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1 /*
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2 * Copyright 2001-2007 Sun Microsystems, Inc. All Rights Reserved.
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3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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4 *
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5 * This code is free software; you can redistribute it and/or modify it
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6 * under the terms of the GNU General Public License version 2 only, as
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7 * published by the Free Software Foundation.
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8 *
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9 * This code is distributed in the hope that it will be useful, but WITHOUT
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10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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11 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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12 * version 2 for more details (a copy is included in the LICENSE file that
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13 * accompanied this code).
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14 *
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15 * You should have received a copy of the GNU General Public License version
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16 * 2 along with this work; if not, write to the Free Software Foundation,
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17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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18 *
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19 * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
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20 * CA 95054 USA or visit www.sun.com if you need additional information or
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21 * have any questions.
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22 *
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23 */
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24
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25 // COTracker keeps track of the concurrent overhead of a GC thread.
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26
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27 // A thread that needs to be tracked must, itself, start up its
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28 // tracker with the start() method and then call the update() method
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29 // at regular intervals. What the tracker does is to calculate the
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30 // concurrent overhead of a process at a given update period. The
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31 // tracker starts and when is detects that it has exceeded the given
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32 // period, it calculates the duration of the period in wall-clock time
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33 // and the duration of the period in vtime (i.e. how much time the
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34 // concurrent processes really took up during this period). The ratio
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35 // of the latter over the former is the concurrent overhead of that
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36 // process for that period over a single CPU. This overhead is stored
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37 // on the tracker, "timestamped" with the wall-clock time of the end
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38 // of the period. When the concurrent overhead of this process needs
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39 // to be queried, this last "reading" provides a good approximation
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40 // (we assume that the concurrent overhead of a particular thread
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41 // stays largely constant over time). The timestamp is necessary to
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42 // detect when the process has stopped working and the recorded
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43 // reading hasn't been updated for some time.
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44
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45 // Each concurrent GC thread is considered to be part of a "group"
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46 // (i.e. any available concurrent marking threads are part of the
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47 // "concurrent marking thread group"). A COTracker is associated with
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48 // a single group at construction-time. It's up to each collector to
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49 // decide how groups will be mapped to such an id (ids should start
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50 // from 0 and be consecutive; there's a hardcoded max group num
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51 // defined on the GCOverheadTracker class). The notion of a group has
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52 // been introduced to be able to identify how much overhead was
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53 // imposed by each group, instead of getting a single value that
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54 // covers all concurrent overhead.
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55
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56 class COTracker {
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57 private:
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58 // It indicates whether this tracker is enabled or not. When the
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59 // tracker is disabled, then it returns 0.0 as the latest concurrent
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60 // overhead and several methods (reset, start, and update) are not
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61 // supposed to be called on it. This enabling / disabling facility
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62 // is really provided to make a bit more explicit in the code when a
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63 // particulary tracker of a processes that doesn't run all the time
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64 // (e.g. concurrent marking) is supposed to be used and not it's not.
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65 bool _enabled;
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66
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67 // The ID of the group associated with this tracker.
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68 int _group;
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69
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70 // The update period of the tracker. A new value for the concurrent
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71 // overhead of the associated process will be made at intervals no
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72 // smaller than this.
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73 double _update_period_sec;
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74
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75 // The start times (both wall-block time and vtime) of the current
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76 // interval.
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77 double _period_start_time_sec;
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78 double _period_start_vtime_sec;
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79
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80 // Number seq of the concurrent overhead readings within a period
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81 NumberSeq _conc_overhead_seq;
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82
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83 // The latest reading of the concurrent overhead (over a single CPU)
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84 // imposed by the associated concurrent thread, made available at
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85 // the indicated wall-clock time.
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86 double _conc_overhead;
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87 double _time_stamp_sec;
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88
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89 // The number of CPUs that the host machine has (for convenience
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90 // really, as we'd have to keep translating it into a double)
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91 static double _cpu_number;
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92
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93 // Fields that keep a list of all trackers created. This is useful,
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94 // since it allows us to sum up the concurrent overhead without
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95 // having to write code for a specific collector to broadcast a
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96 // request to all its concurrent processes.
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97 COTracker* _next;
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98 static COTracker* _head;
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99
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100 // It indicates that a new period is starting by updating the
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101 // _period_start_time_sec and _period_start_vtime_sec fields.
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102 void resetPeriod(double now_sec, double vnow_sec);
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103 // It updates the latest concurrent overhead reading, taken at a
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104 // given wall-clock time.
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105 void setConcOverhead(double time_stamp_sec, double conc_overhead);
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106
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107 // It determines whether the time stamp of the latest concurrent
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108 // overhead reading is out of date or not.
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109 bool outOfDate(double now_sec) {
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110 // The latest reading is considered out of date, if it was taken
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111 // 1.2x the update period.
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112 return (now_sec - _time_stamp_sec) > 1.2 * _update_period_sec;
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113 }
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114
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115 public:
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116 // The constructor which associates the tracker with a group ID.
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117 COTracker(int group);
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118
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119 // Methods to enable / disable the tracker and query whether it is enabled.
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120 void enable() { _enabled = true; }
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121 void disable() { _enabled = false; }
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122 bool enabled() { return _enabled; }
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123
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124 // It resets the tracker and sets concurrent overhead reading to be
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125 // the given parameter and the associated time stamp to be now.
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126 void reset(double starting_conc_overhead = 0.0);
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127 // The tracker starts tracking. IT should only be called from the
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128 // concurrent thread that is tracked by this tracker.
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129 void start();
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130 // It updates the tracker and, if the current period is longer than
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131 // the update period, the concurrent overhead reading will be
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132 // updated. force_end being true indicates that it's the last call
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133 // to update() by this process before the tracker is disabled (the
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134 // tracker can be re-enabled later if necessary). It should only be
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135 // called from the concurrent thread that is tracked by this tracker
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136 // and while the thread has joined the STS.
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137 void update(bool force_end = false);
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138 // It adjusts the contents of the tracker to take into account a STW
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139 // pause.
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140 void updateForSTW(double start_sec, double end_sec);
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141
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142 // It returns the last concurrent overhead reading over a single
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143 // CPU. If the reading is out of date, or the tracker is disabled,
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144 // it returns 0.0.
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145 double concCPUOverhead(double now_sec) {
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146 if (!_enabled || outOfDate(now_sec))
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147 return 0.0;
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148 else
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149 return _conc_overhead;
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150 }
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151
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152 // It returns the last concurrent overhead reading over all CPUs
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153 // that the host machine has. If the reading is out of date, or the
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154 // tracker is disabled, it returns 0.0.
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155 double concOverhead(double now_sec) {
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156 return concCPUOverhead(now_sec) / _cpu_number;
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157 }
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158
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159 double predConcOverhead();
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160
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161 void resetPred();
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162
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163 // statics
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164
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165 // It notifies all trackers about a STW pause.
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166 static void updateAllForSTW(double start_sec, double end_sec);
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167
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168 // It returns the sum of the concurrent overhead readings of all
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169 // available (and enabled) trackers for the given time stamp. The
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170 // overhead is over all the CPUs of the host machine.
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171
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172 static double totalConcOverhead(double now_sec);
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173 // Like the previous method, but it also sums up the overheads per
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174 // group number. The length of the co_per_group array must be at
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175 // least as large group_num
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176 static double totalConcOverhead(double now_sec,
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177 size_t group_num,
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178 double* co_per_group);
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179
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180 static double totalPredConcOverhead();
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181 };
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