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1 /*
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2 * Copyright 2003-2007 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 // Low Memory Detection Support
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26 // Two memory alarms in the JDK (we called them sensors).
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27 // - Heap memory sensor
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28 // - Non-heap memory sensor
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29 // When the VM detects if the memory usage of a memory pool has reached
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30 // or exceeded its threshold, it will trigger the sensor for the type
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31 // of the memory pool (heap or nonheap or both).
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32 //
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33 // If threshold == -1, no low memory detection is supported and
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34 // the threshold value is not allowed to be changed.
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35 // If threshold == 0, no low memory detection is performed for
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36 // that memory pool. The threshold can be set to any non-negative
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37 // value.
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38 //
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39 // The default threshold of the Hotspot memory pools are:
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40 // Eden space -1
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41 // Survivor space 1 -1
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42 // Survivor space 2 -1
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43 // Old generation 0
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44 // Perm generation 0
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45 // CodeCache 0
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46 //
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47 // For heap memory, detection will be performed when GC finishes
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48 // and also in the slow path allocation.
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49 // For Code cache, detection will be performed in the allocation
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50 // and deallocation.
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51 //
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52 // May need to deal with hysteresis effect.
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53 //
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54
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55 class LowMemoryDetectorThread;
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56 class OopClosure;
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57 class MemoryPool;
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58
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59 class ThresholdSupport : public CHeapObj {
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60 private:
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61 bool _support_high_threshold;
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62 bool _support_low_threshold;
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63 size_t _high_threshold;
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64 size_t _low_threshold;
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65 public:
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66 ThresholdSupport(bool support_high, bool support_low) {
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67 _support_high_threshold = support_high;
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68 _support_low_threshold = support_low;
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69 _high_threshold = 0;
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70 _low_threshold= 0;
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71 }
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72
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73 size_t high_threshold() const { return _high_threshold; }
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74 size_t low_threshold() const { return _low_threshold; }
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75 bool is_high_threshold_supported() { return _support_high_threshold; }
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76 bool is_low_threshold_supported() { return _support_low_threshold; }
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77
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78 bool is_high_threshold_crossed(MemoryUsage usage) {
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79 if (_support_high_threshold && _high_threshold > 0) {
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80 return (usage.used() >= _high_threshold);
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81 }
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82 return false;
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83 }
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84 bool is_low_threshold_crossed(MemoryUsage usage) {
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85 if (_support_low_threshold && _low_threshold > 0) {
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86 return (usage.used() < _low_threshold);
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87 }
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88 return false;
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89 }
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90
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91 size_t set_high_threshold(size_t new_threshold) {
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92 assert(_support_high_threshold, "can only be set if supported");
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93 assert(new_threshold >= _low_threshold, "new_threshold must be >= _low_threshold");
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94 size_t prev = _high_threshold;
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95 _high_threshold = new_threshold;
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96 return prev;
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97 }
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98
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99 size_t set_low_threshold(size_t new_threshold) {
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100 assert(_support_low_threshold, "can only be set if supported");
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101 assert(new_threshold <= _high_threshold, "new_threshold must be <= _high_threshold");
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102 size_t prev = _low_threshold;
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103 _low_threshold = new_threshold;
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104 return prev;
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105 }
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106 };
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107
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108 class SensorInfo : public CHeapObj {
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109 private:
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110 instanceOop _sensor_obj;
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111 bool _sensor_on;
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112 size_t _sensor_count;
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113
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114 // before the actual sensor on flag and sensor count are set
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115 // we maintain the number of pending triggers and clears.
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116 // _pending_trigger_count means the number of pending triggers
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117 // and the sensor count should be incremented by the same number.
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118
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119 int _pending_trigger_count;
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120
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121 // _pending_clear_count takes precedence if it's > 0 which
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122 // indicates the resulting sensor will be off
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123 // Sensor trigger requests will reset this clear count to
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124 // indicate the resulting flag should be on.
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125
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126 int _pending_clear_count;
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127
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128 MemoryUsage _usage;
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129
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130 void clear(int count, TRAPS);
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131 void trigger(int count, TRAPS);
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132 public:
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133 SensorInfo();
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134 void set_sensor(instanceOop sensor) {
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135 assert(_sensor_obj == NULL, "Should be set only once");
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136 _sensor_obj = sensor;
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137 }
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138
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139 bool has_pending_requests() {
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140 return (_pending_trigger_count > 0 || _pending_clear_count > 0);
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141 }
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142
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143 int pending_trigger_count() { return _pending_trigger_count; }
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144 int pending_clear_count() { return _pending_clear_count; }
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145
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146 // When this method is used, the memory usage is monitored
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147 // as a gauge attribute. High and low thresholds are designed
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148 // to provide a hysteresis mechanism to avoid repeated triggering
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149 // of notifications when the attribute value makes small oscillations
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150 // around the high or low threshold value.
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151 //
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152 // The sensor will be triggered if:
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153 // (1) the usage is crossing above the high threshold and
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154 // the sensor is currently off and no pending
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155 // trigger requests; or
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156 // (2) the usage is crossing above the high threshold and
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157 // the sensor will be off (i.e. sensor is currently on
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158 // and has pending clear requests).
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159 //
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160 // Subsequent crossings of the high threshold value do not cause
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161 // any triggers unless the usage becomes less than the low threshold.
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162 //
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163 // The sensor will be cleared if:
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164 // (1) the usage is crossing below the low threshold and
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165 // the sensor is currently on and no pending
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166 // clear requests; or
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167 // (2) the usage is crossing below the low threshold and
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168 // the sensor will be on (i.e. sensor is currently off
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169 // and has pending trigger requests).
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170 //
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171 // Subsequent crossings of the low threshold value do not cause
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172 // any clears unless the usage becomes greater than or equal
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173 // to the high threshold.
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174 //
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175 // If the current level is between high and low threhsold, no change.
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176 //
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177 void set_gauge_sensor_level(MemoryUsage usage, ThresholdSupport* high_low_threshold);
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178
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179 // When this method is used, the memory usage is monitored as a
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180 // simple counter attribute. The sensor will be triggered
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181 // whenever the usage is crossing the threshold to keep track
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182 // of the number of times the VM detects such a condition occurs.
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183 //
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184 // The sensor will be triggered if:
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185 // - the usage is crossing above the high threshold regardless
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186 // of the current sensor state.
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187 //
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188 // The sensor will be cleared if:
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189 // (1) the usage is crossing below the low threshold and
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190 // the sensor is currently on; or
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191 // (2) the usage is crossing below the low threshold and
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192 // the sensor will be on (i.e. sensor is currently off
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193 // and has pending trigger requests).
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194 //
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195 void set_counter_sensor_level(MemoryUsage usage, ThresholdSupport* counter_threshold);
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196
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197 void process_pending_requests(TRAPS);
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198 void oops_do(OopClosure* f);
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199
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200 #ifndef PRODUCT
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201 // printing on default output stream;
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202 void print();
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203 #endif // PRODUCT
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204 };
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205
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206 class LowMemoryDetector : public AllStatic {
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207 friend class LowMemoryDetectorDisabler;
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208 private:
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209 // true if any collected heap has low memory detection enabled
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210 static volatile bool _enabled_for_collected_pools;
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211 // > 0 if temporary disabed
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212 static volatile jint _disabled_count;
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213
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214 static LowMemoryDetectorThread* _detector_thread;
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215 static void low_memory_detector_thread_entry(JavaThread* thread, TRAPS);
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216 static void check_memory_usage();
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217 static bool has_pending_requests();
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218 static bool temporary_disabled() { return _disabled_count > 0; }
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219 static void disable() { Atomic::inc(&_disabled_count); }
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220 static void enable() { Atomic::dec(&_disabled_count); }
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221
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222 public:
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223 static void initialize();
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224 static void detect_low_memory();
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225 static void detect_low_memory(MemoryPool* pool);
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226 static void detect_after_gc_memory(MemoryPool* pool);
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227
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228 static bool is_enabled(MemoryPool* pool) {
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229 // low memory detection is enabled for collected memory pools
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230 // iff one of the collected memory pool has a sensor and the
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231 // threshold set non-zero
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232 if (pool->usage_sensor() == NULL) {
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233 return false;
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234 } else {
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235 ThresholdSupport* threshold_support = pool->usage_threshold();
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236 return (threshold_support->is_high_threshold_supported() ?
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237 (threshold_support->high_threshold() > 0) : false);
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238 }
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239 }
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240
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241 // indicates if low memory detection is enabled for any collected
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242 // memory pools
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243 static inline bool is_enabled_for_collected_pools() {
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244 return !temporary_disabled() && _enabled_for_collected_pools;
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245 }
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246
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247 // recompute enabled flag
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248 static void recompute_enabled_for_collected_pools();
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249
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250 // low memory detection for collected memory pools.
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251 static inline void detect_low_memory_for_collected_pools() {
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252 // no-op if low memory detection not enabled
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253 if (!is_enabled_for_collected_pools()) {
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254 return;
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255 }
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256 int num_memory_pools = MemoryService::num_memory_pools();
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257 for (int i=0; i<num_memory_pools; i++) {
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258 MemoryPool* pool = MemoryService::get_memory_pool(i);
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259
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260 // if low memory detection is enabled then check if the
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261 // current used exceeds the high threshold
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262 if (pool->is_collected_pool() && is_enabled(pool)) {
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263 size_t used = pool->used_in_bytes();
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264 size_t high = pool->usage_threshold()->high_threshold();
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265 if (used > high) {
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266 detect_low_memory(pool);
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267 }
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268 }
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269 }
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270 }
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271
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272 };
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273
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274 class LowMemoryDetectorDisabler: public StackObj {
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275 public:
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276 LowMemoryDetectorDisabler()
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277 {
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278 LowMemoryDetector::disable();
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279 }
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280 ~LowMemoryDetectorDisabler()
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281 {
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282 assert(LowMemoryDetector::temporary_disabled(), "should be disabled!");
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283 LowMemoryDetector::enable();
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284 }
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285 };
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