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 "runtime/mutexLocker.hpp"
  27 #include "runtime/os.inline.hpp"
  28 #include "runtime/safepoint.hpp"
  29 #include "runtime/thread.inline.hpp"
  30 #include "runtime/vmThread.hpp"
  31 
  32 // Mutexes used in the VM (see comment in mutexLocker.hpp):
  33 //
  34 // Note that the following pointers are effectively final -- after having been
  35 // set at JVM startup-time, they should never be subsequently mutated.
  36 // Instead of using pointers to malloc()ed monitors and mutexes we should consider
  37 // eliminating the indirection and using instances instead.
  38 // Consider using GCC's __read_mostly.
  39 
  40 Mutex*   Patching_lock                = NULL;
  41 Monitor* SystemDictionary_lock        = NULL;
  42 Mutex*   ProtectionDomainSet_lock     = NULL;
  43 Mutex*   SharedDictionary_lock        = NULL;
  44 Mutex*   Module_lock                  = NULL;
  45 Mutex*   CompiledIC_lock              = NULL;
  46 Mutex*   InlineCacheBuffer_lock       = NULL;
  47 Mutex*   VMStatistic_lock             = NULL;
  48 Mutex*   JNIGlobalAlloc_lock          = NULL;
  49 Mutex*   JNIGlobalActive_lock         = NULL;
  50 Mutex*   JNIWeakAlloc_lock            = NULL;
  51 Mutex*   JNIWeakActive_lock           = NULL;
  52 Mutex*   StringTableWeakAlloc_lock    = NULL;
  53 Mutex*   StringTableWeakActive_lock   = NULL;
  54 Mutex*   JNIHandleBlockFreeList_lock  = NULL;
  55 Mutex*   VMWeakAlloc_lock             = NULL;
  56 Mutex*   VMWeakActive_lock            = NULL;
  57 Mutex*   ResolvedMethodTableWeakAlloc_lock  = NULL;
  58 Mutex*   ResolvedMethodTableWeakActive_lock = NULL;
  59 Mutex*   JmethodIdCreation_lock       = NULL;
  60 Mutex*   JfieldIdCreation_lock        = NULL;
  61 Monitor* JNICritical_lock             = NULL;
  62 Mutex*   JvmtiThreadState_lock        = NULL;
  63 Monitor* Heap_lock                    = NULL;
  64 Mutex*   ExpandHeap_lock              = NULL;
  65 Mutex*   AdapterHandlerLibrary_lock   = NULL;
  66 Mutex*   SignatureHandlerLibrary_lock = NULL;
  67 Mutex*   VtableStubs_lock             = NULL;
  68 Mutex*   SymbolArena_lock             = NULL;
  69 Monitor* StringDedupQueue_lock        = NULL;
  70 Mutex*   StringDedupTable_lock        = NULL;
  71 Monitor* CodeCache_lock               = NULL;
  72 Mutex*   MethodData_lock              = NULL;
  73 Mutex*   TouchedMethodLog_lock        = NULL;
  74 Mutex*   RetData_lock                 = NULL;
  75 Monitor* VMOperationQueue_lock        = NULL;
  76 Monitor* VMOperationRequest_lock      = NULL;
  77 Monitor* SerializePage_lock           = NULL;
  78 Monitor* Threads_lock                 = NULL;
  79 Mutex*   NonJavaThreadsList_lock      = NULL;
  80 Mutex*   NonJavaThreadsListSync_lock  = NULL;
  81 Monitor* CGC_lock                     = NULL;
  82 Monitor* STS_lock                     = NULL;
  83 Monitor* FullGCCount_lock             = NULL;
  84 Monitor* SATB_Q_CBL_mon               = NULL;
  85 Monitor* DirtyCardQ_CBL_mon           = NULL;
  86 Mutex*   Shared_DirtyCardQ_lock       = NULL;
  87 Mutex*   MarkStackFreeList_lock       = NULL;
  88 Mutex*   MarkStackChunkList_lock      = NULL;
  89 Mutex*   MonitoringSupport_lock       = NULL;
  90 Mutex*   ParGCRareEvent_lock          = NULL;
  91 Mutex*   DerivedPointerTableGC_lock   = NULL;
  92 Monitor* CGCPhaseManager_lock         = NULL;
  93 Mutex*   Compile_lock                 = NULL;
  94 Monitor* MethodCompileQueue_lock      = NULL;
  95 Monitor* CompileThread_lock           = NULL;
  96 Monitor* Compilation_lock             = NULL;
  97 Mutex*   CompileTaskAlloc_lock        = NULL;
  98 Mutex*   CompileStatistics_lock       = NULL;
  99 Mutex*   DirectivesStack_lock         = NULL;
 100 Mutex*   MultiArray_lock              = NULL;
 101 Monitor* Terminator_lock              = NULL;
 102 Monitor* InitCompleted_lock           = NULL;
 103 Monitor* BeforeExit_lock              = NULL;
 104 Monitor* Notify_lock                  = NULL;
 105 Mutex*   ProfilePrint_lock            = NULL;
 106 Mutex*   ExceptionCache_lock          = NULL;
 107 Mutex*   OsrList_lock                 = NULL;
 108 Mutex*   NMethodSweeperStats_lock     = NULL;
 109 #ifndef PRODUCT
 110 Mutex*   FullGCALot_lock              = NULL;
 111 #endif
 112 
 113 Mutex*   Debug1_lock                  = NULL;
 114 Mutex*   Debug2_lock                  = NULL;
 115 Mutex*   Debug3_lock                  = NULL;
 116 
 117 Mutex*   tty_lock                     = NULL;
 118 
 119 Mutex*   RawMonitor_lock              = NULL;
 120 Mutex*   PerfDataMemAlloc_lock        = NULL;
 121 Mutex*   PerfDataManager_lock         = NULL;
 122 Mutex*   OopMapCacheAlloc_lock        = NULL;
 123 
 124 Mutex*   FreeList_lock                = NULL;
 125 Mutex*   OldSets_lock                 = NULL;
 126 Monitor* RootRegionScan_lock          = NULL;
 127 
 128 Monitor* GCTaskManager_lock           = NULL;
 129 
 130 Mutex*   Management_lock              = NULL;
 131 Monitor* Service_lock                 = NULL;
 132 Monitor* PeriodicTask_lock            = NULL;
 133 Monitor* RedefineClasses_lock         = NULL;
 134 
 135 #if INCLUDE_JFR
 136 Mutex*   JfrStacktrace_lock           = NULL;
 137 Monitor* JfrMsg_lock                  = NULL;
 138 Mutex*   JfrBuffer_lock               = NULL;
 139 Mutex*   JfrStream_lock               = NULL;
 140 Monitor* JfrThreadSampler_lock        = NULL;
 141 #endif
 142 
 143 #ifndef SUPPORTS_NATIVE_CX8
 144 Mutex*   UnsafeJlong_lock             = NULL;
 145 #endif
 146 Monitor* CodeHeapStateAnalytics_lock  = NULL;
 147 
 148 Mutex*   MetaspaceExpand_lock         = NULL;
 149 Mutex*   ClassLoaderDataGraph_lock    = NULL;
 150 Monitor* ThreadsSMRDelete_lock        = NULL;
 151 Mutex*   SharedDecoder_lock           = NULL;
 152 Mutex*   DCmdFactory_lock             = NULL;
 153 #if INCLUDE_NMT
 154 Mutex*   NMTQuery_lock                = NULL;
 155 #endif
 156 #if INCLUDE_CDS && INCLUDE_JVMTI
 157 Mutex*   CDSClassFileStream_lock      = NULL;
 158 #endif
 159 
 160 #define MAX_NUM_MUTEX 128
 161 static Monitor * _mutex_array[MAX_NUM_MUTEX];
 162 static int _num_mutex;
 163 
 164 #ifdef ASSERT
 165 void assert_locked_or_safepoint(const Monitor * lock) {
 166   // check if this thread owns the lock (common case)
 167   if (IgnoreLockingAssertions) return;
 168   assert(lock != NULL, "Need non-NULL lock");
 169   if (lock->owned_by_self()) return;
 170   if (SafepointSynchronize::is_at_safepoint()) return;
 171   if (!Universe::is_fully_initialized()) return;
 172   // see if invoker of VM operation owns it
 173   VM_Operation* op = VMThread::vm_operation();
 174   if (op != NULL && op->calling_thread() == lock->owner()) return;
 175   fatal("must own lock %s", lock->name());
 176 }
 177 
 178 // a weaker assertion than the above
 179 void assert_locked_or_safepoint_weak(const Monitor * lock) {
 180   if (IgnoreLockingAssertions) return;
 181   assert(lock != NULL, "Need non-NULL lock");
 182   if (lock->is_locked()) return;
 183   if (SafepointSynchronize::is_at_safepoint()) return;
 184   if (!Universe::is_fully_initialized()) return;
 185   fatal("must own lock %s", lock->name());
 186 }
 187 
 188 // a stronger assertion than the above
 189 void assert_lock_strong(const Monitor * lock) {
 190   if (IgnoreLockingAssertions) return;
 191   assert(lock != NULL, "Need non-NULL lock");
 192   if (lock->owned_by_self()) return;
 193   fatal("must own lock %s", lock->name());
 194 }
 195 #endif
 196 
 197 #define def(var, type, pri, vm_block, safepoint_check_allowed ) {      \
 198   var = new type(Mutex::pri, #var, vm_block, safepoint_check_allowed); \
 199   assert(_num_mutex < MAX_NUM_MUTEX, "increase MAX_NUM_MUTEX");        \
 200   _mutex_array[_num_mutex++] = var;                                      \
 201 }
 202 
 203 // Using Padded subclasses to prevent false sharing of these global monitors and mutexes.
 204 void mutex_init() {
 205   def(tty_lock                     , PaddedMutex  , tty,         true,  Monitor::_safepoint_check_never);      // allow to lock in VM
 206 
 207   def(CGC_lock                     , PaddedMonitor, special,     true,  Monitor::_safepoint_check_never);      // coordinate between fore- and background GC
 208   def(STS_lock                     , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);
 209 
 210   def(VMWeakAlloc_lock             , PaddedMutex  , vmweak,      true,  Monitor::_safepoint_check_never);
 211   def(VMWeakActive_lock            , PaddedMutex  , vmweak-1,    true,  Monitor::_safepoint_check_never);
 212 
 213   def(StringTableWeakAlloc_lock    , PaddedMutex  , vmweak,      true,  Monitor::_safepoint_check_never);
 214   def(StringTableWeakActive_lock   , PaddedMutex  , vmweak-1,    true,  Monitor::_safepoint_check_never);
 215 
 216   def(ResolvedMethodTableWeakAlloc_lock    , PaddedMutex  , vmweak,      true,  Monitor::_safepoint_check_never);
 217   def(ResolvedMethodTableWeakActive_lock   , PaddedMutex  , vmweak-1,    true,  Monitor::_safepoint_check_never);
 218 
 219   if (UseConcMarkSweepGC || UseG1GC) {
 220     def(FullGCCount_lock           , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);      // in support of ExplicitGCInvokesConcurrent
 221   }
 222   if (UseG1GC) {
 223     def(SATB_Q_CBL_mon             , PaddedMonitor, access,      true,  Monitor::_safepoint_check_never);
 224 
 225     def(DirtyCardQ_CBL_mon         , PaddedMonitor, access,      true,  Monitor::_safepoint_check_never);
 226     def(Shared_DirtyCardQ_lock     , PaddedMutex  , access + 1,  true,  Monitor::_safepoint_check_never);
 227 
 228     def(FreeList_lock              , PaddedMutex  , leaf     ,   true,  Monitor::_safepoint_check_never);
 229     def(OldSets_lock               , PaddedMutex  , leaf     ,   true,  Monitor::_safepoint_check_never);
 230     def(RootRegionScan_lock        , PaddedMonitor, leaf     ,   true,  Monitor::_safepoint_check_never);
 231 
 232     def(StringDedupQueue_lock      , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);
 233     def(StringDedupTable_lock      , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 234 
 235     def(MarkStackFreeList_lock     , PaddedMutex  , leaf     ,   true,  Monitor::_safepoint_check_never);
 236     def(MarkStackChunkList_lock    , PaddedMutex  , leaf     ,   true,  Monitor::_safepoint_check_never);
 237 
 238     def(MonitoringSupport_lock     , PaddedMutex  , native   ,   true,  Monitor::_safepoint_check_never);      // used for serviceability monitoring support
 239   }
 240   if (UseShenandoahGC) {
 241     def(SATB_Q_CBL_mon             , PaddedMonitor, access,      true,  Monitor::_safepoint_check_never);
 242 
 243     def(StringDedupQueue_lock      , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);
 244     def(StringDedupTable_lock      , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 245   }
 246   def(ParGCRareEvent_lock          , PaddedMutex  , leaf     ,   true,  Monitor::_safepoint_check_sometimes);
 247   def(DerivedPointerTableGC_lock   , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 248   def(CGCPhaseManager_lock         , PaddedMonitor, leaf,        false, Monitor::_safepoint_check_sometimes);
 249   def(CodeCache_lock               , PaddedMutex  , special,     true,  Monitor::_safepoint_check_never);
 250   def(RawMonitor_lock              , PaddedMutex  , special,     true,  Monitor::_safepoint_check_never);
 251   def(OopMapCacheAlloc_lock        , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // used for oop_map_cache allocation.
 252 
 253   def(MetaspaceExpand_lock         , PaddedMutex  , leaf-1,      true,  Monitor::_safepoint_check_never);
 254   def(ClassLoaderDataGraph_lock    , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_always);
 255 
 256   def(Patching_lock                , PaddedMutex  , special,     true,  Monitor::_safepoint_check_never);      // used for safepointing and code patching.
 257   def(Service_lock                 , PaddedMonitor, special,     true,  Monitor::_safepoint_check_never);      // used for service thread operations
 258   def(JmethodIdCreation_lock       , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // used for creating jmethodIDs.
 259 
 260   def(SystemDictionary_lock        , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_always);     // lookups done by VM thread
 261   def(ProtectionDomainSet_lock     , PaddedMutex  , leaf-1,      true,  Monitor::_safepoint_check_never);
 262   def(SharedDictionary_lock        , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // lookups done by VM thread
 263   def(Module_lock                  , PaddedMutex  , leaf+2,      true,  Monitor::_safepoint_check_always);
 264   def(InlineCacheBuffer_lock       , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 265   def(VMStatistic_lock             , PaddedMutex  , leaf,        false, Monitor::_safepoint_check_always);
 266   def(ExpandHeap_lock              , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // Used during compilation by VM thread
 267   def(JNIHandleBlockFreeList_lock  , PaddedMutex  , leaf-1,      true,  Monitor::_safepoint_check_never);      // handles are used by VM thread
 268   def(SignatureHandlerLibrary_lock , PaddedMutex  , leaf,        false, Monitor::_safepoint_check_always);
 269   def(SymbolArena_lock             , PaddedMutex  , leaf+2,      true,  Monitor::_safepoint_check_never);
 270   def(ProfilePrint_lock            , PaddedMutex  , leaf,        false, Monitor::_safepoint_check_always);     // serial profile printing
 271   def(ExceptionCache_lock          , PaddedMutex  , leaf,        false, Monitor::_safepoint_check_always);     // serial profile printing
 272   def(OsrList_lock                 , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 273   def(Debug1_lock                  , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 274 #ifndef PRODUCT
 275   def(FullGCALot_lock              , PaddedMutex  , leaf,        false, Monitor::_safepoint_check_always);     // a lock to make FullGCALot MT safe
 276 #endif
 277   def(BeforeExit_lock              , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_always);
 278   def(PerfDataMemAlloc_lock        , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // used for allocating PerfData memory for performance data
 279   def(PerfDataManager_lock         , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_always);     // used for synchronized access to PerfDataManager resources
 280 
 281   // CMS_modUnionTable_lock                   leaf
 282   // CMS_bitMap_lock                          leaf 1
 283   // CMS_freeList_lock                        leaf 2
 284 
 285   def(Threads_lock                 , PaddedMonitor, barrier,     true,  Monitor::_safepoint_check_sometimes);
 286   def(NonJavaThreadsList_lock      , PaddedMutex,   leaf,        true,  Monitor::_safepoint_check_never);
 287   def(NonJavaThreadsListSync_lock  , PaddedMutex,   leaf,        true,  Monitor::_safepoint_check_never);
 288 
 289   def(VMOperationQueue_lock        , PaddedMonitor, nonleaf,     true,  Monitor::_safepoint_check_sometimes);  // VM_thread allowed to block on these
 290   def(VMOperationRequest_lock      , PaddedMonitor, nonleaf,     true,  Monitor::_safepoint_check_sometimes);
 291   def(RetData_lock                 , PaddedMutex  , nonleaf,     false, Monitor::_safepoint_check_always);
 292   def(Terminator_lock              , PaddedMonitor, nonleaf,     true,  Monitor::_safepoint_check_sometimes);
 293   def(InitCompleted_lock           , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);
 294   def(VtableStubs_lock             , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_never);
 295   def(Notify_lock                  , PaddedMonitor, nonleaf,     true,  Monitor::_safepoint_check_always);
 296   def(JNIGlobalAlloc_lock          , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_never);
 297   def(JNIGlobalActive_lock         , PaddedMutex  , nonleaf-1,   true,  Monitor::_safepoint_check_never);
 298   def(JNIWeakAlloc_lock            , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_never);
 299   def(JNIWeakActive_lock           , PaddedMutex  , nonleaf-1,   true,  Monitor::_safepoint_check_never);
 300   def(JNICritical_lock             , PaddedMonitor, nonleaf,     true,  Monitor::_safepoint_check_always);     // used for JNI critical regions
 301   def(AdapterHandlerLibrary_lock   , PaddedMutex  , nonleaf,     true,  Monitor::_safepoint_check_always);
 302 
 303   def(Heap_lock                    , PaddedMonitor, nonleaf+1,   false, Monitor::_safepoint_check_sometimes);
 304   def(JfieldIdCreation_lock        , PaddedMutex  , nonleaf+1,   true,  Monitor::_safepoint_check_always);     // jfieldID, Used in VM_Operation
 305 
 306   def(CompiledIC_lock              , PaddedMutex  , nonleaf+2,   false, Monitor::_safepoint_check_never);      // locks VtableStubs_lock, InlineCacheBuffer_lock
 307   def(CompileTaskAlloc_lock        , PaddedMutex  , nonleaf+2,   true,  Monitor::_safepoint_check_always);
 308   def(CompileStatistics_lock       , PaddedMutex  , nonleaf+2,   false, Monitor::_safepoint_check_always);
 309   def(DirectivesStack_lock         , PaddedMutex  , special,     true,  Monitor::_safepoint_check_never);
 310   def(MultiArray_lock              , PaddedMutex  , nonleaf+2,   false, Monitor::_safepoint_check_always);
 311 
 312   def(JvmtiThreadState_lock        , PaddedMutex  , nonleaf+2,   false, Monitor::_safepoint_check_always);     // Used by JvmtiThreadState/JvmtiEventController
 313   def(Management_lock              , PaddedMutex  , nonleaf+2,   false, Monitor::_safepoint_check_always);     // used for JVM management
 314 
 315   def(Compile_lock                 , PaddedMutex  , nonleaf+3,   true,  Monitor::_safepoint_check_always);
 316   def(MethodData_lock              , PaddedMutex  , nonleaf+3,   false, Monitor::_safepoint_check_always);
 317   def(TouchedMethodLog_lock        , PaddedMutex  , nonleaf+3,   false, Monitor::_safepoint_check_always);
 318 
 319   def(MethodCompileQueue_lock      , PaddedMonitor, nonleaf+4,   true,  Monitor::_safepoint_check_always);
 320   def(Debug2_lock                  , PaddedMutex  , nonleaf+4,   true,  Monitor::_safepoint_check_never);
 321   def(Debug3_lock                  , PaddedMutex  , nonleaf+4,   true,  Monitor::_safepoint_check_never);
 322   def(CompileThread_lock           , PaddedMonitor, nonleaf+5,   false, Monitor::_safepoint_check_always);
 323   def(PeriodicTask_lock            , PaddedMonitor, nonleaf+5,   true,  Monitor::_safepoint_check_sometimes);
 324   def(RedefineClasses_lock         , PaddedMonitor, nonleaf+5,   true,  Monitor::_safepoint_check_always);
 325 
 326   if (WhiteBoxAPI) {
 327     def(Compilation_lock           , PaddedMonitor, leaf,        false, Monitor::_safepoint_check_never);
 328   }
 329 
 330 #if INCLUDE_JFR
 331   def(JfrMsg_lock                  , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_always);
 332   def(JfrBuffer_lock               , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 333   def(JfrStream_lock               , PaddedMutex  , leaf+1,      true,  Monitor::_safepoint_check_never);      // ensure to rank lower than 'safepoint'
 334   def(JfrStacktrace_lock           , PaddedMutex  , special,     true,  Monitor::_safepoint_check_sometimes);
 335   def(JfrThreadSampler_lock        , PaddedMonitor, leaf,        true,  Monitor::_safepoint_check_never);
 336 #endif
 337 
 338 #ifndef SUPPORTS_NATIVE_CX8
 339   def(UnsafeJlong_lock             , PaddedMutex  , special,     false, Monitor::_safepoint_check_never);
 340 #endif
 341 
 342   def(CodeHeapStateAnalytics_lock  , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 343 
 344   def(NMethodSweeperStats_lock     , PaddedMutex  , special,     true,  Monitor::_safepoint_check_sometimes);
 345   def(ThreadsSMRDelete_lock        , PaddedMonitor, special,     false, Monitor::_safepoint_check_never);
 346   def(SharedDecoder_lock           , PaddedMutex  , native,      false, Monitor::_safepoint_check_never);
 347   def(DCmdFactory_lock             , PaddedMutex  , leaf,        true,  Monitor::_safepoint_check_never);
 348 #if INCLUDE_NMT
 349   def(NMTQuery_lock                , PaddedMutex  , max_nonleaf, false, Monitor::_safepoint_check_always);
 350 #endif
 351 #if INCLUDE_CDS && INCLUDE_JVMTI
 352   def(CDSClassFileStream_lock      , PaddedMutex  , max_nonleaf, false, Monitor::_safepoint_check_always);
 353 #endif
 354 }
 355 
 356 GCMutexLocker::GCMutexLocker(Monitor * mutex) {
 357   if (SafepointSynchronize::is_at_safepoint()) {
 358     _locked = false;
 359   } else {
 360     _mutex = mutex;
 361     _locked = true;
 362     _mutex->lock();
 363   }
 364 }
 365 
 366 // Print all mutexes/monitors that are currently owned by a thread; called
 367 // by fatal error handler.
 368 void print_owned_locks_on_error(outputStream* st) {
 369   st->print("VM Mutex/Monitor currently owned by a thread: ");
 370   bool none = true;
 371   for (int i = 0; i < _num_mutex; i++) {
 372      // see if it has an owner
 373      if (_mutex_array[i]->owner() != NULL) {
 374        if (none) {
 375           // print format used by Mutex::print_on_error()
 376           st->print_cr(" ([mutex/lock_event])");
 377           none = false;
 378        }
 379        _mutex_array[i]->print_on_error(st);
 380        st->cr();
 381      }
 382   }
 383   if (none) st->print_cr("None");
 384 }