Currently our Multi-process synchronization on Windows is broken when one of the processes exits or crashes. My investigation shows the first process releases the semaphore here
https://github.com/realm/realm-core/blob/dfd5baae3c2d1a6745bcf3a186fa5ba2f3069840/src/realm/util/interprocess_condvar.cpp#L484
and goes and waits for WaitForSingleObject(m_waiters_done which will be signaled only if both processes are able to complete the logic in
https://github.com/realm/realm-core/blob/dfd5baae3c2d1a6745bcf3a186fa5ba2f3069840/src/realm/util/interprocess_condvar.cpp#L310-L315

which if the second process has crashed or exited will never happen.

This leaves the first process hanging on the WaitForSingleObject(m_waiters_done indefinitely

This is pretty reproducible in Electron when if the user closes the window it actually closes the renderer process responsible for that window and the main process of the application is left hanging.