Consider the following transactions with data items P,Q,R and S initialized to…

Consider the following transactions with data items P,Q,R and S initialized to zero:

T1: read (P);

If P = 0 then p: = 2p + 5;

Write (P);

T2: read (Q);

If Q = 0 then Q: = Q + 5;

Write (Q);

T3: read (R);

If R = 0 then R: = R + 10;

Write (R);

T4: read (S);

If S = 0 then S: = S + 1;

Write (S);

Any non-serial interleaving of T1, T2, T3 and T4 for concurrent execution leads to