App-vNext/Polly · error · InvalidOperationException

Unable to accept outcome for a task that is not completed.

Error message

Unable to accept outcome for a task that is not completed.

What it means

AcceptOutcome() only succeeds when ExecutionTaskSafe is completed; otherwise it throws InvalidOperationException. The hedging controller calls AcceptOutcome to promote a hedged task's result, and accepting an incomplete task would lock in a result that has not yet been produced, breaking the hedging decision logic.

Source

Thrown at src/Polly.Core/Hedging/Controller/TaskExecution.cs:76

    public ResilienceContext Context => _activeContext ?? throw new InvalidOperationException("TaskExecution is not initialized.");

    public HedgedTaskType Type { get; set; }

    public Action<TaskExecution<T>>? OnReset { get; set; }

    public TimeSpan ExecutionTime => _timeProvider.GetElapsedTime(_startExecutionTimestamp, _stopExecutionTimestamp);

    public int AttemptNumber { get; private set; }

    public void AcceptOutcome()
    {
        if (ExecutionTaskSafe?.IsCompleted == true)
        {
            IsAccepted = true;
        }
        else
        {
            throw new InvalidOperationException("Unable to accept outcome for a task that is not completed.");
        }
    }

    public void Cancel()
    {
        if (!IsAccepted)
        {
            _cancellationSource!.Cancel();
        }
    }

    public async ValueTask<bool> InitializeAsync<TState>(
        HedgedTaskType type,
        ResilienceContext primaryContext,
        Func<ResilienceContext, TState, ValueTask<Outcome<T>>> primaryCallback,
        TState state,
        int attemptNumber)
    {

View on GitHub (pinned to d0e46bdb1e)

Solutions

1. Await ExecutionTaskSafe (which never throws) to completion before calling AcceptOutcome.
2. If you only need the result, read Outcome after completion instead of forcing acceptance.
3. Let the HedgingResilienceStrategy manage acceptance; do not call AcceptOutcome from user code.

When it happens

Trigger: Calling AcceptOutcome on a TaskExecution whose ExecutionTaskSafe is null or still running. In normal flow the controller only accepts after awaiting completion; a misbehaving custom HedgingHandler or internal race that calls AcceptOutcome too early triggers it.

Common situations: Custom hedging action generators or test doubles that drive TaskExecution manually; instrumentation that races with the controller; a fork that reordered the accept/completion sequence.

Related errors

• TaskExecution is not initialized.
• Cannot add any more resilience strategies to the builder aft
• This instance of 'CircuitBreakerStateProvider' is already in
• No predicates were configured. There must be at least one pr
• Disposing this resilience pipeline is not allowed because it

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/902593e96c348088. Report an issue: GitHub.