1 /*

     2  * Copyright 1997-2007 Sun Microsystems, Inc.  All Rights Reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.

     8  *

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

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

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

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

    13  * accompanied this code).

    14  *

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

    16  * 2 along with this work; if not, write to the Free Software Foundation,

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

    18  *

    19  * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,

    20  * CA 95054 USA or visit www.sun.com if you need additional information or

    21  * have any questions.

    22  *

    23  */

    24 

    25 //

    26 // Safepoint synchronization

    27 ////

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

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

    30 // all JavaThreads forward to a safepoint.

    31 //

    32 // JavaThreads must use the ThreadSafepointState abstraction (defined in

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

    34 //

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

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

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

    38 

    39 

    40 class ThreadSafepointState;

    41 class SnippetCache;

    42 class nmethod;

    43 

    44 //

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

    46 //

    47 class SafepointSynchronize : AllStatic {

    48  public:

    49   enum SynchronizeState {

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

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

    52       _synchronizing    = 1,                   // Synchronizing in progress

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

    54   };

    55 

    56   enum SafepointingThread {

    57       _null_thread  = 0,

    58       _vm_thread    = 1,

    59       _other_thread = 2

    60   };

    61 

    62   enum SafepointTimeoutReason {

    63     _spinning_timeout = 0,

    64     _blocking_timeout = 1

    65   };

    66 

    67   typedef struct {

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

    69     int    _nof_total_threads;                 // total number of Java threads

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

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

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

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

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

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

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

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

    78     jlong  _time_elapsed_since_last_safepoint; // time elasped since last safepoint

    79   } SafepointStats;

    80 

    81  private:

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

    83   static volatile int _waiting_to_block;       // No. of threads we are waiting for to block.

    84 

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

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

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

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

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

    90   // race freedom.

    91 public:

    92   static volatile int _safepoint_counter;

    93 private:

    94 

    95   static jlong   _last_safepoint;      // Time of last safepoint

    96 

    97   // statistics

    98   static SafepointStats*  _safepoint_stats;     // array of SafepointStats struct

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

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

   101   static julong           _coalesced_vmop_count;// coalesced vmop count

   102   static jlong            _max_sync_time;       // maximum sync time in nanos

   103 

   104   static void begin_statistics(int nof_threads, int nof_running);

   105   static void update_statistics_on_spin_end();

   106   static void update_statistics_on_sync_end(jlong end_time);

   107   static void end_statistics(jlong end_time);

   108   static void print_statistics();

   109   inline static void inc_page_trap_count() {

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

   111   }

   112 

   113   // For debug long safepoint

   114   static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);

   115 

   116 public:

   117 

   118   // Main entry points

   119 

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

   121   // VMThread or CMS_thread.

   122   static void begin();

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

   124 

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

   126 

   127   // Query

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

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

   130 

   131   inline static bool do_call_back() {

   132     return (_state != _not_synchronized);

   133   }

   134 

   135   // Called when a thread volantary blocks

   136   static void   block(JavaThread *thread);

   137   static void   signal_thread_at_safepoint()              { _waiting_to_block--; }

   138 

   139   // Exception handling for page polling

   140   static void handle_polling_page_exception(JavaThread *thread);

   141 

   142   // VM Thread interface for determining safepoint rate

   143   static long last_non_safepoint_interval()               { return os::javaTimeMillis() - _last_safepoint; }

   144   static bool is_cleanup_needed();

   145   static void do_cleanup_tasks();

   146 

   147   // debugging

   148   static void print_state()                                PRODUCT_RETURN;

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

   150 

   151   static void deferred_initialize_stat();

   152   static void print_stat_on_exit();

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

   154 

   155   static void set_is_at_safepoint()                        { _state = _synchronized; }

   156   static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }

   157 

   158   // assembly support

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

   160 

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

   162 };

   163 

   164 // State class for a thread suspended at a safepoint

   165 class ThreadSafepointState: public CHeapObj {

   166  public:

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

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

   169   // _running.

   170   enum suspend_type {

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

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

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

   174   };

   175  private:

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

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

   178   bool                           _has_called_back;

   179 

   180   JavaThread *                   _thread;

   181   volatile suspend_type          _type;

   182 

   183 

   184  public:

   185   ThreadSafepointState(JavaThread *thread);

   186 

   187   // examine/roll-forward/restart

   188   void examine_state_of_thread();

   189   void roll_forward(suspend_type type);

   190   void restart();

   191 

   192   // Query

   193   JavaThread*  thread() const         { return _thread; }

   194   suspend_type type() const           { return _type; }

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

   196 

   197   // Support for safepoint timeout (debugging)

   198   bool has_called_back() const                   { return _has_called_back; }

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

   200   bool              is_at_poll_safepoint() { return _at_poll_safepoint; }

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

   202 

   203   void handle_polling_page_exception();

   204 

   205   // debugging

   206   void print_on(outputStream* st) const;

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

   208 

   209   // Initialize

   210   static void create(JavaThread *thread);

   211   static void destroy(JavaThread *thread);

   212 

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

   214     if (ShowSafepointMsgs) {

   215       va_list ap;

   216       va_start(ap, format);

   217       tty->vprint_cr(format, ap);

   218       va_end(ap);

   219     }

   220   }

   221 };

   222 

   223 //

   224 // CounterDecay

   225 //

   226 // Interates through invocation counters and decrements them. This

   227 // is done at each safepoint.

   228 //

   229 class CounterDecay : public AllStatic {

   230   static jlong _last_timestamp;

   231  public:

   232   static  void decay();

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

   234 };