#pragma warning disable CS1591 // Missing XML comment for publicly visible type or member
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using System;
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using System.Threading;
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namespace Cysharp.Threading.Tasks.Internal
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{
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// Same interface as System.Buffers.ArrayPool<T> but only provides Shared.
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internal sealed class ArrayPool<T>
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{
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// Same size as System.Buffers.DefaultArrayPool<T>
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const int DefaultMaxNumberOfArraysPerBucket = 50;
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static readonly T[] EmptyArray = new T[0];
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public static readonly ArrayPool<T> Shared = new ArrayPool<T>();
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readonly MinimumQueue<T[]>[] buckets;
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readonly SpinLock[] locks;
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ArrayPool()
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{
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// see: GetQueueIndex
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buckets = new MinimumQueue<T[]>[18];
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locks = new SpinLock[18];
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for (int i = 0; i < buckets.Length; i++)
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{
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buckets[i] = new MinimumQueue<T[]>(4);
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locks[i] = new SpinLock(false);
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}
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}
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public T[] Rent(int minimumLength)
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{
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if (minimumLength < 0)
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{
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throw new ArgumentOutOfRangeException("minimumLength");
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}
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else if (minimumLength == 0)
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{
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return EmptyArray;
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}
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var size = CalculateSize(minimumLength);
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var index = GetQueueIndex(size);
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if (index != -1)
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{
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var q = buckets[index];
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var lockTaken = false;
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try
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{
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locks[index].Enter(ref lockTaken);
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if (q.Count != 0)
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{
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return q.Dequeue();
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}
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}
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finally
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{
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if (lockTaken) locks[index].Exit(false);
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}
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}
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return new T[size];
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}
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public void Return(T[] array, bool clearArray = false)
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{
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if (array == null || array.Length == 0)
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{
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return;
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}
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var index = GetQueueIndex(array.Length);
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if (index != -1)
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{
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if (clearArray)
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{
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Array.Clear(array, 0, array.Length);
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}
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var q = buckets[index];
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var lockTaken = false;
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try
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{
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locks[index].Enter(ref lockTaken);
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if (q.Count > DefaultMaxNumberOfArraysPerBucket)
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{
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return;
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}
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q.Enqueue(array);
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}
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finally
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{
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if (lockTaken) locks[index].Exit(false);
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}
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}
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}
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static int CalculateSize(int size)
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{
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size--;
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size |= size >> 1;
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size |= size >> 2;
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size |= size >> 4;
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size |= size >> 8;
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size |= size >> 16;
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size += 1;
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if (size < 8)
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{
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size = 8;
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}
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return size;
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}
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static int GetQueueIndex(int size)
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{
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switch (size)
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{
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case 8: return 0;
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case 16: return 1;
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case 32: return 2;
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case 64: return 3;
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case 128: return 4;
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case 256: return 5;
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case 512: return 6;
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case 1024: return 7;
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case 2048: return 8;
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case 4096: return 9;
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case 8192: return 10;
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case 16384: return 11;
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case 32768: return 12;
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case 65536: return 13;
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case 131072: return 14;
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case 262144: return 15;
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case 524288: return 16;
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case 1048576: return 17; // max array length
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default:
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return -1;
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}
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}
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}
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}
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