Avoid generic virtual dispatch for frozen collections alternate lookup #108732

andrewjsaid · 2024-10-09T22:15:00Z

Background

In .NET 9 the Alternate Lookup concept was added to dictionaries where you could look up in a dictionary by a key type different than the original one. The main motivator was reading data off the wire e.g. keying a Dictionary<string, T> using a ReadOnlySpan<char> (or byte). Thus I created a PR in ASP.NET Core to use this new method on FrozenDictionary<string, T> when matching routing but was surprised to find that there's quite a hefty penalty when using Alternate Lookups due to the generic virtual dispatch mechanism itself being a dictionary. Thus while the memory allocations disappeared the performance in terms of speed improved only slightly in the microbenchmarks.

See dotnet/aspnetcore#58305

Solution

FrozenDictionary<string, T> currently exposes a method with the following signature where the actual work happens.

private protected virtual ref readonly TValue GetValueRefOrNullRefCore<TAlternateKey>(TAlternateKey key)

To replace it, a new mechanism was added:

private protected virtual AlternateLookupDelegate<TAlternateKey> GetAlternateLookupDelegate<TAlternateKey>()

internal delegate ref readonly TValue AlternateLookupDelegate<TAlternateKey>(FrozenDictionary<TKey, TValue> dictionary, TAlternateKey key);

The idea is that when the AlternateLookup struct is created it pays the price of the generic virtual dispatch once. It can then use the delegate as follows to avoid generic virtual dispatch:

ref readonly TValue valueRef = ref _alternateLookupDelegate(Dictionary, key);

In concrete types of FrozenDictionary we can then use the following pattern to cache a static instance of the delegate which calls the actual worker method.

// pseudocode - some details removed

private protected override AlternateLookupDelegate<TAlternateKey> GetAlternateLookupDelegate<TAlternateKey>()
    => AlternateKeyDelegateHolder<TAlternateKey>.Instance;

private static class AlternateKeyDelegateHolder<TAlternateKey>
{
    public static AlternateLookupDelegate<TAlternateKey> Instance = (dictionary, key)
        => ref ((DefaultFrozenDictionary<TKey, TValue>)dictionary).GetValueRefOrNullRefCoreAlternate(key);
}

private ref readonly TValue GetValueRefOrNullRefCoreAlternate<TAlternateKey>(TAlternateKey key)
{
    ...
}

In the above example GetAlternateLookupDelegate<TAlternateKey> simply loads a singleton delegate from a nested generic type. The delegate is implemented by calling GetValueRefOrNullRefCoreAlternate<TAlternateKey which although generic importantly is not a virtual method.

In order to avoid repeating this pattern for all the classes inheriting from OrdinalStringFrozenDictionary, a different pattern is used there. Note that in this case we do not need generics as we know that the concrete type of TAlternateKey will be ReadOnlySpan<char>, a fact which is asserted when creating the lookup.

private static AlternateLookupDelegate<ReadOnlySpan<char>> s_alternateLookup = (dictionary, key)
    => ref ((OrdinalStringFrozenDictionary<TValue>)dictionary).GetValueRefOrNullRefCoreAlternate(key);

private protected override AlternateLookupDelegate<TAlternateKey> GetAlternateLookupDelegate<TAlternateKey>()
{
    Debug.Assert(typeof(TAlternateKey) == typeof(ReadOnlySpan<char>));
    return (AlternateLookupDelegate<TAlternateKey>)(object)s_alternateLookup;
}

[MethodImpl(MethodImplOptions.AggressiveInlining)]
private protected virtual ref readonly TValue GetValueRefOrNullRefCoreAlternate(ReadOnlySpan<char> key)
{
    ... existing code
}

In the above example we are able to remove the generics from the worker method, and thus we can make it virtual - still avoiding the combination of generics and virtual dispatch. Thus the derived types can use the existing approach as follows.

private protected override ref readonly TValue GetValueRefOrNullRefCoreAlternate(ReadOnlySpan<char> key) => ref base.GetValueRefOrNullRefCoreAlternate(key);

Note that further investigation is necessary to measure whether it is a good idea to remove the virtual dispatch entirely even for classes inheriting OrdinalStringFrozenDictionary. It would result in more complex code but could be faster depending on how expensive the (non-generic) virtual dispatch is.

Conclusion

As we can see from the benchmarks below, the PR does not change the "normal" TryGetValue scenario and improves the "Alternate Lookup" TryGetValue scenario significantly.

This way the alternate lookup still suffers a performance penalty but it's not quite as significant and is more likely to justify it's use if it results in fewer allocations.

Benchmark Results

dotnet/performance Frozen Dictionary benchmarks (https://github.com/dotnet/performance/blob/main/src/benchmarks/micro/libraries/System.Collections/Frozen/Perf_FrozenDictionary_String.cs) were modified locally to add a case to use the AlternateLookup feature. I didn't create a PR as I couldn't find a clean way to add it with conditional compilation for .NET 9+

DefaultFrozenDictionary

Method	Toolchain	Count	Mean	Error	StdDev	Median	Min	Max	Ratio	RatioSD	Allocated	Alloc Ratio
TryGetValue_True_FrozenDictionary	main	10	24.82 ns	0.233 ns	0.218 ns	24.74 ns	24.45 ns	25.16 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10	24.93 ns	0.249 ns	0.233 ns	24.91 ns	24.65 ns	25.35 ns	1.00	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10	23.37 ns	0.207 ns	0.184 ns	23.30 ns	23.16 ns	23.81 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10	22.61 ns	0.174 ns	0.154 ns	22.55 ns	22.47 ns	22.93 ns	0.97	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10	141.36 ns	0.659 ns	0.584 ns	141.34 ns	140.08 ns	142.49 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10	62.76 ns	0.461 ns	0.409 ns	62.84 ns	61.81 ns	63.13 ns	0.44	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10	121.20 ns	1.008 ns	0.943 ns	121.08 ns	119.80 ns	122.92 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10	46.76 ns	0.294 ns	0.261 ns	46.65 ns	46.43 ns	47.30 ns	0.39	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	100	835.82 ns	9.389 ns	8.783 ns	839.17 ns	821.16 ns	851.62 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	100	812.22 ns	8.532 ns	7.563 ns	815.04 ns	800.04 ns	822.71 ns	0.97	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	100	566.00 ns	1.487 ns	1.161 ns	565.81 ns	564.35 ns	569.07 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionary	pr	100	565.69 ns	3.029 ns	2.833 ns	564.75 ns	562.08 ns	571.06 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	100	2,006.62 ns	13.648 ns	12.767 ns	2,000.68 ns	1,990.83 ns	2,024.54 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	100	1,196.25 ns	7.592 ns	7.102 ns	1,193.14 ns	1,190.27 ns	1,211.04 ns	0.60	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	100	1,467.58 ns	13.478 ns	12.607 ns	1,467.24 ns	1,447.26 ns	1,491.49 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	100	809.94 ns	4.464 ns	4.176 ns	811.04 ns	802.96 ns	815.78 ns	0.55	0.01	-	NA

TryGetValue_True_FrozenDictionary	main	1000	8,698.64 ns	42.144 ns	39.422 ns	8,711.26 ns	8,636.79 ns	8,771.65 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	1000	8,634.08 ns	29.948 ns	26.548 ns	8,631.32 ns	8,574.59 ns	8,669.79 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	1000	7,982.33 ns	67.440 ns	63.083 ns	8,020.97 ns	7,910.93 ns	8,060.76 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	1000	8,026.40 ns	11.676 ns	9.750 ns	8,024.86 ns	8,012.28 ns	8,051.13 ns	1.01	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	1000	19,852.27 ns	150.477 ns	140.757 ns	19,923.25 ns	19,617.70 ns	20,001.71 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	1000	12,404.54 ns	31.612 ns	29.570 ns	12,407.62 ns	12,340.32 ns	12,449.85 ns	0.62	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	1000	16,470.71 ns	77.600 ns	72.587 ns	16,491.01 ns	16,215.28 ns	16,518.22 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	1000	10,038.52 ns	56.170 ns	52.541 ns	10,056.95 ns	9,911.11 ns	10,084.57 ns	0.61	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	10000	173,394.89 ns	765.735 ns	639.423 ns	173,490.45 ns	171,768.40 ns	174,356.74 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10000	168,422.47 ns	2,242.735 ns	2,097.856 ns	167,781.79 ns	165,855.58 ns	172,569.42 ns	0.97	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10000	138,800.01 ns	995.304 ns	931.008 ns	138,332.41 ns	137,750.06 ns	140,323.01 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10000	142,408.54 ns	1,163.682 ns	1,031.574 ns	142,248.41 ns	140,787.56 ns	144,191.36 ns	1.03	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10000	330,175.06 ns	5,147.664 ns	4,815.128 ns	332,063.56 ns	324,248.27 ns	338,772.74 ns	1.00	0.02	1 B	1.00
TryGetValue_True_FrozenDictionaryLookup	pr	10000	223,406.27 ns	2,984.179 ns	2,791.403 ns	224,066.34 ns	218,652.50 ns	227,634.64 ns	0.68	0.01	1 B	1.00

TryGetValue_False_FrozenDictionaryLookup	main	10000	233,352.88 ns	950.977 ns	742.460 ns	233,392.26 ns	232,108.02 ns	234,459.24 ns	1.00	0.00	1 B	1.00
TryGetValue_False_FrozenDictionaryLookup	pr	10000	172,137.36 ns	1,150.259 ns	960.519 ns	172,313.38 ns	170,510.33 ns	173,503.94 ns	0.74	0.00	-	0.00

LengthBucketsFrozenDictionary

Method	Toolchain	Count	ItemsPerBucket	Mean	Error	StdDev	Median	Min	Max	Ratio	RatioSD	Allocated	Alloc Ratio
TryGetValue_True_FrozenDictionary	main	10	1	19.902 ns	0.1293 ns	0.1080 ns	19.914 ns	19.732 ns	20.044 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10	1	20.099 ns	0.1980 ns	0.1852 ns	20.111 ns	19.815 ns	20.473 ns	1.01	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10	1	8.641 ns	0.1863 ns	0.1742 ns	8.630 ns	8.381 ns	9.011 ns	1.00	0.03	-	NA
TryGetValue_False_FrozenDictionary	pr	10	1	8.827 ns	0.1284 ns	0.1138 ns	8.823 ns	8.648 ns	9.015 ns	1.02	0.02	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10	1	142.569 ns	0.8472 ns	0.7924 ns	142.567 ns	141.324 ns	144.147 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10	1	50.636 ns	0.3343 ns	0.3127 ns	50.754 ns	50.135 ns	51.069 ns	0.36	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10	1	105.402 ns	0.7166 ns	0.6352 ns	105.667 ns	104.272 ns	106.178 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10	1	18.745 ns	0.1785 ns	0.1670 ns	18.683 ns	18.514 ns	19.066 ns	0.18	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	10	5	75.388 ns	0.4839 ns	0.4527 ns	75.218 ns	74.953 ns	76.199 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10	5	75.815 ns	0.6499 ns	0.6079 ns	76.034 ns	74.771 ns	76.590 ns	1.01	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10	5	8.964 ns	0.0512 ns	0.0478 ns	8.966 ns	8.873 ns	9.049 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10	5	8.990 ns	0.0672 ns	0.0596 ns	8.986 ns	8.867 ns	9.106 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10	5	198.743 ns	1.6434 ns	1.3723 ns	199.309 ns	196.262 ns	199.941 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10	5	114.005 ns	0.7425 ns	0.6582 ns	113.873 ns	113.278 ns	115.215 ns	0.57	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10	5	105.027 ns	0.7483 ns	0.7000 ns	105.267 ns	103.690 ns	105.595 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10	5	18.512 ns	0.2034 ns	0.1803 ns	18.572 ns	18.258 ns	18.764 ns	0.18	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	100	1	190.921 ns	1.2957 ns	1.2120 ns	190.475 ns	189.531 ns	192.608 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	100	1	191.816 ns	1.2793 ns	1.1341 ns	192.120 ns	189.424 ns	193.094 ns	1.00	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	100	1	72.753 ns	0.5778 ns	0.5405 ns	72.924 ns	71.989 ns	73.566 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	100	1	73.241 ns	0.5564 ns	0.4932 ns	73.311 ns	72.368 ns	73.965 ns	1.01	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	100	1	1,421.168 ns	13.9540 ns	11.6522 ns	1,419.412 ns	1,402.696 ns	1,449.842 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	100	1	494.229 ns	5.8461 ns	5.4685 ns	496.437 ns	481.493 ns	499.093 ns	0.35	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	100	1	1,041.986 ns	6.3858 ns	5.6609 ns	1,042.127 ns	1,034.252 ns	1,055.021 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	100	1	179.455 ns	1.1414 ns	0.9531 ns	179.811 ns	177.226 ns	180.135 ns	0.17	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	100	5	773.623 ns	5.2743 ns	4.9336 ns	775.966 ns	763.302 ns	778.488 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	100	5	772.435 ns	4.6678 ns	4.1379 ns	773.435 ns	760.933 ns	775.983 ns	1.00	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	100	5	73.001 ns	0.3449 ns	0.3226 ns	73.078 ns	72.371 ns	73.569 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	100	5	72.374 ns	0.3982 ns	0.3325 ns	72.306 ns	71.948 ns	73.207 ns	0.99	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	100	5	1,987.912 ns	17.1403 ns	16.0331 ns	1,995.164 ns	1,956.139 ns	2,005.592 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	100	5	1,137.256 ns	11.9771 ns	11.2034 ns	1,134.633 ns	1,123.508 ns	1,156.275 ns	0.57	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	100	5	1,040.490 ns	8.2041 ns	7.6741 ns	1,042.214 ns	1,028.159 ns	1,052.716 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	100	5	178.391 ns	1.5918 ns	1.4890 ns	177.725 ns	176.828 ns	181.733 ns	0.17	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	1000	1	2,142.619 ns	9.0847 ns	7.0928 ns	2,141.511 ns	2,134.290 ns	2,159.042 ns	1.00	0.00	-	NA
TryGetValue_True_FrozenDictionary	pr	1000	1	2,124.494 ns	17.4370 ns	15.4574 ns	2,118.313 ns	2,108.085 ns	2,157.025 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	1000	1	964.540 ns	5.0478 ns	4.7217 ns	962.929 ns	959.170 ns	973.696 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	1000	1	962.343 ns	8.6689 ns	7.2389 ns	960.085 ns	955.258 ns	979.858 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	1000	1	14,031.125 ns	45.7480 ns	40.5544 ns	14,022.326 ns	13,967.770 ns	14,109.108 ns	1.00	0.00	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	1000	1	4,775.847 ns	14.4875 ns	12.0977 ns	4,782.256 ns	4,756.205 ns	4,790.342 ns	0.34	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	1000	1	10,419.083 ns	118.5014 ns	105.0484 ns	10,369.367 ns	10,325.502 ns	10,686.005 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	1000	1	1,751.941 ns	4.3219 ns	3.6090 ns	1,752.104 ns	1,747.471 ns	1,760.421 ns	0.17	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	1000	5	7,563.892 ns	55.5537 ns	49.2469 ns	7,545.850 ns	7,512.330 ns	7,672.709 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	1000	5	7,818.676 ns	19.7715 ns	15.4363 ns	7,819.761 ns	7,793.648 ns	7,842.421 ns	1.03	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	1000	5	915.250 ns	1.7844 ns	1.5818 ns	915.346 ns	912.014 ns	917.874 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionary	pr	1000	5	910.566 ns	12.8763 ns	12.0445 ns	914.497 ns	891.573 ns	929.127 ns	0.99	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	1000	5	19,447.402 ns	170.0298 ns	150.7270 ns	19,370.762 ns	19,286.242 ns	19,729.391 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	1000	5	11,133.069 ns	92.3892 ns	81.9006 ns	11,139.811 ns	10,872.462 ns	11,221.569 ns	0.57	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	1000	5	10,437.497 ns	23.2264 ns	21.7260 ns	10,431.583 ns	10,410.619 ns	10,475.481 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	1000	5	1,763.392 ns	10.4994 ns	8.7674 ns	1,766.299 ns	1,752.242 ns	1,776.463 ns	0.17	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	10000	1	44,812.807 ns	236.4552 ns	221.1803 ns	44,755.250 ns	44,492.446 ns	45,244.679 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10000	1	46,652.041 ns	316.4328 ns	264.2357 ns	46,742.992 ns	45,857.045 ns	46,815.311 ns	1.04	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10000	1	24,743.250 ns	82.2079 ns	72.8752 ns	24,733.853 ns	24,628.742 ns	24,873.955 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionary	pr	10000	1	24,348.403 ns	128.3899 ns	120.0960 ns	24,298.454 ns	24,211.070 ns	24,574.111 ns	0.98	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10000	1	175,395.295 ns	2,061.6356 ns	1,928.4552 ns	175,724.157 ns	172,247.612 ns	179,175.772 ns	1.00	0.02	1 B	1.00
TryGetValue_True_FrozenDictionaryLookup	pr	10000	1	73,207.400 ns	916.1985 ns	857.0126 ns	73,653.932 ns	71,877.670 ns	74,152.553 ns	0.42	0.01	-	0.00

TryGetValue_False_FrozenDictionaryLookup	main	10000	1	187,889.132 ns	527.7729 ns	467.8569 ns	187,847.210 ns	187,278.943 ns	188,844.122 ns	1.00	0.00	1 B	1.00
TryGetValue_False_FrozenDictionaryLookup	pr	10000	1	38,704.869 ns	477.7125 ns	446.8526 ns	38,588.712 ns	38,127.456 ns	39,391.137 ns	0.21	0.00	-	0.00

TryGetValue_True_FrozenDictionary	main	10000	5	123,066.227 ns	746.0009 ns	697.8097 ns	122,825.843 ns	122,026.190 ns	124,332.341 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10000	5	123,737.585 ns	1,127.2591 ns	1,054.4389 ns	124,112.354 ns	122,209.229 ns	125,384.033 ns	1.01	0.01	1 B	NA

TryGetValue_False_FrozenDictionary	main	10000	5	21,487.233 ns	54.2720 ns	45.3195 ns	21,497.945 ns	21,402.457 ns	21,573.108 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionary	pr	10000	5	21,377.274 ns	56.0457 ns	43.7568 ns	21,374.646 ns	21,284.362 ns	21,442.488 ns	0.99	0.00	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10000	5	237,950.423 ns	2,776.5169 ns	2,597.1556 ns	236,306.250 ns	234,870.865 ns	241,643.365 ns	1.00	0.01	1 B	1.00
TryGetValue_True_FrozenDictionaryLookup	pr	10000	5	149,147.012 ns	340.2931 ns	318.3104 ns	149,128.988 ns	148,492.798 ns	149,720.476 ns	0.63	0.01	-	0.00

TryGetValue_False_FrozenDictionaryLookup	main	10000	5	135,478.543 ns	1,252.3472 ns	1,171.4464 ns	135,349.306 ns	134,010.897 ns	138,020.673 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10000	5	34,230.881 ns	322.2512 ns	301.4340 ns	34,058.756 ns	33,992.887 ns	34,774.708 ns	0.25	0.00	-	NA

SingleCharFrozenDictionary

Method	Toolchain	Count	Mean	Error	StdDev	Median	Min	Max	Ratio	RatioSD	Allocated	Alloc Ratio
TryGetValue_True_FrozenDictionary	main	10	25.03 ns	0.243 ns	0.228 ns	25.10 ns	24.57 ns	25.29 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10	24.90 ns	0.222 ns	0.186 ns	24.86 ns	24.67 ns	25.20 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10	19.65 ns	0.162 ns	0.143 ns	19.63 ns	19.41 ns	19.94 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10	19.77 ns	0.305 ns	0.285 ns	19.70 ns	19.46 ns	20.37 ns	1.01	0.02	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10	140.36 ns	1.577 ns	1.475 ns	140.66 ns	137.81 ns	143.01 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10	62.38 ns	0.469 ns	0.416 ns	62.52 ns	61.58 ns	62.96 ns	0.44	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10	109.58 ns	0.625 ns	0.488 ns	109.66 ns	108.76 ns	110.50 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10	44.69 ns	0.432 ns	0.404 ns	44.44 ns	44.09 ns	45.20 ns	0.41	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	100	233.23 ns	1.298 ns	1.084 ns	232.70 ns	232.12 ns	235.95 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	100	235.70 ns	3.162 ns	2.803 ns	234.32 ns	232.76 ns	241.40 ns	1.01	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	100	185.09 ns	1.358 ns	1.204 ns	184.73 ns	183.93 ns	188.03 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	100	185.88 ns	1.629 ns	1.444 ns	185.39 ns	184.27 ns	189.42 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	100	1,393.50 ns	12.781 ns	11.956 ns	1,386.02 ns	1,382.84 ns	1,414.38 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	100	629.05 ns	3.471 ns	3.246 ns	629.29 ns	623.57 ns	633.37 ns	0.45	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	100	1,088.17 ns	11.327 ns	10.041 ns	1,087.82 ns	1,076.58 ns	1,107.27 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	100	440.47 ns	2.459 ns	2.300 ns	440.07 ns	436.87 ns	445.37 ns	0.40	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	1000	2,336.32 ns	22.456 ns	21.006 ns	2,326.63 ns	2,312.30 ns	2,374.77 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	1000	2,353.42 ns	22.241 ns	20.805 ns	2,354.64 ns	2,328.50 ns	2,391.99 ns	1.01	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	1000	1,840.32 ns	22.863 ns	21.386 ns	1,831.90 ns	1,816.67 ns	1,886.92 ns	1.00	0.02	-	NA
TryGetValue_False_FrozenDictionary	pr	1000	1,846.40 ns	11.044 ns	9.222 ns	1,847.02 ns	1,819.15 ns	1,858.81 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	1000	13,916.96 ns	120.841 ns	113.035 ns	13,860.22 ns	13,811.26 ns	14,182.77 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	1000	6,188.74 ns	31.218 ns	29.202 ns	6,191.14 ns	6,092.64 ns	6,212.75 ns	0.44	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	1000	10,887.83 ns	107.889 ns	95.641 ns	10,908.08 ns	10,760.05 ns	11,016.79 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	1000	4,404.70 ns	36.506 ns	30.484 ns	4,415.44 ns	4,328.23 ns	4,426.62 ns	0.40	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	10000	23,729.13 ns	237.473 ns	222.132 ns	23,613.20 ns	23,526.62 ns	24,179.01 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10000	23,474.17 ns	213.858 ns	200.043 ns	23,347.04 ns	23,302.09 ns	23,809.62 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10000	18,378.85 ns	178.328 ns	158.083 ns	18,322.70 ns	18,160.98 ns	18,636.55 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10000	18,669.90 ns	102.371 ns	85.484 ns	18,700.51 ns	18,483.41 ns	18,790.11 ns	1.02	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10000	139,030.12 ns	1,236.323 ns	1,095.968 ns	138,585.77 ns	137,877.46 ns	141,096.93 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10000	61,809.42 ns	561.201 ns	497.490 ns	61,818.97 ns	61,136.20 ns	62,674.75 ns	0.44	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10000	108,375.03 ns	776.887 ns	726.701 ns	107,949.27 ns	107,731.72 ns	109,919.27 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10000	44,318.31 ns	405.006 ns	338.198 ns	44,431.91 ns	43,727.75 ns	44,770.61 ns	0.41	0.00	-	NA

SubstringFrozenDictionary

Method	Toolchain	Count	Mean	Error	StdDev	Median	Min	Max	Ratio	RatioSD	Allocated	Alloc Ratio
TryGetValue_True_FrozenDictionary	main	10	45.27 ns	0.500 ns	0.468 ns	45.44 ns	44.60 ns	45.85 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10	45.02 ns	0.415 ns	0.388 ns	45.16 ns	44.07 ns	45.47 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10	40.94 ns	0.396 ns	0.351 ns	41.08 ns	40.23 ns	41.23 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10	40.96 ns	0.407 ns	0.339 ns	40.88 ns	40.26 ns	41.73 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10	162.46 ns	1.747 ns	1.634 ns	162.78 ns	159.01 ns	164.37 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10	86.32 ns	0.231 ns	0.193 ns	86.25 ns	86.12 ns	86.83 ns	0.53	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10	134.82 ns	0.525 ns	0.465 ns	134.65 ns	134.17 ns	135.47 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	10	66.03 ns	0.621 ns	0.581 ns	66.04 ns	65.37 ns	67.28 ns	0.49	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	100	443.41 ns	2.826 ns	2.360 ns	443.62 ns	438.81 ns	446.23 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	100	449.38 ns	3.174 ns	2.814 ns	450.13 ns	443.66 ns	453.04 ns	1.01	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	100	401.50 ns	3.153 ns	2.949 ns	400.04 ns	398.29 ns	406.15 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	100	405.78 ns	2.313 ns	2.050 ns	405.61 ns	400.66 ns	408.83 ns	1.01	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	100	1,722.86 ns	11.579 ns	9.669 ns	1,721.56 ns	1,711.42 ns	1,748.19 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	100	902.06 ns	8.528 ns	7.560 ns	905.34 ns	885.24 ns	910.35 ns	0.52	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	100	1,510.85 ns	14.059 ns	13.151 ns	1,504.99 ns	1,496.83 ns	1,543.33 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	100	675.14 ns	11.842 ns	11.077 ns	675.65 ns	662.45 ns	699.63 ns	0.45	0.01	-	NA

TryGetValue_True_FrozenDictionary	main	1000	4,668.98 ns	49.785 ns	41.573 ns	4,677.99 ns	4,577.36 ns	4,724.13 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	1000	4,617.27 ns	18.507 ns	16.406 ns	4,614.33 ns	4,592.06 ns	4,651.68 ns	0.99	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	1000	4,211.73 ns	49.914 ns	46.690 ns	4,202.37 ns	4,153.66 ns	4,298.69 ns	1.00	0.02	-	NA
TryGetValue_False_FrozenDictionary	pr	1000	4,223.29 ns	31.447 ns	24.552 ns	4,228.95 ns	4,164.89 ns	4,250.04 ns	1.00	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	1000	17,170.39 ns	182.861 ns	171.049 ns	17,211.10 ns	16,890.11 ns	17,438.16 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	1000	9,088.65 ns	86.163 ns	80.597 ns	9,080.74 ns	8,955.43 ns	9,243.28 ns	0.53	0.01	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	1000	13,326.46 ns	46.269 ns	38.636 ns	13,327.35 ns	13,265.45 ns	13,407.01 ns	1.00	0.00	-	NA
TryGetValue_False_FrozenDictionaryLookup	pr	1000	6,814.56 ns	22.840 ns	20.247 ns	6,818.63 ns	6,784.58 ns	6,860.84 ns	0.51	0.00	-	NA

TryGetValue_True_FrozenDictionary	main	10000	65,610.00 ns	432.958 ns	383.806 ns	65,489.76 ns	65,173.58 ns	66,425.34 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionary	pr	10000	67,624.61 ns	887.689 ns	830.344 ns	67,540.84 ns	66,634.56 ns	68,936.38 ns	1.03	0.01	-	NA

TryGetValue_False_FrozenDictionary	main	10000	52,710.36 ns	497.305 ns	465.179 ns	52,784.55 ns	51,919.11 ns	53,485.47 ns	1.00	0.01	-	NA
TryGetValue_False_FrozenDictionary	pr	10000	51,204.82 ns	454.698 ns	403.078 ns	51,180.96 ns	50,629.71 ns	52,061.91 ns	0.97	0.01	-	NA

TryGetValue_True_FrozenDictionaryLookup	main	10000	226,872.14 ns	1,032.339 ns	965.651 ns	226,859.96 ns	224,795.47 ns	228,671.11 ns	1.00	0.01	-	NA
TryGetValue_True_FrozenDictionaryLookup	pr	10000	116,339.56 ns	301.862 ns	252.068 ns	116,278.31 ns	116,054.50 ns	116,958.27 ns	0.51	0.00	-	NA

TryGetValue_False_FrozenDictionaryLookup	main	10000	143,789.02 ns	1,235.081 ns	1,155.296 ns	143,830.91 ns	142,057.74 ns	146,136.64 ns	1.00	0.01	1 B	1.00
TryGetValue_False_FrozenDictionaryLookup	pr	10000	76,627.32 ns	354.240 ns	295.806 ns	76,555.06 ns	76,329.85 ns	77,399.18 ns	0.53	0.00	-	0.00

dotnet-policy-service · 2024-10-09T22:15:50Z

Tagging subscribers to this area: @dotnet/area-system-collections
See info in area-owners.md if you want to be subscribed.

andrewjsaid · 2024-10-29T10:25:58Z

@stephentoub I would greatly appreciate any feedback on this PR if you have the time

…virtual-dispatch

andrewjsaid · 2024-12-05T11:15:20Z

@adamsitnik I would greatly appreciate any feedback on this PR if you have the time

eiriktsarpalis · 2024-12-05T13:15:13Z

@andrewjsaid Apologies for the delay in getting this reviewed. We will get back to this as soon as possible.

...llections.Immutable/src/System/Collections/Frozen/DefaultFrozenDictionary.AlternateLookup.cs

...stem.Collections.Immutable/src/System/Collections/Frozen/DefaultFrozenSet.AlternateLookup.cs

...llections.Immutable/src/System/Collections/Frozen/DefaultFrozenDictionary.AlternateLookup.cs

...stem.Collections.Immutable/src/System/Collections/Frozen/DefaultFrozenSet.AlternateLookup.cs

...stem.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.AlternateLookup.cs

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenDictionary.cs

src/libraries/System.Collections.Immutable/src/System/Collections/Frozen/FrozenSet.cs

...tions.Immutable/src/System/Collections/Frozen/Int32/Int32FrozenDictionary.AlternateLookup.cs

....Collections.Immutable/src/System/Collections/Frozen/Int32/Int32FrozenSet.AlternateLookup.cs

stephentoub

This generally looks reasonable. Thanks for the improvement.

…virtual-dispatch

andrewjsaid · 2025-01-09T12:07:17Z

@stephentoub I've completed all the changes and am awaiting next steps.

…virtual-dispatch

stephentoub

Thanks.

@adamsitnik or @eiriktsarpalis , can you please take a look as well? Thanks.

stephentoub · 2025-01-28T06:09:06Z

/ba-g unrelated interop failure

* main: (31 commits) Fix linux-x86 build (dotnet#111861) Add FrozenDictionary specialization for integers / enums (dotnet#111886) [SRM] Refactor reading from streams. (dotnet#111323) Sign the DAC and DBI during the build process instead of in separate steps (dotnet#111416) Removing Entry2MethodDesc as it is unnecessary (dotnet#111756) Cross Product for Vector2 and Vector4 (dotnet#111265) Handle unicode in absolute URI path for combine. (dotnet#111710) Drop RequiresProcessIsolation on mcc tests (dotnet#111887) [main] Update dependencies from dotnet/roslyn (dotnet#111691) new trimmer feature System.TimeZoneInfo.Invariant (dotnet#111215) [browser] reduce msbuild memory footprint (dotnet#111751) Add debugging checks for stack overflow tests failure (dotnet#111867) Localized file check-in by OneLocBuild Task: Build definition ID 679: Build ID 2629821 (dotnet#111884) Bump main to preview2 (dotnet#111882) Avoid generic virtual dispatch for frozen collections alternate lookup (dotnet#108732) Bump main versioning to preview1 (dotnet#111880) Switch OneLoc to main (dotnet#111872) Improve docs on building ILVerify (dotnet#111851) Update Debian version to 13 (dotnet#111768) win32: add fallback to environment vars for system folder (dotnet#109673) ...

Avoid generic virtual dispatch for frozen collections alternate lookup

074ee80

dotnet-issue-labeler bot added the area-System.Collections label Oct 9, 2024

dotnet-policy-service bot added the community-contribution Indicates that the PR has been added by a community member label Oct 9, 2024

andrewjsaid mentioned this pull request Oct 9, 2024

Use new Dictionary AlternateLookup to avoid allocation in DictionaryJumpTable dotnet/aspnetcore#58305

Merged

build-analysis bot mentioned this pull request Oct 10, 2024

restarted. Azure DevOps can't recover from restarts. dotnet/dnceng#3879

Open

3 tasks

BrennanConroy requested a review from stephentoub October 16, 2024 17:20

Merge branch 'main' into frozen-collections-alternate-lookup-generic-…

0084c26

…virtual-dispatch

BrennanConroy requested a review from adamsitnik November 19, 2024 17:31

Merge branch 'main' into frozen-collections-alternate-lookup-generic-…

71ddb83

…virtual-dispatch

This was referenced Nov 26, 2024

The hosted runner encountered an error while running your job. (Error Type: Disconnect). dotnet/dnceng#1919

Open

SIGKILL (OOM?) while running LibraryImportGenerator.Tests w/o actionable log messages or artifacts dotnet/dnceng#2496

Open