1 /*
   2  * Copyright (c) 1997, 2014, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 #ifndef SHARE_VM_RUNTIME_SAFEPOINT_HPP
  26 #define SHARE_VM_RUNTIME_SAFEPOINT_HPP
  27 
  28 #include "asm/assembler.hpp"
  29 #include "code/nmethod.hpp"
  30 #include "memory/allocation.hpp"
  31 #include "runtime/extendedPC.hpp"
  32 #include "runtime/mutexLocker.hpp"
  33 #include "runtime/os.hpp"
  34 #include "utilities/ostream.hpp"
  35 
  36 //
  37 // Safepoint synchronization
  38 ////
  39 // The VMThread or CMS_thread uses the SafepointSynchronize::begin/end
  40 // methods to enter/exit a safepoint region. The begin method will roll
  41 // all JavaThreads forward to a safepoint.
  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
 130   static void print_safepoint_timeout(SafepointTimeoutReason timeout_reason);
 131 
 132 public:
 133 
 134   // Main entry points
 135 
 136   // Roll all threads forward to safepoint. Must be called by the
 137   // VMThread or CMS_thread.
 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   inline static int safepoint_counter()  { return _safepoint_counter; }
 149 
 150   inline static bool do_call_back() {
 151     return (_state != _not_synchronized);
 152   }
 153 
 154   inline static void increment_jni_active_count() {
 155     assert_locked_or_safepoint(Safepoint_lock);
 156     _current_jni_active_count++;
 157   }
 158 
 159   // Called when a thread voluntarily blocks
 160   static void   block(JavaThread *thread);
 161   static void   signal_thread_at_safepoint()              { _waiting_to_block--; }
 162 
 163   // Exception handling for page polling
 164   static void handle_polling_page_exception(JavaThread *thread);
 165 
 166   // VM Thread interface for determining safepoint rate
 167   static long last_non_safepoint_interval() {
 168     return os::javaTimeMillis() - _end_of_last_safepoint;
 169   }
 170   static long end_of_last_safepoint() {
 171     return _end_of_last_safepoint;
 172   }
 173   static bool is_cleanup_needed();
 174   static void do_cleanup_tasks();
 175 
 176   // Debugging
 177   static void print_state()                                PRODUCT_RETURN;
 178   static void safepoint_msg(const char* format, ...) ATTRIBUTE_PRINTF(1, 2) PRODUCT_RETURN;
 179 
 180   static void deferred_initialize_stat();
 181   static void print_stat_on_exit();
 182   inline static void inc_vmop_coalesced_count() { _coalesced_vmop_count++; }
 183 
 184   static void set_is_at_safepoint()                        { _state = _synchronized; }
 185   static void set_is_not_at_safepoint()                    { _state = _not_synchronized; }
 186 
 187   // Assembly support
 188   static address address_of_state()                        { return (address)&_state; }
 189 
 190   static address safepoint_counter_addr()                  { return (address)&_safepoint_counter; }
 191 };
 192 
 193 // State class for a thread suspended at a safepoint
 194 class ThreadSafepointState: public CHeapObj<mtInternal> {
 195  public:
 196   // These states are maintained by VM thread while threads are being brought
 197   // to a safepoint.  After SafepointSynchronize::end(), they are reset to
 198   // _running.
 199   enum suspend_type {
 200     _running                =  0, // Thread state not yet determined (i.e., not at a safepoint yet)
 201     _at_safepoint           =  1, // Thread at a safepoint (f.ex., when blocked on a lock)
 202     _call_back              =  2  // Keep executing and wait for callback (if thread is in interpreted or vm)
 203   };
 204  private:
 205   volatile bool _at_poll_safepoint;  // At polling page safepoint (NOT a poll return safepoint)
 206   // Thread has called back the safepoint code (for debugging)
 207   bool                           _has_called_back;
 208 
 209   JavaThread *                   _thread;
 210   volatile suspend_type          _type;
 211   JavaThreadState                _orig_thread_state;
 212 
 213 
 214  public:
 215   ThreadSafepointState(JavaThread *thread);
 216 
 217   // examine/roll-forward/restart
 218   void examine_state_of_thread();
 219   void roll_forward(suspend_type type);
 220   void restart();
 221 
 222   // Query
 223   JavaThread*  thread() const         { return _thread; }
 224   suspend_type type() const           { return _type; }
 225   bool         is_running() const     { return (_type==_running); }
 226   JavaThreadState orig_thread_state() const { return _orig_thread_state; }
 227 
 228   // Support for safepoint timeout (debugging)
 229   bool has_called_back() const                   { return _has_called_back; }
 230   void set_has_called_back(bool val)             { _has_called_back = val; }
 231   bool              is_at_poll_safepoint() { return _at_poll_safepoint; }
 232   void              set_at_poll_safepoint(bool val) { _at_poll_safepoint = val; }
 233 
 234   void handle_polling_page_exception();
 235 
 236   // debugging
 237   void print_on(outputStream* st) const;
 238   void print() const                        { print_on(tty); }
 239 
 240   // Initialize
 241   static void create(JavaThread *thread);
 242   static void destroy(JavaThread *thread);
 243 
 244   void safepoint_msg(const char* format, ...) ATTRIBUTE_PRINTF(2, 3) {
 245     if (ShowSafepointMsgs) {
 246       va_list ap;
 247       va_start(ap, format);
 248       tty->vprint_cr(format, ap);
 249       va_end(ap);
 250     }
 251   }
 252 };
 253 
 254 
 255 
 256 #endif // SHARE_VM_RUNTIME_SAFEPOINT_HPP