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91 lines
3.1 KiB
91 lines
3.1 KiB
using System;
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using System.Collections.Generic;
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using System.Linq;
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using System.Text;
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namespace System.Runtime.CompilerServices
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{
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public sealed class ConditionalWeakTable<TKey, TValue> where TKey : class where TValue : class
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{
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private readonly Dictionary<WeakReference<TKey>, TValue> items = new Dictionary<WeakReference<TKey>, TValue>();
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private readonly object _lock = new object();
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private sealed class KeyComparer : IEqualityComparer<WeakReference<TKey>>
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{
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public bool Equals(WeakReference<TKey> x, WeakReference<TKey> y)
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=> x.TryGetTarget(out var keyX) && y.TryGetTarget(out var keyY) && ReferenceEquals(keyX, keyY);
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public int GetHashCode(WeakReference<TKey> obj)
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=> obj.TryGetTarget(out var key) ? key.GetHashCode() : 0;
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}
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private static WeakReference<TKey> WeakRef(TKey key)
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=> new WeakReference<TKey>(key);
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private sealed class GCTracker
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{
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public static event Action OnGC;
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private static readonly WeakReference<GCTracker> tracker = new WeakReference<GCTracker>(new GCTracker());
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~GCTracker()
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{
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OnGC?.Invoke();
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if (!AppDomain.CurrentDomain.IsFinalizingForUnload() && !Environment.HasShutdownStarted)
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tracker.SetTarget(new GCTracker());
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}
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}
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public void Add(TKey key, TValue value)
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{
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lock (_lock)
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items.Add(WeakRef(key), value);
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}
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public bool TryGetValue(TKey key, out TValue value)
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{
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if (key == null)
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throw new ArgumentException("Null key", nameof(key));
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value = null;
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lock (_lock)
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return items.TryGetValue(WeakRef(key), out value);
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}
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public delegate TValue CreateValueCallback(TKey key);
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public TValue GetValue(TKey key, CreateValueCallback createValueCallback)
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{
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if (createValueCallback == null)
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throw new ArgumentException("Null create delegate", nameof(createValueCallback));
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lock (_lock)
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{
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if (TryGetValue(key, out var value))
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return value;
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else
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{
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value = createValueCallback(key);
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Add(key, value);
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return value;
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}
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}
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}
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public TValue GetOrCreateValue(TKey key)
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=> GetValue(key, k => Activator.CreateInstance<TValue>());
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public bool Remove(TKey key)
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=> items.Remove(WeakRef(key));
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public ConditionalWeakTable()
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=> GCTracker.OnGC += OnGC;
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~ConditionalWeakTable()
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=> GCTracker.OnGC -= OnGC;
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private void OnGC()
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{
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// on each GC, we want to clear the entire set of empty keys
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var nullWeakRef = WeakRef(null);
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while (items.Remove(nullWeakRef)) ; // just loop
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}
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}
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}
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