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1 /*
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2 * Copyright 2001-2006 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 class ConcurrentMarkSweepGeneration;
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26 class CMSCollector;
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27
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28 // The Concurrent Mark Sweep GC Thread (could be several in the future).
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29 class ConcurrentMarkSweepThread: public ConcurrentGCThread {
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30 friend class VMStructs;
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31 friend class ConcurrentMarkSweepGeneration; // XXX should remove friendship
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32 friend class CMSCollector;
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33 public:
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34 virtual void run();
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35
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36 private:
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37 static ConcurrentMarkSweepThread* _cmst;
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38 static CMSCollector* _collector;
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39 static SurrogateLockerThread* _slt;
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40 static SurrogateLockerThread::SLT_msg_type _sltBuffer;
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41 static Monitor* _sltMonitor;
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42
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43 ConcurrentMarkSweepThread* _next;
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44
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45 static bool _should_terminate;
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46
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47 enum CMS_flag_type {
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48 CMS_nil = NoBits,
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49 CMS_cms_wants_token = nth_bit(0),
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50 CMS_cms_has_token = nth_bit(1),
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51 CMS_vm_wants_token = nth_bit(2),
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52 CMS_vm_has_token = nth_bit(3)
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53 };
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54
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55 static int _CMS_flag;
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56
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57 static bool CMS_flag_is_set(int b) { return (_CMS_flag & b) != 0; }
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58 static bool set_CMS_flag(int b) { return (_CMS_flag |= b) != 0; }
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59 static bool clear_CMS_flag(int b) { return (_CMS_flag &= ~b) != 0; }
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60 void sleepBeforeNextCycle();
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61
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62 // CMS thread should yield for a young gen collection, direct allocation,
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63 // and iCMS activity.
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64 static char _pad_1[64 - sizeof(jint)]; // prevent cache-line sharing
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65 static volatile jint _pending_yields;
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66 static volatile jint _pending_decrements; // decrements to _pending_yields
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67 static char _pad_2[64 - sizeof(jint)]; // prevent cache-line sharing
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68
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69 // Tracing messages, enabled by CMSTraceThreadState.
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70 static inline void trace_state(const char* desc);
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71
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72 static volatile bool _icms_enabled; // iCMS enabled?
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73 static volatile bool _should_run; // iCMS may run
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74 static volatile bool _should_stop; // iCMS should stop
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75
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76 // debugging
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77 void verify_ok_to_terminate() const PRODUCT_RETURN;
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78
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79 public:
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80 // Constructor
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81 ConcurrentMarkSweepThread(CMSCollector* collector);
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82
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83 static void makeSurrogateLockerThread(TRAPS);
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84 static SurrogateLockerThread* slt() { return _slt; }
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85
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86 // Tester
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87 bool is_ConcurrentGC_thread() const { return true; }
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88
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89 static void threads_do(ThreadClosure* tc);
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90
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91 // Printing
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92 void print_on(outputStream* st) const;
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93 void print() const { print_on(tty); }
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94 static void print_all_on(outputStream* st);
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95 static void print_all() { print_all_on(tty); }
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96
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97 // Returns the CMS Thread
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98 static ConcurrentMarkSweepThread* cmst() { return _cmst; }
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99 static CMSCollector* collector() { return _collector; }
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100
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101 // Create and start the CMS Thread, or stop it on shutdown
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102 static ConcurrentMarkSweepThread* start(CMSCollector* collector);
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103 static void stop();
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104 static bool should_terminate() { return _should_terminate; }
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105
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106 // Synchronization using CMS token
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107 static void synchronize(bool is_cms_thread);
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108 static void desynchronize(bool is_cms_thread);
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109 static bool vm_thread_has_cms_token() {
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110 return CMS_flag_is_set(CMS_vm_has_token);
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111 }
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112 static bool cms_thread_has_cms_token() {
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113 return CMS_flag_is_set(CMS_cms_has_token);
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114 }
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115 static bool vm_thread_wants_cms_token() {
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116 return CMS_flag_is_set(CMS_vm_wants_token);
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117 }
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118 static bool cms_thread_wants_cms_token() {
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119 return CMS_flag_is_set(CMS_cms_wants_token);
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120 }
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121
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122 // Wait on CMS lock until the next synchronous GC
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123 // or given timeout, whichever is earlier.
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124 void wait_on_cms_lock(long t); // milliseconds
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125
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126 // The CMS thread will yield during the work portion of it's cycle
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127 // only when requested to. Both synchronous and asychronous requests
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128 // are provided. A synchronous request is used for young gen
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129 // collections and direct allocations. The requesting thread increments
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130 // pending_yields at the beginning of an operation, and decrements it when
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131 // the operation is completed. The CMS thread yields when pending_yields
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132 // is positive. An asynchronous request is used by iCMS in the stop_icms()
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133 // operation. A single yield satisfies the outstanding asynch yield requests.
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134 // The requesting thread increments both pending_yields and pending_decrements.
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135 // After yielding, the CMS thread decrements both by the amount in
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136 // pending_decrements.
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137 // Note that, while "_pending_yields >= _pending_decrements" is an invariant,
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138 // we cannot easily test that invariant, since the counters are manipulated via
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139 // atomic instructions without explicit locking and we cannot read
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140 // the two counters atomically together: one suggestion is to
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141 // use (for example) 16-bit counters so as to be able to read the
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142 // two counters atomically even on 32-bit platforms. Notice that
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143 // the second assert in acknowledge_yield_request() does indeed
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144 // check a form of the above invariant, albeit indirectly.
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145
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146 static void increment_pending_yields() {
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147 Atomic::inc(&_pending_yields);
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148 assert(_pending_yields >= 0, "can't be negative");
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149 }
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150 static void decrement_pending_yields() {
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151 Atomic::dec(&_pending_yields);
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152 assert(_pending_yields >= 0, "can't be negative");
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153 }
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154 static void asynchronous_yield_request() {
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155 increment_pending_yields();
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156 Atomic::inc(&_pending_decrements);
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157 assert(_pending_decrements >= 0, "can't be negative");
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158 }
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159 static void acknowledge_yield_request() {
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160 jint decrement = _pending_decrements;
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161 if (decrement > 0) {
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162 // Order important to preserve: _pending_yields >= _pending_decrements
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163 Atomic::add(-decrement, &_pending_decrements);
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164 Atomic::add(-decrement, &_pending_yields);
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165 assert(_pending_decrements >= 0, "can't be negative");
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166 assert(_pending_yields >= 0, "can't be negative");
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167 }
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168 }
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169 static bool should_yield() { return _pending_yields > 0; }
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170
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171 // CMS incremental mode.
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172 static void start_icms(); // notify thread to start a quantum of work
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173 static void stop_icms(); // request thread to stop working
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174 void icms_wait(); // if asked to stop, wait until notified to start
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175
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176 // Incremental mode is enabled globally by the flag CMSIncrementalMode. It
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177 // must also be enabled/disabled dynamically to allow foreground collections.
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178 static inline void enable_icms() { _icms_enabled = true; }
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179 static inline void disable_icms() { _icms_enabled = false; }
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180 static inline void set_icms_enabled(bool val) { _icms_enabled = val; }
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181 static inline bool icms_enabled() { return _icms_enabled; }
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182 };
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183
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184 inline void ConcurrentMarkSweepThread::trace_state(const char* desc) {
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185 if (CMSTraceThreadState) {
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186 char buf[128];
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187 TimeStamp& ts = gclog_or_tty->time_stamp();
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188 if (!ts.is_updated()) {
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189 ts.update();
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190 }
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191 jio_snprintf(buf, sizeof(buf), " [%.3f: CMSThread %s] ",
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192 ts.seconds(), desc);
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193 buf[sizeof(buf) - 1] = '\0';
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194 gclog_or_tty->print(buf);
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195 }
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196 }
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197
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198 // For scoped increment/decrement of yield requests
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199 class CMSSynchronousYieldRequest: public StackObj {
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200 public:
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201 CMSSynchronousYieldRequest() {
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202 ConcurrentMarkSweepThread::increment_pending_yields();
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203 }
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204 ~CMSSynchronousYieldRequest() {
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205 ConcurrentMarkSweepThread::decrement_pending_yields();
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206 }
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207 };
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208
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209 // Used to emit a warning in case of unexpectedly excessive
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210 // looping (in "apparently endless loops") in CMS code.
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211 class CMSLoopCountWarn: public StackObj {
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212 private:
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213 const char* _src;
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214 const char* _msg;
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215 const intx _threshold;
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216 intx _ticks;
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217
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218 public:
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219 inline CMSLoopCountWarn(const char* src, const char* msg,
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220 const intx threshold) :
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221 _src(src), _msg(msg), _threshold(threshold), _ticks(0) { }
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222
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223 inline void tick() {
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224 _ticks++;
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225 if (CMSLoopWarn && _ticks % _threshold == 0) {
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226 warning("%s has looped %d times %s", _src, _ticks, _msg);
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227 }
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228 }
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229 };
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