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<?php
/**
* 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 log4php
*/
/**
* The NDC class implements <i>nested diagnostic contexts</i>.
*
* NDC was defined by Neil Harrison in the article "Patterns for Logging
* Diagnostic Messages" part of the book <i>"Pattern Languages of
* Program Design 3"</i> edited by Martin et al.
*
* A Nested Diagnostic Context, or NDC in short, is an instrument
* to distinguish interleaved log output from different sources. Log
* output is typically interleaved when a server handles multiple
* clients near-simultaneously.
*
* This class is similar to the {@link LoggerMDC} class except that it is
* based on a stack instead of a map.
*
* Interleaved log output can still be meaningful if each log entry
* from different contexts had a distinctive stamp. This is where NDCs
* come into play.
*
* <b>Note that NDCs are managed on a per thread basis</b>.
*
* NDC operations such as {@link push()}, {@link pop()},
* {@link clear()}, {@link getDepth()} and {@link setMaxDepth()}
* affect the NDC of the <i>current</i> thread only. NDCs of other
* threads remain unaffected.
*
* For example, a servlet can build a per client request NDC
* consisting the clients host name and other information contained in
* the the request. <i>Cookies</i> are another source of distinctive
* information. To build an NDC one uses the {@link push()}
* operation.
*
* Simply put,
*
* - Contexts can be nested.
* - When entering a context, call <kbd>LoggerNDC::push()</kbd>
* As a side effect, if there is no nested diagnostic context for the
* current thread, this method will create it.
* - When leaving a context, call <kbd>LoggerNDC::pop()</kbd>
* - <b>When exiting a thread make sure to call {@link remove()}</b>
*
* There is no penalty for forgetting to match each
* <kbd>push</kbd> operation with a corresponding <kbd>pop</kbd>,
* except the obvious mismatch between the real application context
* and the context set in the NDC.
*
* If configured to do so, {@link LoggerPatternLayout} and {@link LoggerLayoutTTCC}
* instances automatically retrieve the nested diagnostic
* context for the current thread without any user intervention.
* Hence, even if a servlet is serving multiple clients
* simultaneously, the logs emanating from the same code (belonging to
* the same category) can still be distinguished because each client
* request will have a different NDC tag.
*
* Example:
*
* {@example ../../examples/php/ndc.php 19}<br>
*
* With the properties file:
*
* {@example ../../examples/resources/ndc.properties 18}<br>
*
* Will result in the following (notice the conn and client ids):
*
* <pre>
* 2009-09-13 19:04:27 DEBUG root conn=1234: just received a new connection in src/examples/php/ndc.php at 23
* 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: some more messages that can in src/examples/php/ndc.php at 25
* 2009-09-13 19:04:27 DEBUG root conn=1234 client=ab23: now related to a client in src/examples/php/ndc.php at 26
* 2009-09-13 19:04:27 DEBUG root : back and waiting for new connections in src/examples/php/ndc.php at 29
* </pre>
*
* @version $Revision: 1350602 $
* @package log4php
* @since 0.3
*/
class LoggerNDC {
/** This is the repository of NDC stack */
private static $stack = array();
/**
* Clear any nested diagnostic information if any. This method is
* useful in cases where the same thread can be potentially used
* over and over in different unrelated contexts.
*
* <p>This method is equivalent to calling the {@link setMaxDepth()}
* method with a zero <var>maxDepth</var> argument.
*/
public static function clear() {
self::$stack = array();
}
/**
* Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead.
* @return array
*/
public static function get() {
return implode(' ', self::$stack);
}
/**
* Get the current nesting depth of this diagnostic context.
*
* @see setMaxDepth()
* @return integer
*/
public static function getDepth() {
return count(self::$stack);
}
/**
* Clients should call this method before leaving a diagnostic
* context.
*
* <p>The returned value is the value that was pushed last. If no
* context is available, then the empty string "" is returned.</p>
*
* @return string The innermost diagnostic context.
*/
public static function pop() {
if(count(self::$stack) > 0) {
return array_pop(self::$stack);
} else {
return '';
}
}
/**
* Looks at the last diagnostic context at the top of this NDC
* without removing it.
*
* <p>The returned value is the value that was pushed last. If no
* context is available, then the empty string "" is returned.</p>
* @return string The innermost diagnostic context.
*/
public static function peek() {
if(count(self::$stack) > 0) {
return end(self::$stack);
} else {
return '';
}
}
/**
* Push new diagnostic context information for the current thread.
*
* <p>The contents of the <var>message</var> parameter is
* determined solely by the client.
*
* @param string $message The new diagnostic context information.
*/
public static function push($message) {
array_push(self::$stack, (string)$message);
}
/**
* Remove the diagnostic context for this thread.
*/
public static function remove() {
LoggerNDC::clear();
}
/**
* Set maximum depth of this diagnostic context. If the current
* depth is smaller or equal to <var>maxDepth</var>, then no
* action is taken.
*
* <p>This method is a convenient alternative to multiple
* {@link pop()} calls. Moreover, it is often the case that at
* the end of complex call sequences, the depth of the NDC is
* unpredictable. The {@link setMaxDepth()} method circumvents
* this problem.
*
* @param integer $maxDepth
* @see getDepth()
*/
public static function setMaxDepth($maxDepth) {
$maxDepth = (int)$maxDepth;
if(LoggerNDC::getDepth() > $maxDepth) {
self::$stack = array_slice(self::$stack, 0, $maxDepth);
}
}
}