How does Replica Island make sure its input system is thread safe?

[Ethan Steinberg]

I am investigating how Replica Island transfers its input events from the UI thread to the game thread in a thread safe manner. I am hoping to create a similar system in my own application.

https://code.google.com/p/replicaisland/source/browse/trunk/src/com/replica/replicaisland/InputGameInterface.java seems to be the code dealing with the transfer.

It appears that Replica Island merely creates a copy of the current input states without using any locks.

Why does Replica Island do this? How does Replica Island know that the input will not change in the middle of the update?