From 556d05d1e2ac687463ce2877cb4acd1b0589deed Mon Sep 17 00:00:00 2001 From: Pierrick Bouvier Date: Thu, 15 May 2025 10:46:41 -0700 Subject: [PATCH] system/main: comment lock rationale Signed-off-by: Pierrick Bouvier Reviewed-by: Richard Henderson Signed-off-by: Richard Henderson Message-ID: <20250515174641.4000309-1-pierrick.bouvier@linaro.org> --- system/main.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/system/main.c b/system/main.c index 1c02206734..b8f7157cc3 100644 --- a/system/main.c +++ b/system/main.c @@ -69,8 +69,21 @@ int (*qemu_main)(void) = os_darwin_cfrunloop_main; int main(int argc, char **argv) { qemu_init(argc, argv); + + /* + * qemu_init acquires the BQL and replay mutex lock. BQL is acquired when + * initializing cpus, to block associated threads until initialization is + * complete. Replay_mutex lock is acquired on initialization, because it + * must be held when configuring icount_mode. + * + * On MacOS, qemu main event loop runs in a background thread, as main + * thread must be reserved for UI. Thus, we need to transfer lock ownership, + * and the simplest way to do that is to release them, and reacquire them + * from qemu_default_main. + */ bql_unlock(); replay_mutex_unlock(); + if (qemu_main) { QemuThread main_loop_thread; qemu_thread_create(&main_loop_thread, "qemu_main", -- 2.39.5