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The ATOMIC UPDATE Directive

In HPF_CRAFT, the ATOMIC UPDATE directive tells the compiler that a particular data item or the elements of a particular array for a specified operation must be updated atomically. This can be used within loops or in array syntax and applies to both the elements of an array with an assignment of a permutation and the elements of an array within a loop.

In the following example, all references to R(IX(I)) occur atomically, thus eliminating the possibility that different iterations might try to modify the same element concurently.

 
	REAL R(200), S(1000)

	INTEGER IX(1000)

!HPF$	DISTRIBUTE R(BLOCK), S(BLOCK), IX(BLOCK)

!HPF$	INDEPENDENT (I) ON S(I)

	DO I = 1, 1000

!HPF$		ATOMIC UPDATE

		R(IX(I)) = R(IX(I)) + S(I)

	END DO