operating system

Question

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2 ??

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How u solve it m not getting question actually

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S1=1, S2=0;

P1                                    P2

P(S2);                              P(S1);
R1 ;                                  R1;
R2 ;                                  V(S2);
V(S1);                               P(S1);
P(S2);                               R2;
R3;                                    R3;
R4 ;                                  V(S2);
V(S1);                                P(S1);     
                                          R4;