annotate Implab/Components/LazyAndWeak.cs @ 209:a867536c68fc v2

Bound promise to CancellationToken Added new states to ExecutionSate enum. Added Safe.Guard() method to handle cleanup of the result of the promise
author cin
date Wed, 16 Nov 2016 03:06:08 +0300
parents 76e8f2ba12b8
children 3a6e18c432be
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1 using System;
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2 using System.Threading;
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3
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4 namespace Implab.Components {
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5 /// <summary>
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6 /// Creates an instace on-demand and allows it to be garbage collected.
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7 /// </summary>
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8 /// <remarks>
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9 /// Usefull when dealing with memory-intensive objects which are frequently used.
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10 /// This class is similar to <see cref="ObjectPool{T}"/> except it is a singleton.
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11 /// </remarks>
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12 public class LazyAndWeak<T> where T : class {
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13
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14 readonly Func<T> m_factory;
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15 readonly object m_lock;
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16 WeakReference m_reference;
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19 public LazyAndWeak(Func<T> factory, bool useLock) {
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20 Safe.ArgumentNotNull(factory, "factory");
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21 m_factory = factory;
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22 m_lock = useLock ? new object() : null;
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23 }
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24
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25 public LazyAndWeak(Func<T> factory) : this(factory, false) {
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26 }
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27
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28 public T Value {
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29 get {
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30 while (true) {
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31 var weak = m_reference;
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32 T value;
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33 if (weak != null) {
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34 value = weak.Target as T;
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35 if (value != null)
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36 return value;
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37 }
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38
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39 if (m_lock == null) {
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40 value = m_factory();
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41
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42 if (Interlocked.CompareExchange(ref m_reference, new WeakReference(value), weak) == weak)
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43 return value;
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44 } else {
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45 lock (m_lock) {
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46 // double check
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47 weak = m_reference;
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48 if (weak != null) {
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49 value = weak.Target as T;
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50 if (value != null)
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51 return value;
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52 }
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53 // we are safe to write
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54 value = m_factory();
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55 m_reference = new WeakReference(value);
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56 return value;
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57 }
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58 }
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59 }
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60 }
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61 }
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62 }
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