replace delete this with safe async deletion in IBusInputContext

[lzwind]

The previous code used 'delete this' in a service watcher callback, causing use-after-free when D-Bus clients disconnect unexpectedly.

Reproduction:

1. Start fcitx5 and IBus application (gedit)
2. Force kill: kill -9 $(pgrep gedit)
3. fcitx5 may crash due to use-after-free

[wengxt]

I don't think it should happen, what's the version of fcitx you're using?

[lzwind]

The version I'm using is 5.1.16. This issue reproduces frequently in our environment when IBus applications crash unexpectedly. After applying the eventDispatcher().schedule() fix, the problem has been resolved - no more crashes observed in our testing.

The race condition is confirmed by the code comment in servicewatcher.cpp: "this maybe deleted as well because it's a member in lambda."

[wengxt]

the bug is on line 48, not really here

[lzwind]

The ServiceWatcher fix only addresses the serviceOwnerAsync callback, but the NameOwnerChanged signal handler still directly calls entry() without any protection. This path can still trigger immediate 'delete this' in frontend callbacks, causing use-after-free conditions. The eventDispatcher().schedule() approach provides comprehensive protection for all callback paths.