Use Array.Clone() to copy arrays, and avoid copy where applicable

[drieseng]

Use Array.Clone()to copy arrays, and avoid copy on overloads that do not take an array as argument (but would previously result in a IEnumerable<TSource>.ToArray() on an empty array).

BenchmarkDotNet=v0.10.13, OS=Windows 10.0.17134
Intel Core i7-6700K CPU 4.00GHz (Skylake), 1 CPU, 8 logical cores and 4 physical cores
Frequency=3914069 Hz, Resolution=255.4886 ns, Timer=TSC
.NET Core SDK=2.1.400
  [Host]     : .NET Core 2.2.0-preview3-26927-02 (CoreCLR 4.6.26927.02, CoreFX 4.6.26927.02), 64bit RyuJIT
  Job-GXNCHM : .NET Core 2.2.0-preview3-26927-02 (CoreCLR 4.6.26927.02, CoreFX 4.6.26927.02), 64bit RyuJIT

Runtime=Core  Server=True  Toolchain=.NET Core 2.2  
RunStrategy=Throughput  

Before:

Method	Mean	Error	StdDev	Op/s	Gen 0	Allocated
Segment_IEnumerable	61.65 ns	0.3671 ns	0.3434 ns	16,220,567.5	0.0010	88 B
Segment_Array	88.65 ns	0.9344 ns	0.8283 ns	11,279,681.3	0.0010	88 B
ParameterPart_Name	85.28 ns	0.3587 ns	0.2996 ns	11,725,692.8	0.0006	56 B
ParameterPart_NameAndDefault	89.95 ns	0.8693 ns	0.8131 ns	11,116,857.3	0.0008	80 B
ParameterPart_NameAndDefaultAndKind	94.33 ns	0.3389 ns	0.3170 ns	10,600,945.5	0.0008	80 B
ParameterPart_NameAndDefaultAndKindPolicies_IEnumerable	91.43 ns	1.3934 ns	1.3034 ns	10,937,076.2	0.0015	144 B
ParameterPart_NameAndDefaultAndKindPolicies_Array	110.10 ns	0.4493 ns	0.3983 ns	9,082,426.6	0.0015	144 B
Pattern_Segments_Array	1,213.76 ns	3.5435 ns	2.9590 ns	823,882.8	0.0019	232 B
Pattern_Segments_IEnumerable	1,199.66 ns	9.2345 ns	8.6379 ns	833,570.6	0.0019	232 B

After:

Method	Mean	Error	StdDev	Op/s	Gen 0	Allocated
Segment_IEnumerable	64.51 ns	1.3240 ns	1.5761 ns	15,500,607.3	0.0010	88 B
Segment_Array	54.87 ns	0.3814 ns	0.3381 ns	18,223,443.5	0.0010	88 B
ParameterPart_Name	27.38 ns	0.0366 ns	0.0305 ns	36,523,385.3	0.0007	56 B
ParameterPart_NameAndDefault	31.40 ns	0.4519 ns	0.4227 ns	31,845,325.5	0.0009	80 B
ParameterPart_NameAndDefaultAndKind	31.11 ns	0.0830 ns	0.0648 ns	32,147,564.8	0.0009	80 B
ParameterPart_NameAndDefaultAndKindPolicies_IEnumerable	91.52 ns	0.5890 ns	0.5509 ns	10,926,313.6	0.0015	144 B
ParameterPart_NameAndDefaultAndKindPolicies_Array	81.79 ns	0.4686 ns	0.4154 ns	12,226,700.0	0.0015	144 B
Pattern_Segments_Array	1,207.43 ns	1.5503 ns	1.3743 ns	828,205.4	0.0019	232 B
Pattern_Segments_IEnumerable	1,188.09 ns	6.9480 ns	6.4991 ns	841,688.0	0.0019	232 B

[drieseng]

If this approach is ok, I'll speed up the Pattern(…) overloads (that take an array) as well.

[JamesNK]

Where is the performance benefit coming from? Are there specific cases that are no longer copying, or is it from using Array.Clone?

I wonder why ToArray doesn't use Array.Clone internally if it is faster.

[drieseng]

Where is the performance benefit coming from? Are there specific cases that are no longer copying, or is it from using Array.Clone? I wonder why ToArray doesn't use Array.Clone internally if it is faster.

The speedup comes from the fact that previously an array was passed to - for example - ParameterPartCore(…) as an IEnumerable\ on which subsequently the ToArray<T>() extension method was invoked. This one treats an array of T as an ICollection\ to create a new array. It doesn't special case T[] so it can't just clone the array.

This was even done when we knew the array was empty, and as such no copy was necessary. Now the copy (clone) is done on the caller size, and the resulting array is then passed to ParameterPartCore(…) as an array. There's no Linq involved in the array case, and no virtual dispatch.

In case of factory method that does not take an array or IEnumerable, we avoid the copy altogether. This explains why the (micro)benefit is bigger for - for example - the ParameterPart_Name benchmark.

[drieseng]

Unrelated, but why doesn't the template for MatcherAzureBenchmarkBase combine multiple HTTP methods for a given endpoint in a single RouteEndpoint with a HttpMethodMetadata containing all HTTP methods for that endpoint? Wouldn't this be more representative?

Currently we have this:

            ...
            Endpoints[138] = CreateEndpoint("/portalsettings/signin", "PUT");
            Endpoints[139] = CreateEndpoint("/portalsettings/signin", "PATCH");
            Endpoints[140] = CreateEndpoint("/portalsettings/signin", "GET");
            ...

[rynowak]

Wouldn't this be more representative?

No not really. Typically these would be separate action methods.

[drieseng]

All PR feedback should have been addressed now.

For reference, the benchmark is now available here.