Call a function before synchronous call
===

I have a simple question (but the answer does not seem to be simple).

I have a synchronous AJAX call in my code and I want to call a function before this synchronous call.

The function I want to call is simply 

    $.blockUI();

from jQuery BlockUI Plugin.

I simply tried to put that line before my $.ajax call but the blockUI seems to be called after the synchronous call.

I then tried to use the beforeSend option of $.ajax, same problem as above.

Thanks in advance for any answer you could bring (except using asynchronous call which is just impossible in my case...)