Polly Timeout Policy test doesn't work as expected

Question

I am testing a Polly TimeOut policy

public static IAsyncPolicy<HttpResponseMessage> GetTimeoutPolicy(int timeoutSeconds)
{
    return Policy.TimeoutAsync<HttpResponseMessage>(
       timeout: TimeSpan.FromSeconds(timeoutSeconds),
       timeoutStrategy: TimeoutStrategy.Optimistic);
}

with the following test:

[Fact]
public async Task GetTimeoutPolicy_ThrowsTimeoutRejectedException2()
{
    int timeoutSeconds = 1;
    var policy = HttpPolicies.HttpPolicies.GetTimeoutPolicy(timeoutSeconds);

    await policy.Awaiting(p => p.ExecuteAsync(async () =>
    {
      await Task.Delay(TimeSpan.FromSeconds(2));
      return new HttpResponseMessage(System.Net.HttpStatusCode.OK);
    })).Should().ThrowAsync<TimeoutRejectedException>();
}

The test fails if I don't use the TimeoutStrategy.Pessimistic strategy, it is the Task.Delay that cause the issue? How can I solve the issue?

Peter Csala · Accepted Answer · 2024-07-08 15:05:08Z

There are 4 different scenarios based on

your decorated code is synchronous or asynchronous
your timeout is using optimistic or pessimistic strategy

Sync Policy + Pessimistic strategy

var syncTimeoutPessimistic = Policy.Timeout(
    TimeSpan.FromSeconds(3), 
    TimeoutStrategy.Pessimistic, 
    (_, __, ___) =>
{
    "onTimeout is fired".Dump();
});

try
{
    syncTimeoutPessimistic.Execute(() =>
    {
        Thread.Sleep(5_000);
        "Decorated operation is finished".Dump();
    });
} 
catch(TimeoutRejectedException)
{
    "Timeout has kicked in".Dump();
}

Sync Policy + Optimistic strategy

CancellationToken should be respected otherwise it won't work

var syncTimeoutOptimistic = Policy.Timeout(
    TimeSpan.FromSeconds(3), 
    TimeoutStrategy.Optimistic, 
    (_, __, ___) =>
{
    "onTimeout is fired".Dump();
});

try
{
    syncTimeoutOptimistic.Execute((ct) =>
    {
        var result = Task.Run(() => { Thread.Sleep(5_000); return Task.CompletedTask; });
        result.Wait(ct);
        "Decorated operation is finished".Dump();
    }, CancellationToken.None);
} 
catch(TimeoutRejectedException)
{
    "Timeout has kicked in".Dump();
}

It is more like a hack than a suggested way.

Async Policy + Pessimistic strategy

var asyncTimeoutPessimistic = Policy.TimeoutAsync(
    TimeSpan.FromSeconds(3), 
    TimeoutStrategy.Pessimistic, 
    (_, __, ___) =>
{
    "onTimeout is fired".Dump();
    return Task.CompletedTask;
});

try
{
    await asyncTimeoutPessimistic.ExecuteAsync(async () =>
    {
        await Task.Delay(5_000);
        "Decorated operation is finished".Dump();
    });
} 
catch(TimeoutRejectedException)
{
    "Timeout has kicked in".Dump();
}

Async + Optimistic strategy

CancellationToken should be respected otherwise it won't work

var asyncTimeoutOptimistic = Policy.TimeoutAsync(
    TimeSpan.FromSeconds(3), 
    TimeoutStrategy.Optimistic, 
    (_, __, ___) =>
{
    "onTimeout is fired".Dump();
    return Task.CompletedTask;
});

try
{
    await asyncTimeoutOptimistic.ExecuteAsync(async (ct) =>
    {
        await Task.Delay(5_000, ct);
        "Decorated operation is finished".Dump();
    }, CancellationToken.None);
} 
catch(TimeoutRejectedException)
{
    "Timeout has kicked in".Dump();
}

In all cases you should see the following output:

Dumping object(String)
 onTimeout is fired
Dumping object(String)
 Timeout has kicked in

So, for your code (async Policy + Pessimistic strategy) you should use a different overload of ExecuteAsync which utilizes the CancellationToken. Don't forget to pass the ct to the Task.Delay!!!

p => p.ExecuteAsync(async ct =>
{
    await Task.Delay(TimeSpan.FromSeconds(2) ct);
    return new HttpResponseMessage(System.Net.HttpStatusCode.OK);
}, CancellationToken.None)

Collectives™ on Stack Overflow

Polly Timeout Policy test doesn't work as expected

1 Answer 1

Sync Policy + Pessimistic strategy

Sync Policy + Optimistic strategy

Async Policy + Pessimistic strategy

Async + Optimistic strategy

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Collectives™ on Stack Overflow

1 Answer 1

Sync Policy + Pessimistic strategy

Sync Policy + Optimistic strategy

Async Policy + Pessimistic strategy

Async + Optimistic strategy

Comments

Your Answer

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