1 /*
   2  * Copyright (c) 1997, 2019, 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 #include "precompiled.hpp"
  26 #include "classfile/classLoaderDataGraph.inline.hpp"
  27 #include "classfile/dictionary.hpp"
  28 #include "classfile/stringTable.hpp"
  29 #include "classfile/symbolTable.hpp"
  30 #include "classfile/systemDictionary.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "code/icBuffer.hpp"
  33 #include "code/nmethod.hpp"
  34 #include "code/pcDesc.hpp"
  35 #include "code/scopeDesc.hpp"
  36 #include "gc/shared/collectedHeap.hpp"
  37 #include "gc/shared/gcLocker.hpp"
  38 #include "gc/shared/strongRootsScope.hpp"
  39 #include "gc/shared/workgroup.hpp"
  40 #include "interpreter/interpreter.hpp"
  41 #include "jfr/jfrEvents.hpp"
  42 #include "logging/log.hpp"
  43 #include "logging/logStream.hpp"
  44 #include "memory/resourceArea.hpp"
  45 #include "memory/universe.hpp"
  46 #include "oops/oop.inline.hpp"
  47 #include "oops/symbol.hpp"
  48 #include "runtime/atomic.hpp"
  49 #include "runtime/compilationPolicy.hpp"
  50 #include "runtime/deoptimization.hpp"
  51 #include "runtime/frame.inline.hpp"
  52 #include "runtime/handles.inline.hpp"
  53 #include "runtime/interfaceSupport.inline.hpp"
  54 #include "runtime/mutexLocker.hpp"
  55 #include "runtime/orderAccess.hpp"
  56 #include "runtime/osThread.hpp"
  57 #include "runtime/safepoint.hpp"
  58 #include "runtime/safepointMechanism.inline.hpp"
  59 #include "runtime/signature.hpp"
  60 #include "runtime/stubCodeGenerator.hpp"
  61 #include "runtime/stubRoutines.hpp"
  62 #include "runtime/sweeper.hpp"
  63 #include "runtime/synchronizer.hpp"
  64 #include "runtime/thread.inline.hpp"
  65 #include "runtime/threadSMR.hpp"
  66 #include "runtime/timerTrace.hpp"
  67 #include "services/runtimeService.hpp"
  68 #include "utilities/events.hpp"
  69 #include "utilities/macros.hpp"
  70 
  71 static void post_safepoint_begin_event(EventSafepointBegin& event,
  72                                        uint64_t safepoint_id,
  73                                        int thread_count,
  74                                        int critical_thread_count) {
  75   if (event.should_commit()) {
  76     event.set_safepointId(safepoint_id);
  77     event.set_totalThreadCount(thread_count);
  78     event.set_jniCriticalThreadCount(critical_thread_count);
  79     event.commit();
  80   }
  81 }
  82 
  83 static void post_safepoint_cleanup_event(EventSafepointCleanup& event, uint64_t safepoint_id) {
  84   if (event.should_commit()) {
  85     event.set_safepointId(safepoint_id);
  86     event.commit();
  87   }
  88 }
  89 
  90 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
  91                                              uint64_t safepoint_id,
  92                                              int initial_number_of_threads,
  93                                              int threads_waiting_to_block,
  94                                              uint64_t iterations) {
  95   if (event.should_commit()) {
  96     event.set_safepointId(safepoint_id);
  97     event.set_initialThreadCount(initial_number_of_threads);
  98     event.set_runningThreadCount(threads_waiting_to_block);
  99     event.set_iterations(iterations);
 100     event.commit();
 101   }
 102 }
 103 
 104 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask& event,
 105                                               uint64_t safepoint_id,
 106                                               const char* name) {
 107   if (event.should_commit()) {
 108     event.set_safepointId(safepoint_id);
 109     event.set_name(name);
 110     event.commit();
 111   }
 112 }
 113 
 114 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
 115   if (event.should_commit()) {
 116     event.set_safepointId(safepoint_id);
 117     event.commit();
 118   }
 119 }
 120 
 121 // --------------------------------------------------------------------------------------------------
 122 // Implementation of Safepoint begin/end
 123 
 124 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
 125 int SafepointSynchronize::_waiting_to_block = 0;
 126 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
 127 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
 128 int SafepointSynchronize::_current_jni_active_count = 0;
 129 
 130 WaitBarrier* SafepointSynchronize::_wait_barrier;
 131 
 132 static volatile bool PageArmed = false;        // safepoint polling page is RO|RW vs PROT_NONE
 133 static bool timeout_error_printed = false;
 134 
 135 // Statistic related
 136 static jlong _safepoint_begin_time = 0;
 137 static volatile int _nof_threads_hit_polling_page = 0;
 138 
 139 void SafepointSynchronize::init(Thread* vmthread) {
 140   // WaitBarrier should never be destroyed since we will have
 141   // threads waiting on it while exiting.
 142   _wait_barrier = new WaitBarrier(vmthread);
 143   SafepointTracing::init();
 144 }
 145 
 146 void SafepointSynchronize::increment_jni_active_count() {
 147   assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
 148   ++_current_jni_active_count;
 149 }
 150 
 151 void SafepointSynchronize::decrement_waiting_to_block() {
 152   assert(_waiting_to_block > 0, "sanity check");
 153   assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
 154   --_waiting_to_block;
 155 }
 156 
 157 static bool thread_not_running(ThreadSafepointState *cur_state) {
 158   if (!cur_state->is_running()) {
 159     return true;
 160   }
 161   cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
 162   if (!cur_state->is_running()) {
 163     return true;
 164   }
 165   LogTarget(Trace, safepoint) lt;
 166   if (lt.is_enabled()) {
 167     ResourceMark rm;
 168     LogStream ls(lt);
 169     cur_state->print_on(&ls);
 170   }
 171   return false;
 172 }
 173 
 174 #ifdef ASSERT
 175 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
 176   int a = 0;
 177   const ThreadSafepointState *tmp_tss = tss_head;
 178   while (tmp_tss != NULL) {
 179     ++a;
 180     assert(tmp_tss->is_running(), "Illegal initial state");
 181     tmp_tss = tmp_tss->get_next();
 182   }
 183   assert(a == still_running, "Must be the same");
 184 }
 185 #endif // ASSERT
 186 
 187 static void back_off(int64_t start_time) {
 188   // We start with fine-grained nanosleeping until a millisecond has
 189   // passed, at which point we resort to plain naked_short_sleep.
 190   if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
 191     os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
 192   } else {
 193     os::naked_short_sleep(1);
 194   }
 195 }
 196 
 197 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
 198 {
 199   JavaThreadIteratorWithHandle jtiwh;
 200 
 201 #ifdef ASSERT
 202   for (; JavaThread *cur = jtiwh.next(); ) {
 203     assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 204   }
 205   jtiwh.rewind();
 206 #endif // ASSERT
 207 
 208   // Iterate through all threads until it has been determined how to stop them all at a safepoint.
 209   int still_running = nof_threads;
 210   ThreadSafepointState *tss_head = NULL;
 211   ThreadSafepointState **p_prev = &tss_head;
 212   for (; JavaThread *cur = jtiwh.next(); ) {
 213     ThreadSafepointState *cur_tss = cur->safepoint_state();
 214     assert(cur_tss->get_next() == NULL, "Must be NULL");
 215     if (thread_not_running(cur_tss)) {
 216       --still_running;
 217     } else {
 218       *p_prev = cur_tss;
 219       p_prev = cur_tss->next_ptr();
 220     }
 221   }
 222   *p_prev = NULL;
 223 
 224   DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
 225 
 226   *initial_running = still_running;
 227 
 228   // If there is no thread still running, we are already done.
 229   if (still_running <= 0) {
 230     assert(tss_head == NULL, "Must be empty");
 231     return 1;
 232   }
 233 
 234   int iterations = 1; // The first iteration is above.
 235   int64_t start_time = os::javaTimeNanos();
 236 
 237   do {
 238     // Check if this has taken too long:
 239     if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 240       print_safepoint_timeout();
 241     }
 242     if (int(iterations) == -1) { // overflow - something is wrong.
 243       // We can only overflow here when we are using global
 244       // polling pages. We keep this guarantee in its original
 245       // form so that searches of the bug database for this
 246       // failure mode find the right bugs.
 247       guarantee (!PageArmed, "invariant");
 248     }
 249 
 250     p_prev = &tss_head;
 251     ThreadSafepointState *cur_tss = tss_head;
 252     while (cur_tss != NULL) {
 253       assert(cur_tss->is_running(), "Illegal initial state");
 254       if (thread_not_running(cur_tss)) {
 255         --still_running;
 256         *p_prev = NULL;
 257         ThreadSafepointState *tmp = cur_tss;
 258         cur_tss = cur_tss->get_next();
 259         tmp->set_next(NULL);
 260       } else {
 261         *p_prev = cur_tss;
 262         p_prev = cur_tss->next_ptr();
 263         cur_tss = cur_tss->get_next();
 264       }
 265     }
 266 
 267     DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
 268 
 269     if (still_running > 0) {
 270       back_off(start_time);
 271     }
 272 
 273     iterations++;
 274   } while (still_running > 0);
 275 
 276   assert(tss_head == NULL, "Must be empty");
 277 
 278   return iterations;
 279 }
 280 
 281 void SafepointSynchronize::arm_safepoint() {
 282   // Begin the process of bringing the system to a safepoint.
 283   // Java threads can be in several different states and are
 284   // stopped by different mechanisms:
 285   //
 286   //  1. Running interpreted
 287   //     When executing branching/returning byte codes interpreter
 288   //     checks if the poll is armed, if so blocks in SS::block().
 289   //     When using global polling the interpreter dispatch table
 290   //     is changed to force it to check for a safepoint condition
 291   //     between bytecodes.
 292   //  2. Running in native code
 293   //     When returning from the native code, a Java thread must check
 294   //     the safepoint _state to see if we must block.  If the
 295   //     VM thread sees a Java thread in native, it does
 296   //     not wait for this thread to block.  The order of the memory
 297   //     writes and reads of both the safepoint state and the Java
 298   //     threads state is critical.  In order to guarantee that the
 299   //     memory writes are serialized with respect to each other,
 300   //     the VM thread issues a memory barrier instruction.
 301   //  3. Running compiled Code
 302   //     Compiled code reads the local polling page that
 303   //     is set to fault if we are trying to get to a safepoint.
 304   //  4. Blocked
 305   //     A thread which is blocked will not be allowed to return from the
 306   //     block condition until the safepoint operation is complete.
 307   //  5. In VM or Transitioning between states
 308   //     If a Java thread is currently running in the VM or transitioning
 309   //     between states, the safepointing code will poll the thread state
 310   //     until the thread blocks itself when it attempts transitions to a
 311   //     new state or locking a safepoint checked monitor.
 312 
 313   // We must never miss a thread with correct safepoint id, so we must make sure we arm
 314   // the wait barrier for the next safepoint id/counter.
 315   // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
 316   _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
 317 
 318   assert((_safepoint_counter & 0x1) == 0, "must be even");
 319   // The store to _safepoint_counter must happen after any stores in arming.
 320   OrderAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
 321 
 322   // We are synchronizing
 323   OrderAccess::storestore(); // Ordered with _safepoint_counter
 324   _state = _synchronizing;
 325 
 326   if (SafepointMechanism::uses_thread_local_poll()) {
 327     // Arming the per thread poll while having _state != _not_synchronized means safepointing
 328     log_trace(safepoint)("Setting thread local yield flag for threads");
 329     OrderAccess::storestore(); // storestore, global state -> local state
 330     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 331       // Make sure the threads start polling, it is time to yield.
 332       SafepointMechanism::arm_local_poll(cur);
 333     }
 334   }
 335   OrderAccess::fence(); // storestore|storeload, global state -> local state
 336 
 337   if (SafepointMechanism::uses_global_page_poll()) {
 338     // Make interpreter safepoint aware
 339     Interpreter::notice_safepoints();
 340 
 341     // Make polling safepoint aware
 342     guarantee (!PageArmed, "invariant") ;
 343     PageArmed = true;
 344     os::make_polling_page_unreadable();
 345   }
 346 }
 347 
 348 // Roll all threads forward to a safepoint and suspend them all
 349 void SafepointSynchronize::begin() {
 350   assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
 351 
 352   EventSafepointBegin begin_event;
 353   SafepointTracing::begin(VMThread::vm_op_type());
 354 
 355   Universe::heap()->safepoint_synchronize_begin();
 356 
 357   // By getting the Threads_lock, we assure that no threads are about to start or
 358   // exit. It is released again in SafepointSynchronize::end().
 359   Threads_lock->lock();
 360 
 361   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 362 
 363   int nof_threads = Threads::number_of_threads();
 364 
 365   _nof_threads_hit_polling_page = 0;
 366 
 367   log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
 368 
 369   // Reset the count of active JNI critical threads
 370   _current_jni_active_count = 0;
 371 
 372   // Set number of threads to wait for
 373   _waiting_to_block = nof_threads;
 374 
 375   jlong safepoint_limit_time = 0;
 376   if (SafepointTimeout) {
 377     // Set the limit time, so that it can be compared to see if this has taken
 378     // too long to complete.
 379     safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)SafepointTimeoutDelay * (NANOUNITS / MILLIUNITS);
 380     timeout_error_printed = false;
 381   }
 382 
 383   EventSafepointStateSynchronization sync_event;
 384   int initial_running = 0;
 385 
 386   // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
 387   arm_safepoint();
 388 
 389   // Will spin until all threads are safe.
 390   int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
 391   assert(_waiting_to_block == 0, "No thread should be running");
 392 
 393 #ifndef PRODUCT
 394   if (safepoint_limit_time != 0) {
 395     jlong current_time = os::javaTimeNanos();
 396     if (safepoint_limit_time < current_time) {
 397       log_warning(safepoint)("# SafepointSynchronize: Finished after "
 398                     INT64_FORMAT_W(6) " ms",
 399                     (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
 400     }
 401   }
 402 #endif
 403 
 404   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 405 
 406   // Record state
 407   _state = _synchronized;
 408 
 409   OrderAccess::fence();
 410 
 411 #ifdef ASSERT
 412   // Make sure all the threads were visited.
 413   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 414     assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
 415   }
 416 #endif // ASSERT
 417 
 418   // Update the count of active JNI critical regions
 419   GCLocker::set_jni_lock_count(_current_jni_active_count);
 420 
 421   post_safepoint_synchronize_event(sync_event,
 422                                    _safepoint_counter,
 423                                    initial_running,
 424                                    _waiting_to_block, iterations);
 425 
 426   SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
 427 
 428   // We do the safepoint cleanup first since a GC related safepoint
 429   // needs cleanup to be completed before running the GC op.
 430   EventSafepointCleanup cleanup_event;
 431   do_cleanup_tasks();
 432   post_safepoint_cleanup_event(cleanup_event, _safepoint_counter);
 433 
 434   post_safepoint_begin_event(begin_event, _safepoint_counter, nof_threads, _current_jni_active_count);
 435   SafepointTracing::cleanup();
 436 }
 437 
 438 void SafepointSynchronize::disarm_safepoint() {
 439   uint64_t safepoint_id = _safepoint_counter;
 440   {
 441     JavaThreadIteratorWithHandle jtiwh;
 442 #ifdef ASSERT
 443     // A pending_exception cannot be installed during a safepoint.  The threads
 444     // may install an async exception after they come back from a safepoint into
 445     // pending_exception after they unblock.  But that should happen later.
 446     for (; JavaThread *cur = jtiwh.next(); ) {
 447       assert (!(cur->has_pending_exception() &&
 448                 cur->safepoint_state()->is_at_poll_safepoint()),
 449               "safepoint installed a pending exception");
 450     }
 451 #endif // ASSERT
 452 
 453     if (SafepointMechanism::uses_global_page_poll()) {
 454       guarantee (PageArmed, "invariant");
 455       // Make polling safepoint aware
 456       os::make_polling_page_readable();
 457       PageArmed = false;
 458       // Remove safepoint check from interpreter
 459       Interpreter::ignore_safepoints();
 460     }
 461 
 462     OrderAccess::fence(); // keep read and write of _state from floating up
 463     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 464 
 465     // Change state first to _not_synchronized.
 466     // No threads should see _synchronized when running.
 467     _state = _not_synchronized;
 468 
 469     // Set the next dormant (even) safepoint id.
 470     assert((_safepoint_counter & 0x1) == 1, "must be odd");
 471     OrderAccess::release_store(&_safepoint_counter, _safepoint_counter + 1);
 472 
 473     OrderAccess::fence(); // Keep the local state from floating up.
 474 
 475     jtiwh.rewind();
 476     for (; JavaThread *current = jtiwh.next(); ) {
 477       // Clear the visited flag to ensure that the critical counts are collected properly.
 478       DEBUG_ONLY(current->reset_visited_for_critical_count(safepoint_id);)
 479       ThreadSafepointState* cur_state = current->safepoint_state();
 480       assert(!cur_state->is_running(), "Thread not suspended at safepoint");
 481       cur_state->restart(); // TSS _running
 482       assert(cur_state->is_running(), "safepoint state has not been reset");
 483 
 484       SafepointMechanism::disarm_if_needed(current, false /* NO release */);
 485     }
 486   } // ~JavaThreadIteratorWithHandle
 487 
 488   // Release threads lock, so threads can be created/destroyed again.
 489   Threads_lock->unlock();
 490 
 491   // Wake threads after local state is correctly set.
 492   _wait_barrier->disarm();
 493 }
 494 
 495 // Wake up all threads, so they are ready to resume execution after the safepoint
 496 // operation has been carried out
 497 void SafepointSynchronize::end() {
 498   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 499   EventSafepointEnd event;
 500   uint64_t safepoint_id = _safepoint_counter;
 501   assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
 502 
 503   disarm_safepoint();
 504 
 505   Universe::heap()->safepoint_synchronize_end();
 506 
 507   SafepointTracing::end();
 508 
 509   post_safepoint_end_event(event, safepoint_id);
 510 }
 511 
 512 bool SafepointSynchronize::is_cleanup_needed() {
 513   // Need a safepoint if there are many monitors to deflate.
 514   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 515   // Need a safepoint if some inline cache buffers is non-empty
 516   if (!InlineCacheBuffer::is_empty()) return true;
 517   if (StringTable::needs_rehashing()) return true;
 518   if (SymbolTable::needs_rehashing()) return true;
 519   return false;
 520 }
 521 
 522 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 523 private:
 524   CodeBlobClosure* _nmethod_cl;
 525   DeflateMonitorCounters* _counters;
 526 
 527 public:
 528   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 529     _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL),
 530     _counters(counters) {}
 531 
 532   void do_thread(Thread* thread) {
 533     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 534     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 535         ! thread->is_Code_cache_sweeper_thread()) {
 536       JavaThread* jt = (JavaThread*) thread;
 537       jt->nmethods_do(_nmethod_cl);
 538     }
 539   }
 540 };
 541 
 542 class ParallelSPCleanupTask : public AbstractGangTask {
 543 private:
 544   SubTasksDone _subtasks;
 545   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 546   uint _num_workers;
 547   DeflateMonitorCounters* _counters;
 548 public:
 549   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 550     AbstractGangTask("Parallel Safepoint Cleanup"),
 551     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 552     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 553     _num_workers(num_workers),
 554     _counters(counters) {}
 555 
 556   void work(uint worker_id) {
 557     uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
 558     // All threads deflate monitors and mark nmethods (if necessary).
 559     Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
 560 
 561     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 562       const char* name = "deflating global idle monitors";
 563       EventSafepointCleanupTask event;
 564       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 565       ObjectSynchronizer::deflate_idle_monitors(_counters);
 566 
 567       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 568     }
 569 
 570     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 571       const char* name = "updating inline caches";
 572       EventSafepointCleanupTask event;
 573       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 574       InlineCacheBuffer::update_inline_caches();
 575 
 576       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 577     }
 578 
 579     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 580       const char* name = "compilation policy safepoint handler";
 581       EventSafepointCleanupTask event;
 582       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 583       CompilationPolicy::policy()->do_safepoint_work();
 584 
 585       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 586     }
 587 
 588     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 589       if (SymbolTable::needs_rehashing()) {
 590         const char* name = "rehashing symbol table";
 591         EventSafepointCleanupTask event;
 592         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 593         SymbolTable::rehash_table();
 594 
 595         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 596       }
 597     }
 598 
 599     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 600       if (StringTable::needs_rehashing()) {
 601         const char* name = "rehashing string table";
 602         EventSafepointCleanupTask event;
 603         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 604         StringTable::rehash_table();
 605 
 606         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 607       }
 608     }
 609 
 610     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 611       if (ClassLoaderDataGraph::should_purge_and_reset()) {
 612         // CMS delays purging the CLDG until the beginning of the next safepoint and to
 613         // make sure concurrent sweep is done
 614         const char* name = "purging class loader data graph";
 615         EventSafepointCleanupTask event;
 616         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 617         ClassLoaderDataGraph::purge();
 618 
 619         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 620       }
 621     }
 622 
 623     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
 624       if (Dictionary::does_any_dictionary_needs_resizing()) {
 625         const char* name = "resizing system dictionaries";
 626         EventSafepointCleanupTask event;
 627         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 628         ClassLoaderDataGraph::resize_dictionaries();
 629 
 630         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 631       }
 632     }
 633 
 634     _subtasks.all_tasks_completed(_num_workers);
 635   }
 636 };
 637 
 638 // Various cleaning tasks that should be done periodically at safepoints.
 639 void SafepointSynchronize::do_cleanup_tasks() {
 640 
 641   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 642 
 643   // Prepare for monitor deflation.
 644   DeflateMonitorCounters deflate_counters;
 645   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 646 
 647   CollectedHeap* heap = Universe::heap();
 648   assert(heap != NULL, "heap not initialized yet?");
 649   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 650   if (cleanup_workers != NULL) {
 651     // Parallel cleanup using GC provided thread pool.
 652     uint num_cleanup_workers = cleanup_workers->active_workers();
 653     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 654     StrongRootsScope srs(num_cleanup_workers);
 655     cleanup_workers->run_task(&cleanup);
 656   } else {
 657     // Serial cleanup using VMThread.
 658     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 659     StrongRootsScope srs(1);
 660     cleanup.work(0);
 661   }
 662 
 663   // Needs to be done single threaded by the VMThread.  This walks
 664   // the thread stacks looking for references to metadata before
 665   // deciding to remove it from the metaspaces.
 666   if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) {
 667     const char* name = "cleanup live ClassLoaderData metaspaces";
 668     TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 669     ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces();
 670   }
 671 
 672   // Finish monitor deflation.
 673   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 674 
 675   assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
 676 }
 677 
 678 // Methods for determining if a JavaThread is safepoint safe.
 679 
 680 // False means unsafe with undetermined state.
 681 // True means a determined state, but it may be an unsafe state.
 682 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
 683 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
 684   assert((safepoint_count != InactiveSafepointCounter &&
 685           Thread::current() == (Thread*)VMThread::vm_thread() &&
 686           SafepointSynchronize::_state != _not_synchronized)
 687          || safepoint_count == InactiveSafepointCounter, "Invalid check");
 688 
 689   // To handle the thread_blocked state on the backedge of the WaitBarrier from
 690   // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
 691   // re-read state after we read thread safepoint id. The JavaThread changes its
 692   // thread state from thread_blocked before resetting safepoint id to 0.
 693   // This guarantees the second read will be from an updated thread state. It can
 694   // either be different state making this an unsafe state or it can see blocked
 695   // again. When we see blocked twice with a 0 safepoint id, either:
 696   // - It is normally blocked, e.g. on Mutex, TBIVM.
 697   // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
 698   // - It was in SS:block() but now on a Mutex.
 699   // All of these cases are safe.
 700 
 701   *state = thread->thread_state();
 702   OrderAccess::loadload();
 703   uint64_t sid = thread->safepoint_state()->get_safepoint_id();  // Load acquire
 704   if (sid != InactiveSafepointCounter && sid != safepoint_count) {
 705     // In an old safepoint, state not relevant.
 706     return false;
 707   }
 708   return *state == thread->thread_state();
 709 }
 710 
 711 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
 712   switch(state) {
 713   case _thread_in_native:
 714     // native threads are safe if they have no java stack or have walkable stack
 715     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 716 
 717   case _thread_blocked:
 718     // On wait_barrier or blocked.
 719     // Blocked threads should already have walkable stack.
 720     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 721     return true;
 722 
 723   default:
 724     return false;
 725   }
 726 }
 727 
 728 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
 729   // This function must be called with the Threads_lock held so an externally
 730   // suspended thread cannot be resumed thus it is safe.
 731   assert(Threads_lock->owned_by_self() && Thread::current()->is_VM_thread(),
 732          "Must hold Threads_lock and be VMThread");
 733   if (thread->is_ext_suspended() || thread->is_terminated()) {
 734     return true;
 735   }
 736   JavaThreadState stable_state;
 737   if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
 738     return safepoint_safe_with(thread, stable_state);
 739   }
 740   return false;
 741 }
 742 
 743 // See if the thread is running inside a lazy critical native and
 744 // update the thread critical count if so.  Also set a suspend flag to
 745 // cause the native wrapper to return into the JVM to do the unlock
 746 // once the native finishes.
 747 static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 748   if (state == _thread_in_native &&
 749       thread->has_last_Java_frame() &&
 750       thread->frame_anchor()->walkable()) {
 751     // This thread might be in a critical native nmethod so look at
 752     // the top of the stack and increment the critical count if it
 753     // is.
 754     frame wrapper_frame = thread->last_frame();
 755     CodeBlob* stub_cb = wrapper_frame.cb();
 756     if (stub_cb != NULL &&
 757         stub_cb->is_nmethod() &&
 758         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 759       // A thread could potentially be in a critical native across
 760       // more than one safepoint, so only update the critical state on
 761       // the first one.  When it returns it will perform the unlock.
 762       if (!thread->do_critical_native_unlock()) {
 763 #ifdef ASSERT
 764         if (!thread->in_critical()) {
 765           GCLocker::increment_debug_jni_lock_count();
 766         }
 767 #endif
 768         thread->enter_critical();
 769         // Make sure the native wrapper calls back on return to
 770         // perform the needed critical unlock.
 771         thread->set_critical_native_unlock();
 772       }
 773     }
 774   }
 775 }
 776 
 777 // -------------------------------------------------------------------------------------------------------
 778 // Implementation of Safepoint blocking point
 779 
 780 void SafepointSynchronize::block(JavaThread *thread) {
 781   assert(thread != NULL, "thread must be set");
 782   assert(thread->is_Java_thread(), "not a Java thread");
 783 
 784   // Threads shouldn't block if they are in the middle of printing, but...
 785   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 786 
 787   // Only bail from the block() call if the thread is gone from the
 788   // thread list; starting to exit should still block.
 789   if (thread->is_terminated()) {
 790      // block current thread if we come here from native code when VM is gone
 791      thread->block_if_vm_exited();
 792 
 793      // otherwise do nothing
 794      return;
 795   }
 796 
 797   JavaThreadState state = thread->thread_state();
 798   thread->frame_anchor()->make_walkable(thread);
 799 
 800   uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
 801   // Check that we have a valid thread_state at this point
 802   switch(state) {
 803     case _thread_in_vm_trans:
 804     case _thread_in_Java:        // From compiled code
 805     case _thread_in_native_trans:
 806     case _thread_blocked_trans:
 807     case _thread_new_trans:
 808 
 809       // We have no idea where the VMThread is, it might even be at next safepoint.
 810       // So we can miss this poll, but stop at next.
 811 
 812       // Load dependent store, it must not pass loading of safepoint_id.
 813       thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
 814 
 815       // This part we can skip if we notice we miss or are in a future safepoint.
 816       OrderAccess::storestore();
 817       // Load in wait barrier should not float up
 818       thread->set_thread_state_fence(_thread_blocked);
 819 
 820       _wait_barrier->wait(static_cast<int>(safepoint_id));
 821       assert(_state != _synchronized, "Can't be");
 822 
 823       // If barrier is disarmed stop store from floating above loads in barrier.
 824       OrderAccess::loadstore();
 825       thread->set_thread_state(state);
 826 
 827       // Then we reset the safepoint id to inactive.
 828       thread->safepoint_state()->reset_safepoint_id(); // Release store
 829 
 830       OrderAccess::fence();
 831 
 832       break;
 833 
 834     default:
 835      fatal("Illegal threadstate encountered: %d", state);
 836   }
 837   guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
 838             "The safepoint id should be set only in block path");
 839 
 840   // Check for pending. async. exceptions or suspends - except if the
 841   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 842   // is called last since it grabs a lock and we only want to do that when
 843   // we must.
 844   //
 845   // Note: we never deliver an async exception at a polling point as the
 846   // compiler may not have an exception handler for it. The polling
 847   // code will notice the async and deoptimize and the exception will
 848   // be delivered. (Polling at a return point is ok though). Sure is
 849   // a lot of bother for a deprecated feature...
 850   //
 851   // We don't deliver an async exception if the thread state is
 852   // _thread_in_native_trans so JNI functions won't be called with
 853   // a surprising pending exception. If the thread state is going back to java,
 854   // async exception is checked in check_special_condition_for_native_trans().
 855 
 856   if (state != _thread_blocked_trans &&
 857       state != _thread_in_vm_trans &&
 858       thread->has_special_runtime_exit_condition()) {
 859     thread->handle_special_runtime_exit_condition(
 860       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 861   }
 862 
 863   // cross_modify_fence is done by SafepointMechanism::block_if_requested_slow
 864   // which is the only caller here.
 865 }
 866 
 867 // ------------------------------------------------------------------------------------------------------
 868 // Exception handlers
 869 
 870 
 871 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 872   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 873   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 874   if (!ThreadLocalHandshakes) {
 875     assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 876   }
 877 
 878   if (log_is_enabled(Info, safepoint, stats)) {
 879     Atomic::inc(&_nof_threads_hit_polling_page);
 880   }
 881 
 882   ThreadSafepointState* state = thread->safepoint_state();
 883 
 884   state->handle_polling_page_exception();
 885 }
 886 
 887 
 888 void SafepointSynchronize::print_safepoint_timeout() {
 889   if (!timeout_error_printed) {
 890     timeout_error_printed = true;
 891     // Print out the thread info which didn't reach the safepoint for debugging
 892     // purposes (useful when there are lots of threads in the debugger).
 893     LogTarget(Warning, safepoint) lt;
 894     if (lt.is_enabled()) {
 895       ResourceMark rm;
 896       LogStream ls(lt);
 897 
 898       ls.cr();
 899       ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
 900       ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 901       ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 902       for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 903         if (cur_thread->safepoint_state()->is_running()) {
 904           ls.print("# ");
 905           cur_thread->print_on(&ls);
 906           ls.cr();
 907         }
 908       }
 909       ls.print_cr("# SafepointSynchronize::begin: (End of list)");
 910     }
 911   }
 912 
 913   // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
 914   // ShowMessageBoxOnError.
 915   if (AbortVMOnSafepointTimeout) {
 916     // Send the blocking thread a signal to terminate and write an error file.
 917     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 918       if (cur_thread->safepoint_state()->is_running()) {
 919         if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
 920           break; // Could not send signal. Report fatal error.
 921         }
 922         // Give cur_thread a chance to report the error and terminate the VM.
 923         os::sleep(Thread::current(), 3000, false);
 924       }
 925     }
 926     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 927           SafepointTimeoutDelay, VMThread::vm_operation()->name());
 928   }
 929 }
 930 
 931 // -------------------------------------------------------------------------------------------------------
 932 // Implementation of ThreadSafepointState
 933 
 934 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
 935   : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
 936     _safepoint_id(SafepointSynchronize::InactiveSafepointCounter),
 937     _orig_thread_state(_thread_uninitialized), _next(NULL) {
 938 }
 939 
 940 void ThreadSafepointState::create(JavaThread *thread) {
 941   ThreadSafepointState *state = new ThreadSafepointState(thread);
 942   thread->set_safepoint_state(state);
 943 }
 944 
 945 void ThreadSafepointState::destroy(JavaThread *thread) {
 946   if (thread->safepoint_state()) {
 947     delete(thread->safepoint_state());
 948     thread->set_safepoint_state(NULL);
 949   }
 950 }
 951 
 952 uint64_t ThreadSafepointState::get_safepoint_id() const {
 953   return OrderAccess::load_acquire(&_safepoint_id);
 954 }
 955 
 956 void ThreadSafepointState::reset_safepoint_id() {
 957   OrderAccess::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
 958 }
 959 
 960 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
 961   OrderAccess::release_store(&_safepoint_id, safepoint_id);
 962 }
 963 
 964 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
 965   assert(is_running(), "better be running or just have hit safepoint poll");
 966 
 967   JavaThreadState stable_state;
 968   if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
 969     // We could not get stable state of the JavaThread.
 970     // Consider it running and just return.
 971     return;
 972   }
 973 
 974   // Save the state at the start of safepoint processing.
 975   _orig_thread_state = stable_state;
 976 
 977   // Check for a thread that is suspended. Note that thread resume tries
 978   // to grab the Threads_lock which we own here, so a thread cannot be
 979   // resumed during safepoint synchronization.
 980 
 981   // We check to see if this thread is suspended without locking to
 982   // avoid deadlocking with a third thread that is waiting for this
 983   // thread to be suspended. The third thread can notice the safepoint
 984   // that we're trying to start at the beginning of its SR_lock->wait()
 985   // call. If that happens, then the third thread will block on the
 986   // safepoint while still holding the underlying SR_lock. We won't be
 987   // able to get the SR_lock and we'll deadlock.
 988   //
 989   // We don't need to grab the SR_lock here for two reasons:
 990   // 1) The suspend flags are both volatile and are set with an
 991   //    Atomic::cmpxchg() call so we should see the suspended
 992   //    state right away.
 993   // 2) We're being called from the safepoint polling loop; if
 994   //    we don't see the suspended state on this iteration, then
 995   //    we'll come around again.
 996   //
 997   bool is_suspended = _thread->is_ext_suspended();
 998   if (is_suspended) {
 999     account_safe_thread();
1000     return;
1001   }
1002 
1003   if (safepoint_safe_with(_thread, stable_state)) {
1004     check_for_lazy_critical_native(_thread, stable_state);
1005     account_safe_thread();
1006     return;
1007   }
1008 
1009   // All other thread states will continue to run until they
1010   // transition and self-block in state _blocked
1011   // Safepoint polling in compiled code causes the Java threads to do the same.
1012   // Note: new threads may require a malloc so they must be allowed to finish
1013 
1014   assert(is_running(), "examine_state_of_thread on non-running thread");
1015   return;
1016 }
1017 
1018 void ThreadSafepointState::account_safe_thread() {
1019   SafepointSynchronize::decrement_waiting_to_block();
1020   if (_thread->in_critical()) {
1021     // Notice that this thread is in a critical section
1022     SafepointSynchronize::increment_jni_active_count();
1023   }
1024   DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
1025   assert(!_safepoint_safe, "Must be unsafe before safe");
1026   _safepoint_safe = true;
1027 }
1028 
1029 void ThreadSafepointState::restart() {
1030   assert(_safepoint_safe, "Must be safe before unsafe");
1031   _safepoint_safe = false;
1032 }
1033 
1034 void ThreadSafepointState::print_on(outputStream *st) const {
1035   const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
1036 
1037   st->print_cr("Thread: " INTPTR_FORMAT
1038               "  [0x%2x] State: %s _at_poll_safepoint %d",
1039                p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
1040 
1041   _thread->print_thread_state_on(st);
1042 }
1043 
1044 void ThreadSafepointState::print() const { print_on(tty); }
1045 
1046 // ---------------------------------------------------------------------------------------------------------------------
1047 
1048 // Block the thread at poll or poll return for safepoint/handshake.
1049 void ThreadSafepointState::handle_polling_page_exception() {
1050 
1051   // If we're using a global poll, then the thread should not be
1052   // marked as safepoint safe yet.
1053   assert(!SafepointMechanism::uses_global_page_poll() || !_safepoint_safe,
1054          "polling page exception on thread safepoint safe");
1055 
1056   // Step 1: Find the nmethod from the return address
1057   address real_return_addr = thread()->saved_exception_pc();
1058 
1059   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1060   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1061   CompiledMethod* nm = (CompiledMethod*)cb;
1062 
1063   // Find frame of caller
1064   frame stub_fr = thread()->last_frame();
1065   CodeBlob* stub_cb = stub_fr.cb();
1066   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1067   RegisterMap map(thread(), true);
1068   frame caller_fr = stub_fr.sender(&map);
1069 
1070   // Should only be poll_return or poll
1071   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1072 
1073   // This is a poll immediately before a return. The exception handling code
1074   // has already had the effect of causing the return to occur, so the execution
1075   // will continue immediately after the call. In addition, the oopmap at the
1076   // return point does not mark the return value as an oop (if it is), so
1077   // it needs a handle here to be updated.
1078   if( nm->is_at_poll_return(real_return_addr) ) {
1079     // See if return type is an oop.
1080     bool return_oop = nm->method()->is_returning_oop();
1081     Handle return_value;
1082     if (return_oop) {
1083       // The oop result has been saved on the stack together with all
1084       // the other registers. In order to preserve it over GCs we need
1085       // to keep it in a handle.
1086       oop result = caller_fr.saved_oop_result(&map);
1087       assert(oopDesc::is_oop_or_null(result), "must be oop");
1088       return_value = Handle(thread(), result);
1089       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1090     }
1091 
1092     // Block the thread
1093     SafepointMechanism::block_if_requested(thread());
1094 
1095     // restore oop result, if any
1096     if (return_oop) {
1097       caller_fr.set_saved_oop_result(&map, return_value());
1098     }
1099   }
1100 
1101   // This is a safepoint poll. Verify the return address and block.
1102   else {
1103     set_at_poll_safepoint(true);
1104 
1105     // verify the blob built the "return address" correctly
1106     assert(real_return_addr == caller_fr.pc(), "must match");
1107 
1108     // Block the thread
1109     SafepointMechanism::block_if_requested(thread());
1110     set_at_poll_safepoint(false);
1111 
1112     // If we have a pending async exception deoptimize the frame
1113     // as otherwise we may never deliver it.
1114     if (thread()->has_async_condition()) {
1115       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1116       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1117     }
1118 
1119     // If an exception has been installed we must check for a pending deoptimization
1120     // Deoptimize frame if exception has been thrown.
1121 
1122     if (thread()->has_pending_exception() ) {
1123       RegisterMap map(thread(), true);
1124       frame caller_fr = stub_fr.sender(&map);
1125       if (caller_fr.is_deoptimized_frame()) {
1126         // The exception patch will destroy registers that are still
1127         // live and will be needed during deoptimization. Defer the
1128         // Async exception should have deferred the exception until the
1129         // next safepoint which will be detected when we get into
1130         // the interpreter so if we have an exception now things
1131         // are messed up.
1132 
1133         fatal("Exception installed and deoptimization is pending");
1134       }
1135     }
1136   }
1137 }
1138 
1139 
1140 // -------------------------------------------------------------------------------------------------------
1141 // Implementation of SafepointTracing
1142 
1143 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1144 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1145 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1146 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1147 jlong SafepointTracing::_last_safepoint_end_time_epoch_ms = 0;
1148 jlong SafepointTracing::_last_app_time_ns = 0;
1149 int SafepointTracing::_nof_threads = 0;
1150 int SafepointTracing::_nof_running = 0;
1151 int SafepointTracing::_page_trap = 0;
1152 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1153 jlong     SafepointTracing::_max_sync_time = 0;
1154 jlong     SafepointTracing::_max_vmop_time = 0;
1155 uint64_t  SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1156 
1157 void SafepointTracing::init() {
1158   // Application start
1159   _last_safepoint_end_time_ns = os::javaTimeNanos();
1160   // amount of time since epoch
1161   _last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
1162 }
1163 
1164 // Helper method to print the header.
1165 static void print_header(outputStream* st) {
1166   // The number of spaces is significant here, and should match the format
1167   // specifiers in print_statistics().
1168 
1169   st->print("VM Operation                 "
1170             "[ threads: total initial_running ]"
1171             "[ time:       sync    cleanup       vmop      total ]");
1172 
1173   st->print_cr(" page_trap_count");
1174 }
1175 
1176 // This prints a nice table.  To get the statistics to not shift due to the logging uptime
1177 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1178 void SafepointTracing::statistics_log() {
1179   LogTarget(Info, safepoint, stats) lt;
1180   assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1181   LogStream ls(lt);
1182 
1183   static int _cur_stat_index = 0;
1184 
1185   // Print header every 30 entries
1186   if ((_cur_stat_index % 30) == 0) {
1187     print_header(&ls);
1188     _cur_stat_index = 1;  // wrap
1189   } else {
1190     _cur_stat_index++;
1191   }
1192 
1193   ls.print("%-28s [       "
1194            INT32_FORMAT_W(8) "        " INT32_FORMAT_W(8) " "
1195            "]",
1196            VM_Operation::name(_current_type),
1197            _nof_threads,
1198            _nof_running);
1199   ls.print("[       "
1200            INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1201            INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1202            (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1203            (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1204            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1205            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1206 
1207   ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1208 }
1209 
1210 // This method will be called when VM exits. This tries to summarize the sampling.
1211 // Current thread may already be deleted, so don't use ResourceMark.
1212 void SafepointTracing::statistics_exit_log() {
1213   if (!log_is_enabled(Info, safepoint, stats)) {
1214     return;
1215   }
1216   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1217     if (_op_count[index] != 0) {
1218       log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1219                _op_count[index]);
1220     }
1221   }
1222 
1223   log_info(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1224                               VMThread::get_coalesced_count());
1225   log_info(safepoint, stats)("Maximum sync time  " INT64_FORMAT" ns",
1226                               (int64_t)(_max_sync_time));
1227   log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation)  "
1228                               INT64_FORMAT " ns",
1229                               (int64_t)(_max_vmop_time));
1230 }
1231 
1232 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1233   _op_count[type]++;
1234   _current_type = type;
1235 
1236   // update the time stamp to begin recording safepoint time
1237   _last_safepoint_begin_time_ns = os::javaTimeNanos();
1238   _last_safepoint_sync_time_ns = 0;
1239   _last_safepoint_cleanup_time_ns = 0;
1240 
1241   _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1242   _last_safepoint_end_time_ns = 0;
1243 
1244   RuntimeService::record_safepoint_begin(_last_app_time_ns);
1245 }
1246 
1247 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1248   _last_safepoint_sync_time_ns = os::javaTimeNanos();
1249   _nof_threads = nof_threads;
1250   _nof_running = nof_running;
1251   _page_trap   = traps;
1252   RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1253 }
1254 
1255 void SafepointTracing::cleanup() {
1256   _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1257 }
1258 
1259 void SafepointTracing::end() {
1260   _last_safepoint_end_time_ns = os::javaTimeNanos();
1261   // amount of time since epoch
1262   _last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
1263 
1264   if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1265     _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1266   }
1267   if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1268     _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1269   }
1270   if (log_is_enabled(Info, safepoint, stats)) {
1271     statistics_log();
1272   }
1273 
1274   log_info(safepoint)(
1275      "Safepoint \"%s\", "
1276      "Time since last: " JLONG_FORMAT " ns, "
1277      "Reaching safepoint: " JLONG_FORMAT " ns, "
1278      "At safepoint: " JLONG_FORMAT " ns, "
1279      "Total: " JLONG_FORMAT " ns",
1280       VM_Operation::name(_current_type),
1281       _last_app_time_ns,
1282       _last_safepoint_cleanup_time_ns - _last_safepoint_begin_time_ns,
1283       _last_safepoint_end_time_ns     - _last_safepoint_cleanup_time_ns,
1284       _last_safepoint_end_time_ns     - _last_safepoint_begin_time_ns
1285      );
1286 
1287   RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns);
1288 }