asyncappender.java

apache的log4j源码

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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.
 */

// Contibutors:  Aaron Greenhouse <[e-mail]>
//               Thomas Tuft Muller <[e-mail]>
package org.apache.log4j;

import org.apache.log4j.helpers.AppenderAttachableImpl;
import org.apache.log4j.spi.AppenderAttachable;
import org.apache.log4j.spi.LoggingEvent;

import java.text.MessageFormat;

import java.util.ArrayList;
import java.util.Enumeration;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;


/**
 * The AsyncAppender lets users log events asynchronously.
 * <p/>
 * <p/>
 * The AsyncAppender will collect the events sent to it and then dispatch them
 * to all the appenders that are attached to it. You can attach multiple
 * appenders to an AsyncAppender.
 * </p>
 * <p/>
 * <p/>
 * The AsyncAppender uses a separate thread to serve the events in its buffer.
 * </p>
 * <p/>
 * <b>Important note:</b> The <code>AsyncAppender</code> can only be script
 * configured using the {@link org.apache.log4j.xml.DOMConfigurator}.
 * </p>
 *
 * @author Ceki G&uuml;lc&uuml;
 * @author Curt Arnold
 * @since 0.9.1
 */
public class AsyncAppender extends AppenderSkeleton
  implements AppenderAttachable {
  /**
   * The default buffer size is set to 128 events.
   */
  public static final int DEFAULT_BUFFER_SIZE = 128;

  /**
   * Event buffer, also used as monitor to protect itself and
   * discardMap from simulatenous modifications.
   */
  private final List buffer = new ArrayList();

  /**
   * Map of DiscardSummary objects keyed by logger name.
   */
  private final Map discardMap = new HashMap();

  /**
   * Buffer size.
   */
  private int bufferSize = DEFAULT_BUFFER_SIZE;

  /** Nested appenders. */
  AppenderAttachableImpl aai;

  /**
   * Nested appenders.
   */
  private final AppenderAttachableImpl appenders;

  /**
   * Dispatcher.
   */
  private final Thread dispatcher;

  /**
   * Should location info be included in dispatched messages.
   */
  private boolean locationInfo = false;

  /**
   * Does appender block when buffer is full.
   */
  private boolean blocking = true;

  /**
   * Create new instance.
   */
  public AsyncAppender() {
    appenders = new AppenderAttachableImpl();

    //
    //   only set for compatibility
    aai = appenders;

    dispatcher =
      new Thread(new Dispatcher(this, buffer, discardMap, appenders));

    // It is the user's responsibility to close appenders before
    // exiting.
    dispatcher.setDaemon(true);

    // set the dispatcher priority to lowest possible value
    //        dispatcher.setPriority(Thread.MIN_PRIORITY);
    dispatcher.setName("Dispatcher-" + dispatcher.getName());
    dispatcher.start();
  }

  /**
   * Add appender.
   *
   * @param newAppender appender to add, may not be null.
   */
  public void addAppender(final Appender newAppender) {
    synchronized (appenders) {
      appenders.addAppender(newAppender);
    }
  }

  /**
   * {@inheritDoc}
   */
  public void append(final LoggingEvent event) {
    //
    //   if dispatcher thread has died then
    //      append subsequent events synchronously
    //   See bug 23021
    if ((dispatcher == null) || !dispatcher.isAlive() || (bufferSize <= 0)) {
      synchronized (appenders) {
        appenders.appendLoopOnAppenders(event);
      }

      return;
    }

    // Set the NDC and thread name for the calling thread as these
    // LoggingEvent fields were not set at event creation time.
    event.getNDC();
    event.getThreadName();
    // Get a copy of this thread's MDC.
    event.getMDCCopy();
    if (locationInfo) {
      event.getLocationInformation();
    }

    synchronized (buffer) {
      while (true) {
        int previousSize = buffer.size();

        if (previousSize < bufferSize) {
          buffer.add(event);

          //
          //   if buffer had been empty
          //       signal all threads waiting on buffer
          //       to check their conditions.
          //
          if (previousSize == 0) {
            buffer.notifyAll();
          }

          break;
        }

        //
        //   Following code is only reachable if buffer is full
        //
        //
        //   if blocking and thread is not already interrupted
        //      and not the dispatcher then
        //      wait for a buffer notification
        boolean discard = true;
        if (blocking
                && !Thread.interrupted()
                && Thread.currentThread() != dispatcher) {
          try {
            buffer.wait();
            discard = false;
          } catch (InterruptedException e) {
            //
            //  reset interrupt status so
            //    calling code can see interrupt on
            //    their next wait or sleep.
            Thread.currentThread().interrupt();
          }
        }

        //
        //   if blocking is false or thread has been interrupted
        //   add event to discard map.
        //
        if (discard) {
          String loggerName = event.getLoggerName();
          DiscardSummary summary = (DiscardSummary) discardMap.get(loggerName);

          if (summary == null) {
            summary = new DiscardSummary(event);
            discardMap.put(loggerName, summary);
          } else {
            summary.add(event);
          }

          break;
        }
      }
    }
  }

  /**
   * Close this <code>AsyncAppender</code> by interrupting the dispatcher
   * thread which will process all pending events before exiting.
   */
  public void close() {
    /**
     * Set closed flag and notify all threads to check their conditions.
     * Should result in dispatcher terminating.
     */
    synchronized (buffer) {
      closed = true;
      buffer.notifyAll();
    }

    try {
      dispatcher.join();
    } catch (InterruptedException e) {
      Thread.currentThread().interrupt();
      org.apache.log4j.helpers.LogLog.error(
        "Got an InterruptedException while waiting for the "
        + "dispatcher to finish.", e);
    }

    //
    //    close all attached appenders.
    //
    synchronized (appenders) {
      Enumeration iter = appenders.getAllAppenders();

      if (iter != null) {
        while (iter.hasMoreElements()) {
          Object next = iter.nextElement();

          if (next instanceof Appender) {
            ((Appender) next).close();
          }
        }
      }
    }
  }

  /**
   * Get iterator over attached appenders.
   * @return iterator or null if no attached appenders.
   */
  public Enumeration getAllAppenders() {
    synchronized (appenders) {
      return appenders.getAllAppenders();
    }
  }

  /**
   * Get appender by name.
   *
   * @param name name, may not be null.
   * @return matching appender or null.
   */
  public Appender getAppender(final String name) {
    synchronized (appenders) {
      return appenders.getAppender(name);
    }
  }

  /**
   * Gets whether the location of the logging request call
   * should be captured.
   *
   * @return the current value of the <b>LocationInfo</b> option.
   */
  public boolean getLocationInfo() {
    return locationInfo;
  }