dotnet/reactive · error · ArgumentOutOfRangeException

Specified argument was out of the range of valid values…

Error message

Specified argument was out of the range of valid values. (Parameter 'capacity')

What it means

The capacity parameter bounds how many groups may exist concurrently and must be non-negative. Passing a negative value throws ArgumentOutOfRangeException at GroupByUntil.cs:57. This is a fail-fast range check applied when the capacity overload is invoked.

Solutions

1. Clamp the capacity before the call: Math.Max(0, computedCapacity)
2. Fix the config/arithmetic source producing the negative value
3. Validate user- or config-supplied capacity at load time and reject negatives early

Example fix

// before
int capacity = config.MaxGroups - activeGroups; // can be negative
var groups = source.GroupByUntil(x => x.Key, g => g.Take(1), capacity);
// after
int capacity = Math.Max(0, config.MaxGroups - activeGroups);
var groups = source.GroupByUntil(x => x.Key, g => g.Take(1), capacity);

if (capacity < 0) throw new ArgumentException("capacity must be >= 0"); // or clamp: capacity = Math.Max(0, capacity);

bool IsValidCapacity(int capacity) => capacity >= 0;

try { var groups = source.GroupByUntil(ks, ds, capacity); } catch (ArgumentOutOfRangeException ex) when (ex.ParamName == "capacity") { capacity = 0; /* retry or log bad config */ }

When it happens

Trigger: Calling AsyncObservable.GroupByUntil(source, keySelector, durationSelector, -1) — typically a computed capacity like limit - consumed that went negative, or an uninitialized/default-initialized sentinel.

Common situations: Capacity derived from configuration where a negative or unparsed value slipped in; arithmetic like expectedCount - actualCount producing -1; int fields defaulted to -1 as 'unset'.

Related errors

• capacity
• nameof(index)
• Specified argument was out of the range of valid values…
• Value cannot be null. (Parameter 'keySelector')
• Value cannot be null. (Parameter 'durationSelector')

AI-assisted analysis of dotnet/reactive@94b5d5ab91 (2026-09-15). Data as JSON: /api/errors/8d7ab099cf54e6ca. Report an issue: GitHub.

Appendix: source

Thrown at AsyncRx.NET/System.Reactive.Async/Linq/Operators/GroupByUntil.cs:57

            if (comparer == null)
                throw new ArgumentNullException(nameof(comparer));

            return CreateAsyncObservable<IGroupedAsyncObservable<TKey, TSource>>.From(
                source,
                (keySelector, durationSelector, comparer),
                static (source, state, observer) => GroupByUntilCore<TSource, TKey, TSource, TDuration>(source, observer, (o, d) => AsyncObserver.GroupByUntil(o, d, state.keySelector, state.durationSelector, state.comparer)));
        }

        public static IAsyncObservable<IGroupedAsyncObservable<TKey, TSource>> GroupByUntil<TSource, TKey, TDuration>(this IAsyncObservable<TSource> source, Func<TSource, TKey> keySelector, Func<IGroupedAsyncObservable<TKey, TSource>, IAsyncObservable<TDuration>> durationSelector, int capacity)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (keySelector == null)
                throw new ArgumentNullException(nameof(keySelector));
            if (durationSelector == null)
                throw new ArgumentNullException(nameof(durationSelector));
            if (capacity < 0)
                throw new ArgumentOutOfRangeException(nameof(capacity));

            return CreateAsyncObservable<IGroupedAsyncObservable<TKey, TSource>>.From(
                source,
                (keySelector, durationSelector, capacity),
                static (source, state, observer) => GroupByUntilCore<TSource, TKey, TSource, TDuration>(source, observer, (o, d) => AsyncObserver.GroupByUntil(o, d, state.keySelector, state.durationSelector, state.capacity)));
        }

        public static IAsyncObservable<IGroupedAsyncObservable<TKey, TSource>> GroupByUntil<TSource, TKey, TDuration>(this IAsyncObservable<TSource> source, Func<TSource, TKey> keySelector, Func<IGroupedAsyncObservable<TKey, TSource>, IAsyncObservable<TDuration>> durationSelector, int capacity, IEqualityComparer<TKey> comparer)
        {
            if (source == null)
                throw new ArgumentNullException(nameof(source));
            if (keySelector == null)
                throw new ArgumentNullException(nameof(keySelector));
            if (durationSelector == null)
                throw new ArgumentNullException(nameof(durationSelector));
            if (capacity < 0)
                throw new ArgumentOutOfRangeException(nameof(capacity));
            if (comparer == null)

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