1: <?php
2: /**
3: * Licensed to the Apache Software Foundation (ASF) under one or more
4: * contributor license agreements. See the NOTICE file distributed with
5: * this work for additional information regarding copyright ownership.
6: * The ASF licenses this file to You under the Apache License, Version 2.0
7: * (the "License"); you may not use this file except in compliance with
8: * the License. You may obtain a copy of the License at
9: *
10: * http://www.apache.org/licenses/LICENSE-2.0
11: *
12: * Unless required by applicable law or agreed to in writing, software
13: * distributed under the License is distributed on an "AS IS" BASIS,
14: * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15: * See the License for the specific language governing permissions and
16: * limitations under the License.
17: *
18: * @package log4php
19: */
20:
21: /**
22: * The NDC class implements <i>nested diagnostic contexts</i>.
23: *
24: * NDC was defined by Neil Harrison in the article "Patterns for Logging
25: * Diagnostic Messages" part of the book <i>"Pattern Languages of
26: * Program Design 3"</i> edited by Martin et al.
27: *
28: * A Nested Diagnostic Context, or NDC in short, is an instrument
29: * to distinguish interleaved log output from different sources. Log
30: * output is typically interleaved when a server handles multiple
31: * clients near-simultaneously.
32: *
33: * This class is similar to the {@link LoggerMDC} class except that it is
34: * based on a stack instead of a map.
35: *
36: * Interleaved log output can still be meaningful if each log entry
37: * from different contexts had a distinctive stamp. This is where NDCs
38: * come into play.
39: *
40: * <b>Note that NDCs are managed on a per thread basis</b>.
41: *
42: * NDC operations such as {@link push()}, {@link pop()},
43: * {@link clear()}, {@link getDepth()} and {@link setMaxDepth()}
44: * affect the NDC of the <i>current</i> thread only. NDCs of other
45: * threads remain unaffected.
46: *
47: * For example, a servlet can build a per client request NDC
48: * consisting the clients host name and other information contained in
49: * the the request. <i>Cookies</i> are another source of distinctive
50: * information. To build an NDC one uses the {@link push()}
51: * operation.
52: *
53: * Simply put,
54: *
55: * - Contexts can be nested.
56: * - When entering a context, call <kbd>LoggerNDC::push()</kbd>
57: * As a side effect, if there is no nested diagnostic context for the
58: * current thread, this method will create it.
59: * - When leaving a context, call <kbd>LoggerNDC::pop()</kbd>
60: * - <b>When exiting a thread make sure to call {@link remove()}</b>
61: *
62: * There is no penalty for forgetting to match each
63: * <kbd>push</kbd> operation with a corresponding <kbd>pop</kbd>,
64: * except the obvious mismatch between the real application context
65: * and the context set in the NDC.
66: *
67: * If configured to do so, {@link LoggerPatternLayout} and {@link LoggerLayoutTTCC}
68: * instances automatically retrieve the nested diagnostic
69: * context for the current thread without any user intervention.
70: * Hence, even if a servlet is serving multiple clients
71: * simultaneously, the logs emanating from the same code (belonging to
72: * the same category) can still be distinguished because each client
73: * request will have a different NDC tag.
74: *
75: * Example:
76: *
77: * {@example ../../examples/php/ndc.php 19}<br>
78: *
79: * With the properties file:
80: *
81: * {@example ../../examples/resources/ndc.properties 18}<br>
82: *
83: * Will result in the following (notice the conn and client ids):
84: *
85: * <pre>
86: * 2009-09-13 19:04:27 DEBUG root conn=1234: just received a new connection in src/examples/php/ndc.php at 23
87: * 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
88: * 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
89: * 2009-09-13 19:04:27 DEBUG root : back and waiting for new connections in src/examples/php/ndc.php at 29
90: * </pre>
91: *
92: * @version $Revision: 1350602 $
93: * @package log4php
94: * @since 0.3
95: */
96: class LoggerNDC {
97:
98: /** This is the repository of NDC stack */
99: private static $stack = array();
100:
101: /**
102: * Clear any nested diagnostic information if any. This method is
103: * useful in cases where the same thread can be potentially used
104: * over and over in different unrelated contexts.
105: *
106: * <p>This method is equivalent to calling the {@link setMaxDepth()}
107: * method with a zero <var>maxDepth</var> argument.
108: */
109: public static function clear() {
110: self::$stack = array();
111: }
112:
113: /**
114: * Never use this method directly, use the {@link LoggerLoggingEvent::getNDC()} method instead.
115: * @return array
116: */
117: public static function get() {
118: return implode(' ', self::$stack);
119: }
120:
121: /**
122: * Get the current nesting depth of this diagnostic context.
123: *
124: * @see setMaxDepth()
125: * @return integer
126: */
127: public static function getDepth() {
128: return count(self::$stack);
129: }
130:
131: /**
132: * Clients should call this method before leaving a diagnostic
133: * context.
134: *
135: * <p>The returned value is the value that was pushed last. If no
136: * context is available, then the empty string "" is returned.</p>
137: *
138: * @return string The innermost diagnostic context.
139: */
140: public static function pop() {
141: if(count(self::$stack) > 0) {
142: return array_pop(self::$stack);
143: } else {
144: return '';
145: }
146: }
147:
148: /**
149: * Looks at the last diagnostic context at the top of this NDC
150: * without removing it.
151: *
152: * <p>The returned value is the value that was pushed last. If no
153: * context is available, then the empty string "" is returned.</p>
154: * @return string The innermost diagnostic context.
155: */
156: public static function peek() {
157: if(count(self::$stack) > 0) {
158: return end(self::$stack);
159: } else {
160: return '';
161: }
162: }
163:
164: /**
165: * Push new diagnostic context information for the current thread.
166: *
167: * <p>The contents of the <var>message</var> parameter is
168: * determined solely by the client.
169: *
170: * @param string $message The new diagnostic context information.
171: */
172: public static function push($message) {
173: array_push(self::$stack, (string)$message);
174: }
175:
176: /**
177: * Remove the diagnostic context for this thread.
178: */
179: public static function remove() {
180: LoggerNDC::clear();
181: }
182:
183: /**
184: * Set maximum depth of this diagnostic context. If the current
185: * depth is smaller or equal to <var>maxDepth</var>, then no
186: * action is taken.
187: *
188: * <p>This method is a convenient alternative to multiple
189: * {@link pop()} calls. Moreover, it is often the case that at
190: * the end of complex call sequences, the depth of the NDC is
191: * unpredictable. The {@link setMaxDepth()} method circumvents
192: * this problem.
193: *
194: * @param integer $maxDepth
195: * @see getDepth()
196: */
197: public static function setMaxDepth($maxDepth) {
198: $maxDepth = (int)$maxDepth;
199: if(LoggerNDC::getDepth() > $maxDepth) {
200: self::$stack = array_slice(self::$stack, 0, $maxDepth);
201: }
202: }
203: }
204: