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/*
*
* 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.qpid.server.logging.actors;
import org.apache.qpid.server.logging.LogActor;
import java.util.EmptyStackException;
import java.util.Stack;
/**
* The CurrentActor is a ThreadLocal wrapper that allows threads in the broker
* to retrieve an actor to perform logging. This approach is used so for two
* reasons:
* 1) We do not have to pass a logging actor around the system
* 2) We can set new actors at the point we have enough information. i.e.
* - Set a low level ConnectionActor when processing bytes from the wire.
* - Set a ChannelActor when we are processing the frame
* - Set a SubscriptionActor when we are handling the subscription.
* <p/>
* The code performing the logging need not worry about what type of actor is
* currently set so can perform its logging. The resulting log entry though will
* contain customised details from the the currently set Actor.
* <p/>
* The Actor model also allows the pre-creation of fixed messages so the
* performance impact of the additional logging data is minimised.
* <p/>
* This class does not perform any checks to ensure that there is an Actor set
* when calling remove or get. As a result the application developer must ensure
* that they have called set before they attempt to use the actor via get or
* remove the set actor.
* <p/>
* The checking of the return via get should not be done as the logging is
* desired. It is preferable to cause the NullPointerException to highlight the
* programming error rather than miss a log message.
* <p/>
* The same is true for the remove. A NPE will occur if no set has been called
* highlighting the programming error.
*/
public class CurrentActor
{
/** The ThreadLocal variable with initialiser */
private static final ThreadLocal<Stack<LogActor>> _currentActor = new ThreadLocal<Stack<LogActor>>()
{
// Initialise the CurrentActor to be an empty List
protected Stack<LogActor> initialValue()
{
return new Stack<LogActor>();
}
};
private static LogActor _defaultActor;
/**
* Set a new {@link LogActor} to be the Current Actor
* <p/>
* This pushes the Actor in to the LIFO Queue
*
* @param actor The new LogActor
*/
public static void set(LogActor actor)
{
Stack<LogActor> stack = _currentActor.get();
stack.push(actor);
}
/**
* Remove all {@link LogActor}s
*/
public static void removeAll()
{
Stack<LogActor> stack = _currentActor.get();
stack.clear();
}
/**
* Remove the current {@link LogActor}.
* <p/>
* Calling remove without calling set will result in an EmptyStackException.
*/
public static void remove()
{
Stack<LogActor> stack = _currentActor.get();
stack.pop();
}
/**
* Return the current head of the list of {@link LogActor}s.
*
* @return Current LogActor
*/
public static LogActor get()
{
try
{
return _currentActor.get().peek();
}
catch (EmptyStackException ese)
{
return _defaultActor;
}
}
public static void setDefault(LogActor defaultActor)
{
_defaultActor = defaultActor;
}
}
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