/*

 * 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

 * questions.

 *

 */

//

// 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; }

};