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comparison Implab/Parallels/MTQueue.cs @ 14:e943453e5039 promises

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Implemented interllocked queue fixed promise syncronization
author cin
date Wed, 06 Nov 2013 17:49:12 +0400
parents
children e3935fdf59a2
comparison
equal deleted inserted replaced
13:b0feb5b9ad1c 14:e943453e5039
1 using System;
2 using System.Collections.Generic;
3 using System.Linq;
4 using System.Text;
5 using System.Threading;
6
7 namespace Implab.Parallels {
8 public class MTQueue<T> {
9 class Node {
10 public Node(T value) {
11 this.value = value;
12 }
13 public readonly T value;
14 public Node next;
15 }
16
17 Node m_first;
18 Node m_last;
19
20 public void Enqueue(T value) {
21 var last = m_last;
22 var next = new Node(value);
23
24 while (last != Interlocked.CompareExchange(ref m_last, next, last))
25 last = m_last;
26
27 if (last != null)
28 last.next = next;
29 else
30 m_first = next;
31 }
32
33 public bool TryDequeue(out T value) {
34 Node first;
35 Node next = null;
36 value = default(T);
37
38 do {
39 first = m_first;
40 if (first == null)
41 return false;
42 next = first.next;
43 if (next == null) {
44 // this is the last element,
45 // then try to update tail
46 if (first != Interlocked.CompareExchange(ref m_last, null, first)) {
47 // this is inconsistent situation which means that the queue is empty
48 if (m_last == null)
49 return false;
50 // tail has been changed, that means that we need to restart
51 continue;
52 }
53
54 // tail succesfully updated and first.next will never be changed
55 // other readers will fail due to inconsistency m_last != m_fist, but m_first.next == null
56 // but the writer may update the m_first since the m_last is null
57
58 // so we need to fix inconsistency by setting m_first to null, but if it already has been
59 // updated by a writer then we should just give up
60 Interlocked.CompareExchange(ref m_first, null, first);
61 break;
62
63 } else {
64 if (first == Interlocked.CompareExchange(ref m_first, next, first))
65 // head succesfully updated
66 break;
67 }
68 } while (true);
69
70 value = first.value;
71 return true;
72 }
73 }
74 }