An XCHG instruction in Intel Processor is used. It is one of mechanism to implement proper Synchronization .
Let Us first discuss the working of Xchg Instruction
Syntax is xchg(oldvalue, newvalue) . An instruction is executed successfully if we swap the old value with newValue and in return get oldvalue . this is an atomic instruction .
Whoever executed this instruction fast will have acess to Cs . Hence with having small knowledge of xchg instruction you can say that FIFO order is not maintained, A slow process will have to starve , and yes no proceess can enter at same time (since it is atomic )
So solution for the above question is 1