When NoMachine is left running on Mac 10.9 for some days without rebooting the host machine, the  Display Service starts to fill logs in the /Library/Application Support/NoMachine/var/log/  with hundreds of messages like:

663 240 18:31:16 307.504 Semaphore: WARNING! Try wait of semaphore at 0x103dc5408 failed.

or:

39233 973 10:54:52 477.301 Semaphore: ERROR! Failed to destroy the semaphore.