Polly Policy.TimeoutAsync 没有给出 TimeoutRejected 异常

Question

Here is my sample code:

var timeoutPolicy = Policy.TimeoutAsync(TimeSpan.FromMilliseconds(_configOptions.ResponseTimeout), TimeoutStrategy.Pessimistic);
            
try
{
    return await timeoutPolicy.ExecuteAsync(async ct => await Somemethod(request, ct), CancellationToken.None);
}
catch (TimeoutRejectedException ex)
{
    _//Some logging to go here/
}

configOptions.ResponseTimeout is configured in config file, I am expecting the method await Somemethod(request, ct) , CancellationToken.None should throw TimeoutRejectedException based on the value given in config.

But it is not throwing any exception. Can anyone please help me to identify where I am going wrong?

Help will be much appreciated.

Answer 1

Optimistic timeout

The delegate does support cancellation.

The to be executed delegate

private static async Task SomeMethodAsync(CancellationToken ct = default)
{
    Console.WriteLine($"{nameof(SomeMethodAsync)} has been called.");
    await Task.Delay(15000, ct); //It is aware of the CancellationToken
}

The timeout policy

 private static AsyncTimeoutPolicy GetTimeoutPolicy
    => Policy
        .TimeoutAsync(
            TimeSpan.FromMilliseconds(1000),
            TimeoutStrategy.Optimistic,
            (context, timeout, _, exception) =>
            {
                Console.WriteLine($"{"Timeout",-10}{timeout,-10:ss\\.fff}: {exception.GetType().Name}");
                return Task.CompletedTask;
            });

The usage

var strategy = GetTimeoutPolicy;
var result = await strategy.ExecuteAsync(async (ct) => await SomeMethodAsync(ct), CancellationToken.None);

The output

SomeMethodAsync has been called.
Timeout   01.000    : TaskCanceledException
Unhandled exception. Polly.Timeout.TimeoutRejectedException: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
 ---> System.Threading.Tasks.TaskCanceledException: A task was canceled.
...

Pessimistic timeout

The delegate does not support cancellation.

The to be executed delegate

private static async Task SomeMethodAsync(CancellationToken ct = default)
{
    Console.WriteLine($"{nameof(SomeMethodAsync)} has been called.");
    await Task.Delay(15000); //It is NOT aware of the CancellationToken
}

The timeout policy

 private static AsyncTimeoutPolicy GetTimeoutPolicy
    => Policy
        .TimeoutAsync(
            TimeSpan.FromMilliseconds(1000),
            TimeoutStrategy.Pessimistic,
            (context, timeout, _, exception) =>
            {
                Console.WriteLine($"{"Timeout",-10}{timeout,-10:ss\\.fff}: {exception.GetType().Name}");
                return Task.CompletedTask;
            });

The usage

var strategy = GetTimeoutPolicy;
var result = await strategy.ExecuteAsync(async () => await SomeMethodAsync());

The output

SomeMethodAsync has been called.
Timeout   01.000    : TaskCanceledException
Unhandled exception. Polly.Timeout.TimeoutRejectedException: The delegate executed asynchronously through TimeoutPolicy did not complete within the timeout.
 ---> System.Threading.Tasks.TaskCanceledException: A task was canceled.
...