App-vNext/Polly · error · ArgumentOutOfRangeException

Value must be greater than zero.

Error message

Value must be greater than zero.

What it means

Thrown as ArgumentOutOfRangeException(nameof(maxParallelization)) when constructing a non-generic BulkheadPolicy via Policy.Bulkhead(...) with maxParallelization <= 0. The guard at BulkheadSyntax.cs:55–59 fires at policy construction time, before any semaphores are created. maxParallelization controls how many actions may execute concurrently through the bulkhead.

Solutions

1. Ensure the configuration value for maxParallelization is at least 1
2. Add a fallback default when reading from configuration: config.GetValue("MaxParallel", 10)
3. Validate the value at application startup and fail fast with a clear message

Example fix

// before
var maxPar = config.GetValue<int>("Bulkhead:MaxParallelization"); // 0 if missing
var policy = Policy.Bulkhead(maxPar, 10, _ => { }); // throws

// after
var maxPar = config.GetValue<int>("Bulkhead:MaxParallelization");
if (maxPar <= 0) maxPar = Environment.ProcessorCount;
var policy = Policy.Bulkhead(maxPar, 10, _ => { });

if (maxParallelization <= 0)
{
    throw new InvalidOperationException($"Invalid maxParallelization: {maxParallelization}. Must be >= 1.");
}
var policy = Policy.Bulkhead(maxParallelization, maxQueuingActions, onReject);

public static bool IsValidParallelization(int value) => value > 0;

When it happens

Trigger: Calling Policy.Bulkhead(maxParallelization, ...) where maxParallelization is 0 or negative. Common when the value comes from configuration that defaults to 0 or is computed from a formula that yields a non-positive result.

Common situations: Reading maxParallelization from appsettings.json where the key is missing (binds to default int 0). Calculating parallelization as a percentage of processor count with rounding to zero. Environment variable not set, parsing to 0.

Related errors

• Value must be greater than or equal to zero.
• Value must be greater than or equal to zero.
• Value must be greater than zero.
• Value cannot be null.
• Value cannot be null.

AI-assisted analysis of App-vNext/Polly@d0e46bdb1e (2026-08-13). Data as JSON: /api/errors/6b77e5fb52030aea. Report an issue: GitHub.

Appendix: source

Thrown at src/Polly/Bulkhead/BulkheadSyntax.cs:55

    public static BulkheadPolicy Bulkhead(int maxParallelization, int maxQueuingActions)
        => Bulkhead(maxParallelization, maxQueuingActions, EmptyAction);

    /// <summary>
    /// Builds a bulkhead isolation <see cref="Policy" />, which limits the maximum concurrency of actions executed through the policy.  Imposing a maximum concurrency limits the potential of governed actions, when faulting, to bring down the system.
    /// <para>When an execution would cause the number of actions executing concurrently through the policy to exceed <paramref name="maxParallelization" />, the policy allows a further <paramref name="maxQueuingActions" /> executions to queue, waiting for a concurrent execution slot.  When an execution would cause the number of queuing actions to exceed <paramref name="maxQueuingActions" />, a <see cref="BulkheadRejectedException" /> is thrown.</para>
    /// </summary>
    /// <param name="maxParallelization">The maximum number of concurrent actions that may be executing through the policy.</param>
    /// <param name="maxQueuingActions">The maximum number of actions that may be queuing, waiting for an execution slot.</param>
    /// <param name="onBulkheadRejected">An action to call, if the bulkhead rejects execution due to oversubscription.</param>
    /// <returns>The policy instance.</returns>
    /// <exception cref="ArgumentOutOfRangeException">maxParallelization;Value must be greater than zero.</exception>
    /// <exception cref="ArgumentOutOfRangeException">maxQueuingActions;Value must be greater than or equal to zero.</exception>
    /// <exception cref="ArgumentNullException">Thrown when <paramref name="onBulkheadRejected"/> is <see langword="null"/>.</exception>
    public static BulkheadPolicy Bulkhead(int maxParallelization, int maxQueuingActions, Action<Context> onBulkheadRejected)
    {
        if (maxParallelization <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(maxParallelization), "Value must be greater than zero.");
        }

        if (maxQueuingActions < 0)
        {
            throw new ArgumentOutOfRangeException(nameof(maxQueuingActions), "Value must be greater than or equal to zero.");
        }

        if (onBulkheadRejected == null)
        {
            throw new ArgumentNullException(nameof(onBulkheadRejected));
        }

        return new BulkheadPolicy(
            maxParallelization,
            maxQueuingActions,
            onBulkheadRejected);
    }

View on GitHub (pinned to d0e46bdb1e)