timeout.md

Timeout resilience strategy

About

• Options: TimeoutStrategyOptions
• Extensions: AddTimeout
• Strategy Type: Proactive
• Exceptions:
  • TimeoutRejectedException: Thrown when a delegate executed through a timeout strategy does not complete before the timeout.

---

Usage

// Add timeout using the default options.
// See https://www.pollydocs.org/strategies/timeout#defaults for defaults.
new ResiliencePipelineBuilder()
    .AddTimeout(new TimeoutStrategyOptions());

// To add a timeout with a custom TimeSpan duration
new ResiliencePipelineBuilder()
    .AddTimeout(TimeSpan.FromSeconds(3));

// To add a timeout using a custom timeout generator function
new ResiliencePipelineBuilder()
    .AddTimeout(new TimeoutStrategyOptions
    {
        TimeoutGenerator = args =>
        {
            // Note: the timeout generator supports asynchronous operations
            return new ValueTask<TimeSpan>(TimeSpan.FromSeconds(123));
        }
    });

// To add a timeout and listen for timeout events
new ResiliencePipelineBuilder()
    .AddTimeout(new TimeoutStrategyOptions
    {
        TimeoutGenerator = args =>
        {
            // Note: the timeout generator supports asynchronous operations
            return new ValueTask<TimeSpan>(TimeSpan.FromSeconds(123));
        },
        OnTimeout = args =>
        {
            Console.WriteLine($"{args.Context.OperationKey}: Execution timed out after {args.Timeout.TotalSeconds} seconds.");
            return default;
        }
    });

Example execution:

var pipeline = new ResiliencePipelineBuilder()
    .AddTimeout(TimeSpan.FromSeconds(3))
    .Build();

HttpResponseMessage httpResponse = await pipeline.ExecuteAsync(
      async ct =>
      {
          // Execute a delegate that takes a CancellationToken as an input parameter.
          return await httpClient.GetAsync(endpoint, ct);
      },
      cancellationToken);

Defaults

Property	Default Value	Description
Timeout	30 seconds	The default timeout used by the strategy.
TimeoutGenerator	null	Generates the timeout for a given execution.
OnTimeout	null	Event that is raised when timeout occurs.

Diagrams

Happy path sequence diagram

%%{init: {'theme':'dark'}}%%
sequenceDiagram
    actor C as Caller
    participant P as Pipeline
    participant T as Timeout
    participant D as DecoratedUserCallback

    C->>P: Calls ExecuteAsync
    P->>T: Calls ExecuteCore
    T->>+D: Invokes
    D->>D: Performs <br/>long-running <br/>operation
    D->>-T: Returns result
    T->>P: Returns result
    P->>C: Returns result

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Unhappy path sequence diagram

%%{init: {'theme':'dark'}}%%
sequenceDiagram
    actor C as Caller
    participant P as Pipeline
    participant T as Timeout
    participant D as DecoratedUserCallback

    C->>P: Calls ExecuteAsync
    P->>T: Calls ExecuteCore
    T->>+D: Invokes
    activate T
    activate D
    D->>D: Performs <br/>long-running <br/>operation
    T->T: Times out
    deactivate T
    T->>D: Propagates cancellation
    deactivate D
    T->>P: Throws <br/>TimeoutRejectedException
    P->>C: Propagates exception

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