Reduce allocations in TokenSegment.TryMatch

[nkolev92]

Bug

Related: NuGet/Home#12728

Also internal workitem.

Regression? Last working version:

Description

This uses ReadOnlyMemory<char>.Slice() instead of string.Substring() to reduce allocations when pattern matching. This also needs to cache the matches with a Dictionary<ReadOnlyMemory<char>, object> in PatternTable so I needed to re-use an ordinal comparer that I found in another repo. The rest of the changes are fallout from changing the pattern we're looking for from a string to ReadOnlyMemory<char>. The reason I'm using ReadOnlyMemory<T> instead of ReadOnlySpan<T> is that ReadOnlySpan<T> is a readonly ref struct and can't be used as a type parameter.

I had to change the public API of NuGet.ContentModel.ContentPropertyDefinition and NuGet.ContentModel.PatternTable.TryLookup. I'm not sure how widely those are used by anyone so I marked the associated issue as a "breaking change" just to be safe.

This PR:

Name                                                                                                                                                                                                                     	Inc %	          Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.1	   99,485,616
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	   37,982,336
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.3	   22,924,920
+ nuget.packaging!NuGet.ContentModel.ContentItem.get_Properties()                                                                                                                                                        	  0.2	   16,821,344
+ system.memory.ni!?                                                                                                                                                                                                     	  0.1	   11,678,544
+ clr!JIT_New                                                                                                                                                                                                            	  0.1	   10,078,472

Name                                                                                                                                                                                                                     	Inc %	           Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.1	   100,373,768
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	    35,133,768
+ nuget.packaging!NuGet.ContentModel.ContentItem.get_Properties()                                                                                                                                                        	  0.3	    24,102,992
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.2	    21,077,912
+ system.memory.ni!?                                                                                                                                                                                                     	  0.1	    10,791,424
+ clr!JIT_New                                                                                                                                                                                                            	  0.1	     9,267,672

Name                                                                                                                                                                                                                     	Inc %	          Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.0	   93,417,816
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	   32,911,760
+ nuget.packaging!NuGet.ContentModel.ContentItem.get_Properties()                                                                                                                                                        	  0.2	   20,449,768
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.2	   19,134,128
+ system.memory.ni!?                                                                                                                                                                                                     	  0.1	   11,734,512
+ clr!JIT_New                                                                                                                                                                                                            	  0.1	    9,187,648

17.11 P3

Name                                                                                                                                                                                                                     	Inc %	           Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.3	   110,683,792
+ mscorlib.ni!System.String.Substring(Int32, Int32)                                                                                                                                                                      	  0.4	    37,942,624
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	    35,833,368
+ clr!JIT_New                                                                                                                                                                                                            	  0.4	    32,210,392
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.1	     4,697,408

Name                                                                                                                                                                                                                     	Inc %	           Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.1	   100,833,848
+ mscorlib.ni!System.String.Substring(Int32, Int32)                                                                                                                                                                      	  0.4	    35,158,928
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	    33,438,144
+ clr!JIT_New                                                                                                                                                                                                            	  0.3	    25,918,536
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.1	     6,318,240

Name                                                                                                                                                                                                                     	Inc %	           Inc
 nuget.packaging!NuGet.ContentModel.Infrastructure.PatternExpression+TokenSegment.TryMatch(class NuGet.ContentModel.ContentItem&,class System.String,class System.Collections.Generic.IReadOnlyDictionary`2,int32,int32&)	  1.3	   111,532,960
+ mscorlib.ni!System.String.Substring(Int32, Int32)                                                                                                                                                                      	  0.5	    40,336,008
+ mscorlib.ni!System.Collections.Generic.Dictionary`2[System.__Canon,System.__Canon].Insert(System.__Canon, System.__Canon, Boolean)                                                                                     	  0.4	    34,488,920
+ clr!JIT_New                                                                                                                                                                                                            	  0.3	    30,443,528
+ nuget.packaging!ContentPropertyDefinition.TryLookup                                                                                                                                                                    	  0.1	     6,264,504

3 runs each, on average, it's about 10MB for OrchardCore.
1/3 runs were a bit noisy and showing similar results.

Dictionary is the same amount of allocations, no substring allocations.
TryLookup is worse because of the ToString actualizations. A bit of a trade-off.

Note

This PR is not the last PR in this space.

• After this has been merged, I'll PR a change improving the allocations in GetRelatedFileExtensionProperty, going from ~12MB to ~8MB on OrchardCore. dev...dev-nkolev92-Jeff-TryMatch has some of the things I'm playing with.
• I'll investigate some string actualization deduplication. There's a bunch of codepaths that have it, but not all.
• We may work on https://github.com/NuGet/Client.Engineering/issues/2780, but it's a bigger thing.

PR Checklist

• PR has a meaningful title

• PR has a linked issue.

• Described changes

• Tests

  • Automated tests added
  • OR
  • Test exception - Updated existing tests
  • OR
  • N/A

• Documentation

  • Documentation PR or issue filled
  • OR
  • N/A

[nkolev92]

I got a couple of changes that depend on this one, so if anyone's not focusing on somethig unrelating, this would be a great PR to review :)

[nkolev92]

Thank you for the reviews @jeffkl, @dtivel, and @zivkan!