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// 
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// to whom the Software is furnished to do so, subject to the following conditions:
// 
// The above copyright notice and this permission notice shall be included in all copies or
// substantial portions of the Software.
// 
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE
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using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.Threading;

namespace ICSharpCode.NRefactory.Utils
{
	/// <summary>
	/// Allows caching values for a specific resolve context.
	/// A CacheManager consists of two dictionaries: one for shared instances (shared among all threads working with that resolve context),
	/// and one for thread-local instances.
	/// Additionally, it provides a Dispose() event that can be used to clear any external caches when
	/// leaving the "using (var ctx = context.Synchronize())" block.
	/// </summary>
	/// <remarks>This class is thread-safe</remarks>
	public sealed class CacheManager : IDisposable
	{
		readonly ConcurrentDictionary<object, object> sharedDict = new ConcurrentDictionary<object, object>(ReferenceComparer.Instance);
		readonly ThreadLocal<Dictionary<object, object>> localDict = new ThreadLocal<Dictionary<object, object>>(() => new Dictionary<object, object>(ReferenceComparer.Instance));
		
		public object GetShared(object key)
		{
			object val;
			sharedDict.TryGetValue(key, out val);
			return val;
		}
		
		public void SetShared(object key, object val)
		{
			sharedDict[key] = val;
		}
		
		public object GetThreadLocal(object key)
		{
			object val;
			localDict.Value.TryGetValue(key, out val);
			return val;
		}
		
		public void SetThreadLocal(object key, object val)
		{
			localDict.Value[key] = val;
		}
		
		public event EventHandler Disposed;
		
		/// <summary>
		/// Invokes the <see cref="Disposed"/> event.
		/// </summary>
		public void Dispose()
		{
			sharedDict.Clear();
			localDict.Dispose(); // dispose the ThreadLocal<T>
			// TODO: test whether this frees the referenced value on all threads
			
			// fire Disposed() only once by removing the old event handlers
			EventHandler disposed = Interlocked.Exchange(ref Disposed, null);
			if (disposed != null)
				disposed(this, EventArgs.Empty);
		}
	}
}