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 $Revision$ * @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. * *

This method is equivalent to calling the {@link setMaxDepth()} * method with a zero maxDepth argument. * * @static */ public static function clear() { self::$stack = array(); } /** * Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead. * @static * @return array */ public static function get() { return implode(' ', self::$stack); } /** * Get the current nesting depth of this diagnostic context. * * @see setMaxDepth() * @return integer * @static */ public static function getDepth() { return count(self::$stack); } /** * 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(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. * *

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(self::$stack) > 0) { return end(self::$stack); } 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(self::$stack, (string)$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(LoggerNDC::getDepth() > $maxDepth) { self::$stack = array_slice(self::$stack, 0, $maxDepth); } } }