Forget the semaphore
It gives 98% stability and I was [un]lucky enough to come twice into the other 2% during a one month testing. The most stable way is to comment out
fbrereader/src/fbreader/TimeUpdater.cpp:37
// ZLApplication::Instance().refreshWindow();
The clock is repainted on the next window refresh (caused by e.g. next/prev page flip).
P.S. Thank you for the very easy compilation process!