MTQueue.cs
143 lines
| 4.2 KiB
| text/x-csharp
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r93 | using System.Threading; | ||
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r97 | using System.Collections.Generic; | ||
| using System; | ||||
| using System.Collections; | ||||
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r14 | |||
| namespace Implab.Parallels { | ||||
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r97 | public class MTQueue<T> : IEnumerable<T> { | ||
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r14 | class Node { | ||
| public Node(T value) { | ||||
| this.value = value; | ||||
| } | ||||
| public readonly T value; | ||||
| public Node next; | ||||
| } | ||||
| Node m_first; | ||||
| Node m_last; | ||||
| public void Enqueue(T value) { | ||||
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r80 | Thread.MemoryBarrier(); | ||
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r14 | var last = m_last; | ||
| var next = new Node(value); | ||||
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r97 | // Interlocaked.CompareExchange implies Thread.MemoryBarrier(); | ||
| // to ensure that the next node is completely constructed | ||||
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r14 | while (last != Interlocked.CompareExchange(ref m_last, next, last)) | ||
| last = m_last; | ||||
| if (last != null) | ||||
| last.next = next; | ||||
| else | ||||
| m_first = next; | ||||
| } | ||||
| public bool TryDequeue(out T value) { | ||||
| Node first; | ||||
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r93 | Node next; | ||
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r14 | value = default(T); | ||
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r80 | Thread.MemoryBarrier(); | ||
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r14 | do { | ||
| first = m_first; | ||||
| if (first == null) | ||||
| return false; | ||||
| next = first.next; | ||||
| if (next == null) { | ||||
| // this is the last element, | ||||
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r19 | // then try to update the tail | ||
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r14 | if (first != Interlocked.CompareExchange(ref m_last, null, first)) { | ||
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r71 | // this is the race condition | ||
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r14 | if (m_last == null) | ||
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r19 | // the queue is empty | ||
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r14 | return false; | ||
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r71 | // tail has been changed, we need to restart | ||
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r14 | continue; | ||
| } | ||||
| // tail succesfully updated and first.next will never be changed | ||||
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r71 | // other readers will fail due to inconsistency m_last != m_fist && m_first.next == null | ||
| // however the parallel writer may update the m_first since the m_last is null | ||||
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r14 | |||
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r71 | // so we need to fix inconsistency by setting m_first to null or if it has been | ||
| // updated by the writer already then we should just to give up | ||||
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r14 | Interlocked.CompareExchange(ref m_first, null, first); | ||
| break; | ||||
| } | ||||
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r93 | if (first == Interlocked.CompareExchange(ref m_first, next, first)) | ||
| // head succesfully updated | ||||
| break; | ||||
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r14 | } while (true); | ||
| value = first.value; | ||||
| return true; | ||||
| } | ||||
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r97 | |||
| #region IEnumerable implementation | ||||
| class Enumerator : IEnumerator<T> { | ||||
| Node m_current; | ||||
| Node m_first; | ||||
| public Enumerator(Node first) { | ||||
| m_first = first; | ||||
| } | ||||
| #region IEnumerator implementation | ||||
| public bool MoveNext() { | ||||
| m_current = m_current == null ? m_first : m_current.next; | ||||
| return m_current != null; | ||||
| } | ||||
| public void Reset() { | ||||
| m_current = null; | ||||
| } | ||||
| public object IEnumerator.Current { | ||||
| get { | ||||
| if (m_current == null) | ||||
| throw new InvalidOperationException(); | ||||
| return m_current.value; | ||||
| } | ||||
| } | ||||
| #endregion | ||||
| #region IDisposable implementation | ||||
| public void Dispose() { | ||||
| } | ||||
| #endregion | ||||
| #region IEnumerator implementation | ||||
| public T Current { | ||||
| get { | ||||
| if (m_current == null) | ||||
| throw new InvalidOperationException(); | ||||
| return m_current.value; | ||||
| } | ||||
| } | ||||
| #endregion | ||||
| } | ||||
| public IEnumerator<T> GetEnumerator() { | ||||
| return new Enumerator(m_first); | ||||
| } | ||||
| #endregion | ||||
| #region IEnumerable implementation | ||||
| IEnumerator IEnumerable.GetEnumerator() { | ||||
| return GetEnumerator(); | ||||
| } | ||||
| #endregion | ||||
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r14 | } | ||
| } | ||||