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src/hotspot/share/services/threadService.hpp

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rev 47674 : Port 09.17.Thread_SMR_logging_update from JDK9 to JDK10
rev 47677 : eosterlund CR - need more inline fixes.
   1 /*
   2  * Copyright (c) 2003, 2013, 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 #ifndef SHARE_VM_SERVICES_THREADSERVICE_HPP
  26 #define SHARE_VM_SERVICES_THREADSERVICE_HPP
  27 
  28 #include "classfile/javaClasses.hpp"
  29 #include "runtime/handles.hpp"
  30 #include "runtime/init.hpp"
  31 #include "runtime/jniHandles.hpp"
  32 #include "runtime/objectMonitor.hpp"
  33 #include "runtime/objectMonitor.inline.hpp"
  34 #include "runtime/perfData.hpp"

  35 #include "services/management.hpp"
  36 #include "services/serviceUtil.hpp"
  37 
  38 class OopClosure;
  39 class ThreadDumpResult;
  40 class ThreadStackTrace;
  41 class ThreadSnapshot;
  42 class StackFrameInfo;
  43 class ThreadConcurrentLocks;
  44 class DeadlockCycle;
  45 
  46 // VM monitoring and management support for the thread and
  47 // synchronization subsystem
  48 //
  49 // Thread contention monitoring is disabled by default.
  50 // When enabled, the VM will begin measuring the accumulated
  51 // elapsed time a thread blocked on synchronization.
  52 //
  53 class ThreadService : public AllStatic {
  54 private:


  92   static jlong get_live_thread_count()        { return _live_threads_count->get_value() - _exiting_threads_count; }
  93   static jlong get_daemon_thread_count()      { return _daemon_threads_count->get_value() - _exiting_daemon_threads_count; }
  94 
  95   static int   exiting_threads_count()        { return _exiting_threads_count; }
  96   static int   exiting_daemon_threads_count() { return _exiting_daemon_threads_count; }
  97 
  98   // Support for thread dump
  99   static void   add_thread_dump(ThreadDumpResult* dump);
 100   static void   remove_thread_dump(ThreadDumpResult* dump);
 101 
 102   static Handle get_current_contended_monitor(JavaThread* thread);
 103 
 104   // This function is called by JVM_DumpThreads.
 105   static Handle dump_stack_traces(GrowableArray<instanceHandle>* threads,
 106                                   int num_threads, TRAPS);
 107 
 108   static void   reset_peak_thread_count();
 109   static void   reset_contention_count_stat(JavaThread* thread);
 110   static void   reset_contention_time_stat(JavaThread* thread);
 111 
 112   static DeadlockCycle*       find_deadlocks_at_safepoint(bool object_monitors_only);
 113 
 114   // GC support
 115   static void   oops_do(OopClosure* f);
 116   static void   metadata_do(void f(Metadata*));
 117 };
 118 
 119 // Per-thread Statistics for synchronization
 120 class ThreadStatistics : public CHeapObj<mtInternal> {
 121 private:
 122   // The following contention statistics are only updated by
 123   // the thread owning these statistics when contention occurs.
 124 
 125   jlong        _contended_enter_count;
 126   elapsedTimer _contended_enter_timer;
 127   jlong        _monitor_wait_count;
 128   elapsedTimer _monitor_wait_timer;
 129   jlong        _sleep_count;
 130   elapsedTimer _sleep_timer;
 131 
 132 


 172   void monitor_wait_end()                  { _monitor_wait_timer.stop(); check_and_reset_timer(); }
 173 
 174   void thread_sleep()                      { check_and_reset_count(); _sleep_count++; }
 175   void thread_sleep_begin()                { check_and_reset_timer(); _sleep_timer.start(); }
 176   void thread_sleep_end()                  { _sleep_timer.stop(); check_and_reset_timer(); }
 177 
 178   void contended_enter()                   { check_and_reset_count(); _contended_enter_count++; }
 179   void contended_enter_begin()             { check_and_reset_timer(); _contended_enter_timer.start(); }
 180   void contended_enter_end()               { _contended_enter_timer.stop(); check_and_reset_timer(); }
 181 
 182   void reset_count_stat()                  { _count_pending_reset = true; }
 183   void reset_time_stat()                   { _timer_pending_reset = true; }
 184 
 185   int* perf_recursion_counts_addr()        { return _perf_recursion_counts; }
 186   elapsedTimer* perf_timers_addr()         { return _perf_timers; }
 187 };
 188 
 189 // Thread snapshot to represent the thread state and statistics
 190 class ThreadSnapshot : public CHeapObj<mtInternal> {
 191 private:


 192   JavaThread* _thread;
 193   oop         _threadObj;
 194   java_lang_Thread::ThreadStatus _thread_status;
 195 
 196   bool    _is_ext_suspended;
 197   bool    _is_in_native;
 198 
 199   jlong   _contended_enter_ticks;
 200   jlong   _contended_enter_count;
 201   jlong   _monitor_wait_ticks;
 202   jlong   _monitor_wait_count;
 203   jlong   _sleep_ticks;
 204   jlong   _sleep_count;
 205   oop     _blocker_object;
 206   oop     _blocker_object_owner;
 207 
 208   ThreadStackTrace*      _stack_trace;
 209   ThreadConcurrentLocks* _concurrent_locks;
 210   ThreadSnapshot*        _next;
 211 
 212 public:
 213   // Dummy snapshot
 214   ThreadSnapshot() : _thread(NULL), _threadObj(NULL), _stack_trace(NULL), _concurrent_locks(NULL), _next(NULL),
 215                      _blocker_object(NULL), _blocker_object_owner(NULL) {};
 216   ThreadSnapshot(JavaThread* thread);
 217   ~ThreadSnapshot();
 218 
 219   java_lang_Thread::ThreadStatus thread_status() { return _thread_status; }
 220 
 221   oop         threadObj() const           { return _threadObj; }
 222 
 223   void        set_next(ThreadSnapshot* n) { _next = n; }
 224 
 225   bool        is_ext_suspended()          { return _is_ext_suspended; }
 226   bool        is_in_native()              { return _is_in_native; }
 227 
 228   jlong       contended_enter_count()     { return _contended_enter_count; }
 229   jlong       contended_enter_ticks()     { return _contended_enter_ticks; }
 230   jlong       monitor_wait_count()        { return _monitor_wait_count; }
 231   jlong       monitor_wait_ticks()        { return _monitor_wait_ticks; }
 232   jlong       sleep_count()               { return _sleep_count; }
 233   jlong       sleep_ticks()               { return _sleep_ticks; }
 234 
 235 
 236   oop         blocker_object()            { return _blocker_object; }


 293   ~StackFrameInfo() {
 294     if (_locked_monitors != NULL) {
 295       delete _locked_monitors;
 296     }
 297   };
 298   Method*   method() const       { return _method; }
 299   int       bci()    const       { return _bci; }
 300   void      oops_do(OopClosure* f);
 301   void      metadata_do(void f(Metadata*));
 302 
 303   int       num_locked_monitors()       { return (_locked_monitors != NULL ? _locked_monitors->length() : 0); }
 304   GrowableArray<oop>* locked_monitors() { return _locked_monitors; }
 305 
 306   void      print_on(outputStream* st) const;
 307 };
 308 
 309 class ThreadConcurrentLocks : public CHeapObj<mtInternal> {
 310 private:
 311   GrowableArray<instanceOop>* _owned_locks;
 312   ThreadConcurrentLocks*      _next;






 313   JavaThread*                 _thread;
 314  public:
 315   ThreadConcurrentLocks(JavaThread* thread);
 316   ~ThreadConcurrentLocks();
 317 
 318   void                        add_lock(instanceOop o);
 319   void                        set_next(ThreadConcurrentLocks* n) { _next = n; }
 320   ThreadConcurrentLocks*      next() { return _next; }
 321   JavaThread*                 java_thread()                      { return _thread; }
 322   GrowableArray<instanceOop>* owned_locks()                      { return _owned_locks; }
 323   void                        oops_do(OopClosure* f);
 324 };
 325 
 326 class ConcurrentLocksDump : public StackObj {
 327  private:
 328   ThreadConcurrentLocks* _map;
 329   ThreadConcurrentLocks* _last;   // Last ThreadConcurrentLocks in the map
 330   bool                   _retain_map_on_free;
 331 
 332   void build_map(GrowableArray<oop>* aos_objects);
 333   void add_lock(JavaThread* thread, instanceOop o);
 334 
 335  public:
 336   ConcurrentLocksDump(bool retain_map_on_free) : _map(NULL), _last(NULL), _retain_map_on_free(retain_map_on_free) {};
 337   ConcurrentLocksDump() : _map(NULL), _last(NULL), _retain_map_on_free(false) {};




 338   ~ConcurrentLocksDump();
 339 
 340   void                        dump_at_safepoint();
 341   ThreadConcurrentLocks*      thread_concurrent_locks(JavaThread* thread);
 342   void                        print_locks_on(JavaThread* t, outputStream* st);
 343 };
 344 
 345 class ThreadDumpResult : public StackObj {
 346  private:
 347   int                  _num_threads;
 348   int                  _num_snapshots;
 349   ThreadSnapshot*      _snapshots;
 350   ThreadSnapshot*      _last;
 351   ThreadDumpResult*    _next;



 352  public:
 353   ThreadDumpResult();
 354   ThreadDumpResult(int num_threads);
 355   ~ThreadDumpResult();
 356 
 357   void                 add_thread_snapshot(ThreadSnapshot* ts);
 358   void                 set_next(ThreadDumpResult* next) { _next = next; }
 359   ThreadDumpResult*    next()                           { return _next; }
 360   int                  num_threads()                    { return _num_threads; }
 361   int                  num_snapshots()                  { return _num_snapshots; }
 362   ThreadSnapshot*      snapshots()                      { return _snapshots; }



 363   void                 oops_do(OopClosure* f);
 364   void                 metadata_do(void f(Metadata*));
 365 };
 366 
 367 class DeadlockCycle : public CHeapObj<mtInternal> {
 368  private:
 369   bool _is_deadlock;
 370   GrowableArray<JavaThread*>* _threads;
 371   DeadlockCycle*              _next;
 372  public:
 373   DeadlockCycle();
 374   ~DeadlockCycle();
 375 
 376   DeadlockCycle* next()                     { return _next; }
 377   void           set_next(DeadlockCycle* d) { _next = d; }
 378   void           add_thread(JavaThread* t)  { _threads->append(t); }
 379   void           reset()                    { _is_deadlock = false; _threads->clear(); }
 380   void           set_deadlock(bool value)   { _is_deadlock = value; }
 381   bool           is_deadlock()              { return _is_deadlock; }
 382   int            num_threads()              { return _threads->length(); }
 383   GrowableArray<JavaThread*>* threads()     { return _threads; }
 384   void           print_on(outputStream* st) const;
 385 };
 386 
 387 // Utility class to get list of java threads.
 388 class ThreadsListEnumerator : public StackObj {
 389 private:
 390   GrowableArray<instanceHandle>* _threads_array;
 391 public:
 392   ThreadsListEnumerator(Thread* cur_thread,
 393                         bool include_jvmti_agent_threads = false,
 394                         bool include_jni_attaching_threads = true);
 395   int            num_threads()            { return _threads_array->length(); }
 396   instanceHandle get_threadObj(int index) { return _threads_array->at(index); }
 397 };
 398 
 399 
 400 // abstract utility class to set new thread states, and restore previous after the block exits
 401 class JavaThreadStatusChanger : public StackObj {
 402  private:
 403   java_lang_Thread::ThreadStatus _old_state;
 404   JavaThread*  _java_thread;


   1 /*
   2  * Copyright (c) 2003, 2017, 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 #ifndef SHARE_VM_SERVICES_THREADSERVICE_HPP
  26 #define SHARE_VM_SERVICES_THREADSERVICE_HPP
  27 
  28 #include "classfile/javaClasses.hpp"
  29 #include "runtime/handles.hpp"
  30 #include "runtime/init.hpp"
  31 #include "runtime/jniHandles.hpp"
  32 #include "runtime/objectMonitor.hpp"
  33 #include "runtime/objectMonitor.inline.hpp"
  34 #include "runtime/perfData.hpp"
  35 #include "runtime/thread.hpp"
  36 #include "services/management.hpp"
  37 #include "services/serviceUtil.hpp"
  38 
  39 class OopClosure;
  40 class ThreadDumpResult;
  41 class ThreadStackTrace;
  42 class ThreadSnapshot;
  43 class StackFrameInfo;
  44 class ThreadConcurrentLocks;
  45 class DeadlockCycle;
  46 
  47 // VM monitoring and management support for the thread and
  48 // synchronization subsystem
  49 //
  50 // Thread contention monitoring is disabled by default.
  51 // When enabled, the VM will begin measuring the accumulated
  52 // elapsed time a thread blocked on synchronization.
  53 //
  54 class ThreadService : public AllStatic {
  55 private:


  93   static jlong get_live_thread_count()        { return _live_threads_count->get_value() - _exiting_threads_count; }
  94   static jlong get_daemon_thread_count()      { return _daemon_threads_count->get_value() - _exiting_daemon_threads_count; }
  95 
  96   static int   exiting_threads_count()        { return _exiting_threads_count; }
  97   static int   exiting_daemon_threads_count() { return _exiting_daemon_threads_count; }
  98 
  99   // Support for thread dump
 100   static void   add_thread_dump(ThreadDumpResult* dump);
 101   static void   remove_thread_dump(ThreadDumpResult* dump);
 102 
 103   static Handle get_current_contended_monitor(JavaThread* thread);
 104 
 105   // This function is called by JVM_DumpThreads.
 106   static Handle dump_stack_traces(GrowableArray<instanceHandle>* threads,
 107                                   int num_threads, TRAPS);
 108 
 109   static void   reset_peak_thread_count();
 110   static void   reset_contention_count_stat(JavaThread* thread);
 111   static void   reset_contention_time_stat(JavaThread* thread);
 112 
 113   static DeadlockCycle*       find_deadlocks_at_safepoint(ThreadsList * t_list, bool object_monitors_only);
 114 
 115   // GC support
 116   static void   oops_do(OopClosure* f);
 117   static void   metadata_do(void f(Metadata*));
 118 };
 119 
 120 // Per-thread Statistics for synchronization
 121 class ThreadStatistics : public CHeapObj<mtInternal> {
 122 private:
 123   // The following contention statistics are only updated by
 124   // the thread owning these statistics when contention occurs.
 125 
 126   jlong        _contended_enter_count;
 127   elapsedTimer _contended_enter_timer;
 128   jlong        _monitor_wait_count;
 129   elapsedTimer _monitor_wait_timer;
 130   jlong        _sleep_count;
 131   elapsedTimer _sleep_timer;
 132 
 133 


 173   void monitor_wait_end()                  { _monitor_wait_timer.stop(); check_and_reset_timer(); }
 174 
 175   void thread_sleep()                      { check_and_reset_count(); _sleep_count++; }
 176   void thread_sleep_begin()                { check_and_reset_timer(); _sleep_timer.start(); }
 177   void thread_sleep_end()                  { _sleep_timer.stop(); check_and_reset_timer(); }
 178 
 179   void contended_enter()                   { check_and_reset_count(); _contended_enter_count++; }
 180   void contended_enter_begin()             { check_and_reset_timer(); _contended_enter_timer.start(); }
 181   void contended_enter_end()               { _contended_enter_timer.stop(); check_and_reset_timer(); }
 182 
 183   void reset_count_stat()                  { _count_pending_reset = true; }
 184   void reset_time_stat()                   { _timer_pending_reset = true; }
 185 
 186   int* perf_recursion_counts_addr()        { return _perf_recursion_counts; }
 187   elapsedTimer* perf_timers_addr()         { return _perf_timers; }
 188 };
 189 
 190 // Thread snapshot to represent the thread state and statistics
 191 class ThreadSnapshot : public CHeapObj<mtInternal> {
 192 private:
 193   // This JavaThread* is protected by being stored in objects that are
 194   // protected by a ThreadsListSetter (ThreadDumpResult).
 195   JavaThread* _thread;
 196   oop         _threadObj;
 197   java_lang_Thread::ThreadStatus _thread_status;
 198 
 199   bool    _is_ext_suspended;
 200   bool    _is_in_native;
 201 
 202   jlong   _contended_enter_ticks;
 203   jlong   _contended_enter_count;
 204   jlong   _monitor_wait_ticks;
 205   jlong   _monitor_wait_count;
 206   jlong   _sleep_ticks;
 207   jlong   _sleep_count;
 208   oop     _blocker_object;
 209   oop     _blocker_object_owner;
 210 
 211   ThreadStackTrace*      _stack_trace;
 212   ThreadConcurrentLocks* _concurrent_locks;
 213   ThreadSnapshot*        _next;
 214 
 215 public:
 216   // Dummy snapshot
 217   ThreadSnapshot() : _thread(NULL), _threadObj(NULL), _stack_trace(NULL), _concurrent_locks(NULL), _next(NULL),
 218                      _blocker_object(NULL), _blocker_object_owner(NULL) {};
 219   ThreadSnapshot(ThreadsList * t_list, JavaThread* thread);
 220   ~ThreadSnapshot();
 221 
 222   java_lang_Thread::ThreadStatus thread_status() { return _thread_status; }
 223 
 224   oop         threadObj() const           { return _threadObj; }
 225 
 226   void        set_next(ThreadSnapshot* n) { _next = n; }
 227 
 228   bool        is_ext_suspended()          { return _is_ext_suspended; }
 229   bool        is_in_native()              { return _is_in_native; }
 230 
 231   jlong       contended_enter_count()     { return _contended_enter_count; }
 232   jlong       contended_enter_ticks()     { return _contended_enter_ticks; }
 233   jlong       monitor_wait_count()        { return _monitor_wait_count; }
 234   jlong       monitor_wait_ticks()        { return _monitor_wait_ticks; }
 235   jlong       sleep_count()               { return _sleep_count; }
 236   jlong       sleep_ticks()               { return _sleep_ticks; }
 237 
 238 
 239   oop         blocker_object()            { return _blocker_object; }


 296   ~StackFrameInfo() {
 297     if (_locked_monitors != NULL) {
 298       delete _locked_monitors;
 299     }
 300   };
 301   Method*   method() const       { return _method; }
 302   int       bci()    const       { return _bci; }
 303   void      oops_do(OopClosure* f);
 304   void      metadata_do(void f(Metadata*));
 305 
 306   int       num_locked_monitors()       { return (_locked_monitors != NULL ? _locked_monitors->length() : 0); }
 307   GrowableArray<oop>* locked_monitors() { return _locked_monitors; }
 308 
 309   void      print_on(outputStream* st) const;
 310 };
 311 
 312 class ThreadConcurrentLocks : public CHeapObj<mtInternal> {
 313 private:
 314   GrowableArray<instanceOop>* _owned_locks;
 315   ThreadConcurrentLocks*      _next;
 316   // This JavaThread* is protected in one of two different ways
 317   // depending on the usage of the ThreadConcurrentLocks object:
 318   // 1) by being stored in objects that are only allocated and used at a
 319   // safepoint (ConcurrentLocksDump), or 2) by being stored in objects
 320   // that are protected by a ThreadsListSetter (ThreadSnapshot inside
 321   // ThreadDumpResult).
 322   JavaThread*                 _thread;
 323  public:
 324   ThreadConcurrentLocks(JavaThread* thread);
 325   ~ThreadConcurrentLocks();
 326 
 327   void                        add_lock(instanceOop o);
 328   void                        set_next(ThreadConcurrentLocks* n) { _next = n; }
 329   ThreadConcurrentLocks*      next() { return _next; }
 330   JavaThread*                 java_thread()                      { return _thread; }
 331   GrowableArray<instanceOop>* owned_locks()                      { return _owned_locks; }
 332   void                        oops_do(OopClosure* f);
 333 };
 334 
 335 class ConcurrentLocksDump : public StackObj {
 336  private:
 337   ThreadConcurrentLocks* _map;
 338   ThreadConcurrentLocks* _last;   // Last ThreadConcurrentLocks in the map
 339   bool                   _retain_map_on_free;
 340 
 341   void build_map(GrowableArray<oop>* aos_objects);
 342   void add_lock(JavaThread* thread, instanceOop o);
 343 
 344  public:
 345   ConcurrentLocksDump(bool retain_map_on_free) : _map(NULL), _last(NULL), _retain_map_on_free(retain_map_on_free) {
 346     assert(SafepointSynchronize::is_at_safepoint(), "Must be constructed at a safepoint.");
 347   };
 348   ConcurrentLocksDump() : _map(NULL), _last(NULL), _retain_map_on_free(false) {
 349     assert(SafepointSynchronize::is_at_safepoint(), "Must be constructed at a safepoint.");
 350   };
 351   ~ConcurrentLocksDump();
 352 
 353   void                        dump_at_safepoint();
 354   ThreadConcurrentLocks*      thread_concurrent_locks(JavaThread* thread);
 355   void                        print_locks_on(JavaThread* t, outputStream* st);
 356 };
 357 
 358 class ThreadDumpResult : public StackObj {
 359  private:
 360   int                  _num_threads;
 361   int                  _num_snapshots;
 362   ThreadSnapshot*      _snapshots;
 363   ThreadSnapshot*      _last;
 364   ThreadDumpResult*    _next;
 365   ThreadsListSetter    _setter;  // Helper to set hazard ptr in the originating thread
 366                                  // which protects the JavaThreads in _snapshots.
 367 
 368  public:
 369   ThreadDumpResult();
 370   ThreadDumpResult(int num_threads);
 371   ~ThreadDumpResult();
 372 
 373   void                 add_thread_snapshot(ThreadSnapshot* ts);
 374   void                 set_next(ThreadDumpResult* next) { _next = next; }
 375   ThreadDumpResult*    next()                           { return _next; }
 376   int                  num_threads()                    { return _num_threads; }
 377   int                  num_snapshots()                  { return _num_snapshots; }
 378   ThreadSnapshot*      snapshots()                      { return _snapshots; }
 379   void                 set_t_list()                     { _setter.set(); }
 380   ThreadsList*         t_list();
 381   bool                 t_list_has_been_set()            { return _setter.target_needs_release(); }
 382   void                 oops_do(OopClosure* f);
 383   void                 metadata_do(void f(Metadata*));
 384 };
 385 
 386 class DeadlockCycle : public CHeapObj<mtInternal> {
 387  private:
 388   bool _is_deadlock;
 389   GrowableArray<JavaThread*>* _threads;
 390   DeadlockCycle*              _next;
 391  public:
 392   DeadlockCycle();
 393   ~DeadlockCycle();
 394 
 395   DeadlockCycle* next()                     { return _next; }
 396   void           set_next(DeadlockCycle* d) { _next = d; }
 397   void           add_thread(JavaThread* t)  { _threads->append(t); }
 398   void           reset()                    { _is_deadlock = false; _threads->clear(); }
 399   void           set_deadlock(bool value)   { _is_deadlock = value; }
 400   bool           is_deadlock()              { return _is_deadlock; }
 401   int            num_threads()              { return _threads->length(); }
 402   GrowableArray<JavaThread*>* threads()     { return _threads; }
 403   void           print_on_with(ThreadsList * t_list, outputStream* st) const;
 404 };
 405 
 406 // Utility class to get list of java threads.
 407 class ThreadsListEnumerator : public StackObj {
 408 private:
 409   GrowableArray<instanceHandle>* _threads_array;
 410 public:
 411   ThreadsListEnumerator(Thread* cur_thread,
 412                         bool include_jvmti_agent_threads = false,
 413                         bool include_jni_attaching_threads = true);
 414   int            num_threads()            { return _threads_array->length(); }
 415   instanceHandle get_threadObj(int index) { return _threads_array->at(index); }
 416 };
 417 
 418 
 419 // abstract utility class to set new thread states, and restore previous after the block exits
 420 class JavaThreadStatusChanger : public StackObj {
 421  private:
 422   java_lang_Thread::ThreadStatus _old_state;
 423   JavaThread*  _java_thread;


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