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178
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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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180
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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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182
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10 /// This class is similar to <see cref="ObjectPool{T}"/> except it is a singleton.
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264
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11 /// This class can't be used to hold diposable objects.
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180
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12 /// </remarks>
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178
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13 public class LazyAndWeak<T> where T : class {
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14
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15 readonly Func<T> m_factory;
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16 readonly object m_lock;
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17 WeakReference m_reference;
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18
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19
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20 public LazyAndWeak(Func<T> factory, bool useLock) {
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21 Safe.ArgumentNotNull(factory, "factory");
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22 m_factory = factory;
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23 m_lock = useLock ? new object() : null;
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24 }
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25
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26 public LazyAndWeak(Func<T> factory) : this(factory, false) {
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27 }
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28
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29 public T Value {
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30 get {
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31 while (true) {
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32 var weak = m_reference;
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33 T value;
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34 if (weak != null) {
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35 value = weak.Target as T;
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36 if (value != null)
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37 return value;
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38 }
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39
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40 if (m_lock == null) {
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41 value = m_factory();
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42
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43 if (Interlocked.CompareExchange(ref m_reference, new WeakReference(value), weak) == weak)
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44 return value;
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45 } else {
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180
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46 lock (m_lock) {
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47 // double check
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182
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48 weak = m_reference;
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180
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49 if (weak != null) {
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50 value = weak.Target as T;
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51 if (value != null)
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52 return value;
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53 }
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54 // we are safe to write
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55 value = m_factory();
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56 m_reference = new WeakReference(value);
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57 return value;
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58 }
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178
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59 }
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60 }
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61 }
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62 }
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63 }
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64 }
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65
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