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