CODEWITHSUNDEEP
c#loopsfor-loop
m0fo
m0fo

Reputation: 2189

Parallel.For loops the same items

I have this Parallel.For code:

foreach (string g in allGames)
{
    eventsList.Add(game);
}

eventsList.Distinct();

Parallel.For(0, eventsList.Count, i =>
                {
                    Console.WriteLine(eventsList[i]);
                });

The allGames array contains the following strings:

String A: Lee, Stephen - Cope, Jamie
String B: Carter, Ali - Stevens, M
String C: Dott, G - McManus, Alan
String D: Bingham, S - Liu Song
String E: Davis, Mark - Joyce, Mark
String F: Walden, R - Liu Chuang

My result looks like:

Game: Lee, Stephen - Cope, Jamie
Game: Lee, Stephen - Cope, Jamie
Game: Lee, Stephen - Cope, Jamie
Game: Lee, Stephen - Cope, Jamie
Game: Carter, Ali - Stevens, M
Game: Dott, G - McManus, Alan
Game: Bingham, S - Liu Song
Game: Davis, Mark - Joyce, Mark
Game: Walden, R - Liu Chuang

It seems like it goes on same iteration for 4 times (it happens many times in the code).

I confirmed that the eventsList list DOES NOT contain any duplicates, thats 100% confirmed.

Any clue how can I solve this issue to make it works only once on each element?

Thanks!

Upvotes: 1

Views: 271

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1500535

This may be the problem - or at least it's a bug in your code:

eventsList.Distinct();

That doesn't do anything - like all other LINQ operators, it returns a new sequence, rather than modifying the existing one. Try:

eventsList = eventsList.Distinct().ToList();

I know you say you're 100% sure that the list doesn't contain any duplicates - but in that case you wouldn't need the distinct call, would you? Either way, it was a useless line of code.

The Parallel.For code you've given is fine, although it would be neater with Parallel.ForEach:

Parallel.ForEach(eventsList, Console.WriteLine);

If that still fails, please post a short but complete program demonstrating the problem.

Upvotes: 4

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