nested diagnostic contexts.
*
* NDC was defined by Neil Harrison in the article "Patterns for Logging
* Diagnostic Messages" part of the book "Pattern Languages of
* Program Design 3" 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.
*
* Note that NDCs are managed on a per thread basis.
*
* NDC operations such as {@link push()}, {@link pop()},
* {@link clear()}, {@link getDepth()} and {@link setMaxDepth()}
* affect the NDC of the current 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. Cookies 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 LoggerNDC::push()
* 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 LoggerNDC::pop()
* - When exiting a thread make sure to call {@link remove()}
*
* There is no penalty for forgetting to match each
* push operation with a corresponding pop,
* 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}
*
* With the properties file:
*
* {@example ../../examples/resources/ndc.properties 18}
*
* Will result in the following (notice the conn and client ids):
*
*
* 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 ** * @version $Revision: 883114 $ * @package log4php * @since 0.3 */ class LoggerNDC { const HT_SIZE = 7; /** * 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. * *
This method is equivalent to calling the {@link setMaxDepth()} * method with a zero maxDepth argument. * * @static */ public static function clear() { $GLOBALS['log4php.LoggerNDC.ht'] = array(); } /** * Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead. * @static * @return array */ public static function get() { if(!array_key_exists('log4php.LoggerNDC.ht', $GLOBALS)) { LoggerNDC::clear(); } return $GLOBALS['log4php.LoggerNDC.ht']; } /** * Get the current nesting depth of this diagnostic context. * * @see setMaxDepth() * @return integer * @static */ public static function getDepth() { return count($GLOBALS['log4php.LoggerNDC.ht']); } /** * Clients should call this method before leaving a diagnostic * context. * *
The returned value is the value that was pushed last. If no * context is available, then the empty string "" is returned.
* * @return string The innermost diagnostic context. * @static */ public static function pop() { if(count($GLOBALS['log4php.LoggerNDC.ht']) > 0) { return array_pop($GLOBALS['log4php.LoggerNDC.ht']); } else { return ''; } } /** * Looks at the last diagnostic context at the top of this NDC * without removing it. * *The returned value is the value that was pushed last. If no * context is available, then the empty string "" is returned.
* @return string The innermost diagnostic context. * @static */ public static function peek(){ if(count($GLOBALS['log4php.LoggerNDC.ht']) > 0) { return end($GLOBALS['log4php.LoggerNDC.ht']); } else { return ''; } } /** * Push new diagnostic context information for the current thread. * *The contents of the message parameter is * determined solely by the client. * * @param string $message The new diagnostic context information. * @static */ public static function push($message) { array_push($GLOBALS['log4php.LoggerNDC.ht'], (string)$message); } /** * Remove the diagnostic context for this thread. * @static */ public static function remove() { LoggerNDC::clear(); } /** * Set maximum depth of this diagnostic context. If the current * depth is smaller or equal to maxDepth, then no * action is taken. * *
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 $maxDepth * @see getDepth() * @static */ public static function setMaxDepth($maxDepth) { $maxDepth = (int)$maxDepth; if($maxDepth <= self::HT_SIZE) { if(LoggerNDC::getDepth() > $maxDepth) { $GLOBALS['log4php.LoggerNDC.ht'] = array_slice($GLOBALS['log4php.LoggerNDC.ht'], $maxDepth); } } } }