_emscripten_run_callback_on_thread causing deadlocks

[Stephan Bergmann]

After upgrading emsdk to something that includes
<https://github.com/emscripten-core/emscripten/commit/c41f6590b1f9fcda12b2adb2d32cd352f163e717>
"Remove use of legacy proxy API from library_html5.js. NFC (#20370)"
(which switched code from calling `queueEventHandlerOnThread_iiii` ->
`_emscripten_dispatch_to_thread_` to calling
`_emscripten_run_callback_on_thread` -> `emscripten_proxy_sync`), I now
started to get deadlocks, in a somewhat complex scenario running a
Qt5-based LibreOffice with -sPROXY_TO_PTHREAD.

I can get rid of those deadlocks if I change
`_emscripten_run_callback_on_thread` (in `system/lib/html5/callback.c`)
from calling `emscripten_proxy_sync` to `emscripten_proxy_async`, and I
wonder if the use of the `sync` variant was intentional in the above commit?

[Sam Clegg]

That looks like a regression.  Could you open a bug for this?

Also, can you confirm that https://github.com/emscripten-core/emscripten/commit/c41f6590b1f9fcda12b2adb2d32cd352f163e717 is the culprit?  i.e. reverting this fixes the issue for you?

cheers,

sam

[Stephan Bergmann]

On 8/22/24 18:02, Sam Clegg wrote:
> That looks like a regression.  Could you open a bug for this?

see <https://github.com/emscripten-core/emscripten/issues/22442>
"Deadlock with -sPROXY_TO_PTHREAD and
_emscripten_set_resize_callback_on_thread"

> Also, can you confirm that

> https://github.com/emscripten-core/emscripten/commit/c41f6590b1f9fcda12b2adb2d32cd352f163e717 <https://github.com/emscripten-core/emscripten/commit/c41f6590b1f9fcda12b2adb2d32cd352f163e717> is the culprit?  i.e. reverting this fixes the issue for you?

yes, confirmed