Different summation results with Parallel.ForEach

user_210778 0
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I have a foreach loop that I am parallelizing and I noticed something odd. The code looks like

double sum = 0.0;

Parallel.ForEach(myCollection, arg =>
{
     sum += ComplicatedFunction(arg);
});

// Use sum variable below

When I use a regular foreach loop I get different results. There may be something deeper down inside the ComplicatedFunction but it is possible that the sum variable is being unexpectantly affected by the parallelization?

task parallel-processing c#
4 Answers

Or you can use Parallel Aggregation Operations, as properly defined in .Net. Here is the code

        object locker = new object();
        double sum= 0.0;
        Parallel.ForEach(mArray,
                        () => 0.0,                 // Initialize the local value.
                        (i, state, localResult) => localResult + ComplicatedFunction(i), localTotal =>   // Body delegate which returns the new local total.                                                                                                                                           // Add the local value
                            {
                                lock (locker) sum4+= localTotal;
                            }    // to the master value.
                        );
user_31423650
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