Review Session 2 Problem Solutions 

Additional Problem 1

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Additional Problem 2

Y (T2->T1)
Y (l-S1(X) r1(X) l-S2(X) r2(X) l-X2(Y) w2(Y) u2(Y) l-S1(Y) r1(Y) l-X1(Z) w1(Z) u1(X) u2(X) u1(Y) u1(Z))
N (r1(X) r2(X) V2 w2(Y) r1(Y) V1 w1(Z) -> V1 does not validate) 
N (if r1(X) precedes r2(X), then r1(Y) must also precede w2(Y) according to the tree access pattern )


Additional Problem 3 

Note: the order of some actions may differ depending on the scheduler

Wait-die:
T1 acquires l-S(A)
T2 acquires l-S(B)
T1 acquires l-X(C)
T2 acquires l-X(D)
T3 tries to acquire l-S(C) but dies
T1 tries to acquire l-X(B) but waits for T2
T4 tries to acquire l-X(D) but dies
T2 tries to acquire l-X(A) but dies 
T1 acquires l-X(B) and finishes 

Wound-wait: 
T1 acquires l-S(A)
T2 acquires l-S(B)
T1 acquires l-X(C)
T2 acquires l-X(D)
T3 tries to acquire l-S(C) but waits
T1 acquires l-X(B) and wounds T2 and finishes
T3 acquires l-S(C) and finishes
T4 acquires l-X(D) and finishes