bufferingappenderskeleton.cs

详细讲述了数据库编程

#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;

using log4net.Util;
using log4net.Core;

namespace log4net.Appender
{
	/// <summary>
	/// Abstract base class implementation of <see cref="IAppender"/> that 
	/// buffers events in a fixed size buffer.
	/// </summary>
	/// <remarks>
	/// <para>
	/// This base class should be used by appenders that need to buffer a 
	/// number of events before logging them. For example the <see cref="AdoNetAppender"/> 
	/// buffers events and then submits the entire contents of the buffer to 
	/// the underlying database in one go.
	/// </para>
	/// <para>
	/// Subclasses should override the <see cref="SendBuffer(LoggingEvent[])"/>
	/// method to deliver the buffered events.
	/// </para>
	/// <para>The BufferingAppenderSkeleton maintains a fixed size cyclic 
	/// buffer of events. The size of the buffer is set using 
	/// the <see cref="BufferSize"/> property.
	/// </para>
	/// <para>A <see cref="ITriggeringEventEvaluator"/> is used to inspect 
	/// each event as it arrives in the appender. If the <see cref="Evaluator"/> 
	/// triggers, then the current buffer is sent immediately 
	/// (see <see cref="SendBuffer(LoggingEvent[])"/>). Otherwise the event 
	/// is stored in the buffer. For example, an evaluator can be used to 
	/// deliver the events immediately when an ERROR event arrives.
	/// </para>
	/// <para>
	/// The buffering appender can be configured in a <see cref="Lossy"/> mode. 
	/// By default the appender is NOT lossy. When the buffer is full all 
	/// the buffered events are sent with <see cref="SendBuffer(LoggingEvent[])"/>.
	/// If the <see cref="Lossy"/> property is set to <c>true</c> then the 
	/// buffer will not be sent when it is full, and new events arriving 
	/// in the appender will overwrite the oldest event in the buffer. 
	/// In lossy mode the buffer will only be sent when the <see cref="Evaluator"/>
	/// triggers. This can be useful behavior when you need to know about 
	/// ERROR events but not about events with a lower level, configure an 
	/// evaluator that will trigger when an ERROR event arrives, the whole 
	/// buffer will be sent which gives a history of events leading up to
	/// the ERROR event.
	/// </para>
	/// </remarks>
	/// <author>Nicko Cadell</author>
	/// <author>Gert Driesen</author>
	public abstract class BufferingAppenderSkeleton : AppenderSkeleton
	{
		#region Protected Instance Constructors

		/// <summary>
		/// Initializes a new instance of the <see cref="BufferingAppenderSkeleton" /> class.
		/// </summary>
		/// <remarks>
		/// <para>
		/// Protected default constructor to allow subclassing.
		/// </para>
		/// </remarks>
		protected BufferingAppenderSkeleton() : this(true)
		{
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="BufferingAppenderSkeleton" /> class.
		/// </summary>
		/// <param name="eventMustBeFixed">the events passed through this appender must be
		/// fixed by the time that they arrive in the derived class' <c>SendBuffer</c> method.</param>
		/// <remarks>
		/// <para>
		/// Protected constructor to allow subclassing.
		/// </para>
		/// <para>
		/// The <paramref name="eventMustBeFixed"/> should be set if the subclass
		/// expects the events delivered to be fixed even if the 
		/// <see cref="BufferSize"/> is set to zero, i.e. when no buffering occurs.
		/// </para>
		/// </remarks>
		protected BufferingAppenderSkeleton(bool eventMustBeFixed) : base()
		{
			m_eventMustBeFixed = eventMustBeFixed;
		}

		#endregion Protected Instance Constructors

		#region Public Instance Properties

		/// <summary>
		/// Gets or sets a value that indicates whether the appender is lossy.
		/// </summary>
		/// <value>
		/// <c>true</c> if the appender is lossy, otherwise <c>false</c>. The default is <c>false</c>.
		/// </value>
		/// <remarks>
		/// <para>
		/// This appender uses a buffer to store logging events before 
		/// delivering them. A triggering event causes the whole buffer
		/// to be send to the remote sink. If the buffer overruns before
		/// a triggering event then logging events could be lost. Set
		/// <see cref="Lossy"/> to <c>false</c> to prevent logging events 
		/// from being lost.
		/// </para>
		/// <para>If <see cref="Lossy"/> is set to <c>true</c> then an
		/// <see cref="Evaluator"/> must be specified.</para>
		/// </remarks>
		public bool Lossy
		{
			get { return m_lossy; }
			set { m_lossy = value; }
		}

		/// <summary>
		/// Gets or sets the size of the cyclic buffer used to hold the 
		/// logging events.
		/// </summary>
		/// <value>
		/// The size of the cyclic buffer used to hold the logging events.
		/// </value>
		/// <remarks>
		/// <para>
		/// The <see cref="BufferSize"/> option takes a positive integer
		/// representing the maximum number of logging events to collect in 
		/// a cyclic buffer. When the <see cref="BufferSize"/> is reached,
		/// oldest events are deleted as new events are added to the
		/// buffer. By default the size of the cyclic buffer is 512 events.
		/// </para>
		/// <para>
		/// If the <see cref="BufferSize"/> is set to a value less than
		/// or equal to 1 then no buffering will occur. The logging event
		/// will be delivered synchronously (depending on the <see cref="Lossy"/>
		/// and <see cref="Evaluator"/> properties). Otherwise the event will
		/// be buffered.
		/// </para>
		/// </remarks>
		public int BufferSize
		{
			get { return m_bufferSize; }
			set { m_bufferSize = value; }
		}

		/// <summary>
		/// Gets or sets the <see cref="ITriggeringEventEvaluator"/> that causes the 
		/// buffer to be sent immediately.
		/// </summary>
		/// <value>
		/// The <see cref="ITriggeringEventEvaluator"/> that causes the buffer to be
		/// sent immediately.
		/// </value>
		/// <remarks>
		/// <para>
		/// The evaluator will be called for each event that is appended to this 
		/// appender. If the evaluator triggers then the current buffer will 
		/// immediately be sent (see <see cref="SendBuffer(LoggingEvent[])"/>).
		/// </para>
		/// <para>If <see cref="Lossy"/> is set to <c>true</c> then an
		/// <see cref="Evaluator"/> must be specified.</para>
		/// </remarks>
		public ITriggeringEventEvaluator Evaluator
		{
			get { return m_evaluator; }
			set	{ m_evaluator = value; }
		}

		/// <summary>
		/// Gets or sets the value of the <see cref="ITriggeringEventEvaluator"/> to use.
		/// </summary>
		/// <value>
		/// The value of the <see cref="ITriggeringEventEvaluator"/> to use.
		/// </value>
		/// <remarks>
		/// <para>
		/// The evaluator will be called for each event that is discarded from this 
		/// appender. If the evaluator triggers then the current buffer will immediately 
		/// be sent (see <see cref="SendBuffer(LoggingEvent[])"/>).
		/// </para>
		/// </remarks>
		public ITriggeringEventEvaluator LossyEvaluator
		{
			get { return m_lossyEvaluator; }
			set	{ m_lossyEvaluator = value; }
		}

		/// <summary>
		/// Gets or sets a value indicating if only part of the logging event data
		/// should be fixed.
		/// </summary>
		/// <value>
		/// <c>true</c> if the appender should only fix part of the logging event 
		/// data, otherwise <c>false</c>. The default is <c>false</c>.
		/// </value>
		/// <remarks>
		/// <para>
		/// Setting this property to <c>true</c> will cause only part of the
		/// event data to be fixed and serialized. This will improve performance.
		/// </para>
		/// <para>
		/// See <see cref="LoggingEvent.FixVolatileData(FixFlags)"/> for more information.
		/// </para>
		/// </remarks>
		[Obsolete("Use Fix property")]
		virtual public bool OnlyFixPartialEventData
		{
			get { return (Fix == FixFlags.Partial); }
			set 
			{ 
				if (value)
				{
					Fix = FixFlags.Partial;
				}
				else
				{
					Fix = FixFlags.All;
				}
			}
		}

		/// <summary>
		/// Gets or sets a the fields that will be fixed in the event
		/// </summary>
		/// <value>
		/// The event fields that will be fixed before the event is buffered
		/// </value>
		/// <remarks>
		/// <para>
		/// The logging event needs to have certain thread specific values 
		/// captured before it can be buffered. See <see cref="LoggingEvent.Fix"/>
		/// for details.
		/// </para>
		/// </remarks>
		/// <seealso cref="LoggingEvent.Fix"/>
		virtual public FixFlags Fix
		{
			get { return m_fixFlags; }
			set { m_fixFlags = value; }
		}

		#endregion Public Instance Properties

		#region Public Methods

		/// <summary>
		/// Flush the currently buffered events
		/// </summary>
		/// <remarks>
		/// <para>
		/// Flushes any events that have been buffered.
		/// </para>
		/// <para>
		/// If the appender is buffering in <see cref="Lossy"/> mode then the contents
		/// of the buffer will NOT be flushed to the appender.
		/// </para>
		/// </remarks>
		public virtual void Flush()
		{
			Flush(false);
		}

		/// <summary>
		/// Flush the currently buffered events
		/// </summary>
		/// <param name="flushLossyBuffer">set to <c>true</c> to flush the buffer of lossy events</param>
		/// <remarks>
		/// <para>
		/// Flushes events that have been buffered. If <paramref name="flushLossyBuffer" /> is
		/// <c>false</c> then events will only be flushed if this buffer is non-lossy mode.
		/// </para>
		/// <para>
		/// If the appender is buffering in <see cref="Lossy"/> mode then the contents
		/// of the buffer will only be flushed if <paramref name="flushLossyBuffer" /> is <c>true</c>.
		/// In this case the contents of the buffer will be tested against the 
		/// <see cref="LossyEvaluator"/> and if triggering will be output. All other buffered
		/// events will be discarded.
		/// </para>
		/// <para>
		/// If <paramref name="flushLossyBuffer" /> is <c>true</c> then the buffer will always
		/// be emptied by calling this method.
		/// </para>
		/// </remarks>
		public virtual void Flush(bool flushLossyBuffer)
		{
			// This method will be called outside of the AppenderSkeleton DoAppend() method
			// therefore it needs to be protected by its own lock. This will block any
			// Appends while the buffer is flushed.
			lock(this)
			{
				if (m_cb != null && m_cb.Length > 0)
				{
					if (m_lossy)
					{
						// If we are allowed to eagerly flush from the lossy buffer
						if (flushLossyBuffer)
						{
							if (m_lossyEvaluator != null)
							{
								// Test the contents of the buffer against the lossy evaluator
								LoggingEvent[] bufferedEvents = m_cb.PopAll();
								ArrayList filteredEvents = new ArrayList(bufferedEvents.Length);

								foreach(LoggingEvent loggingEvent in bufferedEvents)
								{
									if (m_lossyEvaluator.IsTriggeringEvent(loggingEvent))
									{