running two rsync processes, synchronizing the same directories

[cm]

Hi,

first I got to say, thank you to the people who invested certainly
much time to build this tool !!

Nevertheless I need some information, which I couldn't find in
the documentation.

At the moment I have to build a  web based synchronisation backend.
In this case a user can initiate a rsync process to synchronize directories.

Question1:

What happens if two rsync process are running, synchronizing the same
directories. In my case it means if two user are launching the rsync command
at the same time to equalize the same files / directories.

Question2:

How can I benefit from the -n Option (--dry-run) ? Am I right, when I say
before you do a real rsync you can check  it with "-n". Does that mean, if
a rsync with "-n" does function, the real rsync (without -n) should also
work ?

Thanks for taking time to answer.


Best Regards

Christoph