1 /*
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   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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   6  * under the terms of the GNU General Public License version 2 only, as
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  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).
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  24 
  25 #ifndef SHARE_RUNTIME_OBJECTMONITOR_HPP
  26 #define SHARE_RUNTIME_OBJECTMONITOR_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "memory/padded.hpp"
  30 #include "runtime/os.hpp"
  31 #include "runtime/park.hpp"
  32 #include "runtime/perfData.hpp"
  33 
  34 class ObjectMonitor;
  35 
  36 // ObjectWaiter serves as a "proxy" or surrogate thread.
  37 // TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific
  38 // ParkEvent instead.  Beware, however, that the JVMTI code
  39 // knows about ObjectWaiters, so we'll have to reconcile that code.
  40 // See next_waiter(), first_waiter(), etc.
  41 
  42 class ObjectWaiter : public StackObj {
  43  public:
  44   enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };
  45   enum Sorted  { PREPEND, APPEND, SORTED };
  46   ObjectWaiter * volatile _next;
  47   ObjectWaiter * volatile _prev;
  48   Thread*       _thread;
  49   jlong         _notifier_tid;
  50   ParkEvent *   _event;
  51   volatile int  _notified;
  52   volatile TStates TState;
  53   Sorted        _Sorted;           // List placement disposition
  54   bool          _active;           // Contention monitoring is enabled
  55  public:
  56   ObjectWaiter(Thread* thread);
  57 
  58   void wait_reenter_begin(ObjectMonitor *mon);
  59   void wait_reenter_end(ObjectMonitor *mon);
  60 };
  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 TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are
 107 //   enforced.
 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 TEST_VM(SynchronizerTest, sanity) gtest.
 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   JVMCI_ONLY(friend class JVMCIVMStructs;)
 143 
 144   volatile markOop   _header;       // displaced object header word - mark
 145   void*     volatile _object;       // backward object pointer - strong root
 146  public:
 147   ObjectMonitor*     FreeNext;      // Free list linkage
 148  private:
 149   DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,
 150                         sizeof(volatile markOop) + sizeof(void * volatile) +
 151                         sizeof(ObjectMonitor *));
 152  protected:                         // protected for JvmtiRawMonitor
 153   void *  volatile _owner;          // pointer to owning thread OR BasicLock
 154   volatile jlong _previous_owner_tid;  // thread id of the previous owner of the monitor
 155   volatile intptr_t  _recursions;   // recursion count, 0 for first entry
 156   ObjectWaiter * volatile _EntryList; // Threads blocked on entry or reentry.
 157                                       // The list is actually composed of WaitNodes,
 158                                       // acting as proxies for Threads.
 159  private:
 160   ObjectWaiter * volatile _cxq;     // LL of recently-arrived threads blocked on entry.
 161   Thread * volatile _succ;          // Heir presumptive thread - used for futile wakeup throttling
 162   Thread * volatile _Responsible;
 163 
 164   volatile int _Spinner;            // for exit->spinner handoff optimization
 165   volatile int _SpinDuration;
 166 
 167   volatile jint  _contentions;      // Number of active contentions in enter(). It is used by is_busy()
 168                                     // along with other fields to determine if an ObjectMonitor can be
 169                                     // deflated. See ObjectSynchronizer::deflate_monitor().
 170  protected:
 171   ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
 172   volatile jint  _waiters;          // number of waiting threads
 173  private:
 174   volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock
 175 
 176  public:
 177   static void Initialize();
 178 
 179   // Only perform a PerfData operation if the PerfData object has been
 180   // allocated and if the PerfDataManager has not freed the PerfData
 181   // objects which can happen at normal VM shutdown.
 182   //
 183   #define OM_PERFDATA_OP(f, op_str)              \
 184     do {                                         \
 185       if (ObjectMonitor::_sync_ ## f != NULL &&  \
 186           PerfDataManager::has_PerfData()) {     \
 187         ObjectMonitor::_sync_ ## f->op_str;      \
 188       }                                          \
 189     } while (0)
 190 
 191   static PerfCounter * _sync_ContendedLockAttempts;
 192   static PerfCounter * _sync_FutileWakeups;
 193   static PerfCounter * _sync_Parks;
 194   static PerfCounter * _sync_Notifications;
 195   static PerfCounter * _sync_Inflations;
 196   static PerfCounter * _sync_Deflations;
 197   static PerfLongVariable * _sync_MonExtant;
 198 
 199   static int Knob_SpinLimit;
 200 
 201   void* operator new (size_t size) throw();
 202   void* operator new[] (size_t size) throw();
 203   void operator delete(void* p);
 204   void operator delete[] (void *p);
 205 
 206   // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...
 207   // ByteSize would also be an appropriate type.
 208   static int header_offset_in_bytes()      { return offset_of(ObjectMonitor, _header); }
 209   static int object_offset_in_bytes()      { return offset_of(ObjectMonitor, _object); }
 210   static int owner_offset_in_bytes()       { return offset_of(ObjectMonitor, _owner); }
 211   static int recursions_offset_in_bytes()  { return offset_of(ObjectMonitor, _recursions); }
 212   static int cxq_offset_in_bytes()         { return offset_of(ObjectMonitor, _cxq); }
 213   static int succ_offset_in_bytes()        { return offset_of(ObjectMonitor, _succ); }
 214   static int EntryList_offset_in_bytes()   { return offset_of(ObjectMonitor, _EntryList); }
 215 
 216   // ObjectMonitor references can be ORed with markOopDesc::monitor_value
 217   // as part of the ObjectMonitor tagging mechanism. When we combine an
 218   // ObjectMonitor reference with an offset, we need to remove the tag
 219   // value in order to generate the proper address.
 220   //
 221   // We can either adjust the ObjectMonitor reference and then add the
 222   // offset or we can adjust the offset that is added to the ObjectMonitor
 223   // reference. The latter avoids an AGI (Address Generation Interlock)
 224   // stall so the helper macro adjusts the offset value that is returned
 225   // to the ObjectMonitor reference manipulation code:
 226   //
 227   #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \
 228     ((ObjectMonitor::f ## _offset_in_bytes()) - markOopDesc::monitor_value)
 229 
 230   markOop   header() const;
 231   volatile markOop* header_addr();
 232   void      set_header(markOop hdr);
 233 
 234   intptr_t is_busy() const {
 235     // TODO-FIXME: assert _owner == null implies _recursions = 0
 236     return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
 237   }
 238   const char* is_busy_to_string(stringStream* ss);
 239 
 240   intptr_t  is_entered(Thread* current) const;
 241 
 242   void*     owner() const;
 243   void      set_owner(void* owner);
 244 
 245   jint      waiters() const;
 246 
 247   jint      contentions() const;
 248   intptr_t  recursions() const                                         { return _recursions; }
 249 
 250   // JVM/TI GetObjectMonitorUsage() needs this:
 251   ObjectWaiter* first_waiter()                                         { return _WaitSet; }
 252   ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
 253   Thread* thread_of_waiter(ObjectWaiter* o)                            { return o->_thread; }
 254 
 255  protected:
 256   // We don't typically expect or want the ctors or dtors to run.
 257   // normal ObjectMonitors are type-stable and immortal.
 258   ObjectMonitor() { ::memset((void *)this, 0, sizeof(*this)); }
 259 
 260   ~ObjectMonitor() {
 261     // TODO: Add asserts ...
 262     // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
 263     // _contentions == 0 _EntryList  == NULL etc
 264   }
 265 
 266  private:
 267   void Recycle() {
 268     // TODO: add stronger asserts ...
 269     // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
 270     // _contentions == 0 EntryList  == NULL
 271     // _recursions == 0 _WaitSet == NULL
 272     DEBUG_ONLY(stringStream ss;)
 273     assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "
 274            "recursions=" INTPTR_FORMAT, is_busy_to_string(&ss), _recursions);
 275     _succ          = NULL;
 276     _EntryList     = NULL;
 277     _cxq           = NULL;
 278     _WaitSet       = NULL;
 279     _recursions    = 0;
 280   }
 281 
 282  public:
 283 
 284   void*     object() const;
 285   void*     object_addr();
 286   void      set_object(void* obj);
 287 
 288   // Returns true if the specified thread owns the ObjectMonitor. Otherwise
 289   // returns false and throws IllegalMonitorStateException (IMSE).
 290   bool      check_owner(Thread* THREAD);
 291   void      clear();
 292 
 293   void      enter(TRAPS);
 294   void      exit(bool not_suspended, TRAPS);
 295   void      wait(jlong millis, bool interruptable, TRAPS);
 296   void      notify(TRAPS);
 297   void      notifyAll(TRAPS);
 298 
 299   void      print() const;
 300   void      print_on(outputStream* st) const;
 301 
 302 // Use the following at your own risk
 303   intptr_t  complete_exit(TRAPS);
 304   void      reenter(intptr_t recursions, TRAPS);
 305 
 306  private:
 307   void      AddWaiter(ObjectWaiter * waiter);
 308   void      INotify(Thread * Self);
 309   ObjectWaiter * DequeueWaiter();
 310   void      DequeueSpecificWaiter(ObjectWaiter * waiter);
 311   void      EnterI(TRAPS);
 312   void      ReenterI(Thread * Self, ObjectWaiter * SelfNode);
 313   void      UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
 314   int       TryLock(Thread * Self);
 315   int       NotRunnable(Thread * Self, Thread * Owner);
 316   int       TrySpin(Thread * Self);
 317   void      ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
 318   bool      ExitSuspendEquivalent(JavaThread * Self);
 319 };
 320 
 321 #endif // SHARE_RUNTIME_OBJECTMONITOR_HPP