1 /*

     2  * Copyright 1998-2007 Sun Microsystems, Inc.  All Rights Reserved.

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

     4  *

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

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

     7  * published by the Free Software Foundation.

     8  *

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

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

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

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

    13  * accompanied this code).

    14  *

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

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

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

    18  *

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

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

    21  * have any questions.

    22  *

    23  */

    24 

    25 # include "incls/_precompiled.incl"

    26 # include "incls/_vmThread.cpp.incl"

    27 

    28 // Dummy VM operation to act as first element in our circular double-linked list

    29 class VM_Dummy: public VM_Operation {

    30   VMOp_Type type() const { return VMOp_Dummy; }

    31   void  doit() {};

    32 };

    33 

    34 VMOperationQueue::VMOperationQueue() {

    35   // The queue is a circular doubled-linked list, which always contains

    36   // one element (i.e., one element means empty).

    37   for(int i = 0; i < nof_priorities; i++) {

    38     _queue_length[i] = 0;

    39     _queue_counter = 0;

    40     _queue[i] = new VM_Dummy();

    41     _queue[i]->set_next(_queue[i]);

    42     _queue[i]->set_prev(_queue[i]);

    43   }

    44   _drain_list = NULL;

    45 }

    46 

    47 

    48 bool VMOperationQueue::queue_empty(int prio) {

    49   // It is empty if there is exactly one element

    50   bool empty = (_queue[prio] == _queue[prio]->next());

    51   assert( (_queue_length[prio] == 0 && empty) ||

    52           (_queue_length[prio] > 0  && !empty), "sanity check");

    53   return _queue_length[prio] == 0;

    54 }

    55 

    56 // Inserts an element to the right of the q element

    57 void VMOperationQueue::insert(VM_Operation* q, VM_Operation* n) {

    58   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");

    59   n->set_prev(q);

    60   n->set_next(q->next());

    61   q->next()->set_prev(n);

    62   q->set_next(n);

    63 }

    64 

    65 void VMOperationQueue::queue_add_front(int prio, VM_Operation *op) {

    66   _queue_length[prio]++;

    67   insert(_queue[prio]->next(), op);

    68 }

    69 

    70 void VMOperationQueue::queue_add_back(int prio, VM_Operation *op) {

    71   _queue_length[prio]++;

    72   insert(_queue[prio]->prev(), op);

    73 }

    74 

    75 

    76 void VMOperationQueue::unlink(VM_Operation* q) {

    77   assert(q->next()->prev() == q && q->prev()->next() == q, "sanity check");

    78   q->prev()->set_next(q->next());

    79   q->next()->set_prev(q->prev());

    80 }

    81 

    82 VM_Operation* VMOperationQueue::queue_remove_front(int prio) {

    83   if (queue_empty(prio)) return NULL;

    84   assert(_queue_length[prio] >= 0, "sanity check");

    85   _queue_length[prio]--;

    86   VM_Operation* r = _queue[prio]->next();

    87   assert(r != _queue[prio], "cannot remove base element");

    88   unlink(r);

    89   return r;

    90 }

    91 

    92 VM_Operation* VMOperationQueue::queue_drain(int prio) {

    93   if (queue_empty(prio)) return NULL;

    94   DEBUG_ONLY(int length = _queue_length[prio];);

    95   assert(length >= 0, "sanity check");

    96   _queue_length[prio] = 0;

    97   VM_Operation* r = _queue[prio]->next();

    98   assert(r != _queue[prio], "cannot remove base element");

    99   // remove links to base element from head and tail

   100   r->set_prev(NULL);

   101   _queue[prio]->prev()->set_next(NULL);

   102   // restore queue to empty state

   103   _queue[prio]->set_next(_queue[prio]);

   104   _queue[prio]->set_prev(_queue[prio]);

   105   assert(queue_empty(prio), "drain corrupted queue")

   106 #ifdef DEBUG

   107   int len = 0;

   108   VM_Operation* cur;

   109   for(cur = r; cur != NULL; cur=cur->next()) len++;

   110   assert(len == length, "drain lost some ops");

   111 #endif

   112   return r;

   113 }

   114 

   115 void VMOperationQueue::queue_oops_do(int queue, OopClosure* f) {

   116   VM_Operation* cur = _queue[queue];

   117   cur = cur->next();

   118   while (cur != _queue[queue]) {

   119     cur->oops_do(f);

   120     cur = cur->next();

   121   }

   122 }

   123 

   124 void VMOperationQueue::drain_list_oops_do(OopClosure* f) {

   125   VM_Operation* cur = _drain_list;

   126   while (cur != NULL) {

   127     cur->oops_do(f);

   128     cur = cur->next();

   129   }

   130 }

   131 

   132 //-----------------------------------------------------------------

   133 // High-level interface

   134 bool VMOperationQueue::add(VM_Operation *op) {

   135   // Encapsulates VM queue policy. Currently, that

   136   // only involves putting them on the right list

   137   if (op->evaluate_at_safepoint()) {

   138     queue_add_back(SafepointPriority, op);

   139     return true;

   140   }

   141 

   142   queue_add_back(MediumPriority, op);

   143   return true;

   144 }

   145 

   146 VM_Operation* VMOperationQueue::remove_next() {

   147   // Assuming VMOperation queue is two-level priority queue. If there are

   148   // more than two priorities, we need a different scheduling algorithm.

   149   assert(SafepointPriority == 0 && MediumPriority == 1 && nof_priorities == 2,

   150          "current algorithm does not work");

   151 

   152   // simple counter based scheduling to prevent starvation of lower priority

   153   // queue. -- see 4390175

   154   int high_prio, low_prio;

   155   if (_queue_counter++ < 10) {

   156       high_prio = SafepointPriority;

   157       low_prio  = MediumPriority;

   158   } else {

   159       _queue_counter = 0;

   160       high_prio = MediumPriority;

   161       low_prio  = SafepointPriority;

   162   }

   163 

   164   return queue_remove_front(queue_empty(high_prio) ? low_prio : high_prio);

   165 }

   166 

   167 void VMOperationQueue::oops_do(OopClosure* f) {

   168   for(int i = 0; i < nof_priorities; i++) {

   169     queue_oops_do(i, f);

   170   }

   171   drain_list_oops_do(f);

   172 }

   173 

   174 

   175 //------------------------------------------------------------------------------------------------------------------

   176 // Implementation of VMThread stuff

   177 

   178 bool                VMThread::_should_terminate   = false;

   179 bool              VMThread::_terminated         = false;

   180 Monitor*          VMThread::_terminate_lock     = NULL;

   181 VMThread*         VMThread::_vm_thread          = NULL;

   182 VM_Operation*     VMThread::_cur_vm_operation   = NULL;

   183 VMOperationQueue* VMThread::_vm_queue           = NULL;

   184 PerfCounter*      VMThread::_perf_accumulated_vm_operation_time = NULL;

   185 

   186 

   187 void VMThread::create() {

   188   assert(vm_thread() == NULL, "we can only allocate one VMThread");

   189   _vm_thread = new VMThread();

   190 

   191   // Create VM operation queue

   192   _vm_queue = new VMOperationQueue();

   193   guarantee(_vm_queue != NULL, "just checking");

   194 

   195   _terminate_lock = new Monitor(Mutex::safepoint, "VMThread::_terminate_lock", true);

   196 

   197   if (UsePerfData) {

   198     // jvmstat performance counters

   199     Thread* THREAD = Thread::current();

   200     _perf_accumulated_vm_operation_time =

   201                  PerfDataManager::create_counter(SUN_THREADS, "vmOperationTime",

   202                                                  PerfData::U_Ticks, CHECK);

   203   }

   204 }

   205 

   206 

   207 VMThread::VMThread() : Thread() {

   208   // nothing to do

   209 }

   210 

   211 void VMThread::destroy() {

   212   if (_vm_thread != NULL) {

   213     delete _vm_thread;

   214     _vm_thread = NULL;      // VM thread is gone

   215   }

   216 }

   217 

   218 void VMThread::run() {

   219   assert(this == vm_thread(), "check");

   220 

   221   this->initialize_thread_local_storage();

   222   this->record_stack_base_and_size();

   223   // Notify_lock wait checks on active_handles() to rewait in

   224   // case of spurious wakeup, it should wait on the last

   225   // value set prior to the notify

   226   this->set_active_handles(JNIHandleBlock::allocate_block());

   227 

   228   {

   229     MutexLocker ml(Notify_lock);

   230     Notify_lock->notify();

   231   }

   232   // Notify_lock is destroyed by Threads::create_vm()

   233 

   234   int prio = (VMThreadPriority == -1)

   235     ? os::java_to_os_priority[NearMaxPriority]

   236     : VMThreadPriority;

   237   // Note that I cannot call os::set_priority because it expects Java

   238   // priorities and I am *explicitly* using OS priorities so that it's

   239   // possible to set the VM thread priority higher than any Java thread.

   240   os::set_native_priority( this, prio );

   241 

   242   // Wait for VM_Operations until termination

   243   this->loop();

   244 

   245   // Note the intention to exit before safepointing.

   246   // 6295565  This has the effect of waiting for any large tty

   247   // outputs to finish.

   248   if (xtty != NULL) {

   249     ttyLocker ttyl;

   250     xtty->begin_elem("destroy_vm");

   251     xtty->stamp();

   252     xtty->end_elem();

   253     assert(should_terminate(), "termination flag must be set");

   254   }

   255 

   256   // 4526887 let VM thread exit at Safepoint

   257   SafepointSynchronize::begin();

   258 

   259   if (VerifyBeforeExit) {

   260     HandleMark hm(VMThread::vm_thread());

   261     // Among other things, this ensures that Eden top is correct.

   262     Universe::heap()->prepare_for_verify();

   263     os::check_heap();

   264     Universe::verify(true, true); // Silent verification to not polute normal output

   265   }

   266 

   267   CompileBroker::set_should_block();

   268 

   269   // wait for threads (compiler threads or daemon threads) in the

   270   // _thread_in_native state to block.

   271   VM_Exit::wait_for_threads_in_native_to_block();

   272 

   273   // signal other threads that VM process is gone

   274   {

   275     // Note: we must have the _no_safepoint_check_flag. Mutex::lock() allows

   276     // VM thread to enter any lock at Safepoint as long as its _owner is NULL.

   277     // If that happens after _terminate_lock->wait() has unset _owner

   278     // but before it actually drops the lock and waits, the notification below

   279     // may get lost and we will have a hang. To avoid this, we need to use

   280     // Mutex::lock_without_safepoint_check().

   281     MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);

   282     _terminated = true;

   283     _terminate_lock->notify();

   284   }

   285 

   286   // Deletion must be done synchronously by the JNI DestroyJavaVM thread

   287   // so that the VMThread deletion completes before the main thread frees

   288   // up the CodeHeap.

   289 

   290 }

   291 

   292 

   293 // Notify the VMThread that the last non-daemon JavaThread has terminated,

   294 // and wait until operation is performed.

   295 void VMThread::wait_for_vm_thread_exit() {

   296   { MutexLocker mu(VMOperationQueue_lock);

   297     _should_terminate = true;

   298     VMOperationQueue_lock->notify();

   299   }

   300 

   301   // Note: VM thread leaves at Safepoint. We are not stopped by Safepoint

   302   // because this thread has been removed from the threads list. But anything

   303   // that could get blocked by Safepoint should not be used after this point,

   304   // otherwise we will hang, since there is no one can end the safepoint.

   305 

   306   // Wait until VM thread is terminated

   307   // Note: it should be OK to use Terminator_lock here. But this is called

   308   // at a very delicate time (VM shutdown) and we are operating in non- VM

   309   // thread at Safepoint. It's safer to not share lock with other threads.

   310   { MutexLockerEx ml(_terminate_lock, Mutex::_no_safepoint_check_flag);

   311     while(!VMThread::is_terminated()) {

   312         _terminate_lock->wait(Mutex::_no_safepoint_check_flag);

   313     }

   314   }

   315 }

   316 

   317 void VMThread::print_on(outputStream* st) const {

   318   st->print("\"%s\" ", name());

   319   Thread::print_on(st);

   320   st->cr();

   321 }

   322 

   323 void VMThread::evaluate_operation(VM_Operation* op) {

   324   ResourceMark rm;

   325 

   326   {

   327     PerfTraceTime vm_op_timer(perf_accumulated_vm_operation_time());

   328     op->evaluate();

   329   }

   330 

   331   // Last access of info in _cur_vm_operation!

   332   bool c_heap_allocated = op->is_cheap_allocated();

   333 

   334   // Mark as completed

   335   if (!op->evaluate_concurrently()) {

   336     op->calling_thread()->increment_vm_operation_completed_count();

   337   }

   338   // It is unsafe to access the _cur_vm_operation after the 'increment_vm_operation_completed_count' call,

   339   // since if it is stack allocated the calling thread might have deallocated

   340   if (c_heap_allocated) {

   341     delete _cur_vm_operation;

   342   }

   343 }

   344 

   345 

   346 void VMThread::loop() {

   347   assert(_cur_vm_operation == NULL, "no current one should be executing");

   348 

   349   while(true) {

   350     VM_Operation* safepoint_ops = NULL;

   351     //

   352     // Wait for VM operation

   353     //

   354     // use no_safepoint_check to get lock without attempting to "sneak"

   355     { MutexLockerEx mu_queue(VMOperationQueue_lock,

   356                              Mutex::_no_safepoint_check_flag);

   357 

   358       // Look for new operation

   359       assert(_cur_vm_operation == NULL, "no current one should be executing");

   360       _cur_vm_operation = _vm_queue->remove_next();

   361 

   362       // Stall time tracking code

   363       if (PrintVMQWaitTime && _cur_vm_operation != NULL &&

   364           !_cur_vm_operation->evaluate_concurrently()) {

   365         long stall = os::javaTimeMillis() - _cur_vm_operation->timestamp();

   366         if (stall > 0)

   367           tty->print_cr("%s stall: %Ld",  _cur_vm_operation->name(), stall);

   368       }

   369 

   370       while (!should_terminate() && _cur_vm_operation == NULL) {

   371         // wait with a timeout to guarantee safepoints at regular intervals

   372         bool timedout =

   373           VMOperationQueue_lock->wait(Mutex::_no_safepoint_check_flag,

   374                                       GuaranteedSafepointInterval);

   375 

   376         // Support for self destruction

   377         if ((SelfDestructTimer != 0) && !is_error_reported() &&

   378             (os::elapsedTime() > SelfDestructTimer * 60)) {

   379           tty->print_cr("VM self-destructed");

   380           exit(-1);

   381         }

   382 

   383         if (timedout && (SafepointALot ||

   384                          SafepointSynchronize::is_cleanup_needed())) {

   385           MutexUnlockerEx mul(VMOperationQueue_lock,

   386                               Mutex::_no_safepoint_check_flag);

   387           // Force a safepoint since we have not had one for at least

   388           // 'GuaranteedSafepointInterval' milliseconds.  This will run all

   389           // the clean-up processing that needs to be done regularly at a

   390           // safepoint

   391           SafepointSynchronize::begin();

   392           #ifdef ASSERT

   393             if (GCALotAtAllSafepoints) InterfaceSupport::check_gc_alot();

   394           #endif

   395           SafepointSynchronize::end();

   396         }

   397         _cur_vm_operation = _vm_queue->remove_next();

   398 

   399         // If we are at a safepoint we will evaluate all the operations that

   400         // follow that also require a safepoint

   401         if (_cur_vm_operation != NULL &&

   402             _cur_vm_operation->evaluate_at_safepoint()) {

   403           safepoint_ops = _vm_queue->drain_at_safepoint_priority();

   404         }

   405       }

   406 

   407       if (should_terminate()) break;

   408     } // Release mu_queue_lock

   409 

   410     //

   411     // Execute VM operation

   412     //

   413     { HandleMark hm(VMThread::vm_thread());

   414 

   415       EventMark em("Executing VM operation: %s", vm_operation()->name());

   416       assert(_cur_vm_operation != NULL, "we should have found an operation to execute");

   417 

   418       // Give the VM thread an extra quantum.  Jobs tend to be bursty and this

   419       // helps the VM thread to finish up the job.

   420       // FIXME: When this is enabled and there are many threads, this can degrade

   421       // performance significantly.

   422       if( VMThreadHintNoPreempt )

   423         os::hint_no_preempt();

   424 

   425       // If we are at a safepoint we will evaluate all the operations that

   426       // follow that also require a safepoint

   427       if (_cur_vm_operation->evaluate_at_safepoint()) {

   428 

   429         if (PrintGCApplicationConcurrentTime) {

   430            gclog_or_tty->print_cr("Application time: %3.7f seconds",

   431                                   RuntimeService::last_application_time_sec());

   432         }

   433 

   434         _vm_queue->set_drain_list(safepoint_ops); // ensure ops can be scanned

   435 

   436         SafepointSynchronize::begin();

   437         evaluate_operation(_cur_vm_operation);

   438         // now process all queued safepoint ops, iteratively draining

   439         // the queue until there are none left

   440         do {

   441           _cur_vm_operation = safepoint_ops;

   442           if (_cur_vm_operation != NULL) {

   443             do {

   444               // evaluate_operation deletes the op object so we have

   445               // to grab the next op now

   446               VM_Operation* next = _cur_vm_operation->next();

   447               _vm_queue->set_drain_list(next);

   448               evaluate_operation(_cur_vm_operation);

   449               _cur_vm_operation = next;

   450               if (PrintSafepointStatistics) {

   451                 SafepointSynchronize::inc_vmop_coalesced_count();

   452               }

   453             } while (_cur_vm_operation != NULL);

   454           }

   455           // There is a chance that a thread enqueued a safepoint op

   456           // since we released the op-queue lock and initiated the safepoint.

   457           // So we drain the queue again if there is anything there, as an

   458           // optimization to try and reduce the number of safepoints.

   459           // As the safepoint synchronizes us with JavaThreads we will see

   460           // any enqueue made by a JavaThread, but the peek will not

   461           // necessarily detect a concurrent enqueue by a GC thread, but

   462           // that simply means the op will wait for the next major cycle of the

   463           // VMThread - just as it would if the GC thread lost the race for

   464           // the lock.

   465           if (_vm_queue->peek_at_safepoint_priority()) {

   466             // must hold lock while draining queue

   467             MutexLockerEx mu_queue(VMOperationQueue_lock,

   468                                      Mutex::_no_safepoint_check_flag);

   469             safepoint_ops = _vm_queue->drain_at_safepoint_priority();

   470           } else {

   471             safepoint_ops = NULL;

   472           }

   473         } while(safepoint_ops != NULL);

   474 

   475         _vm_queue->set_drain_list(NULL);

   476 

   477         // Complete safepoint synchronization

   478         SafepointSynchronize::end();

   479 

   480         if (PrintGCApplicationStoppedTime) {

   481           gclog_or_tty->print_cr("Total time for which application threads "

   482                                  "were stopped: %3.7f seconds",

   483                                  RuntimeService::last_safepoint_time_sec());

   484         }

   485 

   486       } else {  // not a safepoint operation

   487         if (TraceLongCompiles) {

   488           elapsedTimer t;

   489           t.start();

   490           evaluate_operation(_cur_vm_operation);

   491           t.stop();

   492           double secs = t.seconds();

   493           if (secs * 1e3 > LongCompileThreshold) {

   494             // XXX - _cur_vm_operation should not be accessed after

   495             // the completed count has been incremented; the waiting

   496             // thread may have already freed this memory.

   497             tty->print_cr("vm %s: %3.7f secs]", _cur_vm_operation->name(), secs);

   498           }

   499         } else {

   500           evaluate_operation(_cur_vm_operation);

   501         }

   502 

   503         _cur_vm_operation = NULL;

   504       }

   505     }

   506 

   507     //

   508     //  Notify (potential) waiting Java thread(s) - lock without safepoint

   509     //  check so that sneaking is not possible

   510     { MutexLockerEx mu(VMOperationRequest_lock,

   511                        Mutex::_no_safepoint_check_flag);

   512       VMOperationRequest_lock->notify_all();

   513     }

   514 

   515     //

   516     // We want to make sure that we get to a safepoint regularly.

   517     //

   518     if (SafepointALot || SafepointSynchronize::is_cleanup_needed()) {

   519       long interval          = SafepointSynchronize::last_non_safepoint_interval();

   520       bool max_time_exceeded = GuaranteedSafepointInterval != 0 && (interval > GuaranteedSafepointInterval);

   521       if (SafepointALot || max_time_exceeded) {

   522         HandleMark hm(VMThread::vm_thread());

   523         SafepointSynchronize::begin();

   524         SafepointSynchronize::end();

   525       }

   526     }

   527   }

   528 }

   529 

   530 void VMThread::execute(VM_Operation* op) {

   531   Thread* t = Thread::current();

   532 

   533   if (!t->is_VM_thread()) {

   534     // JavaThread or WatcherThread

   535     t->check_for_valid_safepoint_state(true);

   536 

   537     // New request from Java thread, evaluate prologue

   538     if (!op->doit_prologue()) {

   539       return;   // op was cancelled

   540     }

   541 

   542     // Setup VM_operations for execution

   543     op->set_calling_thread(t, Thread::get_priority(t));

   544 

   545     // It does not make sense to execute the epilogue, if the VM operation object is getting

   546     // deallocated by the VM thread.

   547     bool concurrent     = op->evaluate_concurrently();

   548     bool execute_epilog = !op->is_cheap_allocated();

   549     assert(!concurrent || op->is_cheap_allocated(), "concurrent => cheap_allocated");

   550 

   551     // Get ticket number for non-concurrent VM operations

   552     int ticket = 0;

   553     if (!concurrent) {

   554       ticket = t->vm_operation_ticket();

   555     }

   556 

   557     // Add VM operation to list of waiting threads. We are guaranteed not to block while holding the

   558     // VMOperationQueue_lock, so we can block without a safepoint check. This allows vm operation requests

   559     // to be queued up during a safepoint synchronization.

   560     {

   561       VMOperationQueue_lock->lock_without_safepoint_check();

   562       bool ok = _vm_queue->add(op);

   563       op->set_timestamp(os::javaTimeMillis());

   564       VMOperationQueue_lock->notify();

   565       VMOperationQueue_lock->unlock();

   566       // VM_Operation got skipped

   567       if (!ok) {

   568         assert(concurrent, "can only skip concurrent tasks");

   569         if (op->is_cheap_allocated()) delete op;

   570         return;

   571       }

   572     }

   573 

   574     if (!concurrent) {

   575       // Wait for completion of request (non-concurrent)

   576       // Note: only a JavaThread triggers the safepoint check when locking

   577       MutexLocker mu(VMOperationRequest_lock);

   578       while(t->vm_operation_completed_count() < ticket) {

   579         VMOperationRequest_lock->wait(!t->is_Java_thread());

   580       }

   581     }

   582 

   583     if (execute_epilog) {

   584       op->doit_epilogue();

   585     }

   586   } else {

   587     // invoked by VM thread; usually nested VM operation

   588     assert(t->is_VM_thread(), "must be a VM thread");

   589     VM_Operation* prev_vm_operation = vm_operation();

   590     if (prev_vm_operation != NULL) {

   591       // Check the VM operation allows nested VM operation. This normally not the case, e.g., the compiler

   592       // does not allow nested scavenges or compiles.

   593       if (!prev_vm_operation->allow_nested_vm_operations()) {

   594         fatal2("Nested VM operation %s requested by operation %s", op->name(), vm_operation()->name());

   595       }

   596       op->set_calling_thread(prev_vm_operation->calling_thread(), prev_vm_operation->priority());

   597     }

   598 

   599     EventMark em("Executing %s VM operation: %s", prev_vm_operation ? "nested" : "", op->name());

   600 

   601     // Release all internal handles after operation is evaluated

   602     HandleMark hm(t);

   603     _cur_vm_operation = op;

   604 

   605     if (op->evaluate_at_safepoint() && !SafepointSynchronize::is_at_safepoint()) {

   606       SafepointSynchronize::begin();

   607       op->evaluate();

   608       SafepointSynchronize::end();

   609     } else {

   610       op->evaluate();

   611     }

   612 

   613     // Free memory if needed

   614     if (op->is_cheap_allocated()) delete op;

   615 

   616     _cur_vm_operation = prev_vm_operation;

   617   }

   618 }

   619 

   620 

   621 void VMThread::oops_do(OopClosure* f) {

   622   Thread::oops_do(f);

   623   _vm_queue->oops_do(f);

   624 }

   625 

   626 //------------------------------------------------------------------------------------------------------------------

   627 #ifndef PRODUCT

   628 

   629 void VMOperationQueue::verify_queue(int prio) {

   630   // Check that list is correctly linked

   631   int length = _queue_length[prio];

   632   VM_Operation *cur = _queue[prio];

   633   int i;

   634 

   635   // Check forward links

   636   for(i = 0; i < length; i++) {

   637     cur = cur->next();

   638     assert(cur != _queue[prio], "list to short (forward)");

   639   }

   640   assert(cur->next() == _queue[prio], "list to long (forward)");

   641 

   642   // Check backwards links

   643   cur = _queue[prio];

   644   for(i = 0; i < length; i++) {

   645     cur = cur->prev();

   646     assert(cur != _queue[prio], "list to short (backwards)");

   647   }

   648   assert(cur->prev() == _queue[prio], "list to long (backwards)");

   649 }

   650 

   651 #endif

   652 

   653 void VMThread::verify() {

   654   oops_do(&VerifyOopClosure::verify_oop);

   655 }