src/share/vm/runtime/safepoint.hpp
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src/share/vm/runtime/safepoint.hpp

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rev 5732 : [mq]: comments2


  42 //
  43 // JavaThreads must use the ThreadSafepointState abstraction (defined in
  44 // thread.hpp) to indicate that that they are at a safepoint.
  45 //
  46 // The Mutex/Condition variable and ObjectLocker classes calls the enter/
  47 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
  48 // exit points *must* be at a safepoint.
  49 
  50 
  51 class ThreadSafepointState;
  52 class SnippetCache;
  53 class nmethod;
  54 
  55 //
  56 // Implements roll-forward to safepoint (safepoint synchronization)
  57 //
  58 class SafepointSynchronize : AllStatic {
  59  public:
  60   enum SynchronizeState {
  61       _not_synchronized = 0,                   // Threads not synchronized at a safepoint
  62                                                // Keep this value 0. See the coment in do_call_back()
  63       _synchronizing    = 1,                   // Synchronizing in progress
  64       _synchronized     = 2                    // All Java threads are stopped at a safepoint. Only VM thread is running
  65   };
  66 
  67   enum SafepointingThread {
  68       _null_thread  = 0,
  69       _vm_thread    = 1,
  70       _other_thread = 2
  71   };
  72 
  73   enum SafepointTimeoutReason {
  74     _spinning_timeout = 0,
  75     _blocking_timeout = 1
  76   };
  77 
  78   typedef struct {
  79     float  _time_stamp;                        // record when the current safepoint occurs in seconds
  80     int    _vmop_type;                         // type of VM operation triggers the safepoint
  81     int    _nof_total_threads;                 // total number of Java threads
  82     int    _nof_initial_running_threads;       // total number of initially seen running threads
  83     int    _nof_threads_wait_to_block;         // total number of threads waiting for to block
  84     bool   _page_armed;                        // true if polling page is armed, false otherwise
  85     int    _nof_threads_hit_page_trap;         // total number of threads hitting the page trap
  86     jlong  _time_to_spin;                      // total time in millis spent in spinning
  87     jlong  _time_to_wait_to_block;             // total time in millis spent in waiting for to block
  88     jlong  _time_to_do_cleanups;               // total time in millis spent in performing cleanups
  89     jlong  _time_to_sync;                      // total time in millis spent in getting to _synchronized
  90     jlong  _time_to_exec_vmop;                 // total time in millis spent in vm operation itself
  91   } SafepointStats;
  92 
  93  private:
  94   static volatile SynchronizeState _state;     // Threads might read this flag directly, without acquireing the Threads_lock
  95   static volatile int _waiting_to_block;       // number of threads we are waiting for to block
  96   static int _current_jni_active_count;        // Counts the number of active critical natives during the safepoint
  97 
  98   // This counter is used for fast versions of jni_Get<Primitive>Field.
  99   // An even value means there is no ongoing safepoint operations.
 100   // The counter is incremented ONLY at the beginning and end of each
 101   // safepoint. The fact that Threads_lock is held throughout each pair of
 102   // increments (at the beginning and end of each safepoint) guarantees
 103   // race freedom.
 104 public:
 105   static volatile int _safepoint_counter;
 106 private:
 107   static long       _end_of_last_safepoint;     // Time of last safepoint in milliseconds
 108 
 109   // statistics
 110   static jlong            _safepoint_begin_time;     // time when safepoint begins
 111   static SafepointStats*  _safepoint_stats;          // array of SafepointStats struct
 112   static int              _cur_stat_index;           // current index to the above array
 113   static julong           _safepoint_reasons[];      // safepoint count for each VM op
 114   static julong           _coalesced_vmop_count;     // coalesced vmop count
 115   static jlong            _max_sync_time;            // maximum sync time in nanos
 116   static jlong            _max_vmop_time;            // maximum vm operation time in nanos
 117   static float            _ts_of_current_safepoint;  // time stamp of current safepoint in seconds
 118 
 119   static void begin_statistics(int nof_threads, int nof_running);
 120   static void update_statistics_on_spin_end();
 121   static void update_statistics_on_sync_end(jlong end_time);
 122   static void update_statistics_on_cleanup_end(jlong end_time);
 123   static void end_statistics(jlong end_time);
 124   static void print_statistics();
 125   inline static void inc_page_trap_count() {
 126     Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
 127   }
 128 
 129   // For debug long safepoint


 138   static void begin();
 139   static void end();                    // Start all suspended threads again...
 140 
 141   static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
 142 
 143   static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state);
 144 
 145   // Query
 146   inline static bool is_at_safepoint()   { return _state == _synchronized;  }
 147   inline static bool is_synchronizing()  { return _state == _synchronizing;  }
 148 
 149   inline static bool do_call_back() {
 150     return (_state != _not_synchronized);
 151   }
 152 
 153   inline static void increment_jni_active_count() {
 154     assert_locked_or_safepoint(Safepoint_lock);
 155     _current_jni_active_count++;
 156   }
 157 
 158   // Called when a thread volantary blocks
 159   static void   block(JavaThread *thread);
 160   static void   signal_thread_at_safepoint()              { _waiting_to_block--; }
 161 
 162   // Exception handling for page polling
 163   static void handle_polling_page_exception(JavaThread *thread);
 164 
 165   // VM Thread interface for determining safepoint rate
 166   static long last_non_safepoint_interval() {
 167     return os::javaTimeMillis() - _end_of_last_safepoint;
 168   }
 169   static long end_of_last_safepoint() {
 170     return _end_of_last_safepoint;
 171   }
 172   static bool is_cleanup_needed();
 173   static void do_cleanup_tasks();
 174 
 175   // debugging
 176   static void print_state()                                PRODUCT_RETURN;
 177   static void safepoint_msg(const char* format, ...)       PRODUCT_RETURN;
 178 
 179   static void deferred_initialize_stat();
 180   static void print_stat_on_exit();
 181   inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
 182 
 183   static void set_is_at_safepoint()                        { _state = _synchronized; }
 184   static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }
 185 
 186   // assembly support
 187   static address address_of_state()                        { return (address)&_state; }
 188 
 189   static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }
 190 };
 191 
 192 // State class for a thread suspended at a safepoint
 193 class ThreadSafepointState: public CHeapObj<mtInternal> {
 194  public:
 195   // These states are maintained by VM thread while threads are being brought
 196   // to a safepoint.  After SafepointSynchronize::end(), they are reset to
 197   // _running.
 198   enum suspend_type {
 199     _running                =  0, // Thread state not yet determined (i.e., not at a safepoint yet)
 200     _at_safepoint           =  1, // Thread at a safepoint (f.ex., when blocked on a lock)
 201     _call_back              =  2  // Keep executing and wait for callback (if thread is in interpreted or vm)
 202   };
 203  private:
 204   volatile bool _at_poll_safepoint;  // At polling page safepoint (NOT a poll return safepoint)
 205   // Thread has called back the safepoint code (for debugging)
 206   bool                           _has_called_back;




  42 //
  43 // JavaThreads must use the ThreadSafepointState abstraction (defined in
  44 // thread.hpp) to indicate that that they are at a safepoint.
  45 //
  46 // The Mutex/Condition variable and ObjectLocker classes calls the enter/
  47 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/
  48 // exit points *must* be at a safepoint.
  49 
  50 
  51 class ThreadSafepointState;
  52 class SnippetCache;
  53 class nmethod;
  54 
  55 //
  56 // Implements roll-forward to safepoint (safepoint synchronization)
  57 //
  58 class SafepointSynchronize : AllStatic {
  59  public:
  60   enum SynchronizeState {
  61       _not_synchronized = 0,                   // Threads not synchronized at a safepoint
  62                                                // Keep this value 0. See the comment in do_call_back()
  63       _synchronizing    = 1,                   // Synchronizing in progress
  64       _synchronized     = 2                    // All Java threads are stopped at a safepoint. Only VM thread is running
  65   };
  66 
  67   enum SafepointingThread {
  68       _null_thread  = 0,
  69       _vm_thread    = 1,
  70       _other_thread = 2
  71   };
  72 
  73   enum SafepointTimeoutReason {
  74     _spinning_timeout = 0,
  75     _blocking_timeout = 1
  76   };
  77 
  78   typedef struct {
  79     float  _time_stamp;                        // record when the current safepoint occurs in seconds
  80     int    _vmop_type;                         // type of VM operation triggers the safepoint
  81     int    _nof_total_threads;                 // total number of Java threads
  82     int    _nof_initial_running_threads;       // total number of initially seen running threads
  83     int    _nof_threads_wait_to_block;         // total number of threads waiting for to block
  84     bool   _page_armed;                        // true if polling page is armed, false otherwise
  85     int    _nof_threads_hit_page_trap;         // total number of threads hitting the page trap
  86     jlong  _time_to_spin;                      // total time in millis spent in spinning
  87     jlong  _time_to_wait_to_block;             // total time in millis spent in waiting for to block
  88     jlong  _time_to_do_cleanups;               // total time in millis spent in performing cleanups
  89     jlong  _time_to_sync;                      // total time in millis spent in getting to _synchronized
  90     jlong  _time_to_exec_vmop;                 // total time in millis spent in vm operation itself
  91   } SafepointStats;
  92 
  93  private:
  94   static volatile SynchronizeState _state;     // Threads might read this flag directly, without acquiring the Threads_lock
  95   static volatile int _waiting_to_block;       // number of threads we are waiting for to block
  96   static int _current_jni_active_count;        // Counts the number of active critical natives during the safepoint
  97 
  98   // This counter is used for fast versions of jni_Get<Primitive>Field.
  99   // An even value means there is no ongoing safepoint operations.
 100   // The counter is incremented ONLY at the beginning and end of each
 101   // safepoint. The fact that Threads_lock is held throughout each pair of
 102   // increments (at the beginning and end of each safepoint) guarantees
 103   // race freedom.
 104 public:
 105   static volatile int _safepoint_counter;
 106 private:
 107   static long       _end_of_last_safepoint;     // Time of last safepoint in milliseconds
 108 
 109   // Statistics
 110   static jlong            _safepoint_begin_time;     // time when safepoint begins
 111   static SafepointStats*  _safepoint_stats;          // array of SafepointStats struct
 112   static int              _cur_stat_index;           // current index to the above array
 113   static julong           _safepoint_reasons[];      // safepoint count for each VM op
 114   static julong           _coalesced_vmop_count;     // coalesced vmop count
 115   static jlong            _max_sync_time;            // maximum sync time in nanos
 116   static jlong            _max_vmop_time;            // maximum vm operation time in nanos
 117   static float            _ts_of_current_safepoint;  // time stamp of current safepoint in seconds
 118 
 119   static void begin_statistics(int nof_threads, int nof_running);
 120   static void update_statistics_on_spin_end();
 121   static void update_statistics_on_sync_end(jlong end_time);
 122   static void update_statistics_on_cleanup_end(jlong end_time);
 123   static void end_statistics(jlong end_time);
 124   static void print_statistics();
 125   inline static void inc_page_trap_count() {
 126     Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);
 127   }
 128 
 129   // For debug long safepoint


 138   static void begin();
 139   static void end();                    // Start all suspended threads again...
 140 
 141   static bool safepoint_safe(JavaThread *thread, JavaThreadState state);
 142 
 143   static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state);
 144 
 145   // Query
 146   inline static bool is_at_safepoint()   { return _state == _synchronized;  }
 147   inline static bool is_synchronizing()  { return _state == _synchronizing;  }
 148 
 149   inline static bool do_call_back() {
 150     return (_state != _not_synchronized);
 151   }
 152 
 153   inline static void increment_jni_active_count() {
 154     assert_locked_or_safepoint(Safepoint_lock);
 155     _current_jni_active_count++;
 156   }
 157 
 158   // Called when a thread voluntarily blocks
 159   static void   block(JavaThread *thread);
 160   static void   signal_thread_at_safepoint()              { _waiting_to_block--; }
 161 
 162   // Exception handling for page polling
 163   static void handle_polling_page_exception(JavaThread *thread);
 164 
 165   // VM Thread interface for determining safepoint rate
 166   static long last_non_safepoint_interval() {
 167     return os::javaTimeMillis() - _end_of_last_safepoint;
 168   }
 169   static long end_of_last_safepoint() {
 170     return _end_of_last_safepoint;
 171   }
 172   static bool is_cleanup_needed();
 173   static void do_cleanup_tasks();
 174 
 175   // Debugging
 176   static void print_state()                                PRODUCT_RETURN;
 177   static void safepoint_msg(const char* format, ...)       PRODUCT_RETURN;
 178 
 179   static void deferred_initialize_stat();
 180   static void print_stat_on_exit();
 181   inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
 182 
 183   static void set_is_at_safepoint()                        { _state = _synchronized; }
 184   static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }
 185 
 186   // Assembly support
 187   static address address_of_state()                        { return (address)&_state; }
 188 
 189   static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }
 190 };
 191 
 192 // State class for a thread suspended at a safepoint
 193 class ThreadSafepointState: public CHeapObj<mtInternal> {
 194  public:
 195   // These states are maintained by VM thread while threads are being brought
 196   // to a safepoint.  After SafepointSynchronize::end(), they are reset to
 197   // _running.
 198   enum suspend_type {
 199     _running                =  0, // Thread state not yet determined (i.e., not at a safepoint yet)
 200     _at_safepoint           =  1, // Thread at a safepoint (f.ex., when blocked on a lock)
 201     _call_back              =  2  // Keep executing and wait for callback (if thread is in interpreted or vm)
 202   };
 203  private:
 204   volatile bool _at_poll_safepoint;  // At polling page safepoint (NOT a poll return safepoint)
 205   // Thread has called back the safepoint code (for debugging)
 206   bool                           _has_called_back;


src/share/vm/runtime/safepoint.hpp
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