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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. 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.) Signed-off-by: Phil Dennis-Jordan <phil@philjordan.eu> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com> Tested-by: Akihiko Odaki <akihiko.odaki@daynix.com> Message-ID: <20241223221645.29911-2-phil@philjordan.eu> [PMD: Declare 'qemu_main' symbol in tests/qtest/fuzz/fuzz.c, add missing g_assert_not_reached() call in main()] Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org> |
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| authz | ||
| block | ||
| chardev | ||
| crypto | ||
| disas | ||
| exec | ||
| fpu | ||
| gdbstub | ||
| hw | ||
| io | ||
| libdecnumber | ||
| migration | ||
| monitor | ||
| net | ||
| qapi | ||
| qemu | ||
| qom | ||
| scsi | ||
| semihosting | ||
| standard-headers | ||
| system | ||
| tcg | ||
| ui | ||
| user | ||
| elf.h | ||
| glib-compat.h | ||
| qemu-io.h | ||
| qemu-main.h | ||