globalcontextproperties.cs

精通SQL Server2005项目开发

#region Copyright & License
//
// Copyright 2001-2005 The Apache Software Foundation
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
#endregion

using System;
using System.Collections;

namespace log4net.Util
{
	/// <summary>
	/// Implementation of Properties collection for the <see cref="log4net.GlobalContext"/>
	/// </summary>
	/// <remarks>
	/// <para>
	/// This class implements a properties collection that is thread safe and supports both
	/// storing properties and capturing a read only copy of the current propertied.
	/// </para>
	/// <para>
	/// This class is optimized to the scenario where the properties are read frequently
	/// and are modified infrequently.
	/// </para>
	/// </remarks>
	/// <author>Nicko Cadell</author>
	public sealed class GlobalContextProperties : ContextPropertiesBase
	{
		#region Private Instance Fields

		/// <summary>
		/// The read only copy of the properties.
		/// </summary>
		/// <remarks>
		/// <para>
		/// This variable is declared <c>volatile</c> to prevent the compiler and JIT from
		/// reordering reads and writes of this thread performed on different threads.
		/// </para>
		/// </remarks>
#if NETCF
		private ReadOnlyPropertiesDictionary m_readOnlyProperties = new ReadOnlyPropertiesDictionary();
#else
		private volatile ReadOnlyPropertiesDictionary m_readOnlyProperties = new ReadOnlyPropertiesDictionary();
#endif

		/// <summary>
		/// Lock object used to synchronize updates within this instance
		/// </summary>
		private readonly object m_syncRoot = new object();

		#endregion Private Instance Fields

		#region Public Instance Constructors

		/// <summary>
		/// Constructor
		/// </summary>
		/// <remarks>
		/// <para>
		/// Initializes a new instance of the <see cref="GlobalContextProperties" /> class.
		/// </para>
		/// </remarks>
		internal GlobalContextProperties()
		{
		}

		#endregion Public Instance Constructors

		#region Public Instance Properties

		/// <summary>
		/// Gets or sets the value of a property
		/// </summary>
		/// <value>
		/// The value for the property with the specified key
		/// </value>
		/// <remarks>
		/// <para>
		/// Reading the value for a key is faster than setting the value.
		/// When the value is written a new read only copy of 
		/// the properties is created.
		/// </para>
		/// </remarks>
		override public object this[string key]
		{
			get 
			{ 
				return m_readOnlyProperties[key];
			}
			set
			{
				lock(m_syncRoot)
				{
					PropertiesDictionary mutableProps = new PropertiesDictionary(m_readOnlyProperties);

					mutableProps[key] = value;

					m_readOnlyProperties = new ReadOnlyPropertiesDictionary(mutableProps);
				}
			}
		}

		#endregion Public Instance Properties

		#region Public Instance Methods

		/// <summary>
		/// Remove a property from the global context
		/// </summary>
		/// <param name="key">the key for the entry to remove</param>
		/// <remarks>
		/// <para>
		/// Removing an entry from the global context properties is relatively expensive compared
		/// with reading a value. 
		/// </para>
		/// </remarks>
		public void Remove(string key)
		{
			lock(m_syncRoot)
			{
				if (m_readOnlyProperties.Contains(key))
				{
					PropertiesDictionary mutableProps = new PropertiesDictionary(m_readOnlyProperties);

					mutableProps.Remove(key);

					m_readOnlyProperties = new ReadOnlyPropertiesDictionary(mutableProps);
				}
			}
		}

		/// <summary>
		/// Clear the global context properties
		/// </summary>
		public void Clear()
		{
			lock(m_syncRoot)
			{
				m_readOnlyProperties = new ReadOnlyPropertiesDictionary();
			}
		}

		#endregion Public Instance Methods

		#region Internal Instance Methods

		/// <summary>
		/// Get a readonly immutable copy of the properties
		/// </summary>
		/// <returns>the current global context properties</returns>
		/// <remarks>
		/// <para>
		/// This implementation is fast because the GlobalContextProperties class
		/// stores a readonly copy of the properties.
		/// </para>
		/// </remarks>
		internal ReadOnlyPropertiesDictionary GetReadOnlyProperties()
		{
			return m_readOnlyProperties;
		}

		#endregion Internal Instance Methods
	}
}