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The Apache Log4j Implementation
/*
* 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.
*/
package org.apache.logging.log4j.core.appender;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.TransferQueue;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.logging.log4j.core.AbstractLogEvent;
import org.apache.logging.log4j.core.Appender;
import org.apache.logging.log4j.core.Core;
import org.apache.logging.log4j.core.Filter;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.async.ArrayBlockingQueueFactory;
import org.apache.logging.log4j.core.async.AsyncQueueFullMessageUtil;
import org.apache.logging.log4j.core.async.AsyncQueueFullPolicy;
import org.apache.logging.log4j.core.async.AsyncQueueFullPolicyFactory;
import org.apache.logging.log4j.core.async.BlockingQueueFactory;
import org.apache.logging.log4j.core.async.DiscardingAsyncQueueFullPolicy;
import org.apache.logging.log4j.core.async.EventRoute;
import org.apache.logging.log4j.core.async.InternalAsyncUtil;
import org.apache.logging.log4j.core.config.AppenderControl;
import org.apache.logging.log4j.core.config.AppenderRef;
import org.apache.logging.log4j.core.config.Configuration;
import org.apache.logging.log4j.core.config.ConfigurationException;
import org.apache.logging.log4j.core.config.Property;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginAliases;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderAttribute;
import org.apache.logging.log4j.core.config.plugins.PluginBuilderFactory;
import org.apache.logging.log4j.core.config.plugins.PluginConfiguration;
import org.apache.logging.log4j.core.config.plugins.PluginElement;
import org.apache.logging.log4j.core.config.plugins.validation.constraints.Required;
import org.apache.logging.log4j.core.filter.AbstractFilterable;
import org.apache.logging.log4j.core.impl.Log4jLogEvent;
import org.apache.logging.log4j.core.util.Log4jThread;
import org.apache.logging.log4j.spi.AbstractLogger;
/**
* Appends to one or more Appenders asynchronously. You can configure an AsyncAppender with one or more Appenders and an
* Appender to append to if the queue is full. The AsyncAppender does not allow a filter to be specified on the Appender
* references.
*/
@Plugin(name = "Async", category = Core.CATEGORY_NAME, elementType = Appender.ELEMENT_TYPE, printObject = true)
public final class AsyncAppender extends AbstractAppender {
private static final int DEFAULT_QUEUE_SIZE = 1024;
private static final LogEvent SHUTDOWN_LOG_EVENT = new AbstractLogEvent() {
private static final long serialVersionUID = -1761035149477086330L;
};
private static final AtomicLong THREAD_SEQUENCE = new AtomicLong(1);
private final BlockingQueue queue;
private final int queueSize;
private final boolean blocking;
private final long shutdownTimeout;
private final Configuration config;
private final AppenderRef[] appenderRefs;
private final String errorRef;
private final boolean includeLocation;
private AppenderControl errorAppender;
private AsyncThread thread;
private AsyncQueueFullPolicy asyncQueueFullPolicy;
private AsyncAppender(final String name, final Filter filter, final AppenderRef[] appenderRefs,
final String errorRef, final int queueSize, final boolean blocking, final boolean ignoreExceptions,
final long shutdownTimeout, final Configuration config, final boolean includeLocation,
final BlockingQueueFactory blockingQueueFactory, final Property[] properties) {
super(name, filter, null, ignoreExceptions, properties);
this.queue = blockingQueueFactory.create(queueSize);
this.queueSize = queueSize;
this.blocking = blocking;
this.shutdownTimeout = shutdownTimeout;
this.config = config;
this.appenderRefs = appenderRefs;
this.errorRef = errorRef;
this.includeLocation = includeLocation;
}
@Override
public void start() {
final Map map = config.getAppenders();
final List appenders = new ArrayList<>();
for (final AppenderRef appenderRef : appenderRefs) {
final Appender appender = map.get(appenderRef.getRef());
if (appender != null) {
appenders.add(new AppenderControl(appender, appenderRef.getLevel(), appenderRef.getFilter()));
} else {
LOGGER.error("No appender named {} was configured", appenderRef);
}
}
if (errorRef != null) {
final Appender appender = map.get(errorRef);
if (appender != null) {
errorAppender = new AppenderControl(appender, null, null);
} else {
LOGGER.error("Unable to set up error Appender. No appender named {} was configured", errorRef);
}
}
if (appenders.size() > 0) {
thread = new AsyncThread(appenders, queue);
thread.setName("AsyncAppender-" + getName());
} else if (errorRef == null) {
throw new ConfigurationException("No appenders are available for AsyncAppender " + getName());
}
asyncQueueFullPolicy = AsyncQueueFullPolicyFactory.create();
thread.start();
super.start();
}
@Override
public boolean stop(final long timeout, final TimeUnit timeUnit) {
setStopping();
super.stop(timeout, timeUnit, false);
LOGGER.trace("AsyncAppender stopping. Queue still has {} events.", queue.size());
thread.shutdown();
try {
thread.join(shutdownTimeout);
} catch (final InterruptedException ex) {
LOGGER.warn("Interrupted while stopping AsyncAppender {}", getName());
}
LOGGER.trace("AsyncAppender stopped. Queue has {} events.", queue.size());
if (DiscardingAsyncQueueFullPolicy.getDiscardCount(asyncQueueFullPolicy) > 0) {
LOGGER.trace("AsyncAppender: {} discarded {} events.", asyncQueueFullPolicy,
DiscardingAsyncQueueFullPolicy.getDiscardCount(asyncQueueFullPolicy));
}
setStopped();
return true;
}
/**
* Actual writing occurs here.
*
* @param logEvent The LogEvent.
*/
@Override
public void append(final LogEvent logEvent) {
if (!isStarted()) {
throw new IllegalStateException("AsyncAppender " + getName() + " is not active");
}
final Log4jLogEvent memento = Log4jLogEvent.createMemento(logEvent, includeLocation);
InternalAsyncUtil.makeMessageImmutable(logEvent.getMessage());
if (!transfer(memento)) {
if (blocking) {
if (AbstractLogger.getRecursionDepth() > 1) { // LOG4J2-1518, LOG4J2-2031
// If queue is full AND we are in a recursive call, call appender directly to prevent deadlock
AsyncQueueFullMessageUtil.logWarningToStatusLogger();
logMessageInCurrentThread(logEvent);
} else {
// delegate to the event router (which may discard, enqueue and block, or log in current thread)
final EventRoute route = asyncQueueFullPolicy.getRoute(thread.getId(), memento.getLevel());
route.logMessage(this, memento);
}
} else {
error("Appender " + getName() + " is unable to write primary appenders. queue is full");
logToErrorAppenderIfNecessary(false, memento);
}
}
}
private boolean transfer(final LogEvent memento) {
return queue instanceof TransferQueue
? ((TransferQueue) queue).tryTransfer(memento)
: queue.offer(memento);
}
/**
* FOR INTERNAL USE ONLY.
*
* @param logEvent the event to log
*/
public void logMessageInCurrentThread(final LogEvent logEvent) {
logEvent.setEndOfBatch(queue.isEmpty());
final boolean appendSuccessful = thread.callAppenders(logEvent);
logToErrorAppenderIfNecessary(appendSuccessful, logEvent);
}
/**
* FOR INTERNAL USE ONLY.
*
* @param logEvent the event to log
*/
public void logMessageInBackgroundThread(final LogEvent logEvent) {
try {
// wait for free slots in the queue
queue.put(logEvent);
} catch (final InterruptedException e) {
final boolean appendSuccessful = handleInterruptedException(logEvent);
logToErrorAppenderIfNecessary(appendSuccessful, logEvent);
}
}
// LOG4J2-1049: Some applications use Thread.interrupt() to send
// messages between application threads. This does not necessarily
// mean that the queue is full. To prevent dropping a log message,
// quickly try to offer the event to the queue again.
// (Yes, this means there is a possibility the same event is logged twice.)
//
// Finally, catching the InterruptedException means the
// interrupted flag has been cleared on the current thread.
// This may interfere with the application's expectation of
// being interrupted, so when we are done, we set the interrupted
// flag again.
private boolean handleInterruptedException(final LogEvent memento) {
final boolean appendSuccessful = queue.offer(memento);
if (!appendSuccessful) {
LOGGER.warn("Interrupted while waiting for a free slot in the AsyncAppender LogEvent-queue {}",
getName());
}
// set the interrupted flag again.
Thread.currentThread().interrupt();
return appendSuccessful;
}
private void logToErrorAppenderIfNecessary(final boolean appendSuccessful, final LogEvent logEvent) {
if (!appendSuccessful && errorAppender != null) {
errorAppender.callAppender(logEvent);
}
}
/**
* Create an AsyncAppender. This method is retained for backwards compatibility. New code should use the
* {@link Builder} instead. This factory will use {@link ArrayBlockingQueueFactory} by default as was the behavior
* pre-2.7.
*
* @param appenderRefs The Appenders to reference.
* @param errorRef An optional Appender to write to if the queue is full or other errors occur.
* @param blocking True if the Appender should wait when the queue is full. The default is true.
* @param shutdownTimeout How many milliseconds the Appender should wait to flush outstanding log events
* in the queue on shutdown. The default is zero which means to wait forever.
* @param size The size of the event queue. The default is 128.
* @param name The name of the Appender.
* @param includeLocation whether to include location information. The default is false.
* @param filter The Filter or null.
* @param config The Configuration.
* @param ignoreExceptions If {@code "true"} (default) exceptions encountered when appending events are logged;
* otherwise they are propagated to the caller.
* @return The AsyncAppender.
* @deprecated use {@link Builder} instead
*/
@Deprecated
public static AsyncAppender createAppender(final AppenderRef[] appenderRefs, final String errorRef,
final boolean blocking, final long shutdownTimeout, final int size,
final String name, final boolean includeLocation, final Filter filter,
final Configuration config, final boolean ignoreExceptions) {
if (name == null) {
LOGGER.error("No name provided for AsyncAppender");
return null;
}
if (appenderRefs == null) {
LOGGER.error("No appender references provided to AsyncAppender {}", name);
}
return new AsyncAppender(name, filter, appenderRefs, errorRef, size, blocking, ignoreExceptions,
shutdownTimeout, config, includeLocation, new ArrayBlockingQueueFactory(), null);
}
@PluginBuilderFactory
public static Builder newBuilder() {
return new Builder();
}
public static class Builder> extends AbstractFilterable.Builder
implements org.apache.logging.log4j.core.util.Builder {
@PluginElement("AppenderRef")
@Required(message = "No appender references provided to AsyncAppender")
private AppenderRef[] appenderRefs;
@PluginBuilderAttribute
@PluginAliases("error-ref")
private String errorRef;
@PluginBuilderAttribute
private boolean blocking = true;
@PluginBuilderAttribute
private long shutdownTimeout = 0L;
@PluginBuilderAttribute
private int bufferSize = DEFAULT_QUEUE_SIZE;
@PluginBuilderAttribute
@Required(message = "No name provided for AsyncAppender")
private String name;
@PluginBuilderAttribute
private boolean includeLocation = false;
@PluginConfiguration
private Configuration configuration;
@PluginBuilderAttribute
private boolean ignoreExceptions = true;
@PluginElement(BlockingQueueFactory.ELEMENT_TYPE)
private BlockingQueueFactory blockingQueueFactory = new ArrayBlockingQueueFactory<>();
public Builder setAppenderRefs(final AppenderRef[] appenderRefs) {
this.appenderRefs = appenderRefs;
return this;
}
public Builder setErrorRef(final String errorRef) {
this.errorRef = errorRef;
return this;
}
public Builder setBlocking(final boolean blocking) {
this.blocking = blocking;
return this;
}
public Builder setShutdownTimeout(final long shutdownTimeout) {
this.shutdownTimeout = shutdownTimeout;
return this;
}
public Builder setBufferSize(final int bufferSize) {
this.bufferSize = bufferSize;
return this;
}
public Builder setName(final String name) {
this.name = name;
return this;
}
public Builder setIncludeLocation(final boolean includeLocation) {
this.includeLocation = includeLocation;
return this;
}
public Builder setConfiguration(final Configuration configuration) {
this.configuration = configuration;
return this;
}
public Builder setIgnoreExceptions(final boolean ignoreExceptions) {
this.ignoreExceptions = ignoreExceptions;
return this;
}
public Builder setBlockingQueueFactory(final BlockingQueueFactory blockingQueueFactory) {
this.blockingQueueFactory = blockingQueueFactory;
return this;
}
@Override
public AsyncAppender build() {
return new AsyncAppender(name, getFilter(), appenderRefs, errorRef, bufferSize, blocking, ignoreExceptions,
shutdownTimeout, configuration, includeLocation, blockingQueueFactory, getPropertyArray());
}
}
/**
* Thread that calls the Appenders.
*/
private class AsyncThread extends Log4jThread {
private volatile boolean shutdown = false;
private final List appenders;
private final BlockingQueue queue;
public AsyncThread(final List appenders, final BlockingQueue queue) {
super("AsyncAppender-" + THREAD_SEQUENCE.getAndIncrement());
this.appenders = appenders;
this.queue = queue;
setDaemon(true);
}
@Override
public void run() {
while (!shutdown) {
LogEvent event;
try {
event = queue.take();
if (event == SHUTDOWN_LOG_EVENT) {
shutdown = true;
continue;
}
} catch (final InterruptedException ex) {
break; // LOG4J2-830
}
event.setEndOfBatch(queue.isEmpty());
final boolean success = callAppenders(event);
if (!success && errorAppender != null) {
try {
errorAppender.callAppender(event);
} catch (final Exception ex) {
// Silently accept the error.
}
}
}
// Process any remaining items in the queue.
LOGGER.trace("AsyncAppender.AsyncThread shutting down. Processing remaining {} queue events.",
queue.size());
int count = 0;
int ignored = 0;
while (!queue.isEmpty()) {
try {
final LogEvent event = queue.take();
if (event instanceof Log4jLogEvent) {
final Log4jLogEvent logEvent = (Log4jLogEvent) event;
logEvent.setEndOfBatch(queue.isEmpty());
callAppenders(logEvent);
count++;
} else {
ignored++;
LOGGER.trace("Ignoring event of class {}", event.getClass().getName());
}
} catch (final InterruptedException ex) {
// May have been interrupted to shut down.
// Here we ignore interrupts and try to process all remaining events.
}
}
LOGGER.trace("AsyncAppender.AsyncThread stopped. Queue has {} events remaining. "
+ "Processed {} and ignored {} events since shutdown started.", queue.size(), count, ignored);
}
/**
* Calls {@link AppenderControl#callAppender(LogEvent) callAppender} on all registered {@code AppenderControl}
* objects, and returns {@code true} if at least one appender call was successful, {@code false} otherwise. Any
* exceptions are silently ignored.
*
* @param event the event to forward to the registered appenders
* @return {@code true} if at least one appender call succeeded, {@code false} otherwise
*/
boolean callAppenders(final LogEvent event) {
boolean success = false;
for (final AppenderControl control : appenders) {
try {
control.callAppender(event);
success = true;
} catch (final Exception ex) {
// If no appender is successful the error appender will get it.
}
}
return success;
}
public void shutdown() {
shutdown = true;
if (queue.isEmpty()) {
queue.offer(SHUTDOWN_LOG_EVENT);
}
if (getState() == State.TIMED_WAITING || getState() == State.WAITING) {
this.interrupt(); // LOG4J2-1422: if underlying appender is stuck in wait/sleep/join/park call
}
}
}
/**
* Returns the names of the appenders that this asyncAppender delegates to as an array of Strings.
*
* @return the names of the sink appenders
*/
public String[] getAppenderRefStrings() {
final String[] result = new String[appenderRefs.length];
for (int i = 0; i < result.length; i++) {
result[i] = appenderRefs[i].getRef();
}
return result;
}
/**
* Returns {@code true} if this AsyncAppender will take a snapshot of the stack with every log event to determine
* the class and method where the logging call was made.
*
* @return {@code true} if location is included with every event, {@code false} otherwise
*/
public boolean isIncludeLocation() {
return includeLocation;
}
/**
* Returns {@code true} if this AsyncAppender will block when the queue is full, or {@code false} if events are
* dropped when the queue is full.
*
* @return whether this AsyncAppender will block or drop events when the queue is full.
*/
public boolean isBlocking() {
return blocking;
}
/**
* Returns the name of the appender that any errors are logged to or {@code null}.
*
* @return the name of the appender that any errors are logged to or {@code null}
*/
public String getErrorRef() {
return errorRef;
}
public int getQueueCapacity() {
return queueSize;
}
public int getQueueRemainingCapacity() {
return queue.remainingCapacity();
}
/**
* Returns the number of elements in the queue.
*
* @return the number of elements in the queue.
* @since 2.11.1
*/
public int getQueueSize() {
return queue.size();
}
}