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 "compiler/compilationPolicy.hpp"
  37 #include "gc/shared/collectedHeap.hpp"
  38 #include "gc/shared/gcLocker.hpp"
  39 #include "gc/shared/oopStorage.hpp"
  40 #include "gc/shared/strongRootsScope.hpp"
  41 #include "gc/shared/workgroup.hpp"
  42 #include "interpreter/interpreter.hpp"
  43 #include "jfr/jfrEvents.hpp"
  44 #include "logging/log.hpp"
  45 #include "logging/logStream.hpp"
  46 #include "memory/resourceArea.hpp"
  47 #include "memory/universe.hpp"
  48 #include "oops/oop.inline.hpp"
  49 #include "oops/symbol.hpp"
  50 #include "runtime/atomic.hpp"
  51 #include "runtime/deoptimization.hpp"
  52 #include "runtime/frame.inline.hpp"
  53 #include "runtime/handles.inline.hpp"
  54 #include "runtime/interfaceSupport.inline.hpp"
  55 #include "runtime/mutexLocker.hpp"
  56 #include "runtime/orderAccess.hpp"
  57 #include "runtime/osThread.hpp"
  58 #include "runtime/safepoint.hpp"
  59 #include "runtime/safepointMechanism.inline.hpp"
  60 #include "runtime/signature.hpp"
  61 #include "runtime/stubCodeGenerator.hpp"
  62 #include "runtime/stubRoutines.hpp"
  63 #include "runtime/sweeper.hpp"
  64 #include "runtime/synchronizer.hpp"
  65 #include "runtime/thread.inline.hpp"
  66 #include "runtime/threadSMR.hpp"
  67 #include "runtime/timerTrace.hpp"
  68 #include "services/runtimeService.hpp"
  69 #include "utilities/events.hpp"
  70 #include "utilities/macros.hpp"
  71 
  72 static void post_safepoint_begin_event(EventSafepointBegin& event,
  73                                        uint64_t safepoint_id,
  74                                        int thread_count,
  75                                        int critical_thread_count) {
  76   if (event.should_commit()) {
  77     event.set_safepointId(safepoint_id);
  78     event.set_totalThreadCount(thread_count);
  79     event.set_jniCriticalThreadCount(critical_thread_count);
  80     event.commit();
  81   }
  82 }
  83 
  84 static void post_safepoint_cleanup_event(EventSafepointCleanup& event, uint64_t safepoint_id) {
  85   if (event.should_commit()) {
  86     event.set_safepointId(safepoint_id);
  87     event.commit();
  88   }
  89 }
  90 
  91 static void post_safepoint_synchronize_event(EventSafepointStateSynchronization& event,
  92                                              uint64_t safepoint_id,
  93                                              int initial_number_of_threads,
  94                                              int threads_waiting_to_block,
  95                                              uint64_t iterations) {
  96   if (event.should_commit()) {
  97     event.set_safepointId(safepoint_id);
  98     event.set_initialThreadCount(initial_number_of_threads);
  99     event.set_runningThreadCount(threads_waiting_to_block);
 100     event.set_iterations(iterations);
 101     event.commit();
 102   }
 103 }
 104 
 105 static void post_safepoint_cleanup_task_event(EventSafepointCleanupTask& event,
 106                                               uint64_t safepoint_id,
 107                                               const char* name) {
 108   if (event.should_commit()) {
 109     event.set_safepointId(safepoint_id);
 110     event.set_name(name);
 111     event.commit();
 112   }
 113 }
 114 
 115 static void post_safepoint_end_event(EventSafepointEnd& event, uint64_t safepoint_id) {
 116   if (event.should_commit()) {
 117     event.set_safepointId(safepoint_id);
 118     event.commit();
 119   }
 120 }
 121 
 122 // SafepointCheck
 123 SafepointStateTracker::SafepointStateTracker(uint64_t safepoint_id, bool at_safepoint)
 124   : _safepoint_id(safepoint_id), _at_safepoint(at_safepoint) {}
 125 
 126 bool SafepointStateTracker::safepoint_state_changed() {
 127   return _safepoint_id != SafepointSynchronize::safepoint_id() ||
 128     _at_safepoint != SafepointSynchronize::is_at_safepoint();
 129 }
 130 
 131 // --------------------------------------------------------------------------------------------------
 132 // Implementation of Safepoint begin/end
 133 
 134 SafepointSynchronize::SynchronizeState volatile SafepointSynchronize::_state = SafepointSynchronize::_not_synchronized;
 135 int SafepointSynchronize::_waiting_to_block = 0;
 136 volatile uint64_t SafepointSynchronize::_safepoint_counter = 0;
 137 uint64_t SafepointSynchronize::_safepoint_id = 0;
 138 const uint64_t SafepointSynchronize::InactiveSafepointCounter = 0;
 139 int SafepointSynchronize::_current_jni_active_count = 0;
 140 
 141 WaitBarrier* SafepointSynchronize::_wait_barrier;
 142 
 143 static volatile bool PageArmed = false;        // safepoint polling page is RO|RW vs PROT_NONE
 144 static bool timeout_error_printed = false;
 145 
 146 // Statistic related
 147 static jlong _safepoint_begin_time = 0;
 148 static volatile int _nof_threads_hit_polling_page = 0;
 149 
 150 void SafepointSynchronize::init(Thread* vmthread) {
 151   // WaitBarrier should never be destroyed since we will have
 152   // threads waiting on it while exiting.
 153   _wait_barrier = new WaitBarrier(vmthread);
 154   SafepointTracing::init();
 155 }
 156 
 157 void SafepointSynchronize::increment_jni_active_count() {
 158   assert(Thread::current()->is_VM_thread(), "Only VM thread may increment");
 159   ++_current_jni_active_count;
 160 }
 161 
 162 void SafepointSynchronize::decrement_waiting_to_block() {
 163   assert(_waiting_to_block > 0, "sanity check");
 164   assert(Thread::current()->is_VM_thread(), "Only VM thread may decrement");
 165   --_waiting_to_block;
 166 }
 167 
 168 bool SafepointSynchronize::thread_not_running(ThreadSafepointState *cur_state) {
 169   if (!cur_state->is_running()) {
 170     return true;
 171   }
 172   cur_state->examine_state_of_thread(SafepointSynchronize::safepoint_counter());
 173   if (!cur_state->is_running()) {
 174     return true;
 175   }
 176   LogTarget(Trace, safepoint) lt;
 177   if (lt.is_enabled()) {
 178     ResourceMark rm;
 179     LogStream ls(lt);
 180     cur_state->print_on(&ls);
 181   }
 182   return false;
 183 }
 184 
 185 #ifdef ASSERT
 186 static void assert_list_is_valid(const ThreadSafepointState* tss_head, int still_running) {
 187   int a = 0;
 188   const ThreadSafepointState *tmp_tss = tss_head;
 189   while (tmp_tss != NULL) {
 190     ++a;
 191     assert(tmp_tss->is_running(), "Illegal initial state");
 192     tmp_tss = tmp_tss->get_next();
 193   }
 194   assert(a == still_running, "Must be the same");
 195 }
 196 #endif // ASSERT
 197 
 198 static void back_off(int64_t start_time) {
 199   // We start with fine-grained nanosleeping until a millisecond has
 200   // passed, at which point we resort to plain naked_short_sleep.
 201   if (os::javaTimeNanos() - start_time < NANOSECS_PER_MILLISEC) {
 202     os::naked_short_nanosleep(10 * (NANOUNITS / MICROUNITS));
 203   } else {
 204     os::naked_short_sleep(1);
 205   }
 206 }
 207 
 208 int SafepointSynchronize::synchronize_threads(jlong safepoint_limit_time, int nof_threads, int* initial_running)
 209 {
 210   JavaThreadIteratorWithHandle jtiwh;
 211 
 212 #ifdef ASSERT
 213   for (; JavaThread *cur = jtiwh.next(); ) {
 214     assert(cur->safepoint_state()->is_running(), "Illegal initial state");
 215   }
 216   jtiwh.rewind();
 217 #endif // ASSERT
 218 
 219   // Iterate through all threads until it has been determined how to stop them all at a safepoint.
 220   int still_running = nof_threads;
 221   ThreadSafepointState *tss_head = NULL;
 222   ThreadSafepointState **p_prev = &tss_head;
 223   for (; JavaThread *cur = jtiwh.next(); ) {
 224     ThreadSafepointState *cur_tss = cur->safepoint_state();
 225     assert(cur_tss->get_next() == NULL, "Must be NULL");
 226     if (thread_not_running(cur_tss)) {
 227       --still_running;
 228     } else {
 229       *p_prev = cur_tss;
 230       p_prev = cur_tss->next_ptr();
 231     }
 232   }
 233   *p_prev = NULL;
 234 
 235   DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
 236 
 237   *initial_running = still_running;
 238 
 239   // If there is no thread still running, we are already done.
 240   if (still_running <= 0) {
 241     assert(tss_head == NULL, "Must be empty");
 242     return 1;
 243   }
 244 
 245   int iterations = 1; // The first iteration is above.
 246   int64_t start_time = os::javaTimeNanos();
 247 
 248   do {
 249     // Check if this has taken too long:
 250     if (SafepointTimeout && safepoint_limit_time < os::javaTimeNanos()) {
 251       print_safepoint_timeout();
 252     }
 253     if (int(iterations) == -1) { // overflow - something is wrong.
 254       // We can only overflow here when we are using global
 255       // polling pages. We keep this guarantee in its original
 256       // form so that searches of the bug database for this
 257       // failure mode find the right bugs.
 258       guarantee (!PageArmed, "invariant");
 259     }
 260 
 261     p_prev = &tss_head;
 262     ThreadSafepointState *cur_tss = tss_head;
 263     while (cur_tss != NULL) {
 264       assert(cur_tss->is_running(), "Illegal initial state");
 265       if (thread_not_running(cur_tss)) {
 266         --still_running;
 267         *p_prev = NULL;
 268         ThreadSafepointState *tmp = cur_tss;
 269         cur_tss = cur_tss->get_next();
 270         tmp->set_next(NULL);
 271       } else {
 272         *p_prev = cur_tss;
 273         p_prev = cur_tss->next_ptr();
 274         cur_tss = cur_tss->get_next();
 275       }
 276     }
 277 
 278     DEBUG_ONLY(assert_list_is_valid(tss_head, still_running);)
 279 
 280     if (still_running > 0) {
 281       back_off(start_time);
 282     }
 283 
 284     iterations++;
 285   } while (still_running > 0);
 286 
 287   assert(tss_head == NULL, "Must be empty");
 288 
 289   return iterations;
 290 }
 291 
 292 void SafepointSynchronize::arm_safepoint() {
 293   // Begin the process of bringing the system to a safepoint.
 294   // Java threads can be in several different states and are
 295   // stopped by different mechanisms:
 296   //
 297   //  1. Running interpreted
 298   //     When executing branching/returning byte codes interpreter
 299   //     checks if the poll is armed, if so blocks in SS::block().
 300   //     When using global polling the interpreter dispatch table
 301   //     is changed to force it to check for a safepoint condition
 302   //     between bytecodes.
 303   //  2. Running in native code
 304   //     When returning from the native code, a Java thread must check
 305   //     the safepoint _state to see if we must block.  If the
 306   //     VM thread sees a Java thread in native, it does
 307   //     not wait for this thread to block.  The order of the memory
 308   //     writes and reads of both the safepoint state and the Java
 309   //     threads state is critical.  In order to guarantee that the
 310   //     memory writes are serialized with respect to each other,
 311   //     the VM thread issues a memory barrier instruction.
 312   //  3. Running compiled Code
 313   //     Compiled code reads the local polling page that
 314   //     is set to fault if we are trying to get to a safepoint.
 315   //  4. Blocked
 316   //     A thread which is blocked will not be allowed to return from the
 317   //     block condition until the safepoint operation is complete.
 318   //  5. In VM or Transitioning between states
 319   //     If a Java thread is currently running in the VM or transitioning
 320   //     between states, the safepointing code will poll the thread state
 321   //     until the thread blocks itself when it attempts transitions to a
 322   //     new state or locking a safepoint checked monitor.
 323 
 324   // We must never miss a thread with correct safepoint id, so we must make sure we arm
 325   // the wait barrier for the next safepoint id/counter.
 326   // Arming must be done after resetting _current_jni_active_count, _waiting_to_block.
 327   _wait_barrier->arm(static_cast<int>(_safepoint_counter + 1));
 328 
 329   assert((_safepoint_counter & 0x1) == 0, "must be even");
 330   // The store to _safepoint_counter must happen after any stores in arming.
 331   Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
 332 
 333   // We are synchronizing
 334   OrderAccess::storestore(); // Ordered with _safepoint_counter
 335   _state = _synchronizing;
 336 
 337   if (SafepointMechanism::uses_thread_local_poll()) {
 338     // Arming the per thread poll while having _state != _not_synchronized means safepointing
 339     log_trace(safepoint)("Setting thread local yield flag for threads");
 340     OrderAccess::storestore(); // storestore, global state -> local state
 341     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 342       // Make sure the threads start polling, it is time to yield.
 343       SafepointMechanism::arm_local_poll(cur);
 344     }
 345   }
 346   OrderAccess::fence(); // storestore|storeload, global state -> local state
 347 
 348   if (SafepointMechanism::uses_global_page_poll()) {
 349     // Make interpreter safepoint aware
 350     Interpreter::notice_safepoints();
 351 
 352     // Make polling safepoint aware
 353     guarantee (!PageArmed, "invariant") ;
 354     PageArmed = true;
 355     os::make_polling_page_unreadable();
 356   }
 357 }
 358 
 359 // Roll all threads forward to a safepoint and suspend them all
 360 void SafepointSynchronize::begin() {
 361   assert(Thread::current()->is_VM_thread(), "Only VM thread may execute a safepoint");
 362 
 363   EventSafepointBegin begin_event;
 364   SafepointTracing::begin(VMThread::vm_op_type());
 365 
 366   Universe::heap()->safepoint_synchronize_begin();
 367 
 368   // By getting the Threads_lock, we assure that no threads are about to start or
 369   // exit. It is released again in SafepointSynchronize::end().
 370   Threads_lock->lock();
 371 
 372   assert( _state == _not_synchronized, "trying to safepoint synchronize with wrong state");
 373 
 374   int nof_threads = Threads::number_of_threads();
 375 
 376   _nof_threads_hit_polling_page = 0;
 377 
 378   log_debug(safepoint)("Safepoint synchronization initiated using %s wait barrier. (%d threads)", _wait_barrier->description(), nof_threads);
 379 
 380   // Reset the count of active JNI critical threads
 381   _current_jni_active_count = 0;
 382 
 383   // Set number of threads to wait for
 384   _waiting_to_block = nof_threads;
 385 
 386   jlong safepoint_limit_time = 0;
 387   if (SafepointTimeout) {
 388     // Set the limit time, so that it can be compared to see if this has taken
 389     // too long to complete.
 390     safepoint_limit_time = SafepointTracing::start_of_safepoint() + (jlong)SafepointTimeoutDelay * (NANOUNITS / MILLIUNITS);
 391     timeout_error_printed = false;
 392   }
 393 
 394   EventSafepointStateSynchronization sync_event;
 395   int initial_running = 0;
 396 
 397   // Arms the safepoint, _current_jni_active_count and _waiting_to_block must be set before.
 398   arm_safepoint();
 399 
 400   // Will spin until all threads are safe.
 401   int iterations = synchronize_threads(safepoint_limit_time, nof_threads, &initial_running);
 402   assert(_waiting_to_block == 0, "No thread should be running");
 403 
 404 #ifndef PRODUCT
 405   if (safepoint_limit_time != 0) {
 406     jlong current_time = os::javaTimeNanos();
 407     if (safepoint_limit_time < current_time) {
 408       log_warning(safepoint)("# SafepointSynchronize: Finished after "
 409                     INT64_FORMAT_W(6) " ms",
 410                     (int64_t)(current_time - SafepointTracing::start_of_safepoint()) / (NANOUNITS / MILLIUNITS));
 411     }
 412   }
 413 #endif
 414 
 415   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 416 
 417   // Record state
 418   _state = _synchronized;
 419 
 420   OrderAccess::fence();
 421 
 422   // Set the new id
 423   ++_safepoint_id;
 424 
 425 #ifdef ASSERT
 426   // Make sure all the threads were visited.
 427   for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur = jtiwh.next(); ) {
 428     assert(cur->was_visited_for_critical_count(_safepoint_counter), "missed a thread");
 429   }
 430 #endif // ASSERT
 431 
 432   // Update the count of active JNI critical regions
 433   GCLocker::set_jni_lock_count(_current_jni_active_count);
 434 
 435   post_safepoint_synchronize_event(sync_event,
 436                                    _safepoint_id,
 437                                    initial_running,
 438                                    _waiting_to_block, iterations);
 439 
 440   SafepointTracing::synchronized(nof_threads, initial_running, _nof_threads_hit_polling_page);
 441 
 442   // We do the safepoint cleanup first since a GC related safepoint
 443   // needs cleanup to be completed before running the GC op.
 444   EventSafepointCleanup cleanup_event;
 445   do_cleanup_tasks();
 446   post_safepoint_cleanup_event(cleanup_event, _safepoint_id);
 447 
 448   post_safepoint_begin_event(begin_event, _safepoint_id, nof_threads, _current_jni_active_count);
 449   SafepointTracing::cleanup();
 450 }
 451 
 452 void SafepointSynchronize::disarm_safepoint() {
 453   uint64_t active_safepoint_counter = _safepoint_counter;
 454   {
 455     JavaThreadIteratorWithHandle jtiwh;
 456 #ifdef ASSERT
 457     // A pending_exception cannot be installed during a safepoint.  The threads
 458     // may install an async exception after they come back from a safepoint into
 459     // pending_exception after they unblock.  But that should happen later.
 460     for (; JavaThread *cur = jtiwh.next(); ) {
 461       assert (!(cur->has_pending_exception() &&
 462                 cur->safepoint_state()->is_at_poll_safepoint()),
 463               "safepoint installed a pending exception");
 464     }
 465 #endif // ASSERT
 466 
 467     if (SafepointMechanism::uses_global_page_poll()) {
 468       guarantee (PageArmed, "invariant");
 469       // Make polling safepoint aware
 470       os::make_polling_page_readable();
 471       PageArmed = false;
 472       // Remove safepoint check from interpreter
 473       Interpreter::ignore_safepoints();
 474     }
 475 
 476     OrderAccess::fence(); // keep read and write of _state from floating up
 477     assert(_state == _synchronized, "must be synchronized before ending safepoint synchronization");
 478 
 479     // Change state first to _not_synchronized.
 480     // No threads should see _synchronized when running.
 481     _state = _not_synchronized;
 482 
 483     // Set the next dormant (even) safepoint id.
 484     assert((_safepoint_counter & 0x1) == 1, "must be odd");
 485     Atomic::release_store(&_safepoint_counter, _safepoint_counter + 1);
 486 
 487     OrderAccess::fence(); // Keep the local state from floating up.
 488 
 489     jtiwh.rewind();
 490     for (; JavaThread *current = jtiwh.next(); ) {
 491       // Clear the visited flag to ensure that the critical counts are collected properly.
 492       DEBUG_ONLY(current->reset_visited_for_critical_count(active_safepoint_counter);)
 493       ThreadSafepointState* cur_state = current->safepoint_state();
 494       assert(!cur_state->is_running(), "Thread not suspended at safepoint");
 495       cur_state->restart(); // TSS _running
 496       assert(cur_state->is_running(), "safepoint state has not been reset");
 497 
 498       SafepointMechanism::disarm_if_needed(current, false /* NO release */);
 499     }
 500   } // ~JavaThreadIteratorWithHandle
 501 
 502   // Release threads lock, so threads can be created/destroyed again.
 503   Threads_lock->unlock();
 504 
 505   // Wake threads after local state is correctly set.
 506   _wait_barrier->disarm();
 507 }
 508 
 509 // Wake up all threads, so they are ready to resume execution after the safepoint
 510 // operation has been carried out
 511 void SafepointSynchronize::end() {
 512   assert(Threads_lock->owned_by_self(), "must hold Threads_lock");
 513   EventSafepointEnd event;
 514   assert(Thread::current()->is_VM_thread(), "Only VM thread can execute a safepoint");
 515 
 516   disarm_safepoint();
 517 
 518   Universe::heap()->safepoint_synchronize_end();
 519 
 520   SafepointTracing::end();
 521 
 522   post_safepoint_end_event(event, safepoint_id());
 523 }
 524 
 525 bool SafepointSynchronize::is_cleanup_needed() {
 526   // Need a safepoint if there are many monitors to deflate.
 527   if (ObjectSynchronizer::is_cleanup_needed()) return true;
 528   // Need a safepoint if some inline cache buffers is non-empty
 529   if (!InlineCacheBuffer::is_empty()) return true;
 530   if (StringTable::needs_rehashing()) return true;
 531   if (SymbolTable::needs_rehashing()) return true;
 532   return false;
 533 }
 534 
 535 class ParallelSPCleanupThreadClosure : public ThreadClosure {
 536 private:
 537   CodeBlobClosure* _nmethod_cl;
 538   DeflateMonitorCounters* _counters;
 539 
 540 public:
 541   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
 542     _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL),
 543     _counters(counters) {}
 544 
 545   void do_thread(Thread* thread) {
 546     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);
 547     if (_nmethod_cl != NULL && thread->is_Java_thread() &&
 548         ! thread->is_Code_cache_sweeper_thread()) {
 549       JavaThread* jt = (JavaThread*) thread;
 550       jt->nmethods_do(_nmethod_cl);
 551     }
 552   }
 553 };
 554 
 555 class ParallelSPCleanupTask : public AbstractGangTask {
 556 private:
 557   SubTasksDone _subtasks;
 558   ParallelSPCleanupThreadClosure _cleanup_threads_cl;
 559   uint _num_workers;
 560   DeflateMonitorCounters* _counters;
 561 public:
 562   ParallelSPCleanupTask(uint num_workers, DeflateMonitorCounters* counters) :
 563     AbstractGangTask("Parallel Safepoint Cleanup"),
 564     _subtasks(SubTasksDone(SafepointSynchronize::SAFEPOINT_CLEANUP_NUM_TASKS)),
 565     _cleanup_threads_cl(ParallelSPCleanupThreadClosure(counters)),
 566     _num_workers(num_workers),
 567     _counters(counters) {}
 568 
 569   void work(uint worker_id) {
 570     uint64_t safepoint_id = SafepointSynchronize::safepoint_id();
 571     // All threads deflate monitors and mark nmethods (if necessary).
 572     Threads::possibly_parallel_threads_do(true, &_cleanup_threads_cl);
 573 
 574     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_DEFLATE_MONITORS)) {
 575       const char* name = "deflating global idle monitors";
 576       EventSafepointCleanupTask event;
 577       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 578       ObjectSynchronizer::deflate_idle_monitors(_counters);
 579 
 580       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 581     }
 582 
 583     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_UPDATE_INLINE_CACHES)) {
 584       const char* name = "updating inline caches";
 585       EventSafepointCleanupTask event;
 586       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 587       InlineCacheBuffer::update_inline_caches();
 588 
 589       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 590     }
 591 
 592     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_COMPILATION_POLICY)) {
 593       const char* name = "compilation policy safepoint handler";
 594       EventSafepointCleanupTask event;
 595       TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 596       CompilationPolicy::policy()->do_safepoint_work();
 597 
 598       post_safepoint_cleanup_task_event(event, safepoint_id, name);
 599     }
 600 
 601     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYMBOL_TABLE_REHASH)) {
 602       if (SymbolTable::needs_rehashing()) {
 603         const char* name = "rehashing symbol table";
 604         EventSafepointCleanupTask event;
 605         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 606         SymbolTable::rehash_table();
 607 
 608         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 609       }
 610     }
 611 
 612     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_STRING_TABLE_REHASH)) {
 613       if (StringTable::needs_rehashing()) {
 614         const char* name = "rehashing string table";
 615         EventSafepointCleanupTask event;
 616         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 617         StringTable::rehash_table();
 618 
 619         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 620       }
 621     }
 622 
 623     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_CLD_PURGE)) {
 624       if (ClassLoaderDataGraph::should_purge_and_reset()) {
 625         // CMS delays purging the CLDG until the beginning of the next safepoint and to
 626         // make sure concurrent sweep is done
 627         const char* name = "purging class loader data graph";
 628         EventSafepointCleanupTask event;
 629         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 630         ClassLoaderDataGraph::purge();
 631 
 632         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 633       }
 634     }
 635 
 636     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_SYSTEM_DICTIONARY_RESIZE)) {
 637       if (Dictionary::does_any_dictionary_needs_resizing()) {
 638         const char* name = "resizing system dictionaries";
 639         EventSafepointCleanupTask event;
 640         TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 641         ClassLoaderDataGraph::resize_dictionaries();
 642 
 643         post_safepoint_cleanup_task_event(event, safepoint_id, name);
 644       }
 645     }
 646 
 647     if (_subtasks.try_claim_task(SafepointSynchronize::SAFEPOINT_CLEANUP_REQUEST_OOPSTORAGE_CLEANUP)) {
 648       // Don't bother reporting event or time for this very short operation.
 649       // To have any utility we'd also want to report whether needed.
 650       OopStorage::trigger_cleanup_if_needed();
 651     }
 652 
 653     _subtasks.all_tasks_completed(_num_workers);
 654   }
 655 };
 656 
 657 // Various cleaning tasks that should be done periodically at safepoints.
 658 void SafepointSynchronize::do_cleanup_tasks() {
 659 
 660   TraceTime timer("safepoint cleanup tasks", TRACETIME_LOG(Info, safepoint, cleanup));
 661 
 662   // Prepare for monitor deflation.
 663   DeflateMonitorCounters deflate_counters;
 664   ObjectSynchronizer::prepare_deflate_idle_monitors(&deflate_counters);
 665 
 666   CollectedHeap* heap = Universe::heap();
 667   assert(heap != NULL, "heap not initialized yet?");
 668   WorkGang* cleanup_workers = heap->get_safepoint_workers();
 669   if (cleanup_workers != NULL) {
 670     // Parallel cleanup using GC provided thread pool.
 671     uint num_cleanup_workers = cleanup_workers->active_workers();
 672     ParallelSPCleanupTask cleanup(num_cleanup_workers, &deflate_counters);
 673     StrongRootsScope srs(num_cleanup_workers);
 674     cleanup_workers->run_task(&cleanup);
 675   } else {
 676     // Serial cleanup using VMThread.
 677     ParallelSPCleanupTask cleanup(1, &deflate_counters);
 678     StrongRootsScope srs(1);
 679     cleanup.work(0);
 680   }
 681 
 682   // Needs to be done single threaded by the VMThread.  This walks
 683   // the thread stacks looking for references to metadata before
 684   // deciding to remove it from the metaspaces.
 685   if (ClassLoaderDataGraph::should_clean_metaspaces_and_reset()) {
 686     const char* name = "cleanup live ClassLoaderData metaspaces";
 687     TraceTime timer(name, TRACETIME_LOG(Info, safepoint, cleanup));
 688     ClassLoaderDataGraph::walk_metadata_and_clean_metaspaces();
 689   }
 690 
 691   // Finish monitor deflation.
 692   ObjectSynchronizer::finish_deflate_idle_monitors(&deflate_counters);
 693 
 694   assert(InlineCacheBuffer::is_empty(), "should have cleaned up ICBuffer");
 695 }
 696 
 697 // Methods for determining if a JavaThread is safepoint safe.
 698 
 699 // False means unsafe with undetermined state.
 700 // True means a determined state, but it may be an unsafe state.
 701 // If called from a non-safepoint context safepoint_count MUST be InactiveSafepointCounter.
 702 bool SafepointSynchronize::try_stable_load_state(JavaThreadState *state, JavaThread *thread, uint64_t safepoint_count) {
 703   assert((safepoint_count != InactiveSafepointCounter &&
 704           Thread::current() == (Thread*)VMThread::vm_thread() &&
 705           SafepointSynchronize::_state != _not_synchronized)
 706          || safepoint_count == InactiveSafepointCounter, "Invalid check");
 707 
 708   // To handle the thread_blocked state on the backedge of the WaitBarrier from
 709   // previous safepoint and reading the reset value (0/InactiveSafepointCounter) we
 710   // re-read state after we read thread safepoint id. The JavaThread changes its
 711   // thread state from thread_blocked before resetting safepoint id to 0.
 712   // This guarantees the second read will be from an updated thread state. It can
 713   // either be different state making this an unsafe state or it can see blocked
 714   // again. When we see blocked twice with a 0 safepoint id, either:
 715   // - It is normally blocked, e.g. on Mutex, TBIVM.
 716   // - It was in SS:block(), looped around to SS:block() and is blocked on the WaitBarrier.
 717   // - It was in SS:block() but now on a Mutex.
 718   // All of these cases are safe.
 719 
 720   *state = thread->thread_state();
 721   OrderAccess::loadload();
 722   uint64_t sid = thread->safepoint_state()->get_safepoint_id();  // Load acquire
 723   if (sid != InactiveSafepointCounter && sid != safepoint_count) {
 724     // In an old safepoint, state not relevant.
 725     return false;
 726   }
 727   return *state == thread->thread_state();
 728 }
 729 
 730 static bool safepoint_safe_with(JavaThread *thread, JavaThreadState state) {
 731   switch(state) {
 732   case _thread_in_native:
 733     // native threads are safe if they have no java stack or have walkable stack
 734     return !thread->has_last_Java_frame() || thread->frame_anchor()->walkable();
 735 
 736   case _thread_blocked:
 737     // On wait_barrier or blocked.
 738     // Blocked threads should already have walkable stack.
 739     assert(!thread->has_last_Java_frame() || thread->frame_anchor()->walkable(), "blocked and not walkable");
 740     return true;
 741 
 742   default:
 743     return false;
 744   }
 745 }
 746 
 747 bool SafepointSynchronize::handshake_safe(JavaThread *thread) {
 748   // This function must be called with the Threads_lock held so an externally
 749   // suspended thread cannot be resumed thus it is safe.
 750   assert(Threads_lock->owned_by_self() && Thread::current()->is_VM_thread(),
 751          "Must hold Threads_lock and be VMThread");
 752   if (thread->is_ext_suspended() || thread->is_terminated()) {
 753     return true;
 754   }
 755   JavaThreadState stable_state;
 756   if (try_stable_load_state(&stable_state, thread, InactiveSafepointCounter)) {
 757     return safepoint_safe_with(thread, stable_state);
 758   }
 759   return false;
 760 }
 761 
 762 // See if the thread is running inside a lazy critical native and
 763 // update the thread critical count if so.  Also set a suspend flag to
 764 // cause the native wrapper to return into the JVM to do the unlock
 765 // once the native finishes.
 766 static void check_for_lazy_critical_native(JavaThread *thread, JavaThreadState state) {
 767   if (state == _thread_in_native &&
 768       thread->has_last_Java_frame() &&
 769       thread->frame_anchor()->walkable()) {
 770     // This thread might be in a critical native nmethod so look at
 771     // the top of the stack and increment the critical count if it
 772     // is.
 773     frame wrapper_frame = thread->last_frame();
 774     CodeBlob* stub_cb = wrapper_frame.cb();
 775     if (stub_cb != NULL &&
 776         stub_cb->is_nmethod() &&
 777         stub_cb->as_nmethod_or_null()->is_lazy_critical_native()) {
 778       // A thread could potentially be in a critical native across
 779       // more than one safepoint, so only update the critical state on
 780       // the first one.  When it returns it will perform the unlock.
 781       if (!thread->do_critical_native_unlock()) {
 782 #ifdef ASSERT
 783         if (!thread->in_critical()) {
 784           GCLocker::increment_debug_jni_lock_count();
 785         }
 786 #endif
 787         thread->enter_critical();
 788         // Make sure the native wrapper calls back on return to
 789         // perform the needed critical unlock.
 790         thread->set_critical_native_unlock();
 791       }
 792     }
 793   }
 794 }
 795 
 796 // -------------------------------------------------------------------------------------------------------
 797 // Implementation of Safepoint blocking point
 798 
 799 void SafepointSynchronize::block(JavaThread *thread) {
 800   assert(thread != NULL, "thread must be set");
 801   assert(thread->is_Java_thread(), "not a Java thread");
 802 
 803   // Threads shouldn't block if they are in the middle of printing, but...
 804   ttyLocker::break_tty_lock_for_safepoint(os::current_thread_id());
 805 
 806   // Only bail from the block() call if the thread is gone from the
 807   // thread list; starting to exit should still block.
 808   if (thread->is_terminated()) {
 809      // block current thread if we come here from native code when VM is gone
 810      thread->block_if_vm_exited();
 811 
 812      // otherwise do nothing
 813      return;
 814   }
 815 
 816   JavaThreadState state = thread->thread_state();
 817   thread->frame_anchor()->make_walkable(thread);
 818 
 819   uint64_t safepoint_id = SafepointSynchronize::safepoint_counter();
 820   // Check that we have a valid thread_state at this point
 821   switch(state) {
 822     case _thread_in_vm_trans:
 823     case _thread_in_Java:        // From compiled code
 824     case _thread_in_native_trans:
 825     case _thread_blocked_trans:
 826     case _thread_new_trans:
 827 
 828       // We have no idea where the VMThread is, it might even be at next safepoint.
 829       // So we can miss this poll, but stop at next.
 830 
 831       // Load dependent store, it must not pass loading of safepoint_id.
 832       thread->safepoint_state()->set_safepoint_id(safepoint_id); // Release store
 833 
 834       // This part we can skip if we notice we miss or are in a future safepoint.
 835       OrderAccess::storestore();
 836       // Load in wait barrier should not float up
 837       thread->set_thread_state_fence(_thread_blocked);
 838 
 839       _wait_barrier->wait(static_cast<int>(safepoint_id));
 840       assert(_state != _synchronized, "Can't be");
 841 
 842       // If barrier is disarmed stop store from floating above loads in barrier.
 843       OrderAccess::loadstore();
 844       thread->set_thread_state(state);
 845 
 846       // Then we reset the safepoint id to inactive.
 847       thread->safepoint_state()->reset_safepoint_id(); // Release store
 848 
 849       OrderAccess::fence();
 850 
 851       break;
 852 
 853     default:
 854      fatal("Illegal threadstate encountered: %d", state);
 855   }
 856   guarantee(thread->safepoint_state()->get_safepoint_id() == InactiveSafepointCounter,
 857             "The safepoint id should be set only in block path");
 858 
 859   // Check for pending. async. exceptions or suspends - except if the
 860   // thread was blocked inside the VM. has_special_runtime_exit_condition()
 861   // is called last since it grabs a lock and we only want to do that when
 862   // we must.
 863   //
 864   // Note: we never deliver an async exception at a polling point as the
 865   // compiler may not have an exception handler for it. The polling
 866   // code will notice the async and deoptimize and the exception will
 867   // be delivered. (Polling at a return point is ok though). Sure is
 868   // a lot of bother for a deprecated feature...
 869   //
 870   // We don't deliver an async exception if the thread state is
 871   // _thread_in_native_trans so JNI functions won't be called with
 872   // a surprising pending exception. If the thread state is going back to java,
 873   // async exception is checked in check_special_condition_for_native_trans().
 874 
 875   if (state != _thread_blocked_trans &&
 876       state != _thread_in_vm_trans &&
 877       thread->has_special_runtime_exit_condition()) {
 878     thread->handle_special_runtime_exit_condition(
 879       !thread->is_at_poll_safepoint() && (state != _thread_in_native_trans));
 880   }
 881 
 882   // cross_modify_fence is done by SafepointMechanism::block_if_requested_slow
 883   // which is the only caller here.
 884 }
 885 
 886 // ------------------------------------------------------------------------------------------------------
 887 // Exception handlers
 888 
 889 
 890 void SafepointSynchronize::handle_polling_page_exception(JavaThread *thread) {
 891   assert(thread->is_Java_thread(), "polling reference encountered by VM thread");
 892   assert(thread->thread_state() == _thread_in_Java, "should come from Java code");
 893   if (!ThreadLocalHandshakes) {
 894     assert(SafepointSynchronize::is_synchronizing(), "polling encountered outside safepoint synchronization");
 895   }
 896 
 897   if (log_is_enabled(Info, safepoint, stats)) {
 898     Atomic::inc(&_nof_threads_hit_polling_page);
 899   }
 900 
 901   ThreadSafepointState* state = thread->safepoint_state();
 902 
 903   state->handle_polling_page_exception();
 904 }
 905 
 906 
 907 void SafepointSynchronize::print_safepoint_timeout() {
 908   if (!timeout_error_printed) {
 909     timeout_error_printed = true;
 910     // Print out the thread info which didn't reach the safepoint for debugging
 911     // purposes (useful when there are lots of threads in the debugger).
 912     LogTarget(Warning, safepoint) lt;
 913     if (lt.is_enabled()) {
 914       ResourceMark rm;
 915       LogStream ls(lt);
 916 
 917       ls.cr();
 918       ls.print_cr("# SafepointSynchronize::begin: Timeout detected:");
 919       ls.print_cr("# SafepointSynchronize::begin: Timed out while spinning to reach a safepoint.");
 920       ls.print_cr("# SafepointSynchronize::begin: Threads which did not reach the safepoint:");
 921       for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 922         if (cur_thread->safepoint_state()->is_running()) {
 923           ls.print("# ");
 924           cur_thread->print_on(&ls);
 925           ls.cr();
 926         }
 927       }
 928       ls.print_cr("# SafepointSynchronize::begin: (End of list)");
 929     }
 930   }
 931 
 932   // To debug the long safepoint, specify both AbortVMOnSafepointTimeout &
 933   // ShowMessageBoxOnError.
 934   if (AbortVMOnSafepointTimeout) {
 935     // Send the blocking thread a signal to terminate and write an error file.
 936     for (JavaThreadIteratorWithHandle jtiwh; JavaThread *cur_thread = jtiwh.next(); ) {
 937       if (cur_thread->safepoint_state()->is_running()) {
 938         if (!os::signal_thread(cur_thread, SIGILL, "blocking a safepoint")) {
 939           break; // Could not send signal. Report fatal error.
 940         }
 941         // Give cur_thread a chance to report the error and terminate the VM.
 942         os::naked_sleep(3000);
 943       }
 944     }
 945     fatal("Safepoint sync time longer than " INTX_FORMAT "ms detected when executing %s.",
 946           SafepointTimeoutDelay, VMThread::vm_operation()->name());
 947   }
 948 }
 949 
 950 // -------------------------------------------------------------------------------------------------------
 951 // Implementation of ThreadSafepointState
 952 
 953 ThreadSafepointState::ThreadSafepointState(JavaThread *thread)
 954   : _at_poll_safepoint(false), _thread(thread), _safepoint_safe(false),
 955     _safepoint_id(SafepointSynchronize::InactiveSafepointCounter), _next(NULL) {
 956 }
 957 
 958 void ThreadSafepointState::create(JavaThread *thread) {
 959   ThreadSafepointState *state = new ThreadSafepointState(thread);
 960   thread->set_safepoint_state(state);
 961 }
 962 
 963 void ThreadSafepointState::destroy(JavaThread *thread) {
 964   if (thread->safepoint_state()) {
 965     delete(thread->safepoint_state());
 966     thread->set_safepoint_state(NULL);
 967   }
 968 }
 969 
 970 uint64_t ThreadSafepointState::get_safepoint_id() const {
 971   return Atomic::load_acquire(&_safepoint_id);
 972 }
 973 
 974 void ThreadSafepointState::reset_safepoint_id() {
 975   Atomic::release_store(&_safepoint_id, SafepointSynchronize::InactiveSafepointCounter);
 976 }
 977 
 978 void ThreadSafepointState::set_safepoint_id(uint64_t safepoint_id) {
 979   Atomic::release_store(&_safepoint_id, safepoint_id);
 980 }
 981 
 982 void ThreadSafepointState::examine_state_of_thread(uint64_t safepoint_count) {
 983   assert(is_running(), "better be running or just have hit safepoint poll");
 984 
 985   JavaThreadState stable_state;
 986   if (!SafepointSynchronize::try_stable_load_state(&stable_state, _thread, safepoint_count)) {
 987     // We could not get stable state of the JavaThread.
 988     // Consider it running and just return.
 989     return;
 990   }
 991 
 992   // Check for a thread that is suspended. Note that thread resume tries
 993   // to grab the Threads_lock which we own here, so a thread cannot be
 994   // resumed during safepoint synchronization.
 995 
 996   // We check to see if this thread is suspended without locking to
 997   // avoid deadlocking with a third thread that is waiting for this
 998   // thread to be suspended. The third thread can notice the safepoint
 999   // that we're trying to start at the beginning of its SR_lock->wait()
1000   // call. If that happens, then the third thread will block on the
1001   // safepoint while still holding the underlying SR_lock. We won't be
1002   // able to get the SR_lock and we'll deadlock.
1003   //
1004   // We don't need to grab the SR_lock here for two reasons:
1005   // 1) The suspend flags are both volatile and are set with an
1006   //    Atomic::cmpxchg() call so we should see the suspended
1007   //    state right away.
1008   // 2) We're being called from the safepoint polling loop; if
1009   //    we don't see the suspended state on this iteration, then
1010   //    we'll come around again.
1011   //
1012   bool is_suspended = _thread->is_ext_suspended();
1013   if (is_suspended) {
1014     account_safe_thread();
1015     return;
1016   }
1017 
1018   if (safepoint_safe_with(_thread, stable_state)) {
1019     check_for_lazy_critical_native(_thread, stable_state);
1020     account_safe_thread();
1021     return;
1022   }
1023 
1024   // All other thread states will continue to run until they
1025   // transition and self-block in state _blocked
1026   // Safepoint polling in compiled code causes the Java threads to do the same.
1027   // Note: new threads may require a malloc so they must be allowed to finish
1028 
1029   assert(is_running(), "examine_state_of_thread on non-running thread");
1030   return;
1031 }
1032 
1033 void ThreadSafepointState::account_safe_thread() {
1034   SafepointSynchronize::decrement_waiting_to_block();
1035   if (_thread->in_critical()) {
1036     // Notice that this thread is in a critical section
1037     SafepointSynchronize::increment_jni_active_count();
1038   }
1039   DEBUG_ONLY(_thread->set_visited_for_critical_count(SafepointSynchronize::safepoint_counter());)
1040   assert(!_safepoint_safe, "Must be unsafe before safe");
1041   _safepoint_safe = true;
1042 }
1043 
1044 void ThreadSafepointState::restart() {
1045   assert(_safepoint_safe, "Must be safe before unsafe");
1046   _safepoint_safe = false;
1047 }
1048 
1049 void ThreadSafepointState::print_on(outputStream *st) const {
1050   const char *s = _safepoint_safe ? "_at_safepoint" : "_running";
1051 
1052   st->print_cr("Thread: " INTPTR_FORMAT
1053               "  [0x%2x] State: %s _at_poll_safepoint %d",
1054                p2i(_thread), _thread->osthread()->thread_id(), s, _at_poll_safepoint);
1055 
1056   _thread->print_thread_state_on(st);
1057 }
1058 
1059 // ---------------------------------------------------------------------------------------------------------------------
1060 
1061 // Block the thread at poll or poll return for safepoint/handshake.
1062 void ThreadSafepointState::handle_polling_page_exception() {
1063 
1064   // If we're using a global poll, then the thread should not be
1065   // marked as safepoint safe yet.
1066   assert(!SafepointMechanism::uses_global_page_poll() || !_safepoint_safe,
1067          "polling page exception on thread safepoint safe");
1068 
1069   // Step 1: Find the nmethod from the return address
1070   address real_return_addr = thread()->saved_exception_pc();
1071 
1072   CodeBlob *cb = CodeCache::find_blob(real_return_addr);
1073   assert(cb != NULL && cb->is_compiled(), "return address should be in nmethod");
1074   CompiledMethod* nm = (CompiledMethod*)cb;
1075 
1076   // Find frame of caller
1077   frame stub_fr = thread()->last_frame();
1078   CodeBlob* stub_cb = stub_fr.cb();
1079   assert(stub_cb->is_safepoint_stub(), "must be a safepoint stub");
1080   RegisterMap map(thread(), true);
1081   frame caller_fr = stub_fr.sender(&map);
1082 
1083   // Should only be poll_return or poll
1084   assert( nm->is_at_poll_or_poll_return(real_return_addr), "should not be at call" );
1085 
1086   // This is a poll immediately before a return. The exception handling code
1087   // has already had the effect of causing the return to occur, so the execution
1088   // will continue immediately after the call. In addition, the oopmap at the
1089   // return point does not mark the return value as an oop (if it is), so
1090   // it needs a handle here to be updated.
1091   if( nm->is_at_poll_return(real_return_addr) ) {
1092     // See if return type is an oop.
1093     bool return_oop = nm->method()->is_returning_oop();
1094     Handle return_value;
1095     if (return_oop) {
1096       // The oop result has been saved on the stack together with all
1097       // the other registers. In order to preserve it over GCs we need
1098       // to keep it in a handle.
1099       oop result = caller_fr.saved_oop_result(&map);
1100       assert(oopDesc::is_oop_or_null(result), "must be oop");
1101       return_value = Handle(thread(), result);
1102       assert(Universe::heap()->is_in_or_null(result), "must be heap pointer");
1103     }
1104 
1105     // Block the thread
1106     SafepointMechanism::block_if_requested(thread());
1107 
1108     // restore oop result, if any
1109     if (return_oop) {
1110       caller_fr.set_saved_oop_result(&map, return_value());
1111     }
1112   }
1113 
1114   // This is a safepoint poll. Verify the return address and block.
1115   else {
1116     set_at_poll_safepoint(true);
1117 
1118     // verify the blob built the "return address" correctly
1119     assert(real_return_addr == caller_fr.pc(), "must match");
1120 
1121     // Block the thread
1122     SafepointMechanism::block_if_requested(thread());
1123     set_at_poll_safepoint(false);
1124 
1125     // If we have a pending async exception deoptimize the frame
1126     // as otherwise we may never deliver it.
1127     if (thread()->has_async_condition()) {
1128       ThreadInVMfromJavaNoAsyncException __tiv(thread());
1129       Deoptimization::deoptimize_frame(thread(), caller_fr.id());
1130     }
1131 
1132     // If an exception has been installed we must check for a pending deoptimization
1133     // Deoptimize frame if exception has been thrown.
1134 
1135     if (thread()->has_pending_exception() ) {
1136       RegisterMap map(thread(), true);
1137       frame caller_fr = stub_fr.sender(&map);
1138       if (caller_fr.is_deoptimized_frame()) {
1139         // The exception patch will destroy registers that are still
1140         // live and will be needed during deoptimization. Defer the
1141         // Async exception should have deferred the exception until the
1142         // next safepoint which will be detected when we get into
1143         // the interpreter so if we have an exception now things
1144         // are messed up.
1145 
1146         fatal("Exception installed and deoptimization is pending");
1147       }
1148     }
1149   }
1150 }
1151 
1152 
1153 // -------------------------------------------------------------------------------------------------------
1154 // Implementation of SafepointTracing
1155 
1156 jlong SafepointTracing::_last_safepoint_begin_time_ns = 0;
1157 jlong SafepointTracing::_last_safepoint_sync_time_ns = 0;
1158 jlong SafepointTracing::_last_safepoint_cleanup_time_ns = 0;
1159 jlong SafepointTracing::_last_safepoint_end_time_ns = 0;
1160 jlong SafepointTracing::_last_safepoint_end_time_epoch_ms = 0;
1161 jlong SafepointTracing::_last_app_time_ns = 0;
1162 int SafepointTracing::_nof_threads = 0;
1163 int SafepointTracing::_nof_running = 0;
1164 int SafepointTracing::_page_trap = 0;
1165 VM_Operation::VMOp_Type SafepointTracing::_current_type;
1166 jlong     SafepointTracing::_max_sync_time = 0;
1167 jlong     SafepointTracing::_max_vmop_time = 0;
1168 uint64_t  SafepointTracing::_op_count[VM_Operation::VMOp_Terminating] = {0};
1169 
1170 void SafepointTracing::init() {
1171   // Application start
1172   _last_safepoint_end_time_ns = os::javaTimeNanos();
1173   // amount of time since epoch
1174   _last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
1175 }
1176 
1177 // Helper method to print the header.
1178 static void print_header(outputStream* st) {
1179   // The number of spaces is significant here, and should match the format
1180   // specifiers in print_statistics().
1181 
1182   st->print("VM Operation                 "
1183             "[ threads: total initial_running ]"
1184             "[ time:       sync    cleanup       vmop      total ]");
1185 
1186   st->print_cr(" page_trap_count");
1187 }
1188 
1189 // This prints a nice table.  To get the statistics to not shift due to the logging uptime
1190 // decorator, use the option as: -Xlog:safepoint+stats:[outputfile]:none
1191 void SafepointTracing::statistics_log() {
1192   LogTarget(Info, safepoint, stats) lt;
1193   assert (lt.is_enabled(), "should only be called when printing statistics is enabled");
1194   LogStream ls(lt);
1195 
1196   static int _cur_stat_index = 0;
1197 
1198   // Print header every 30 entries
1199   if ((_cur_stat_index % 30) == 0) {
1200     print_header(&ls);
1201     _cur_stat_index = 1;  // wrap
1202   } else {
1203     _cur_stat_index++;
1204   }
1205 
1206   ls.print("%-28s [       "
1207            INT32_FORMAT_W(8) "        " INT32_FORMAT_W(8) " "
1208            "]",
1209            VM_Operation::name(_current_type),
1210            _nof_threads,
1211            _nof_running);
1212   ls.print("[       "
1213            INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " "
1214            INT64_FORMAT_W(10) " " INT64_FORMAT_W(10) " ]",
1215            (int64_t)(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns),
1216            (int64_t)(_last_safepoint_cleanup_time_ns - _last_safepoint_sync_time_ns),
1217            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns),
1218            (int64_t)(_last_safepoint_end_time_ns - _last_safepoint_begin_time_ns));
1219 
1220   ls.print_cr(INT32_FORMAT_W(16), _page_trap);
1221 }
1222 
1223 // This method will be called when VM exits. This tries to summarize the sampling.
1224 // Current thread may already be deleted, so don't use ResourceMark.
1225 void SafepointTracing::statistics_exit_log() {
1226   if (!log_is_enabled(Info, safepoint, stats)) {
1227     return;
1228   }
1229   for (int index = 0; index < VM_Operation::VMOp_Terminating; index++) {
1230     if (_op_count[index] != 0) {
1231       log_info(safepoint, stats)("%-28s" UINT64_FORMAT_W(10), VM_Operation::name(index),
1232                _op_count[index]);
1233     }
1234   }
1235 
1236   log_info(safepoint, stats)("VM operations coalesced during safepoint " INT64_FORMAT,
1237                               VMThread::get_coalesced_count());
1238   log_info(safepoint, stats)("Maximum sync time  " INT64_FORMAT" ns",
1239                               (int64_t)(_max_sync_time));
1240   log_info(safepoint, stats)("Maximum vm operation time (except for Exit VM operation)  "
1241                               INT64_FORMAT " ns",
1242                               (int64_t)(_max_vmop_time));
1243 }
1244 
1245 void SafepointTracing::begin(VM_Operation::VMOp_Type type) {
1246   _op_count[type]++;
1247   _current_type = type;
1248 
1249   // update the time stamp to begin recording safepoint time
1250   _last_safepoint_begin_time_ns = os::javaTimeNanos();
1251   _last_safepoint_sync_time_ns = 0;
1252   _last_safepoint_cleanup_time_ns = 0;
1253 
1254   _last_app_time_ns = _last_safepoint_begin_time_ns - _last_safepoint_end_time_ns;
1255   _last_safepoint_end_time_ns = 0;
1256 
1257   RuntimeService::record_safepoint_begin(_last_app_time_ns);
1258 }
1259 
1260 void SafepointTracing::synchronized(int nof_threads, int nof_running, int traps) {
1261   _last_safepoint_sync_time_ns = os::javaTimeNanos();
1262   _nof_threads = nof_threads;
1263   _nof_running = nof_running;
1264   _page_trap   = traps;
1265   RuntimeService::record_safepoint_synchronized(_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns);
1266 }
1267 
1268 void SafepointTracing::cleanup() {
1269   _last_safepoint_cleanup_time_ns = os::javaTimeNanos();
1270 }
1271 
1272 void SafepointTracing::end() {
1273   _last_safepoint_end_time_ns = os::javaTimeNanos();
1274   // amount of time since epoch
1275   _last_safepoint_end_time_epoch_ms = os::javaTimeMillis();
1276 
1277   if (_max_sync_time < (_last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns)) {
1278     _max_sync_time = _last_safepoint_sync_time_ns - _last_safepoint_begin_time_ns;
1279   }
1280   if (_max_vmop_time < (_last_safepoint_end_time_ns - _last_safepoint_sync_time_ns)) {
1281     _max_vmop_time = _last_safepoint_end_time_ns - _last_safepoint_sync_time_ns;
1282   }
1283   if (log_is_enabled(Info, safepoint, stats)) {
1284     statistics_log();
1285   }
1286 
1287   log_info(safepoint)(
1288      "Safepoint \"%s\", "
1289      "Time since last: " JLONG_FORMAT " ns, "
1290      "Reaching safepoint: " JLONG_FORMAT " ns, "
1291      "At safepoint: " JLONG_FORMAT " ns, "
1292      "Total: " JLONG_FORMAT " ns",
1293       VM_Operation::name(_current_type),
1294       _last_app_time_ns,
1295       _last_safepoint_cleanup_time_ns - _last_safepoint_begin_time_ns,
1296       _last_safepoint_end_time_ns     - _last_safepoint_cleanup_time_ns,
1297       _last_safepoint_end_time_ns     - _last_safepoint_begin_time_ns
1298      );
1299 
1300   RuntimeService::record_safepoint_end(_last_safepoint_end_time_ns - _last_safepoint_cleanup_time_ns);
1301 }