Reduce allocation overhead of Enumerable.Order{Descending} #71564
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Enumerable.OrderBy{Descending} buffers the input into an array. It then allocates a TKey[] from that input to store the keys, and allocates an int[] that's what's actually sorted based on those keys. The enumerator uses that sorted int[] then to decide what element from the buffered input to yield next. In the case of the new Order and OrderDescending methods, though, that TKey[] isn't required; it's just a copy of the buffered input, so we can avoid it.
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Tagging subscribers to this area: @dotnet/area-system-linq Issue DetailsEnumerable.OrderBy{Descending} buffers the input into an array. It then allocates a TKey[] from that input to store the keys, and allocates an int[] that's what's actually sorted based on those keys. The enumerator uses that sorted int[] then to decide what element from the buffered input to yield next. In the case of the new Order and OrderDescending methods, though, that TKey[] isn't required; it's just a copy of the buffered input, so we can avoid it.
[Params(5, 50, 500)]
public int Length { get; set; }
private string[] _arr;
private static readonly Func<IEnumerable<string>, IEnumerable<string>> s_order = typeof(Enumerable).GetMethod("Order", new[] { typeof(IEnumerable<>).MakeGenericType(Type.MakeGenericMethodParameter(0)) })!.MakeGenericMethod(typeof(string)).CreateDelegate<Func<IEnumerable<string>, IEnumerable<string>>>();
private static readonly Func<IEnumerable<string>, Func<string, string>, IEnumerable<string>> s_orderBy = typeof(Enumerable).GetMethod("OrderBy", new[] { typeof(IEnumerable<>).MakeGenericType(Type.MakeGenericMethodParameter(0)), typeof(Func<,>).MakeGenericType(Type.MakeGenericMethodParameter(0), Type.MakeGenericMethodParameter(1)) })!.MakeGenericMethod(typeof(string), typeof(string)).CreateDelegate<Func<IEnumerable<string>, Func<string, string>, IEnumerable<string>>>();
[GlobalSetup]
public void Setup() => _arr = Enumerable.Range(1, Length).Select(i => i.ToString()).Reverse().ToArray();
[Benchmark]
public void Order()
{
foreach (string item in s_order(_arr)) { }
}
[Benchmark]
public void OrderBy()
{
foreach (string item in s_orderBy(_arr, i => i)) { }
}
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deeprobin
approved these changes
Jul 3, 2022
eiriktsarpalis
approved these changes
Jul 7, 2022
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Enumerable.OrderBy{Descending} buffers the input into an array. It then allocates a TKey[] from that input to store the keys, and allocates an int[] that's what's actually sorted based on those keys. The enumerator uses that sorted int[] then to decide what element from the buffered input to yield next. In the case of the new Order and OrderDescending methods, though, that TKey[] isn't required; it's just a copy of the buffered input, so we can avoid it.