1 /*
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   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.
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   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  *
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  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
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  24 
  25 #ifndef SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
  26 #define SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
  27 
  28 #include "memory/padded.hpp"
  29 #include "runtime/os.hpp"
  30 #include "runtime/park.hpp"
  31 #include "runtime/perfData.hpp"
  32 
  33 // ObjectWaiter serves as a "proxy" or surrogate thread.
  34 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
  35 // ParkEvent instead.  Beware, however, that the JVMTI code
  36 // knows about ObjectWaiters, so we'll have to reconcile that code.
  37 // See next_waiter(), first_waiter(), etc.
  38 
  39 class ObjectWaiter : public StackObj {
  40  public:
  41   enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
  42   enum Sorted  { PREPEND, APPEND, SORTED };
  43   ObjectWaiter * volatile _next;
  44   ObjectWaiter * volatile _prev;
  45   Thread*       _thread;
  46   jlong         _notifier_tid;
  47   ParkEvent *   _event;
  48   volatile int  _notified;
  49   volatile TStates TState;
  50   Sorted        _Sorted;           // List placement disposition
  51   bool          _active;           // Contention monitoring is enabled
  52  public:
  53   ObjectWaiter(Thread* thread);
  54 
  55   void wait_reenter_begin(ObjectMonitor *mon);
  56   void wait_reenter_end(ObjectMonitor *mon);
  57 };
  58 
  59 // forward declaration to avoid include tracing.hpp
  60 class EventJavaMonitorWait;
  61 
  62 // The ObjectMonitor class implements the heavyweight version of a
  63 // JavaMonitor. The lightweight BasicLock/stack lock version has been
  64 // inflated into an ObjectMonitor. This inflation is typically due to
  65 // contention or use of Object.wait().
  66 //
  67 // WARNING: This is a very sensitive and fragile class. DO NOT make any
  68 // changes unless you are fully aware of the underlying semantics.
  69 //
  70 // Class JvmtiRawMonitor currently inherits from ObjectMonitor so
  71 // changes in this class must be careful to not break JvmtiRawMonitor.
  72 // These two subsystems should be separated.
  73 //
  74 // ObjectMonitor Layout Overview/Highlights/Restrictions:
  75 //
  76 // - The _header field must be at offset 0 because the displaced header
  77 //   from markOop is stored there. We do not want markOop.hpp to include
  78 //   ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This
  79 //   means that ObjectMonitor cannot inherit from any other class nor can
  80 //   it use any virtual member functions. This restriction is critical to
  81 //   the proper functioning of the VM.
  82 // - The _header and _owner fields should be separated by enough space
  83 //   to avoid false sharing due to parallel access by different threads.
  84 //   This is an advisory recommendation.
  85 // - The general layout of the fields in ObjectMonitor is:
  86 //     _header
  87 //     <lightly_used_fields>
  88 //     <optional padding>
  89 //     _owner
  90 //     <remaining_fields>
  91 // - The VM assumes write ordering and machine word alignment with
  92 //   respect to the _owner field and the <remaining_fields> that can
  93 //   be read in parallel by other threads.
  94 // - Generally fields that are accessed closely together in time should
  95 //   be placed proximally in space to promote data cache locality. That
  96 //   is, temporal locality should condition spatial locality.
  97 // - We have to balance avoiding false sharing with excessive invalidation
  98 //   from coherence traffic. As such, we try to cluster fields that tend
  99 //   to be _written_ at approximately the same time onto the same data
 100 //   cache line.
 101 // - We also have to balance the natural tension between minimizing
 102 //   single threaded capacity misses with excessive multi-threaded
 103 //   coherency misses. There is no single optimal layout for both
 104 //   single-threaded and multi-threaded environments.
 105 //
 106 // - See ObjectMonitor::sanity_checks() for how critical restrictions are
 107 //   enforced and advisory recommendations are reported.
 108 // - Adjacent ObjectMonitors should be separated by enough space to avoid
 109 //   false sharing. This is handled by the ObjectMonitor allocation code
 110 //   in synchronizer.cpp. Also see ObjectSynchronizer::sanity_checks().
 111 //
 112 // Futures notes:
 113 //   - Separating _owner from the <remaining_fields> by enough space to
 114 //     avoid false sharing might be profitable. Given
 115 //     http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate
 116 //     we know that the CAS in monitorenter will invalidate the line
 117 //     underlying _owner. We want to avoid an L1 data cache miss on that
 118 //     same line for monitorexit. Putting these <remaining_fields>:
 119 //     _recursions, _EntryList, _cxq, and _succ, all of which may be
 120 //     fetched in the inflated unlock path, on a different cache line
 121 //     would make them immune to CAS-based invalidation from the _owner
 122 //     field.
 123 //
 124 //   - The _recursions field should be of type int, or int32_t but not
 125 //     intptr_t. There's no reason to use a 64-bit type for this field
 126 //     in a 64-bit JVM.
 127 
 128 class ObjectMonitor {
 129  public:
 130   enum {
 131     OM_OK,                    // no error
 132     OM_SYSTEM_ERROR,          // operating system error
 133     OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
 134     OM_INTERRUPTED,           // Thread.interrupt()
 135     OM_TIMED_OUT              // Object.wait() timed out
 136   };
 137 
 138  private:
 139   friend class ObjectSynchronizer;
 140   friend class ObjectWaiter;
 141   friend class VMStructs;
 142 
 143   volatile markOop   _header;       // displaced object header word - mark
 144   void*     volatile _object;       // backward object pointer - strong root
 145  public:
 146   ObjectMonitor *    FreeNext;      // Free list linkage
 147  private:
 148   DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
 149                         sizeof(volatile markOop) + sizeof(void * volatile) +
 150                         sizeof(ObjectMonitor *));
 151  protected:                         // protected for JvmtiRawMonitor
 152   void *  volatile _owner;          // pointer to owning thread OR BasicLock
 153   volatile jlong _previous_owner_tid;  // thread id of the previous owner of the monitor
 154   volatile intptr_t  _recursions;   // recursion count, 0 for first entry
 155   ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
 156                                       // The list is actually composed of WaitNodes,
 157                                       // acting as proxies for Threads.
 158  private:
 159   ObjectWaiter * volatile _cxq;     // LL of recently-arrived threads blocked on entry.
 160   Thread * volatile _succ;          // Heir presumptive thread - used for futile wakeup throttling
 161   Thread * volatile _Responsible;
 162 
 163   volatile int _Spinner;            // for exit->spinner handoff optimization
 164   volatile int _SpinDuration;
 165 
 166   volatile jint  _count;            // reference count to prevent reclamation/deflation
 167                                     // at stop-the-world time.  See deflate_idle_monitors().
 168                                     // _count is approximately |_WaitSet| + |_EntryList|
 169  protected:
 170   ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
 171   volatile jint  _waiters;          // number of waiting threads
 172  private:
 173   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
 174 
 175  public:
 176   static void Initialize();
 177 
 178   // Only perform a PerfData operation if the PerfData object has been
 179   // allocated and if the PerfDataManager has not freed the PerfData
 180   // objects which can happen at normal VM shutdown.
 181   //
 182   #define OM_PERFDATA_OP(f, op_str)              \
 183     do {                                         \
 184       if (ObjectMonitor::_sync_ ## f != NULL &&  \
 185           PerfDataManager::has_PerfData()) {     \
 186         ObjectMonitor::_sync_ ## f->op_str;      \
 187       }                                          \
 188     } while (0)
 189 
 190   static PerfCounter * _sync_ContendedLockAttempts;
 191   static PerfCounter * _sync_FutileWakeups;
 192   static PerfCounter * _sync_Parks;
 193   static PerfCounter * _sync_EmptyNotifications;
 194   static PerfCounter * _sync_Notifications;
 195   static PerfCounter * _sync_SlowEnter;
 196   static PerfCounter * _sync_SlowExit;
 197   static PerfCounter * _sync_SlowNotify;
 198   static PerfCounter * _sync_SlowNotifyAll;
 199   static PerfCounter * _sync_FailedSpins;
 200   static PerfCounter * _sync_SuccessfulSpins;
 201   static PerfCounter * _sync_PrivateA;
 202   static PerfCounter * _sync_PrivateB;
 203   static PerfCounter * _sync_MonInCirculation;
 204   static PerfCounter * _sync_MonScavenged;
 205   static PerfCounter * _sync_Inflations;
 206   static PerfCounter * _sync_Deflations;
 207   static PerfLongVariable * _sync_MonExtant;
 208 
 209   static int Knob_ExitRelease;
 210   static int Knob_Verbose;
 211   static int Knob_VerifyInUse;
 212   static int Knob_VerifyMatch;
 213   static int Knob_SpinLimit;
 214 
 215   void* operator new (size_t size) throw() {
 216     return AllocateHeap(size, mtInternal);
 217   }
 218   void* operator new[] (size_t size) throw() {
 219     return operator new (size);
 220   }
 221   void operator delete(void* p) {
 222     FreeHeap(p);
 223   }
 224   void operator delete[] (void *p) {
 225     operator delete(p);
 226   }
 227 
 228   // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
 229   // ByteSize would also be an appropriate type.
 230   static int header_offset_in_bytes()      { return offset_of(ObjectMonitor, _header); }
 231   static int object_offset_in_bytes()      { return offset_of(ObjectMonitor, _object); }
 232   static int owner_offset_in_bytes()       { return offset_of(ObjectMonitor, _owner); }
 233   static int count_offset_in_bytes()       { return offset_of(ObjectMonitor, _count); }
 234   static int recursions_offset_in_bytes()  { return offset_of(ObjectMonitor, _recursions); }
 235   static int cxq_offset_in_bytes()         { return offset_of(ObjectMonitor, _cxq); }
 236   static int succ_offset_in_bytes()        { return offset_of(ObjectMonitor, _succ); }
 237   static int EntryList_offset_in_bytes()   { return offset_of(ObjectMonitor, _EntryList); }
 238 
 239   // ObjectMonitor references can be ORed with markOopDesc::monitor_value
 240   // as part of the ObjectMonitor tagging mechanism. When we combine an
 241   // ObjectMonitor reference with an offset, we need to remove the tag
 242   // value in order to generate the proper address.
 243   //
 244   // We can either adjust the ObjectMonitor reference and then add the
 245   // offset or we can adjust the offset that is added to the ObjectMonitor
 246   // reference. The latter avoids an AGI (Address Generation Interlock)
 247   // stall so the helper macro adjusts the offset value that is returned
 248   // to the ObjectMonitor reference manipulation code:
 249   //
 250   #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
 251     ((ObjectMonitor::f ## _offset_in_bytes()) - markOopDesc::monitor_value)
 252 
 253   markOop   header() const;

 254   void      set_header(markOop hdr);
 255 
 256   intptr_t is_busy() const {
 257     // TODO-FIXME: merge _count and _waiters.
 258     // TODO-FIXME: assert _owner == null implies _recursions = 0
 259     // TODO-FIXME: assert _WaitSet != null implies _count > 0
 260     return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
 261   }
 262 
 263   intptr_t  is_entered(Thread* current) const;
 264 
 265   void*     owner() const;
 266   void      set_owner(void* owner);
 267 
 268   jint      waiters() const;
 269 
 270   jint      count() const;
 271   void      set_count(jint count);
 272   jint      contentions() const;
 273   intptr_t  recursions() const                                         { return _recursions; }
 274 
 275   // JVM/TI GetObjectMonitorUsage() needs this:
 276   ObjectWaiter* first_waiter()                                         { return _WaitSet; }
 277   ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
 278   Thread* thread_of_waiter(ObjectWaiter* o)                            { return o->_thread; }
 279 
 280  protected:
 281   // We don't typically expect or want the ctors or dtors to run.
 282   // normal ObjectMonitors are type-stable and immortal.
 283   ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
 284 
 285   ~ObjectMonitor() {
 286     // TODO: Add asserts ...
 287     // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
 288     // _count == 0 _EntryList  == NULL etc
 289   }
 290 
 291  private:
 292   void Recycle() {
 293     // TODO: add stronger asserts ...
 294     // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
 295     // _count == 0 EntryList  == NULL
 296     // _recursions == 0 _WaitSet == NULL
 297     assert(((is_busy()|_recursions) == 0), "freeing inuse monitor");
 298     _succ          = NULL;
 299     _EntryList     = NULL;
 300     _cxq           = NULL;
 301     _WaitSet       = NULL;
 302     _recursions    = 0;
 303   }
 304 
 305  public:
 306 
 307   void*     object() const;
 308   void*     object_addr();
 309   void      set_object(void* obj);
 310 
 311   bool      check(TRAPS);       // true if the thread owns the monitor.
 312   void      check_slow(TRAPS);
 313   void      clear();
 314   static void sanity_checks();  // public for -XX:+ExecuteInternalVMTests
 315                                 // in PRODUCT for -XX:SyncKnobs=Verbose=1
 316 
 317   void      enter(TRAPS);
 318   void      exit(bool not_suspended, TRAPS);
 319   void      wait(jlong millis, bool interruptable, TRAPS);
 320   void      notify(TRAPS);
 321   void      notifyAll(TRAPS);
 322 
 323 // Use the following at your own risk
 324   intptr_t  complete_exit(TRAPS);
 325   void      reenter(intptr_t recursions, TRAPS);
 326 
 327  private:
 328   void      AddWaiter(ObjectWaiter * waiter);
 329   static    void DeferredInitialize();
 330   void      INotify(Thread * Self);
 331   ObjectWaiter * DequeueWaiter();
 332   void      DequeueSpecificWaiter(ObjectWaiter * waiter);
 333   void      EnterI(TRAPS);
 334   void      ReenterI(Thread * Self, ObjectWaiter * SelfNode);
 335   void      UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
 336   int       TryLock(Thread * Self);
 337   int       NotRunnable(Thread * Self, Thread * Owner);
 338   int       TrySpin(Thread * Self);
 339   void      ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
 340   bool      ExitSuspendEquivalent(JavaThread * Self);
 341   void      post_monitor_wait_event(EventJavaMonitorWait * event,
 342                                     jlong notifier_tid,
 343                                     jlong timeout,
 344                                     bool timedout);
 345 
 346 };
 347 
 348 #undef TEVENT
 349 #define TEVENT(nom) { if (SyncVerbose) FEVENT(nom); }
 350 
 351 #define FEVENT(nom)                             \
 352   {                                             \
 353     static volatile int ctr = 0;                \
 354     int v = ++ctr;                              \
 355     if ((v & (v - 1)) == 0) {                   \
 356       tty->print_cr("INFO: " #nom " : %d", v);  \
 357       tty->flush();                             \
 358     }                                           \
 359   }
 360 
 361 #undef  TEVENT
 362 #define TEVENT(nom) {;}
 363 
 364 
 365 #endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
--- EOF ---