I want to write a state machine using queues Meaning :Each state has two or more operations After each operation is there that operation from the given state should be removed ;and only after all operations are done ,the state should be dequeued from the queuue and we should move forward to the next state

Let's visualise that:

[ state1: [ op1; op2; op3 ] ]
[ state2: [ op1; op2; op3; op4 ] ]
[ state3: [ op1; op2; op3; op4; op5; op6 ] ]
[ state4: [ op1; op2; op3; op4; op5 ] ]
[ state5: [ op1; op2 ] ]
[ state6: [ op1; op2; op3; op4 ] ]
[ state7: [ op1; op2; op3 ] ]
[ state8: [ op1; op2; op3; op4 ] ]
[ state9: [ op1; op2 ] ]
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Will all of state1 (or state9) operations be completed before any of state2 (state8)?

If so, just enqueue() a bunch of Thread::Queue objects onto a Thread::Queue. Dequeue() them one at a time and dequeue() each operation one at a time and process it. But that isn't a state machine, it's just a pre-serialised series of operations.

If however, it is your intention that the first operation of any of states 1 thru 9 can be processed in any order -- which would make it a state machine -- then you aren't using a queue for the outer level; you are using a random access data structure. Ie. an array.

So, use an array of queues rather than abusing a queue of queues.