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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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180
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11 /// </remarks>
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178
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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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17
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18
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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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180
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45 lock (m_lock) {
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46 // double check
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182
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47 weak = m_reference;
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180
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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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178
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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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63 }
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64
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