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Avoid allocating the CandidateSet when there's a single match #9622

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Merged
merged 3 commits into from
Apr 22, 2019
Merged

Avoid allocating the CandidateSet when there's a single match #9622

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337fcae
Avoid allocating the CandidateSet when there's a single match
davidfowl Apr 21, 2019
ae20d99
Remove RVD allocation in the fast path
davidfowl Apr 21, 2019
cd3d266
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davidfowl Apr 22, 2019
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6 changes: 3 additions & 3 deletions src/Http/Routing/src/EndpointSelectorContext.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
// Copyright (c) .NET Foundation. All rights reserved.
// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
Expand All @@ -24,7 +24,7 @@ public sealed class EndpointSelectorContext : IEndpointFeature, IRouteValuesFeat
/// </summary>
public RouteValueDictionary RouteValues
{
get => _routeValues;
get => _routeValues ?? (_routeValues = new RouteValueDictionary());
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If we're going to do this, we can take advantage of it in more cases, including the ones that involve cnadidate set.

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@JamesNK JamesNK Apr 21, 2019 •
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This is beyond the scope of this PR, but what about reusing RVD instances? It would be similar to how we're reusing HttpContext et al. It's basically a per-request allocation that is tied to the route values feature.

Reusing RVD, and the routing feature, would save allocations on every request, not just those with no route values.

Caching per-request objects on reused HttpContexts

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We can just straight up do this in Kestrel I fear we won't be able to do the more generic caching for 3.0

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If we're going to do this, we can take advantage of it in more cases, including the ones that involve cnadidate set.

Yes, we can, I just wanted to minimize the code change for now. I have to look at see what things are assuming route values are never null when looking at CandidateState.RouteValues (maybe I can do it statiaclly with #enable nullable 😄 )

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CandidateSet has some special semantics around RVD that should just be removed. If treats null RVD as a shorthand for not-a-match in some APIs.

set
{
_routeValues = value;
Expand Down Expand Up @@ -67,4 +67,4 @@ RouteData IRoutingFeature.RouteData
set => throw new NotSupportedException();
}
}
}
}
28 changes: 24 additions & 4 deletions src/Http/Routing/src/Matching/DfaMatcher.cs
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Original file line number Diff line number Diff line change
@@ -1,4 +1,4 @@
// Copyright (c) .NET Foundation. All rights reserved.
// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
Expand All @@ -16,13 +16,15 @@ internal sealed class DfaMatcher : Matcher
private readonly EndpointSelector _selector;
private readonly DfaState[] _states;
private readonly int _maxSegmentCount;
private readonly bool _isDefaultEndpointSelector;

public DfaMatcher(ILogger<DfaMatcher> logger, EndpointSelector selector, DfaState[] states, int maxSegmentCount)
{
_logger = logger;
_selector = selector;
_states = states;
_maxSegmentCount = maxSegmentCount;
_isDefaultEndpointSelector = selector is DefaultEndpointSelector;
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I'd feel slightly better if this was an exact type equality check. This isn't public, but that would capture the intent better.

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Isn’t it sealed? Future proofing?

}

public sealed override Task MatchAsync(HttpContext httpContext, EndpointSelectorContext context)
Expand Down Expand Up @@ -53,7 +55,8 @@ public sealed override Task MatchAsync(HttpContext httpContext, EndpointSelector
// FindCandidateSet will process the DFA and return a candidate set. This does
// some preliminary matching of the URL (mostly the literal segments).
var (candidates, policies) = FindCandidateSet(httpContext, path, segments);
if (candidates.Length == 0)
var candidateCount = candidates.Length;
if (candidateCount == 0)
{
if (log)
{
Expand All @@ -68,6 +71,23 @@ public sealed override Task MatchAsync(HttpContext httpContext, EndpointSelector
Logger.CandidatesFound(_logger, path, candidates);
}

var policyCount = policies.Length;

// This is a fast path for single candidate, 0 policies and default selector
if (candidateCount == 1 && policyCount == 0 && _isDefaultEndpointSelector)
{
ref var candidate = ref candidates[0];

// Just strict path matching
if (candidate.Flags == Candidate.CandidateFlags.None)
{
context.Endpoint = candidate.Endpoint;

// We're done
return Task.CompletedTask;
}
}

// At this point we have a candidate set, defined as a list of endpoints in
// priority order.
//
Expand All @@ -83,7 +103,7 @@ public sealed override Task MatchAsync(HttpContext httpContext, EndpointSelector
// `candidateSet` is the mutable state that we pass to the EndpointSelector.
var candidateSet = new CandidateSet(candidates);

for (var i = 0; i < candidates.Length; i++)
for (var i = 0; i < candidateCount; i++)
{
// PERF: using ref here to avoid copying around big structs.
//
Expand Down Expand Up @@ -165,7 +185,7 @@ public sealed override Task MatchAsync(HttpContext httpContext, EndpointSelector
}
}

if (policies.Length == 0)
if (policyCount == 0)
{
// Perf: avoid a state machine if there are no polices
return _selector.SelectAsync(httpContext, context, candidateSet);
Expand Down