optimize para performance of buffered stack
This commit is contained in:
Youmu Liu
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//-----------------------------------------------------------------------
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// -----------------------------------------------------------------------
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// file="ConcurrentCapacityFixedStack"
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// Project: StgSharp
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// AuthorGroup: Nitload
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// Copyright (c) Nitload. All rights reserved.
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//
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// Permission is hereby granted, free of charge, to any person obtaining a copy
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// of this software and associated documentation files (the "Software"), to deal
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// in the Software without restriction, including without limitation the rights
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// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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// copies of the Software, and to permit persons to whom the Software is
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// furnished to do so, subject to the following conditions:
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//
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// The above copyright notice and this permission notice shall be included in all
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// copies or substantial portions of the Software.
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//
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// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
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// SOFTWARE.
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//
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// -----------------------------------------------------------------------
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// -----------------------------------------------------------------------
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using System;
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using System.Collections;
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using System.Collections.Generic;
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using System.Runtime.CompilerServices;
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using System.Threading;
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namespace StgSharp.Collections
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{
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/// <summary>
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/// Lock-free, fixed-capacity stack implemented on top of an array using atomic index
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/// operations. - No linked list; only array slots - Uses CAS on a shared top index to
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/// reserve/release slots - Per-slot state flag to safely publish/consume values under races
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/// </summary>
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public class ConcurrentCapacityFixedStack<T> : IEnumerable<T>
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{
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private readonly int[] _states; // 0 = empty, 1 = full
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private readonly T[] _values;
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private readonly int _capacity;
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// Number of full slots (observable count)
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private int _count;
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// Next push position (0.._capacity). Only modified via CAS.
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private int _top;
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public ConcurrentCapacityFixedStack(int capacity)
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{
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if (capacity <= 0) {
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throw new ArgumentOutOfRangeException(nameof(capacity));
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}
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_capacity = capacity;
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_values = new T[capacity];
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_states = new int[capacity];
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_top = 0;
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_count = 0;
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}
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public bool IsEmpty => Count == 0;
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public int Capacity => _capacity;
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public int Count => Volatile.Read(ref _count);
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public void Clear()
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{
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// Pop all elements to return slots to empty state
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while (TryPop(out _)) { }
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}
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public IEnumerator<T> GetEnumerator()
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{
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T[] snap = ToArraySnapshot();
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for (int i = 0; i < snap.Length; i++) {
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yield return snap[i];
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}
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}
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public T Peek()
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{
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if (TryPeek(out T? v)) {
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return v;
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}
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throw new InvalidOperationException("Stack is empty.");
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}
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public T Pop()
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{
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if (TryPop(out T value)) {
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return value;
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}
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throw new InvalidOperationException("Stack is empty.");
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}
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public T[] PopRange(int count)
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{
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if (count <= 0) {
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return Array.Empty<T>();
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}
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T[] result = new T[count];
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int i = 0;
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for (; i < count; i++)
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{
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if (!TryPop(out result[i]))
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{
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break;
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}
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}
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if (i == count) {
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return result;
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}
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if (i == 0) {
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return Array.Empty<T>();
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}
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T[] trimmed = new T[i];
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Array.Copy(result, trimmed, i);
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return trimmed;
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}
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public void Push(T item)
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{
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SpinWait sw = default;
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while (true)
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{
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int oldTop = Volatile.Read(ref _top);
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if (oldTop >= _capacity) {
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throw new InvalidOperationException("Stack is full.");
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}
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if (Interlocked.CompareExchange(ref _top, oldTop + 1, oldTop) != oldTop)
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{
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sw.SpinOnce();
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continue; // failed to reserve slot
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}
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// We exclusively own slot oldTop. Publish value then state.
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_values[oldTop] = item;
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Volatile.Write(ref _states[oldTop], 1); // publish
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_ = Interlocked.Increment(ref _count);
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return;
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}
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}
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public void PushRange(ReadOnlySpan<T> span)
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{
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for (int i = 0; i < span.Length; i++) {
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Push(span[i]);
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}
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}
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/// <summary>
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/// Best-effort snapshot for enumeration; not strongly consistent under concurrent
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/// mutations.
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/// </summary>
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public T[] ToArraySnapshot()
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{
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int expected = Math.Min(Volatile.Read(ref _count), _capacity);
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if (expected == 0) {
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return Array.Empty<T>();
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}
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T[] snap = new T[expected];
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int copied = 0;
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int idx = Volatile.Read(ref _top) - 1;
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while (idx >= 0 && copied < expected)
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{
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if (Volatile.Read(ref _states[idx]) == 1) {
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snap[copied++] = _values[idx];
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}
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idx--;
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}
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if (copied == snap.Length) {
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return snap;
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}
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T[] trimmed = new T[copied];
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Array.Copy(snap, trimmed, copied);
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return trimmed;
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}
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public bool TryPeek(out T value)
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{
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value = default!;
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SpinWait sw = default;
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while (true)
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{
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int top = Volatile.Read(ref _top);
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if (top <= 0) {
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return false;
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}
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int idx = top - 1;
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// If not yet published or racing, retry/spin
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if (Volatile.Read(ref _states[idx]) == 0)
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{
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if (Volatile.Read(ref _top) != top)
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{
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continue; // head moved, retry
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}
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sw.SpinOnce();
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continue;
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}
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T v = _values[idx];
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// Validate consistency
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if (Volatile.Read(ref _top) == top && Volatile.Read(ref _states[idx]) == 1)
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{
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value = v;
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return true;
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}
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}
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}
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public bool TryPop(out T value)
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{
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value = default!;
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SpinWait sw = default;
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while (true)
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{
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int oldTop = Volatile.Read(ref _top);
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if (oldTop <= 0)
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{
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return false; // empty
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}
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int newTop = oldTop - 1; // index to consume
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if (Interlocked.CompareExchange(ref _top, newTop, oldTop) != oldTop)
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{
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sw.SpinOnce();
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continue; // failed to reserve element
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}
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// If producer hasn't published yet, roll back our reservation and retry.
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if (Volatile.Read(ref _states[newTop]) == 0)
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{
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// attempt to restore top; ok if it fails due to concurrent operations
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Interlocked.CompareExchange(ref _top, newTop + 1, newTop);
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sw.SpinOnce();
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continue;
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}
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value = _values[newTop];
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_values[newTop] = default!; // avoid ref retention
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Volatile.Write(ref _states[newTop], 0); // mark empty
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Interlocked.Decrement(ref _count);
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return true;
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}
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}
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public int TryPopRange(Span<T> destination)
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{
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if (destination.IsEmpty) {
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return 0;
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}
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int i = 0;
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for (; i < destination.Length; i++)
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{
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if (!TryPop(out destination[i]))
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{
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break;
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}
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}
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return i;
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}
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IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
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}
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}
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