LibThreading: Execute `on_error` on the original `EventLoop`

As the user might want to have interactions with LibGUI while handling
errors, this code should be executed in the original `EventLoop`.
Similarly to what is done with the error-free path.

1 files changed, 6 insertions, 2 deletions

diff --git a/Userland/Libraries/LibThreading/BackgroundAction.h b/Userland/Libraries/LibThreading/BackgroundAction.h
index 02aa6b3408..1d12128f8e 100644
--- a/Userland/Libraries/LibThreading/BackgroundAction.h
+++ b/Userland/Libraries/LibThreading/BackgroundAction.h
@@ -98,8 +98,12 @@ private:
                     error = result.release_error();
 
                 m_promise->cancel(Error::from_errno(ECANCELED));
-                if (m_on_error)
-                    m_on_error(move(error));
+                if (m_on_error) {
+                    origin_event_loop->deferred_invoke([this, error = move(error)]() mutable {
+                        m_on_error(move(error));
+                    });
+                    origin_event_loop->wake();
+                }
 
                 remove_from_parent();
             }