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With inspiration from other libraries
/**
* Logback: the reliable, generic, fast and flexible logging framework.
* Copyright (C) 1999-2015, QOS.ch. All rights reserved.
*
* This program and the accompanying materials are dual-licensed under
* either the terms of the Eclipse Public License v1.0 as published by
* the Eclipse Foundation
*
* or (per the licensee's choosing)
*
* under the terms of the GNU Lesser General Public License version 2.1
* as published by the Free Software Foundation.
*/
package ch.qos.logback.classic.util;
import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
import java.util.Set;
import org.slf4j.spi.MDCAdapter;
/**
* A Mapped Diagnostic Context, or MDC in short, is an instrument for
* distinguishing interleaved log output from different sources. Log output is
* typically interleaved when a server handles multiple clients
* near-simultaneously.
*
* The MDC is managed on a per thread basis. A child thread
* automatically inherits a copy of the mapped diagnostic context of
* its parent.
*
*
* For more information about MDC, please refer to the online manual at
* http://logback.qos.ch/manual/mdc.html
*
* @author Ceki Gülcü
*/
public class LogbackMDCAdapter implements MDCAdapter {
// The internal map is copied so as
// We wish to avoid unnecessarily copying of the map. To ensure
// efficient/timely copying, we have a variable keeping track of the last
// operation. A copy is necessary on 'put' or 'remove' but only if the last
// operation was a 'get'. Get operations never necessitate a copy nor
// successive 'put/remove' operations, only a get followed by a 'put/remove'
// requires copying the map.
// See http://jira.qos.ch/browse/LOGBACK-620 for the original discussion.
// We no longer use CopyOnInheritThreadLocal in order to solve LBCLASSIC-183
// Initially the contents of the thread local in parent and child threads
// reference the same map. However, as soon as a thread invokes the put()
// method, the maps diverge as they should.
final ThreadLocal> copyOnThreadLocal = new ThreadLocal>();
private static final int WRITE_OPERATION = 1;
private static final int MAP_COPY_OPERATION = 2;
// keeps track of the last operation performed
final ThreadLocal lastOperation = new ThreadLocal();
private Integer getAndSetLastOperation(int op) {
Integer lastOp = lastOperation.get();
lastOperation.set(op);
return lastOp;
}
private boolean wasLastOpReadOrNull(Integer lastOp) {
return lastOp == null || lastOp.intValue() == MAP_COPY_OPERATION;
}
private Map duplicateAndInsertNewMap(Map oldMap) {
Map newMap = Collections.synchronizedMap(new HashMap());
if (oldMap != null) {
// we don't want the parent thread modifying oldMap while we are
// iterating over it
synchronized (oldMap) {
newMap.putAll(oldMap);
}
}
copyOnThreadLocal.set(newMap);
return newMap;
}
/**
* Put a context value (the val parameter) as identified with the
* key parameter into the current thread's context map. Note that
* contrary to log4j, the val parameter can be null.
*
*
* If the current thread does not have a context map it is created as a side
* effect of this call.
*
* @throws IllegalArgumentException in case the "key" parameter is null
*/
public void put(String key, String val) throws IllegalArgumentException {
if (key == null) {
throw new IllegalArgumentException("key cannot be null");
}
Map oldMap = copyOnThreadLocal.get();
Integer lastOp = getAndSetLastOperation(WRITE_OPERATION);
if (wasLastOpReadOrNull(lastOp) || oldMap == null) {
Map newMap = duplicateAndInsertNewMap(oldMap);
newMap.put(key, val);
} else {
oldMap.put(key, val);
}
}
/**
* Remove the the context identified by the key parameter.
*
*/
public void remove(String key) {
if (key == null) {
return;
}
Map oldMap = copyOnThreadLocal.get();
if (oldMap == null)
return;
Integer lastOp = getAndSetLastOperation(WRITE_OPERATION);
if (wasLastOpReadOrNull(lastOp)) {
Map newMap = duplicateAndInsertNewMap(oldMap);
newMap.remove(key);
} else {
oldMap.remove(key);
}
}
/**
* Clear all entries in the MDC.
*/
public void clear() {
lastOperation.set(WRITE_OPERATION);
copyOnThreadLocal.remove();
}
/**
* Get the context identified by the key parameter.
*
*/
public String get(String key) {
final Map map = copyOnThreadLocal.get();
if ((map != null) && (key != null)) {
return map.get(key);
} else {
return null;
}
}
/**
* Get the current thread's MDC as a map. This method is intended to be used
* internally.
*/
public Map getPropertyMap() {
lastOperation.set(MAP_COPY_OPERATION);
return copyOnThreadLocal.get();
}
/**
* Returns the keys in the MDC as a {@link Set}. The returned value can be
* null.
*/
public Set getKeys() {
Map map = getPropertyMap();
if (map != null) {
return map.keySet();
} else {
return null;
}
}
/**
* Return a copy of the current thread's context map. Returned value may be
* null.
*/
public Map getCopyOfContextMap() {
Map hashMap = copyOnThreadLocal.get();
if (hashMap == null) {
return null;
} else {
return new HashMap(hashMap);
}
}
public void setContextMap(Map contextMap) {
lastOperation.set(WRITE_OPERATION);
Map newMap = Collections.synchronizedMap(new HashMap());
newMap.putAll(contextMap);
// the newMap replaces the old one for serialisation's sake
copyOnThreadLocal.set(newMap);
}
}