Parallel.ForEach with tuple return c#

Question

Based on this example I'm trying to make a parallel foreach with tuple return.

double min = double.MaxValue;

object syncObject = new object(); 
Parallel.ForEach(collection, () => double.MaxValue, (item, loopState, 
    localState) =>
    {
        double value = item.PerformComputation();
        return System.Math.Min(localState, value);
    },
    localState =>
    {
        lock(syncObj)
            min = System.Math.Min(min, localState);
    }
);

Console.Write(min + "\n");

The above code works fine but in my occasion(correct minimum value) but i don't want to output the minimum value but the 'name' of that value so i tried something like this:

double min = double.MaxValue;
string minName = "";

object syncObject = new object(); 
Parallel.ForEach(collection, () => Tuple.Create(double.MaxValue, ""), (item, 
    loopState, localState) =>
    {
        double value = PerformComputation(item.Item1.Value);
        string name = item.Item1.Key;

        return //helpHere
    },
    localState =>
    {
        lock(syncObj)
            min = //help here
            minName = //help here
    }
);

Console.Write(minName + "\n");

Tried couple things that didn't work. Also I've read microsoft's example without luck. Any help appreciated.

Peter Duniho · Accepted Answer · 2017-07-22 19:35:36Z

4

There's not very much context in your question. It would have been better for you to provide a good Minimal, Complete, and Verifiable code example that showed exactly what you're doing. But, it appears as though in your second version of the code, you have changed the computational model from an object with a PerformComputation() method, to a PerformComputation() method that is locally defined, and a collection of some kind of Tuple object, where the Item1 member is a KeyValuePair<TKey, TValue> of some sort.

Making those assumptions, something like this should work in your scenario:

Tuple<double, string> result = Tuple.Create(double.MaxValue, "");

object syncObject = new object(); 
Parallel.ForEach(collection, () => Tuple.Create(double.MaxValue, ""),
    (item, loopState, localState) =>
    {
        double value = PerformComputation(item.Item1.Value);

        if (value < localState.Item1)
        {
            localState = Tuple.Create(value, item.Item1.Key);
        }

        return localState;
    },

    localState =>
    {
        lock(syncObj)
        {
            if (localState.Item1 < result.Item1)
            {
                result = localState;
            }
        }
    }
);

answered Jul 22, 2017 at 19:35

Peter Duniho

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1 Comment

user8350967 Over a year ago

Thanks a lot. It helped me and I solved my problem. Sorry for not providing my code example correctly, net time i'll know.

Slai · Accepted Answer · 2017-07-22 19:34:20Z

2

I am not quite sure I understand the example, but should be easier with PLINQ:

string minName = collection.AsParallel()
     .Min(item => Tuple.Create(PerformComputation(item.Item1.Value), item.Item1.Key)).Item2;

answered Jul 22, 2017 at 19:34

Slai

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