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Copy pathConcurrentBuffer.cs
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153 lines (126 loc) · 4.02 KB
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/*
* Copyright (c) 2018 Alexander Nikitin, Stanislav Denisov
*
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to deal
* in the Software without restriction, including without limitation the rights
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
* copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in all
* copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
* SOFTWARE.
*/
using System;
using System.Runtime.InteropServices;
using System.Threading;
namespace NetStack.Threading {
[StructLayout(LayoutKind.Explicit, Size = 192)]
public sealed class ConcurrentBuffer {
[FieldOffset(0)]
private readonly Cell[] _buffer;
[FieldOffset(8)]
private readonly int _bufferMask;
[FieldOffset(64)]
private int _enqueuePosition;
[FieldOffset(128)]
private int _dequeuePosition;
public int Count {
get {
return _enqueuePosition - _dequeuePosition;
}
}
public ConcurrentBuffer(int bufferSize) {
if (bufferSize < 2)
throw new ArgumentException("Buffer size should be greater than or equal to two");
if ((bufferSize & (bufferSize - 1)) != 0)
throw new ArgumentException("Buffer size should be a power of two");
_bufferMask = bufferSize - 1;
_buffer = new Cell[bufferSize];
for (var i = 0; i < bufferSize; i++) {
_buffer[i] = new Cell(i, null);
}
_enqueuePosition = 0;
_dequeuePosition = 0;
}
public void Enqueue(object item) {
while (true) {
if (TryEnqueue(item))
break;
Thread.SpinWait(1);
}
}
public bool TryEnqueue(object item) {
do {
var buffer = _buffer;
var position = _enqueuePosition;
var index = position & _bufferMask;
var cell = buffer[index];
if (cell.Sequence == position && Interlocked.CompareExchange(ref _enqueuePosition, position + 1, position) == position) {
buffer[index].Element = item;
#if NET_4_6 || NET_STANDARD_2_0
Volatile.Write(ref buffer[index].Sequence, position + 1);
#else
Thread.MemoryBarrier();
buffer[index].Sequence = position + 1;
#endif
return true;
}
if (cell.Sequence < position)
return false;
}
while (true);
}
public object Dequeue() {
while (true) {
object element;
if (TryDequeue(out element))
return element;
}
}
public bool TryDequeue(out object result) {
do {
var buffer = _buffer;
var bufferMask = _bufferMask;
var position = _dequeuePosition;
var index = position & bufferMask;
var cell = buffer[index];
if (cell.Sequence == position + 1 && Interlocked.CompareExchange(ref _dequeuePosition, position + 1, position) == position) {
result = cell.Element;
buffer[index].Element = null;
#if NET_4_6 || NET_STANDARD_2_0
Volatile.Write(ref buffer[index].Sequence, position + bufferMask + 1);
#else
Thread.MemoryBarrier();
buffer[index].Sequence = position + bufferMask + 1;
#endif
return true;
}
if (cell.Sequence < position + 1) {
result = default(object);
return false;
}
}
while (true);
}
[StructLayout(LayoutKind.Explicit, Size = 16)]
private struct Cell {
[FieldOffset(0)]
public int Sequence;
[FieldOffset(8)]
public object Element;
public Cell(int sequence, object element) {
Sequence = sequence;
Element = element;
}
}
}
}