RetryAttempt and static lambdas in V8 (Zero heap allocation)

[ArminShoeibi]

Hello there. I have this code, and I need to improve two parts of it. One is the RetryAttempt, which was present in v7, and another is static lambda.

My SamanKishHttpClient class is transient, Do I need to use static lambda at all?

public sealed class SamanKishHttpClient(HttpClient httpClient, IOptions<SamanKishOptions> options, ResiliencePipelineProvider<string> resiliencePipelineProvider, MeterRegistry meterRegistry) : ISamanKishHttpClient
{
    public async Task<ApiCallResult<SamanKishTransactionAckResponseDto?>> VerifyTransactionAsync(SamanKishTransactionAckRequestDto request)
    {
        var context = ResilienceContextPool.Shared.Get();
        context.Properties.Set(PollyResilienceKeys.RETRY_COUNT, 0);
        var pipeline = resiliencePipelineProvider.GetPipeline<ApiCallResult<SamanKishTransactionAckResponseDto?>>(Constants.SAMANKISH_RETRY_VERIFY);
        try
        {
            return await pipeline.ExecuteAsync(callback: async (pipelineContext) =>
            {
                var retryCountExists = pipelineContext.Properties.TryGetValue(PollyResilienceKeys.RETRY_COUNT, out var retryCountValue);
                if (retryCountExists)
                {
                    pipelineContext.Properties.Set(PollyResilienceKeys.RETRY_COUNT, retryCountValue + 1);
                    if (pipelineContext.Properties.GetValue(PollyResilienceKeys.RETRY_COUNT, retryCountValue) > 1)
                    {
                        meterRegistry.SetOpayProviderRetryCount(PaymentProviderType.SamanKish, Constants.VERIFY_REQUEST_TYPE);
                    }
                }
                return await httpClient.PostAsJsonV2Async<SamanKishTransactionAckRequestDto, SamanKishTransactionAckResponseDto?>(options.Value.Verify, request);
            }, context);
        }
        finally
        {
            ResilienceContextPool.Shared.Return(context);
        }
    }

}

HttpClient httpClient -> Transient
IOptions options -> Singleton
MeterRegistry meterRegistry -> Singleton

How can we improve this code in the context of Polly and allocate less?

[martincostello]

You can do something like this:

public sealed class SamanKishHttpClient(HttpClient httpClient, IOptions<SamanKishOptions> options, ResiliencePipelineProvider<string> resiliencePipelineProvider, MeterRegistry meterRegistry) : ISamanKishHttpClient
{
    public async Task<ApiCallResult<SamanKishTransactionAckResponseDto?>> VerifyTransactionAsync(SamanKishTransactionAckRequestDto request)
    {
        var context = ResilienceContextPool.Shared.Get();
        context.Properties.Set(PollyResilienceKeys.RETRY_COUNT, 0);
        var pipeline = resiliencePipelineProvider.GetPipeline<ApiCallResult<SamanKishTransactionAckResponseDto?>>(Constants.SAMANKISH_RETRY_VERIFY);
        try
        {
-           return await pipeline.ExecuteAsync(callback: async (pipelineContext) =>
+           return await pipeline.ExecuteAsync(static async (pipelineContext, state) =>
            {
                var retryCountExists = pipelineContext.Properties.TryGetValue(PollyResilienceKeys.RETRY_COUNT, out var retryCountValue);
                if (retryCountExists)
                {
                    pipelineContext.Properties.Set(PollyResilienceKeys.RETRY_COUNT, retryCountValue + 1);
                    if (pipelineContext.Properties.GetValue(PollyResilienceKeys.RETRY_COUNT, retryCountValue) > 1)
                    {
-                       meterRegistry.SetOpayProviderRetryCount(PaymentProviderType.SamanKish, Constants.VERIFY_REQUEST_TYPE);
+                       state.meterRegistry.SetOpayProviderRetryCount(PaymentProviderType.SamanKish, Constants.VERIFY_REQUEST_TYPE);
                    }
                }
-               return await httpClient.PostAsJsonV2Async<SamanKishTransactionAckRequestDto, SamanKishTransactionAckResponseDto?>(options.Value.Verify, request);
+               return await state.httpClient.PostAsJsonV2Async<SamanKishTransactionAckRequestDto, SamanKishTransactionAckResponseDto?>(state.Verify, state.request);
-           }, context);
+           }, context, (httpClient, options, options.Value.Verify, meterRegistry, request));
        }
        finally
        {
            ResilienceContextPool.Shared.Return(context);
        }
    }
}

[ArminShoeibi]

Thank you @martincostello, Is using a ValueTuple better than using a closure in this code?

[martincostello]

The tuple is just a simplified example of passing the state through the avoid the closure. You could also use a custom data type of your own if you wanted.

Avoiding the closure will avoid allocations related to that, but you should benchmark your specific use case to see which of the two approaches is best for your specific needs.