AsyncAppender.java
/*
* 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 <aarong@cs.cmu.edu>
// Thomas Tuft Muller <ttm@online.no>
package org.apache.log4j;
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;
import org.apache.log4j.helpers.AppenderAttachableImpl;
import org.apache.log4j.spi.AppenderAttachable;
import org.apache.log4j.spi.LoggingEvent;
/**
* 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 Gülcü
* @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("AsyncAppender-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();
}
event.getRenderedMessage();
event.getThrowableStrRep();
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;
}
/**
* Determines if specified appender is attached.
*
* @param appender appender.
* @return true if attached.
*/
public boolean isAttached(final Appender appender) {
synchronized (appenders) {
return appenders.isAttached(appender);
}
}
/**
* {@inheritDoc}
*/
public boolean requiresLayout() {
return false;
}
/**
* Removes and closes all attached appenders.
*/
public void removeAllAppenders() {
synchronized (appenders) {
appenders.removeAllAppenders();
}
}
/**
* Removes an appender.
*
* @param appender appender to remove.
*/
public void removeAppender(final Appender appender) {
synchronized (appenders) {
appenders.removeAppender(appender);
}
}
/**
* Remove appender by name.
*
* @param name name.
*/
public void removeAppender(final String name) {
synchronized (appenders) {
appenders.removeAppender(name);
}
}
/**
* The <b>LocationInfo</b> option takes a boolean value. By default, it is set to false which means there will be no
* effort to extract the location information related to the event. As a result, the event that will be ultimately
* logged will likely to contain the wrong location information (if present in the log format).
* <p/>
* <p/>
* Location information extraction is comparatively very slow and should be avoided unless performance is not a
* concern.
* </p>
*
* @param flag true if location information should be extracted.
*/
public void setLocationInfo(final boolean flag) {
locationInfo = flag;
}
/**
* Sets the number of messages allowed in the event buffer before the calling thread is blocked (if blocking is
* true) or until messages are summarized and discarded. Changing the size will not affect messages already in the
* buffer.
*
* @param size buffer size, must be positive.
*/
public void setBufferSize(final int size) {
//
// log4j 1.2 would throw exception if size was negative
// and deadlock if size was zero.
//
if (size < 0) {
throw new java.lang.NegativeArraySizeException("size");
}
synchronized (buffer) {
//
// don't let size be zero.
//
bufferSize = (size < 1) ? 1 : size;
buffer.notifyAll();
}
}
/**
* Gets the current buffer size.
*
* @return the current value of the <b>BufferSize</b> option.
*/
public int getBufferSize() {
return bufferSize;
}
/**
* Sets whether appender should wait if there is no space available in the event buffer or immediately return.
*
* @param value true if appender should wait until available space in buffer.
* @since 1.2.14
*/
public void setBlocking(final boolean value) {
synchronized (buffer) {
blocking = value;
buffer.notifyAll();
}
}
/**
* Gets whether appender should block calling thread when buffer is full. If false, messages will be counted by
* logger and a summary message appended after the contents of the buffer have been appended.
*
* @return true if calling thread will be blocked when buffer is full.
* @since 1.2.14
*/
public boolean getBlocking() {
return blocking;
}
/**
* Summary of discarded logging events for a logger.
*/
private static final class DiscardSummary {
/**
* First event of the highest severity.
*/
private LoggingEvent maxEvent;
/**
* Total count of messages discarded.
*/
private int count;
/**
* Create new instance.
*
* @param event event, may not be null.
*/
public DiscardSummary(final LoggingEvent event) {
maxEvent = event;
count = 1;
}
/**
* Add discarded event to summary.
*
* @param event event, may not be null.
*/
public void add(final LoggingEvent event) {
if (event.getLevel().toInt() > maxEvent.getLevel().toInt()) {
maxEvent = event;
}
count++;
}
/**
* Create event with summary information.
*
* @return new event.
*/
public LoggingEvent createEvent() {
String msg = MessageFormat.format("Discarded {0} messages due to full event buffer including: {1}",
new Object[] { new Integer(count), maxEvent.getMessage() });
return new LoggingEvent("org.apache.log4j.AsyncAppender.DONT_REPORT_LOCATION",
Logger.getLogger(maxEvent.getLoggerName()), maxEvent.getLevel(), msg, null);
}
}
/**
* Event dispatcher.
*/
private static class Dispatcher implements Runnable {
/**
* Parent AsyncAppender.
*/
private final AsyncAppender parent;
/**
* Event buffer.
*/
private final List buffer;
/**
* Map of DiscardSummary keyed by logger name.
*/
private final Map discardMap;
/**
* Wrapped appenders.
*/
private final AppenderAttachableImpl appenders;
/**
* Create new instance of dispatcher.
*
* @param parent parent AsyncAppender, may not be null.
* @param buffer event buffer, may not be null.
* @param discardMap discard map, may not be null.
* @param appenders appenders, may not be null.
*/
public Dispatcher(final AsyncAppender parent, final List buffer, final Map discardMap,
final AppenderAttachableImpl appenders) {
this.parent = parent;
this.buffer = buffer;
this.appenders = appenders;
this.discardMap = discardMap;
}
/**
* {@inheritDoc}
*/
public void run() {
boolean isActive = true;
//
// if interrupted (unlikely), end thread
//
try {
//
// loop until the AsyncAppender is closed.
//
while (isActive) {
LoggingEvent[] events = null;
//
// extract pending events while synchronized
// on buffer
//
synchronized (buffer) {
int bufferSize = buffer.size();
isActive = !parent.closed;
while ((bufferSize == 0) && isActive) {
buffer.wait();
bufferSize = buffer.size();
isActive = !parent.closed;
}
if (bufferSize > 0) {
events = new LoggingEvent[bufferSize + discardMap.size()];
buffer.toArray(events);
//
// add events due to buffer overflow
//
int index = bufferSize;
for (Iterator iter = discardMap.values().iterator(); iter.hasNext(); ) {
events[index++] = ((DiscardSummary) iter.next()).createEvent();
}
//
// clear buffer and discard map
//
buffer.clear();
discardMap.clear();
//
// allow blocked appends to continue
buffer.notifyAll();
}
}
//
// process events after lock on buffer is released.
//
if (events != null) {
for (int i = 0; i < events.length; i++) {
synchronized (appenders) {
appenders.appendLoopOnAppenders(events[i]);
}
}
}
}
} catch (InterruptedException ex) {
Thread.currentThread().interrupt();
}
}
}
}