu_main()\n");
-    status = qemu_main(gArgc, gArgv, *_NSGetEnviron());
-    COCOA_DEBUG("Second thread: qemu_main() returned, exiting\n");
-    [cbowner release];
-    exit(status);
-}
-
-int main (int argc, char **argv) {
-    QemuThread thread;
-
     COCOA_DEBUG("Entered main()\n");
-    gArgc = argc;
-    gArgv = argv;
+    qemu_event_init(&cbevent, false);
 
-    qemu_sem_init(&display_init_sem, 0);
-    qemu_sem_init(&app_started_sem, 0);
-
-    qemu_thread_create(&thread, "qemu_main", call_qemu_main,
-                       NULL, QEMU_THREAD_DETACHED);
-
-    COCOA_DEBUG("Main thread: waiting for display_init_sem\n");
-    qemu_sem_wait(&display_init_sem);
-    COCOA_DEBUG("Main thread: initializing app\n");
+    /* Takes iothread lock, released in applicationDidFinishLaunching:.  */
+    qemu_init(argc, argv, envp);
+    if (!have_cocoa_ui) {
+         qemu_main_loop();
+         qemu_cleanup();
+         return 0;
+    }
 
     NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
 
@@ -1978,6 +1976,7 @@ int main (int argc, char **argv) {
      */
     add_console_menu_entries();
     addRemovableDevicesMenuItems();
+    cbowner = [[QemuCocoaPasteboardTypeOwner alloc] init];
 
     // Create an Application controller
     QemuCocoaAppController *appController = [[QemuCocoaAppController alloc] 
init];
@@ -2071,24 +2070,13 @@ static void cocoa_refresh(DisplayChangeListener *dcl)
 static void cocoa_display_init(DisplayState *ds, DisplayOptions *opts)
 {
     COCOA_DEBUG("qemu_cocoa: cocoa_display_init\n");
+    have_cocoa_ui = 1;
 
-    /* Tell main thread to go ahead and create the app and enter the run loop 
*/
-    qemu_sem_post(&display_init_sem);
-    qemu_sem_wait(&app_started_sem);
-    COCOA_DEBUG("cocoa_display_init: app start completed\n");
-
-    QemuCocoaAppController *controller = (QemuCocoaAppController 
*)[[NSApplication sharedApplication] delegate];
-    /* if fullscreen mode is to be used */
     if (opts->has_full_screen && opts->full_screen) {
-        dispatch_async(dispatch_get_main_queue(), ^{
-            [NSApp activateIgnoringOtherApps: YES];
-            [controller toggleFullScreen: nil];
-        });
+        full_screen = 1;
     }
     if (opts->u.cocoa.has_full_grab && opts->u.cocoa.full_grab) {
-        dispatch_async(dispatch_get_main_queue(), ^{
-            [controller setFullGrab: nil];
-        });
+        full_grab = 1;
     }
 
     if (opts->has_show_cursor && opts->show_cursor) {
@@ -2101,13 +2089,6 @@ static void cocoa_display_init(DisplayState *ds, 
DisplayOptions *opts)
     if (opts->u.cocoa.has_left_command_key && !opts->u.cocoa.left_command_key) 
{
         left_command_key_enabled = 0;
     }
-
-    // register vga output callbacks
-    register_displaychangelistener(&dcl);
-
-    qemu_event_init(&cbevent, false);
-    cbowner = [[QemuCocoaPasteboardTypeOwner alloc] init];
-    qemu_clipboard_peer_register(&cbpeer);
 }
 
 static QemuDisplay qemu_display_cocoa = {
-- 
2.34.1