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1 /*
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2 * Copyright 1997-2007 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 //
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26 // Safepoint synchronization
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27 ////
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28 // The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
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29 // methods to enter/exit a safepoint region. The begin method will roll
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30 // all JavaThreads forward to a safepoint.
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31 //
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32 // JavaThreads must use the ThreadSafepointState abstraction (defined in
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33 // thread.hpp) to indicate that that they are at a safepoint.
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34 //
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35 // The Mutex/Condition variable and ObjectLocker classes calls the enter/
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36 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
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37 // exit points *must* be at a safepoint.
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38
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39
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40 class ThreadSafepointState;
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41 class SnippetCache;
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42 class nmethod;
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43
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44 //
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45 // Implements roll-forward to safepoint (safepoint synchronization)
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46 //
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47 class SafepointSynchronize : AllStatic {
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48 public:
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49 enum SynchronizeState {
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50 _not_synchronized = 0, // Threads not synchronized at a safepoint
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51 // Keep this value 0. See the coment in do_call_back()
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52 _synchronizing = 1, // Synchronizing in progress
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53 _synchronized = 2 // All Java threads are stopped at a safepoint. Only VM thread is running
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54 };
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55
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56 enum SafepointingThread {
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57 _null_thread = 0,
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58 _vm_thread = 1,
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59 _other_thread = 2
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60 };
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61
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62 enum SafepointTimeoutReason {
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63 _spinning_timeout = 0,
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64 _blocking_timeout = 1
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65 };
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66
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67 typedef struct {
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68 int _vmop_type; // type of VM operation triggers the safepoint
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69 int _nof_total_threads; // total number of Java threads
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70 int _nof_initial_running_threads; // total number of initially seen running threads
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71 int _nof_threads_wait_to_block; // total number of threads waiting for to block
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72 bool _page_armed; // true if polling page is armed, false otherwise
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73 int _nof_threads_hit_page_trap; // total number of threads hitting the page trap
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74 jlong _time_to_spin; // total time in millis spent in spinning
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75 jlong _time_to_wait_to_block; // total time in millis spent in waiting for to block
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76 jlong _time_to_sync; // total time in millis spent in getting to _synchronized
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77 jlong _time_to_exec_vmop; // total time in millis spent in vm operation itself
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78 jlong _time_elapsed_since_last_safepoint; // time elasped since last safepoint
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79 } SafepointStats;
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80
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81 private:
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82 static volatile SynchronizeState _state; // Threads might read this flag directly, without acquireing the Threads_lock
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83 static volatile int _waiting_to_block; // No. of threads we are waiting for to block.
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84
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85 // This counter is used for fast versions of jni_Get<Primitive>Field.
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86 // An even value means there is no ongoing safepoint operations.
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87 // The counter is incremented ONLY at the beginning and end of each
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88 // safepoint. The fact that Threads_lock is held throughout each pair of
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89 // increments (at the beginning and end of each safepoint) guarantees
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90 // race freedom.
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91 public:
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92 static volatile int _safepoint_counter;
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93 private:
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94
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95 static jlong _last_safepoint; // Time of last safepoint
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96
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97 // statistics
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98 static SafepointStats* _safepoint_stats; // array of SafepointStats struct
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99 static int _cur_stat_index; // current index to the above array
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100 static julong _safepoint_reasons[]; // safepoint count for each VM op
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101 static julong _coalesced_vmop_count;// coalesced vmop count
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102 static jlong _max_sync_time; // maximum sync time in nanos
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103
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104 static void begin_statistics(int nof_threads, int nof_running);
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105 static void update_statistics_on_spin_end();
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106 static void update_statistics_on_sync_end(jlong end_time);
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107 static void end_statistics(jlong end_time);
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108 static void print_statistics();
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109 inline static void inc_page_trap_count() {
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110 Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
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111 }
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112
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113 // For debug long safepoint
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114 static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
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115
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116 public:
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117
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118 // Main entry points
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119
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120 // Roll all threads forward to safepoint. Must be called by the
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121 // VMThread or CMS_thread.
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122 static void begin();
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123 static void end(); // Start all suspended threads again...
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124
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125 static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
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126
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127 // Query
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128 inline static bool is_at_safepoint() { return _state == _synchronized; }
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129 inline static bool is_synchronizing() { return _state == _synchronizing; }
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130
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131 inline static bool do_call_back() {
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132 return (_state != _not_synchronized);
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133 }
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134
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135 // Called when a thread volantary blocks
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136 static void block(JavaThread *thread);
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137 static void signal_thread_at_safepoint() { _waiting_to_block--; }
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138
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139 // Exception handling for page polling
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140 static void handle_polling_page_exception(JavaThread *thread);
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141
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142 // VM Thread interface for determining safepoint rate
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143 static long last_non_safepoint_interval() { return os::javaTimeMillis() - _last_safepoint; }
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144 static bool is_cleanup_needed();
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145 static void do_cleanup_tasks();
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146
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147 // debugging
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148 static void print_state() PRODUCT_RETURN;
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149 static void safepoint_msg(const char* format, ...) PRODUCT_RETURN;
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150
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151 static void deferred_initialize_stat();
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152 static void print_stat_on_exit();
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153 inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
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154
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155 static void set_is_at_safepoint() { _state = _synchronized; }
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156 static void set_is_not_at_safepoint() { _state = _not_synchronized; }
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157
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158 // assembly support
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159 static address address_of_state() { return (address)&_state; }
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160
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161 static address safepoint_counter_addr() { return (address)&_safepoint_counter; }
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162 };
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163
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164 // State class for a thread suspended at a safepoint
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165 class ThreadSafepointState: public CHeapObj {
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166 public:
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167 // These states are maintained by VM thread while threads are being brought
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168 // to a safepoint. After SafepointSynchronize::end(), they are reset to
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169 // _running.
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170 enum suspend_type {
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171 _running = 0, // Thread state not yet determined (i.e., not at a safepoint yet)
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172 _at_safepoint = 1, // Thread at a safepoint (f.ex., when blocked on a lock)
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173 _call_back = 2 // Keep executing and wait for callback (if thread is in interpreted or vm)
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174 };
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175 private:
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176 volatile bool _at_poll_safepoint; // At polling page safepoint (NOT a poll return safepoint)
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177 // Thread has called back the safepoint code (for debugging)
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178 bool _has_called_back;
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179
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180 JavaThread * _thread;
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181 volatile suspend_type _type;
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182
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183
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184 public:
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185 ThreadSafepointState(JavaThread *thread);
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186
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187 // examine/roll-forward/restart
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188 void examine_state_of_thread();
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189 void roll_forward(suspend_type type);
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190 void restart();
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191
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192 // Query
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193 JavaThread* thread() const { return _thread; }
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194 suspend_type type() const { return _type; }
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195 bool is_running() const { return (_type==_running); }
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196
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197 // Support for safepoint timeout (debugging)
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198 bool has_called_back() const { return _has_called_back; }
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199 void set_has_called_back(bool val) { _has_called_back = val; }
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200 bool is_at_poll_safepoint() { return _at_poll_safepoint; }
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201 void set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
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202
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203 void handle_polling_page_exception();
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204
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205 // debugging
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206 void print_on(outputStream* st) const;
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207 void print() const { print_on(tty); }
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208
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209 // Initialize
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210 static void create(JavaThread *thread);
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211 static void destroy(JavaThread *thread);
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212
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213 void safepoint_msg(const char* format, ...) {
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214 if (ShowSafepointMsgs) {
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215 va_list ap;
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216 va_start(ap, format);
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217 tty->vprint_cr(format, ap);
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218 va_end(ap);
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219 }
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220 }
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221 };
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222
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223 //
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224 // CounterDecay
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225 //
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226 // Interates through invocation counters and decrements them. This
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227 // is done at each safepoint.
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228 //
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229 class CounterDecay : public AllStatic {
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230 static jlong _last_timestamp;
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231 public:
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232 static void decay();
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233 static bool is_decay_needed() { return (os::javaTimeMillis() - _last_timestamp) > CounterDecayMinIntervalLength; }
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234 };
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