Thread/Event how to excute a method when boolean variable goes true (from other class)

Question

I have one classes that has an array. The code within this class set a bool variable to true (arrayfull=true), I would like to excute a method within other class that process the array.

I would like a independent thread to the set up that automatically response to this event and excute an method (within same namespace). 

Please include source code / demo code how this is done.

Thanks