C# Parallel foreach - System.AggregateException: One or more errors occurred. ---> System.IndexOutOfRangeException
Solution 1
Found the answer, neither did I have to change my logic to introduce ConcurrentBag nor did I have issues of large volume insert.
The mistake in the code was that I was adding data to the wrong list i.e. sendsToday.Add(best);
Instead I had to add it to "localstorage" which is handled with a lock by .Net itself in my Final storage.
So instead of
if (best != null)
sendsToday.Add(best);
The correct code is
if (best != null)
localStorage.SubscriberSends.Add(best);
and final storage finally merges each with a locking mechanism.
Thanks anyways for all the support !
Solution 2
Inside of your inner foreach you are adding to the sendsToday which is a List<>. This is occurring on every thread.
if (best != null)
sendsToday.Add(best);
}
Instead of using List<>, try using one of the System.Collections.Concurrent implementations (e.g. ConcurrentBag). It handles all the locking internally for you and is specifically designed for threading.
var sendsToday = new ConcurrentBag<TSend>();
Solution 3
Since the method that generates the exception is List<T>.Add()
my guess the exception is thrown here:
sendsToday.Add(best);
Add a lock
around the list access and see if that helps.
Murtaza Mandvi
Updated on July 09, 2022Comments
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Murtaza Mandvi almost 2 years
Found the answer, ... The mistake in the code was that I was adding data to the wrong list
I know this has been asked a few times but I am simply unable to figure out why this will give an exception, am I missing a lock somewhere ?
var sendsToday = new List<TSend>(); var threads = _maxNumberOfThreads; if (threads <= 0) threads = 1; Parallel.ForEach(_subscribers, new ParallelOptions { MaxDegreeOfParallelism = threads }, () => new ContentSendLocalStorage<TSend, TMedium>(_contentServices, _logService), (subscriber, loopState, localStorage) => { localStorage.LogService.Warning(string.Format("Choosing content for subscriber {0}", subscriber.SubscriberId)); foreach (var newsletterId in subscriber.SubscribedNewsletterIds) { localStorage.LogService.Warning(string.Format("Choosing content for newsletter {0}", newsletterId)); var clicks = StateBag.Get<LookupList>(StateKeys.LookupList).Clicks.Where(c => c.Subscriber.SubscriberId == subscriber.SubscriberId).Select(c => c.Content.ContentId).ToArray(); foreach (var contentService in _contentServices.Where(contentService => contentService.Contents.Count != 0)) { subscriber.UrlsClicked = contentService.Contents .Where(c => clicks.Contains(c.ContentId)) .GroupBy(g => g.Page.Url) .ToDictionary(k => k.Key, v => 1); var best = contentService.GetBestForSubscriber(subscriber, new TMedium { MediumId = int.Parse(newsletterId) }); if (best != null) sendsToday.Add(best); } } localStorage.LogService.Warning(string.Format("Done choosing content for subscriber {0}", subscriber.SubscriberId)); return localStorage; }, finalStorage => { lock (ContentSendLock) { sendsToday.AddRange(finalStorage.SubscriberSends); } });
I keep getting the exception below :
System.AggregateException: One or more errors occurred. ---> System.IndexOutOfRangeException: Index was outside the bounds of the array. at System.Collections.Generic.List`1.Add(T item) at WFM.Newsletter.Business.CORE.OptimizationEngine`2.<>c__DisplayClassd.<Start>b__4(Subscriber subscriber, ParallelLoopState loopState, ContentSendLocalStorage`2 localStorage) at System.Threading.Tasks.Parallel.<>c__DisplayClass21`2.<ForEachWorker>b__1a(Int32 i, ParallelLoopState state, TLocal local) at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c() at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask) at System.Threading.Tasks.Task.<>c__DisplayClass7.<ExecuteSelfReplicating>b__6(Object ) --- End of inner exception stack trace --- at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions) at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken) at System.Threading.Tasks.Parallel.ForWorker[TLocal](Int32 fromInclusive, Int32 toExclusive, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Func`4 bodyWithLocal, Func`1 localInit, Action`1 localFinally) at System.Threading.Tasks.Parallel.ForEachWorker[TSource,TLocal](TSource[] array, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally) at System.Threading.Tasks.Parallel.ForEachWorker[TSource,TLocal](IEnumerable`1 source, ParallelOptions parallelOptions, Action`1 body, Action`2 bodyWithState, Action`3 bodyWithStateAndIndex, Func`4 bodyWithStateAndLocal, Func`5 bodyWithEverything, Func`1 localInit, Action`1 localFinally) at System.Threading.Tasks.Parallel.ForEach[TSource,TLocal](IEnumerable`1 source, ParallelOptions parallelOptions, Func`1 localInit, Func`4 body, Action`1 localFinally) at WFM.Newsletter.Business.CORE.OptimizationEngine`2.Start() at WFM.Newsletter.Business.CORE.OptimizationService.Start(IEnumerable`1 subscribers, IEnumerable`1 newsletters, LookupList lookupList, LocalConfig config, ILogging logService, Int32 maxNumberOfThreads, String subscriberClicksSourceTableName) ---> (Inner Exception #0) System.IndexOutOfRangeException: Index was outside the bounds of the array. at System.Collections.Generic.List`1.Add(T item) at WFM.Newsletter.Business.CORE.OptimizationEngine`2.<>c__DisplayClassd.<Start>b__4(Subscriber subscriber, ParallelLoopState loopState, ContentSendLocalStorage`2 localStorage) at System.Threading.Tasks.Parallel.<>c__DisplayClass21`2.<ForEachWorker>b__1a(Int32 i, ParallelLoopState state, TLocal local) at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c() at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask) at System.Threading.Tasks.Task.<>c__DisplayClass7.<ExecuteSelfReplicating>b__6(Object )<--- ---> (Inner Exception #1) System.IndexOutOfRangeException: Index was outside the bounds of the array. at System.Collections.Generic.List`1.Add(T item) at WFM.Newsletter.Business.CORE.OptimizationEngine`2.<>c__DisplayClassd.<Start>b__4(Subscriber subscriber, ParallelLoopState loopState, ContentSendLocalStorage`2 localStorage) at System.Threading.Tasks.Parallel.<>c__DisplayClass21`2.<ForEachWorker>b__1a(Int32 i, ParallelLoopState state, TLocal local) at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c() at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask) at System.Threading.Tasks.Task.<>c__DisplayClass7.<ExecuteSelfReplicating>b__6(Object )<--- ---> (Inner Exception #2) System.IndexOutOfRangeException: Index was outside the bounds of the array. at System.Collections.Generic.List`1.Add(T item) at WFM.Newsletter.Business.CORE.OptimizationEngine`2.<>c__DisplayClassd.<Start>b__4(Subscriber subscriber, ParallelLoopState loopState, ContentSendLocalStorage`2 localStorage) at System.Threading.Tasks.Parallel.<>c__DisplayClass21`2.<ForEachWorker>b__1a(Int32 i, ParallelLoopState state, TLocal local) at System.Threading.Tasks.Parallel.<>c__DisplayClassf`1.<ForWorker>b__c() at System.Threading.Tasks.Task.InnerInvoke() at System.Threading.Tasks.Task.InnerInvokeWithArg(Task childTask) at System.Threading.Tasks.Task.<>c__DisplayClass7.<ExecuteSelfReplicating>b__6(Object )<---
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Murtaza Mandvi over 11 yearsso in that case I would not require finalStorage => ?
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Mike Parkhill over 11 yearsThat's right. Since all the threads would be writing directly to the collection you wouldn't need to aggregate at the end.
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Murtaza Mandvi over 11 yearsI still doubt it as an issue with locking since in this case .Net is handling the Parallel separation and then I have a finalStorage which merges them all up, don't you thinks so? Just a thought.
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Mike Parkhill over 11 yearsInside your foreach you're adding directly to sendsToday -> sendsToday.Add(best); so you're trying to change the List<> from each thread.