1 /*
  2  * Copyright (c) 1997, 2023, 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 "gc/shared/gc_globals.hpp"
 27 #include "logging/log.hpp"
 28 #include "logging/logStream.hpp"
 29 #include "memory/resourceArea.hpp"
 30 #include "memory/universe.hpp"
 31 #include "runtime/javaThread.hpp"
 32 #include "runtime/mutexLocker.hpp"
 33 #include "runtime/safepoint.hpp"
 34 #include "runtime/vmThread.hpp"
 35 #include "utilities/vmError.hpp"
 36 
 37 // Mutexes used in the VM (see comment in mutexLocker.hpp):
 38 
 39 Mutex*   Patching_lock                = nullptr;
 40 Mutex*   CompiledMethod_lock          = nullptr;
 41 Monitor* SystemDictionary_lock        = nullptr;
 42 Mutex*   InvokeMethodTypeTable_lock   = nullptr;
 43 Monitor* InvokeMethodIntrinsicTable_lock = nullptr;
 44 Mutex*   SharedDictionary_lock        = nullptr;
 45 Monitor* ClassInitError_lock          = nullptr;
 46 Mutex*   Module_lock                  = nullptr;
 47 Mutex*   CompiledIC_lock              = nullptr;
 48 Mutex*   InlineCacheBuffer_lock       = nullptr;
 49 Mutex*   VMStatistic_lock             = nullptr;
 50 Mutex*   JmethodIdCreation_lock       = nullptr;
 51 Mutex*   JfieldIdCreation_lock        = nullptr;
 52 Monitor* JNICritical_lock             = nullptr;
 53 Mutex*   JvmtiThreadState_lock        = nullptr;
 54 Monitor* EscapeBarrier_lock           = nullptr;
 55 Monitor* JvmtiVTMSTransition_lock     = nullptr;
 56 Monitor* Heap_lock                    = nullptr;
 57 #ifdef INCLUDE_PARALLELGC
 58 Mutex*   PSOldGenExpand_lock      = nullptr;
 59 #endif
 60 Mutex*   AdapterHandlerLibrary_lock   = nullptr;
 61 Mutex*   SignatureHandlerLibrary_lock = nullptr;
 62 Mutex*   VtableStubs_lock             = nullptr;
 63 Mutex*   SymbolArena_lock             = nullptr;
 64 Monitor* StringDedup_lock             = nullptr;
 65 Mutex*   StringDedupIntern_lock       = nullptr;
 66 Monitor* CodeCache_lock               = nullptr;
 67 Mutex*   TouchedMethodLog_lock        = nullptr;
 68 Mutex*   RetData_lock                 = nullptr;
 69 Monitor* VMOperation_lock             = nullptr;
 70 Monitor* Threads_lock                 = nullptr;
 71 Mutex*   NonJavaThreadsList_lock      = nullptr;
 72 Mutex*   NonJavaThreadsListSync_lock  = nullptr;
 73 Monitor* CGC_lock                     = nullptr;
 74 Monitor* STS_lock                     = nullptr;
 75 Monitor* G1OldGCCount_lock            = nullptr;
 76 Mutex*   G1RareEvent_lock             = nullptr;
 77 Mutex*   G1DetachedRefinementStats_lock = nullptr;
 78 Mutex*   MarkStackFreeList_lock       = nullptr;
 79 Mutex*   MarkStackChunkList_lock      = nullptr;
 80 Mutex*   MonitoringSupport_lock       = nullptr;
 81 Monitor* ConcurrentGCBreakpoints_lock = nullptr;
 82 Mutex*   Compile_lock                 = nullptr;
 83 Monitor* MethodCompileQueue_lock      = nullptr;
 84 Monitor* CompileThread_lock           = nullptr;
 85 Monitor* Compilation_lock             = nullptr;
 86 Mutex*   CompileTaskAlloc_lock        = nullptr;
 87 Mutex*   CompileStatistics_lock       = nullptr;
 88 Mutex*   DirectivesStack_lock         = nullptr;
 89 Mutex*   MultiArray_lock              = nullptr;
 90 Monitor* Terminator_lock              = nullptr;
 91 Monitor* InitCompleted_lock           = nullptr;
 92 Monitor* BeforeExit_lock              = nullptr;
 93 Monitor* Notify_lock                  = nullptr;
 94 Mutex*   ExceptionCache_lock          = nullptr;
 95 #ifndef PRODUCT
 96 Mutex*   FullGCALot_lock              = nullptr;
 97 #endif
 98 
 99 Mutex*   tty_lock                     = nullptr;
100 
101 Mutex*   RawMonitor_lock              = nullptr;
102 Mutex*   PerfDataMemAlloc_lock        = nullptr;
103 Mutex*   PerfDataManager_lock         = nullptr;
104 Mutex*   OopMapCacheAlloc_lock        = nullptr;
105 
106 Mutex*   FreeList_lock                = nullptr;
107 Mutex*   OldSets_lock                 = nullptr;
108 Mutex*   Uncommit_lock                = nullptr;
109 Monitor* RootRegionScan_lock          = nullptr;
110 
111 Mutex*   Management_lock              = nullptr;
112 Monitor* MonitorDeflation_lock        = nullptr;
113 Monitor* Service_lock                 = nullptr;
114 Monitor* Notification_lock            = nullptr;
115 Monitor* PeriodicTask_lock            = nullptr;
116 Monitor* RedefineClasses_lock         = nullptr;
117 Mutex*   Verify_lock                  = nullptr;
118 
119 #if INCLUDE_JFR
120 Mutex*   JfrStacktrace_lock           = nullptr;
121 Monitor* JfrMsg_lock                  = nullptr;
122 Mutex*   JfrBuffer_lock               = nullptr;
123 Monitor* JfrThreadSampler_lock        = nullptr;
124 #endif
125 
126 Mutex*   CodeHeapStateAnalytics_lock  = nullptr;
127 
128 Monitor* ContinuationRelativize_lock  = nullptr;
129 
130 Mutex*   Metaspace_lock               = nullptr;
131 Monitor* MetaspaceCritical_lock       = nullptr;
132 Mutex*   ClassLoaderDataGraph_lock    = nullptr;
133 Monitor* ThreadsSMRDelete_lock        = nullptr;
134 Mutex*   ThreadIdTableCreate_lock     = nullptr;
135 Mutex*   SharedDecoder_lock           = nullptr;
136 Mutex*   DCmdFactory_lock             = nullptr;
137 Mutex*   NMTQuery_lock                = nullptr;
138 Mutex*   NMTCompilationCostHistory_lock = nullptr;
139 
140 #if INCLUDE_CDS
141 #if INCLUDE_JVMTI
142 Mutex*   CDSClassFileStream_lock      = nullptr;
143 #endif
144 Mutex*   DumpTimeTable_lock           = nullptr;
145 Mutex*   CDSLambda_lock               = nullptr;
146 Mutex*   DumpRegion_lock              = nullptr;
147 Mutex*   ClassListFile_lock           = nullptr;
148 Mutex*   UnregisteredClassesTable_lock= nullptr;
149 Mutex*   LambdaFormInvokers_lock      = nullptr;
150 Mutex*   ScratchObjects_lock          = nullptr;
151 #endif // INCLUDE_CDS
152 Mutex*   Bootclasspath_lock           = nullptr;
153 
154 #if INCLUDE_JVMCI
155 Monitor* JVMCI_lock                   = nullptr;
156 Monitor* JVMCIRuntime_lock            = nullptr;
157 #endif
158 
159 
160 #define MAX_NUM_MUTEX 128
161 static Mutex* _mutex_array[MAX_NUM_MUTEX];
162 static int _num_mutex;
163 
164 #ifdef ASSERT
165 void assert_locked_or_safepoint(const Mutex* lock) {
166   if (DebuggingContext::is_enabled() || VMError::is_error_reported()) return;
167   // check if this thread owns the lock (common case)
168   assert(lock != nullptr, "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   fatal("must own lock %s", lock->name());
173 }
174 
175 // a stronger assertion than the above
176 void assert_lock_strong(const Mutex* lock) {
177   if (DebuggingContext::is_enabled() || VMError::is_error_reported()) return;
178   assert(lock != nullptr, "Need non-null lock");
179   if (lock->owned_by_self()) return;
180   fatal("must own lock %s", lock->name());
181 }
182 #endif
183 
184 static void add_mutex(Mutex* var) {
185   assert(_num_mutex < MAX_NUM_MUTEX, "increase MAX_NUM_MUTEX");
186   _mutex_array[_num_mutex++] = var;
187 }
188 
189 #define MUTEX_STORAGE_NAME(name) name##_storage
190 #define MUTEX_STORAGE(name, type) alignas(type) static uint8_t MUTEX_STORAGE_NAME(name)[sizeof(type)]
191 #define MUTEX_DEF(name, type, pri, ...) {                                                       \
192   assert(name == nullptr, "Mutex/Monitor initialized twice");                                   \
193   MUTEX_STORAGE(name, type);                                                                    \
194   name = ::new(static_cast<void*>(MUTEX_STORAGE_NAME(name))) type((pri), #name, ##__VA_ARGS__); \
195   add_mutex(name);                                                                              \
196 }
197 #define MUTEX_DEFN(name, type, pri, ...) MUTEX_DEF(name, type, Mutex::pri, ##__VA_ARGS__)
198 
199 // Specify relative ranked lock
200 #ifdef ASSERT
201 #define MUTEX_DEFL(name, type, held_lock, ...) MUTEX_DEF(name, type, (held_lock)->rank() - 1, ##__VA_ARGS__)
202 #else
203 #define MUTEX_DEFL(name, type, held_lock, ...) MUTEX_DEFN(name, type, safepoint, ##__VA_ARGS__)
204 #endif
205 
206 // Using Padded subclasses to prevent false sharing of these global monitors and mutexes.
207 void mutex_init() {
208   MUTEX_DEFN(tty_lock                        , PaddedMutex  , tty);      // allow to lock in VM
209 
210   MUTEX_DEFN(STS_lock                        , PaddedMonitor, nosafepoint);
211 
212   if (UseG1GC) {
213     MUTEX_DEFN(CGC_lock                      , PaddedMonitor, nosafepoint);
214 
215     MUTEX_DEFN(G1DetachedRefinementStats_lock, PaddedMutex  , nosafepoint-2);
216 
217     MUTEX_DEFN(FreeList_lock                 , PaddedMutex  , service-1);
218     MUTEX_DEFN(OldSets_lock                  , PaddedMutex  , nosafepoint);
219     MUTEX_DEFN(Uncommit_lock                 , PaddedMutex  , service-2);
220     MUTEX_DEFN(RootRegionScan_lock           , PaddedMonitor, nosafepoint-1);
221 
222     MUTEX_DEFN(MarkStackFreeList_lock        , PaddedMutex  , nosafepoint);
223     MUTEX_DEFN(MarkStackChunkList_lock       , PaddedMutex  , nosafepoint);
224   }
225   MUTEX_DEFN(MonitoringSupport_lock          , PaddedMutex  , service-1);        // used for serviceability monitoring support
226 
227   MUTEX_DEFN(StringDedup_lock                , PaddedMonitor, nosafepoint);
228   MUTEX_DEFN(StringDedupIntern_lock          , PaddedMutex  , nosafepoint);
229   MUTEX_DEFN(RawMonitor_lock                 , PaddedMutex  , nosafepoint-1);
230 
231   MUTEX_DEFN(Metaspace_lock                  , PaddedMutex  , nosafepoint-3);
232   MUTEX_DEFN(MetaspaceCritical_lock          , PaddedMonitor, nosafepoint-1);
233 
234   MUTEX_DEFN(Patching_lock                   , PaddedMutex  , nosafepoint);      // used for safepointing and code patching.
235   MUTEX_DEFN(MonitorDeflation_lock           , PaddedMonitor, nosafepoint);      // used for monitor deflation thread operations
236   MUTEX_DEFN(Service_lock                    , PaddedMonitor, service);      // used for service thread operations
237 
238   if (UseNotificationThread) {
239     MUTEX_DEFN(Notification_lock             , PaddedMonitor, service);  // used for notification thread operations
240   } else {
241     Notification_lock = Service_lock;
242   }
243 
244   MUTEX_DEFN(JmethodIdCreation_lock          , PaddedMutex  , nosafepoint-2); // used for creating jmethodIDs.
245   MUTEX_DEFN(InvokeMethodTypeTable_lock      , PaddedMutex  , safepoint);
246   MUTEX_DEFN(InvokeMethodIntrinsicTable_lock , PaddedMonitor, safepoint);
247   MUTEX_DEFN(AdapterHandlerLibrary_lock      , PaddedMutex  , safepoint);
248   MUTEX_DEFN(SharedDictionary_lock           , PaddedMutex  , safepoint);
249   MUTEX_DEFN(VMStatistic_lock                , PaddedMutex  , safepoint);
250   MUTEX_DEFN(SignatureHandlerLibrary_lock    , PaddedMutex  , safepoint);
251   MUTEX_DEFN(SymbolArena_lock                , PaddedMutex  , nosafepoint);
252   MUTEX_DEFN(ExceptionCache_lock             , PaddedMutex  , safepoint);
253 #ifndef PRODUCT
254   MUTEX_DEFN(FullGCALot_lock                 , PaddedMutex  , safepoint); // a lock to make FullGCALot MT safe
255 #endif
256   MUTEX_DEFN(BeforeExit_lock                 , PaddedMonitor, safepoint);
257 
258   MUTEX_DEFN(NonJavaThreadsList_lock         , PaddedMutex  , nosafepoint-1);
259   MUTEX_DEFN(NonJavaThreadsListSync_lock     , PaddedMutex  , nosafepoint);
260 
261   MUTEX_DEFN(RetData_lock                    , PaddedMutex  , safepoint);
262   MUTEX_DEFN(Terminator_lock                 , PaddedMonitor, safepoint, true);
263   MUTEX_DEFN(InitCompleted_lock              , PaddedMonitor, nosafepoint);
264   MUTEX_DEFN(Notify_lock                     , PaddedMonitor, safepoint, true);
265 
266   MUTEX_DEFN(JfieldIdCreation_lock           , PaddedMutex  , safepoint);
267 
268   MUTEX_DEFN(CompiledIC_lock                 , PaddedMutex  , nosafepoint);  // locks VtableStubs_lock, InlineCacheBuffer_lock
269   MUTEX_DEFN(MethodCompileQueue_lock         , PaddedMonitor, safepoint);
270   MUTEX_DEFN(CompileStatistics_lock          , PaddedMutex  , safepoint);
271   MUTEX_DEFN(DirectivesStack_lock            , PaddedMutex  , nosafepoint);
272   MUTEX_DEFN(MultiArray_lock                 , PaddedMutex  , safepoint);
273 
274   MUTEX_DEFN(JvmtiThreadState_lock           , PaddedMutex  , safepoint);   // Used by JvmtiThreadState/JvmtiEventController
275   MUTEX_DEFN(EscapeBarrier_lock              , PaddedMonitor, nosafepoint); // Used to synchronize object reallocation/relocking triggered by JVMTI
276   MUTEX_DEFN(JvmtiVTMSTransition_lock        , PaddedMonitor, safepoint);   // used for Virtual Thread Mount State transition management
277   MUTEX_DEFN(Management_lock                 , PaddedMutex  , safepoint);   // used for JVM management
278 
279   MUTEX_DEFN(ConcurrentGCBreakpoints_lock    , PaddedMonitor, safepoint, true);
280   MUTEX_DEFN(TouchedMethodLog_lock           , PaddedMutex  , safepoint);
281 
282   MUTEX_DEFN(CompileThread_lock              , PaddedMonitor, safepoint);
283   MUTEX_DEFN(PeriodicTask_lock               , PaddedMonitor, safepoint, true);
284   MUTEX_DEFN(RedefineClasses_lock            , PaddedMonitor, safepoint);
285   MUTEX_DEFN(Verify_lock                     , PaddedMutex  , safepoint);
286 
287   if (WhiteBoxAPI) {
288     MUTEX_DEFN(Compilation_lock              , PaddedMonitor, nosafepoint);
289   }
290 
291 #if INCLUDE_JFR
292   MUTEX_DEFN(JfrBuffer_lock                  , PaddedMutex  , event);
293   MUTEX_DEFN(JfrMsg_lock                     , PaddedMonitor, event);
294   MUTEX_DEFN(JfrStacktrace_lock              , PaddedMutex  , event);
295   MUTEX_DEFN(JfrThreadSampler_lock           , PaddedMonitor, nosafepoint);
296 #endif
297 
298   MUTEX_DEFN(ContinuationRelativize_lock     , PaddedMonitor, nosafepoint-3);
299   MUTEX_DEFN(CodeHeapStateAnalytics_lock     , PaddedMutex  , safepoint);
300   MUTEX_DEFN(ThreadsSMRDelete_lock           , PaddedMonitor, service-2); // Holds ConcurrentHashTableResize_lock
301   MUTEX_DEFN(ThreadIdTableCreate_lock        , PaddedMutex  , safepoint);
302   MUTEX_DEFN(SharedDecoder_lock              , PaddedMutex  , tty-1);
303   MUTEX_DEFN(DCmdFactory_lock                , PaddedMutex  , nosafepoint);
304   MUTEX_DEFN(NMTQuery_lock                   , PaddedMutex  , safepoint);
305   MUTEX_DEFN(NMTCompilationCostHistory_lock  , PaddedMutex  , nosafepoint);
306 #if INCLUDE_CDS
307 #if INCLUDE_JVMTI
308   MUTEX_DEFN(CDSClassFileStream_lock         , PaddedMutex  , safepoint);
309 #endif
310   MUTEX_DEFN(DumpTimeTable_lock              , PaddedMutex  , nosafepoint);
311   MUTEX_DEFN(CDSLambda_lock                  , PaddedMutex  , nosafepoint);
312   MUTEX_DEFN(DumpRegion_lock                 , PaddedMutex  , nosafepoint);
313   MUTEX_DEFN(ClassListFile_lock              , PaddedMutex  , nosafepoint);
314   MUTEX_DEFN(UnregisteredClassesTable_lock   , PaddedMutex  , nosafepoint-1);
315   MUTEX_DEFN(LambdaFormInvokers_lock         , PaddedMutex  , safepoint);
316   MUTEX_DEFN(ScratchObjects_lock             , PaddedMutex  , nosafepoint-1); // Holds DumpTimeTable_lock
317 #endif // INCLUDE_CDS
318   MUTEX_DEFN(Bootclasspath_lock              , PaddedMutex  , nosafepoint);
319 
320 #if INCLUDE_JVMCI
321   // JVMCIRuntime::_lock must be acquired before JVMCI_lock to avoid deadlock
322   MUTEX_DEFN(JVMCIRuntime_lock               , PaddedMonitor, safepoint, true);
323 #endif
324 
325   // These locks have relative rankings, and inherit safepoint checking attributes from that rank.
326   MUTEX_DEFL(InlineCacheBuffer_lock         , PaddedMutex  , CompiledIC_lock);
327   MUTEX_DEFL(VtableStubs_lock               , PaddedMutex  , CompiledIC_lock);  // Also holds DumpTimeTable_lock
328   MUTEX_DEFL(CodeCache_lock                 , PaddedMonitor, VtableStubs_lock);
329   MUTEX_DEFL(CompiledMethod_lock            , PaddedMutex  , CodeCache_lock);
330 
331   MUTEX_DEFL(Threads_lock                   , PaddedMonitor, CompileThread_lock, true);
332   MUTEX_DEFL(Compile_lock                   , PaddedMutex  , MethodCompileQueue_lock);
333   MUTEX_DEFL(Heap_lock                      , PaddedMonitor, AdapterHandlerLibrary_lock);
334 
335   MUTEX_DEFL(PerfDataMemAlloc_lock          , PaddedMutex  , Heap_lock);
336   MUTEX_DEFL(PerfDataManager_lock           , PaddedMutex  , Heap_lock);
337   MUTEX_DEFL(ClassLoaderDataGraph_lock      , PaddedMutex  , MultiArray_lock);
338   MUTEX_DEFL(VMOperation_lock               , PaddedMonitor, Heap_lock, true);
339   MUTEX_DEFL(ClassInitError_lock            , PaddedMonitor, Threads_lock);
340 
341   if (UseG1GC) {
342     MUTEX_DEFL(G1OldGCCount_lock            , PaddedMonitor, Threads_lock, true);
343     MUTEX_DEFL(G1RareEvent_lock             , PaddedMutex  , Threads_lock, true);
344   }
345 
346   MUTEX_DEFL(CompileTaskAlloc_lock          , PaddedMutex  ,  MethodCompileQueue_lock);
347 #ifdef INCLUDE_PARALLELGC
348   if (UseParallelGC) {
349     MUTEX_DEFL(PSOldGenExpand_lock          , PaddedMutex  , Heap_lock, true);
350   }
351 #endif
352   MUTEX_DEFL(OopMapCacheAlloc_lock          , PaddedMutex  ,  Threads_lock, true);
353   MUTEX_DEFL(Module_lock                    , PaddedMutex  ,  ClassLoaderDataGraph_lock);
354   MUTEX_DEFL(SystemDictionary_lock          , PaddedMonitor, Module_lock);
355   MUTEX_DEFL(JNICritical_lock               , PaddedMonitor, AdapterHandlerLibrary_lock); // used for JNI critical regions
356 #if INCLUDE_JVMCI
357   // JVMCIRuntime_lock must be acquired before JVMCI_lock to avoid deadlock
358   MUTEX_DEFL(JVMCI_lock                     , PaddedMonitor, JVMCIRuntime_lock);
359 #endif
360 }
361 
362 #undef MUTEX_DEFL
363 #undef MUTEX_DEFN
364 #undef MUTEX_DEF
365 #undef MUTEX_STORAGE
366 #undef MUTEX_STORAGE_NAME
367 
368 void MutexLockerImpl::post_initialize() {
369   // Print mutex ranks if requested.
370   LogTarget(Info, vmmutex) lt;
371   if (lt.is_enabled()) {
372     ResourceMark rm;
373     LogStream ls(lt);
374     print_lock_ranks(&ls);
375   }
376 }
377 
378 GCMutexLocker::GCMutexLocker(Mutex* mutex) {
379   if (SafepointSynchronize::is_at_safepoint()) {
380     _locked = false;
381   } else {
382     _mutex = mutex;
383     _locked = true;
384     _mutex->lock();
385   }
386 }
387 
388 // Print all mutexes/monitors that are currently owned by a thread; called
389 // by fatal error handler.
390 void print_owned_locks_on_error(outputStream* st) {
391   st->print("VM Mutex/Monitor currently owned by a thread: ");
392   bool none = true;
393   for (int i = 0; i < _num_mutex; i++) {
394      // see if it has an owner
395      if (_mutex_array[i]->owner() != nullptr) {
396        if (none) {
397           // print format used by Mutex::print_on_error()
398           st->print_cr(" ([mutex/lock_event])");
399           none = false;
400        }
401        _mutex_array[i]->print_on_error(st);
402        st->cr();
403      }
404   }
405   if (none) st->print_cr("None");
406 }
407 
408 void print_lock_ranks(outputStream* st) {
409   st->print_cr("VM Mutex/Monitor ranks: ");
410 
411 #ifdef ASSERT
412   // Be extra defensive and figure out the bounds on
413   // ranks right here. This also saves a bit of time
414   // in the #ranks*#mutexes loop below.
415   int min_rank = INT_MAX;
416   int max_rank = INT_MIN;
417   for (int i = 0; i < _num_mutex; i++) {
418     Mutex* m = _mutex_array[i];
419     int r = (int) m->rank();
420     if (min_rank > r) min_rank = r;
421     if (max_rank < r) max_rank = r;
422   }
423 
424   // Print the listings rank by rank
425   for (int r = min_rank; r <= max_rank; r++) {
426     bool first = true;
427     for (int i = 0; i < _num_mutex; i++) {
428       Mutex* m = _mutex_array[i];
429       if (r != (int) m->rank()) continue;
430 
431       if (first) {
432         st->cr();
433         st->print_cr("Rank \"%s\":", m->rank_name());
434         first = false;
435       }
436       st->print_cr("  %s", m->name());
437     }
438   }
439 #else
440   st->print_cr("  Only known in debug builds.");
441 #endif // ASSERT
442 }