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Remove closure allocations from ServiceCollectionDescriptorExtensions #44696

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Nov 18, 2020
Merged

Remove closure allocations from ServiceCollectionDescriptorExtensions #44696

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38 changes: 28 additions & 10 deletions ....DependencyInjection.Abstractions/src/Extensions/ServiceCollectionDescriptorExtensions.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,7 +4,6 @@
using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Linq;

namespace Microsoft.Extensions.DependencyInjection.Extensions
{
Expand Down Expand Up @@ -85,10 +84,17 @@ public static void TryAdd(
throw new ArgumentNullException(nameof(descriptor));
}

if (!collection.Any(d => d.ServiceType == descriptor.ServiceType))
int count = collection.Count;
for (int i = 0; i < count; i++)
{
collection.Add(descriptor);
if (collection[i].ServiceType == descriptor.ServiceType)
{
// Already added
return;
}
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@stephentoub stephentoub Nov 15, 2020 •
edited
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How many times are these methods called in a typical startup? The fact that you said it's saving ~750 closures suggests it's called to add that many services, and this is O(N^2) (for each service looking at every other service already added)?

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@benaadams benaadams Nov 15, 2020 •
edited
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Yep definitely is; can't get the call counts atm as Tracing in dotTrace is broken for me atm 😢

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It'd be good to understand the actual cost. While saving 750 allocations is good, I'd expect saving 250,000 interface dispatches to be better ;-)

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The service collection needs to store a dictionary and introduce a new interface to check if a service type already exists

}

collection.Add(descriptor);
}

/// <summary>
Expand Down Expand Up @@ -608,12 +614,19 @@ public static void TryAddEnumerable(
nameof(descriptor));
}

if (!services.Any(d =>
d.ServiceType == descriptor.ServiceType &&
d.GetImplementationType() == implementationType))
int count = services.Count;
for (int i = 0; i < count; i++)
{
services.Add(descriptor);
ServiceDescriptor service = services[i];
if (service.ServiceType == descriptor.ServiceType &&
service.GetImplementationType() == implementationType)
{
// Already added
return;
}
}

services.Add(descriptor);
}

/// <summary>
Expand Down Expand Up @@ -674,10 +687,15 @@ public static IServiceCollection Replace(
throw new ArgumentNullException(nameof(descriptor));
}

ServiceDescriptor? registeredServiceDescriptor = collection.FirstOrDefault(s => s.ServiceType == descriptor.ServiceType);
if (registeredServiceDescriptor != null)
// Remove existing
int count = collection.Count;
for (int i = 0; i < count; i++)
{
collection.Remove(registeredServiceDescriptor);
if (collection[i].ServiceType == descriptor.ServiceType)
{
collection.RemoveAt(i);
break;
}
}

collection.Add(descriptor);
Expand Down