Race Conditions

• The result varies unpredictably because the value of X isn’t dependable until the barrier at the end of the do loop.

• Wrong answers produced without warning!

• Solution: Be careful when you use NOWAIT.

C$OMP PARALLEL SHARED (X)

C$OMP& PRIVATE(TMP)

ID = OMP_GET_THREAD_NUM()

C$OMP DO REDUCTION(+:X)

DO 100 I=1,100

TMP = WORK(I)

X = X + TMP

100 CONTINUE

C$OMP END DO NOWAIT

Y(ID) = WORK(X, ID)

C$OMP END PARALLEL

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