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 /*

  * Copyright (c) 1997, 2007, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

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  */

 //

 // Safepoint synchronization

 ////

 // The VMThread or CMS_thread uses the SafepointSynchronize::begin/end

 // methods to enter/exit a safepoint region. The begin method will roll

 // all JavaThreads forward to a safepoint.

 //

 // JavaThreads must use the ThreadSafepointState abstraction (defined in

 // thread.hpp) to indicate that that they are at a safepoint.

 //

 // The Mutex/Condition variable and ObjectLocker classes calls the enter/

 // exit safepoint methods, when a thread is blocked/restarted. Hence, all mutex exter/

 // exit points *must* be at a safepoint.

 class ThreadSafepointState;

 class SnippetCache;

 class nmethod;

 //

 // Implements roll-forward to safepoint (safepoint synchronization)

 //

 class SafepointSynchronize : AllStatic {

  public:

   enum SynchronizeState {

       _not_synchronized = 0,                   // Threads not synchronized at a safepoint

                                                // Keep this value 0. See the coment in do_call_back()

       _synchronizing    = 1,                   // Synchronizing in progress

       _synchronized     = 2                    // All Java threads are stopped at a safepoint. Only VM thread is running

   };

   enum SafepointingThread {

       _null_thread  = 0,

       _vm_thread    = 1,

       _other_thread = 2

   };

   enum SafepointTimeoutReason {

     _spinning_timeout = 0,

     _blocking_timeout = 1

   };

   typedef struct {

     float  _time_stamp;                        // record when the current safepoint occurs in seconds

     int    _vmop_type;                         // type of VM operation triggers the safepoint

     int    _nof_total_threads;                 // total number of Java threads

     int    _nof_initial_running_threads;       // total number of initially seen running threads

     int    _nof_threads_wait_to_block;         // total number of threads waiting for to block

     bool   _page_armed;                        // true if polling page is armed, false otherwise

     int    _nof_threads_hit_page_trap;         // total number of threads hitting the page trap

     jlong  _time_to_spin;                      // total time in millis spent in spinning

     jlong  _time_to_wait_to_block;             // total time in millis spent in waiting for to block

     jlong  _time_to_do_cleanups;               // total time in millis spent in performing cleanups

     jlong  _time_to_sync;                      // total time in millis spent in getting to _synchronized

     jlong  _time_to_exec_vmop;                 // total time in millis spent in vm operation itself

   } SafepointStats;

  private:

   static volatile SynchronizeState _state;     // Threads might read this flag directly, without acquireing the Threads_lock

   static volatile int _waiting_to_block;       // number of threads we are waiting for to block

   // This counter is used for fast versions of jni_Get<Primitive>Field.

   // An even value means there is no ongoing safepoint operations.

   // The counter is incremented ONLY at the beginning and end of each

   // safepoint. The fact that Threads_lock is held throughout each pair of

   // increments (at the beginning and end of each safepoint) guarantees

   // race freedom.

 public:

   static volatile int _safepoint_counter;

 private:

   static long       _end_of_last_safepoint;     // Time of last safepoint in milliseconds

   // statistics

   static jlong            _safepoint_begin_time;     // time when safepoint begins

   static SafepointStats*  _safepoint_stats;          // array of SafepointStats struct

   static int              _cur_stat_index;           // current index to the above array

   static julong           _safepoint_reasons[];      // safepoint count for each VM op

   static julong           _coalesced_vmop_count;     // coalesced vmop count

   static jlong            _max_sync_time;            // maximum sync time in nanos

   static jlong            _max_vmop_time;            // maximum vm operation time in nanos

   static float            _ts_of_current_safepoint;  // time stamp of current safepoint in seconds

   static void begin_statistics(int nof_threads, int nof_running);

   static void update_statistics_on_spin_end();

   static void update_statistics_on_sync_end(jlong end_time);

   static void update_statistics_on_cleanup_end(jlong end_time);

   static void end_statistics(jlong end_time);

   static void print_statistics();

   inline static void inc_page_trap_count() {

     Atomic::inc(&_safepoint_stats[_cur_stat_index]._nof_threads_hit_page_trap);

   }

   // For debug long safepoint

   static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);

 public:

   // Main entry points

   // Roll all threads forward to safepoint. Must be called by the

   // VMThread or CMS_thread.

   static void begin();

   static void end();                    // Start all suspended threads again...

   static bool safepoint_safe(JavaThread *thread, JavaThreadState state);

   // Query

   inline static bool is_at_safepoint()   { return _state == _synchronized;  }

   inline static bool is_synchronizing()  { return _state == _synchronizing;  }

   inline static bool do_call_back() {

     return (_state != _not_synchronized);

   }

   // Called when a thread volantary blocks

   static void   block(JavaThread *thread);

   static void   signal_thread_at_safepoint()              { _waiting_to_block--; }

   // Exception handling for page polling

   static void handle_polling_page_exception(JavaThread *thread);

   // VM Thread interface for determining safepoint rate

   static long last_non_safepoint_interval() {

     return os::javaTimeMillis() - _end_of_last_safepoint;

   }

   static bool is_cleanup_needed();

   static void do_cleanup_tasks();

   // debugging

   static void print_state()                                PRODUCT_RETURN;

   static void safepoint_msg(const char* format, ...)       PRODUCT_RETURN;

   static void deferred_initialize_stat();

   static void print_stat_on_exit();

   inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }

   static void set_is_at_safepoint()                        { _state = _synchronized; }

   static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }

   // assembly support

   static address address_of_state()                        { return (address)&_state; }

   static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }

 };

 // State class for a thread suspended at a safepoint

 class ThreadSafepointState: public CHeapObj {

  public:

   // These states are maintained by VM thread while threads are being brought

   // to a safepoint.  After SafepointSynchronize::end(), they are reset to

   // _running.

   enum suspend_type {

     _running                =  0, // Thread state not yet determined (i.e., not at a safepoint yet)

     _at_safepoint           =  1, // Thread at a safepoint (f.ex., when blocked on a lock)

     _call_back              =  2  // Keep executing and wait for callback (if thread is in interpreted or vm)

   };

  private:

   volatile bool _at_poll_safepoint;  // At polling page safepoint (NOT a poll return safepoint)

   // Thread has called back the safepoint code (for debugging)

   bool                           _has_called_back;

   JavaThread *                   _thread;

   volatile suspend_type          _type;

  public:

   ThreadSafepointState(JavaThread *thread);

   // examine/roll-forward/restart

   void examine_state_of_thread();

   void roll_forward(suspend_type type);

   void restart();

   // Query

   JavaThread*  thread() const         { return _thread; }

   suspend_type type() const           { return _type; }

   bool         is_running() const     { return (_type==_running); }

   // Support for safepoint timeout (debugging)

   bool has_called_back() const                   { return _has_called_back; }

   void set_has_called_back(bool val)             { _has_called_back = val; }

   bool              is_at_poll_safepoint() { return _at_poll_safepoint; }

   void              set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }

   void handle_polling_page_exception();

   // debugging

   void print_on(outputStream* st) const;

   void print() const                        { print_on(tty); }

   // Initialize

   static void create(JavaThread *thread);

   static void destroy(JavaThread *thread);

   void safepoint_msg(const char* format, ...) {

     if (ShowSafepointMsgs) {

       va_list ap;

       va_start(ap, format);

       tty->vprint_cr(format, ap);

       va_end(ap);

     }

   }

 };

 //

 // CounterDecay

 //

 // Interates through invocation counters and decrements them. This

 // is done at each safepoint.

 //

 class CounterDecay : public AllStatic {

   static jlong _last_timestamp;

  public:

   static  void decay();

   static  bool is_decay_needed() { return (os::javaTimeMillis() - _last_timestamp) > CounterDecayMinIntervalLength; }

 };