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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 * published by the Free Software Foundation.

 *

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 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

 * version 2 for more details (a copy is included in the LICENSE file that

 * accompanied this code).

 *

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 * 2 along with this work; if not, write to the Free Software Foundation,

 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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#ifndef SHARE_RUNTIME_OBJECTMONITOR_HPP

#define SHARE_RUNTIME_OBJECTMONITOR_HPP

#include "memory/allocation.hpp"

#include "memory/padded.hpp"

#include "oops/markWord.hpp"

#include "runtime/os.hpp"

#include "runtime/park.hpp"

#include "runtime/perfData.hpp"

class ObjectMonitor;

// ObjectWaiter serves as a "proxy" or surrogate thread.

// TODO-FIXME: Eliminate ObjectWaiter and use the thread-specific

// ParkEvent instead.  Beware, however, that the JVMTI code

// knows about ObjectWaiters, so we'll have to reconcile that code.

// See next_waiter(), first_waiter(), etc.

class ObjectWaiter : public StackObj {

 public:

  enum TStates { TS_UNDEF, TS_READY, TS_RUN, TS_WAIT, TS_ENTER, TS_CXQ };

  ObjectWaiter* volatile _next;

  ObjectWaiter* volatile _prev;

  Thread*       _thread;

  jlong         _notifier_tid;

  ParkEvent *   _event;

  volatile int  _notified;

  volatile TStates TState;

  bool          _active;           // Contention monitoring is enabled

 public:

  ObjectWaiter(Thread* thread);

  void wait_reenter_begin(ObjectMonitor *mon);

  void wait_reenter_end(ObjectMonitor *mon);

};

// The ObjectMonitor class implements the heavyweight version of a

// JavaMonitor. The lightweight BasicLock/stack lock version has been

// inflated into an ObjectMonitor. This inflation is typically due to

// contention or use of Object.wait().

//

// WARNING: This is a very sensitive and fragile class. DO NOT make any

// changes unless you are fully aware of the underlying semantics.

//

// ObjectMonitor Layout Overview/Highlights/Restrictions:

//

// - The _header field must be at offset 0 because the displaced header

//   from markWord is stored there. We do not want markWord.hpp to include

//   ObjectMonitor.hpp to avoid exposing ObjectMonitor everywhere. This

//   means that ObjectMonitor cannot inherit from any other class nor can

//   it use any virtual member functions. This restriction is critical to

//   the proper functioning of the VM.

// - The _header and _owner fields should be separated by enough space

//   to avoid false sharing due to parallel access by different threads.

//   This is an advisory recommendation.

// - The general layout of the fields in ObjectMonitor is:

//     _header

//     <lightly_used_fields>

//     <optional padding>

//     _owner

//     <remaining_fields>

// - The VM assumes write ordering and machine word alignment with

//   respect to the _owner field and the <remaining_fields> that can

//   be read in parallel by other threads.

// - Generally fields that are accessed closely together in time should

//   be placed proximally in space to promote data cache locality. That

//   is, temporal locality should condition spatial locality.

// - We have to balance avoiding false sharing with excessive invalidation

//   from coherence traffic. As such, we try to cluster fields that tend

//   to be _written_ at approximately the same time onto the same data

//   cache line.

// - We also have to balance the natural tension between minimizing

//   single threaded capacity misses with excessive multi-threaded

//   coherency misses. There is no single optimal layout for both

//   single-threaded and multi-threaded environments.

//

// - See TEST_VM(ObjectMonitor, sanity) gtest for how critical restrictions are

//   enforced.

// - Adjacent ObjectMonitors should be separated by enough space to avoid

//   false sharing. This is handled by the ObjectMonitor allocation code

//   in synchronizer.cpp. Also see TEST_VM(SynchronizerTest, sanity) gtest.

//

// Futures notes:

//   - Separating _owner from the <remaining_fields> by enough space to

//     avoid false sharing might be profitable. Given

//     http://blogs.oracle.com/dave/entry/cas_and_cache_trivia_invalidate

//     we know that the CAS in monitorenter will invalidate the line

//     underlying _owner. We want to avoid an L1 data cache miss on that

//     same line for monitorexit. Putting these <remaining_fields>:

//     _recursions, _EntryList, _cxq, and _succ, all of which may be

//     fetched in the inflated unlock path, on a different cache line

//     would make them immune to CAS-based invalidation from the _owner

//     field.

//

//   - The _recursions field should be of type int, or int32_t but not

//     intptr_t. There's no reason to use a 64-bit type for this field

//     in a 64-bit JVM.

class ObjectMonitor {

  friend class ObjectSynchronizer;

  friend class ObjectWaiter;

  friend class VMStructs;

  JVMCI_ONLY(friend class JVMCIVMStructs;)

  // The sync code expects the header field to be at offset zero (0).

  // Enforced by the assert() in header_addr().

  volatile markWord _header;        // displaced object header word - mark

  void* volatile _object;           // backward object pointer - strong root

 public:

  ObjectMonitor* _next_om;          // Next ObjectMonitor* linkage

 private:

  // Separate _header and _owner on different cache lines since both can

  // have busy multi-threaded access. _header and _object are set at

  // initial inflation and _object doesn't change until deflation so

  // _object is a good choice to share the cache line with _header.

  // _next_om shares _header's cache line for pre-monitor list historical

  // reasons. _next_om only changes if the next ObjectMonitor is deflated.

  DEFINE_PAD_MINUS_SIZE(0, DEFAULT_CACHE_LINE_SIZE,

                        sizeof(volatile markWord) + sizeof(void* volatile) +

                        sizeof(ObjectMonitor *));

  void* volatile _owner;            // pointer to owning thread OR BasicLock

  volatile jlong _previous_owner_tid;  // thread id of the previous owner of the monitor

  ObjectWaiter* volatile _EntryList;  // Threads blocked on entry or reentry.

                                      // The list is actually composed of WaitNodes,

                                      // acting as proxies for Threads.

  ObjectWaiter* volatile _cxq;      // LL of recently-arrived threads blocked on entry.

  Thread* volatile _succ;           // Heir presumptive thread - used for futile wakeup throttling

  Thread* volatile _Responsible;

  volatile int _Spinner;            // for exit->spinner handoff optimization

  volatile int _SpinDuration;

  volatile jint  _contentions;      // Number of active contentions in enter(). It is used by is_busy()

                                    // along with other fields to determine if an ObjectMonitor can be

                                    // deflated. See ObjectSynchronizer::deflate_monitor().

 protected:

  ObjectWaiter* volatile _WaitSet;  // LL of threads wait()ing on the monitor

  volatile jint  _waiters;          // number of waiting threads

 private:

  volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock

 public:

  static void Initialize();

  // Only perform a PerfData operation if the PerfData object has been

  // allocated and if the PerfDataManager has not freed the PerfData

  // objects which can happen at normal VM shutdown.

  //

  #define OM_PERFDATA_OP(f, op_str)              \

    do {                                         \

      if (ObjectMonitor::_sync_ ## f != NULL &&  \

          PerfDataManager::has_PerfData()) {     \

        ObjectMonitor::_sync_ ## f->op_str;      \

      }                                          \

    } while (0)

  static PerfCounter * _sync_ContendedLockAttempts;

  static PerfCounter * _sync_FutileWakeups;

  static PerfCounter * _sync_Parks;

  static PerfCounter * _sync_Notifications;

  static PerfCounter * _sync_Inflations;

  static PerfCounter * _sync_Deflations;

  static PerfLongVariable * _sync_MonExtant;

  static int Knob_SpinLimit;

  void* operator new (size_t size) throw();

  void* operator new[] (size_t size) throw();

  void operator delete(void* p);

  void operator delete[] (void* p);

  // TODO-FIXME: the "offset" routines should return a type of off_t instead of int ...

  // ByteSize would also be an appropriate type.

  static int header_offset_in_bytes()      { return offset_of(ObjectMonitor, _header); }

  static int object_offset_in_bytes()      { return offset_of(ObjectMonitor, _object); }

  static int owner_offset_in_bytes()       { return offset_of(ObjectMonitor, _owner); }

  static int recursions_offset_in_bytes()  { return offset_of(ObjectMonitor, _recursions); }

  static int cxq_offset_in_bytes()         { return offset_of(ObjectMonitor, _cxq); }

  static int succ_offset_in_bytes()        { return offset_of(ObjectMonitor, _succ); }

  static int EntryList_offset_in_bytes()   { return offset_of(ObjectMonitor, _EntryList); }

  // ObjectMonitor references can be ORed with markWord::monitor_value

  // as part of the ObjectMonitor tagging mechanism. When we combine an

  // ObjectMonitor reference with an offset, we need to remove the tag

  // value in order to generate the proper address.

  //

  // We can either adjust the ObjectMonitor reference and then add the

  // offset or we can adjust the offset that is added to the ObjectMonitor

  // reference. The latter avoids an AGI (Address Generation Interlock)

  // stall so the helper macro adjusts the offset value that is returned

  // to the ObjectMonitor reference manipulation code:

  //

  #define OM_OFFSET_NO_MONITOR_VALUE_TAG(f) \

    ((ObjectMonitor::f ## _offset_in_bytes()) - markWord::monitor_value)

  markWord           header() const;

  volatile markWord* header_addr();

  void               set_header(markWord hdr);

  intptr_t is_busy() const {

    // TODO-FIXME: assert _owner == null implies _recursions = 0

    return _contentions|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);

  }

  const char* is_busy_to_string(stringStream* ss);

  intptr_t  is_entered(Thread* current) const;

  void*     owner() const;

  void      set_owner(void* owner);

  jint      waiters() const;

  jint      contentions() const;

  // JVM/TI GetObjectMonitorUsage() needs this:

  ObjectWaiter* first_waiter()                                         { return _WaitSet; }

  ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }

  Thread* thread_of_waiter(ObjectWaiter* o)                            { return o->_thread; }

 protected:

  // We don't typically expect or want the ctors or dtors to run.

  // normal ObjectMonitors are type-stable and immortal.

  ObjectMonitor() { ::memset((void*)this, 0, sizeof(*this)); }

  ~ObjectMonitor() {

    // TODO: Add asserts ...

    // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0

    // _contentions == 0 _EntryList  == NULL etc

  }

 private:

  void Recycle() {

    // TODO: add stronger asserts ...

    // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0

    // _contentions == 0 EntryList  == NULL

    // _recursions == 0 _WaitSet == NULL

    DEBUG_ONLY(stringStream ss;)

    assert((is_busy() | _recursions) == 0, "freeing in-use monitor: %s, "

    _succ          = NULL;

    _EntryList     = NULL;

    _cxq           = NULL;

    _WaitSet       = NULL;

    _recursions    = 0;

  }

 public:

  void*     object() const;

  void*     object_addr();

  void      set_object(void* obj);

  // Returns true if the specified thread owns the ObjectMonitor. Otherwise

  // returns false and throws IllegalMonitorStateException (IMSE).

  bool      check_owner(Thread* THREAD);

  void      clear();

  void      enter(TRAPS);

  void      exit(bool not_suspended, TRAPS);

  void      wait(jlong millis, bool interruptable, TRAPS);

  void      notify(TRAPS);

  void      notifyAll(TRAPS);

  void      print() const;

  void      print_on(outputStream* st) const;

// Use the following at your own risk

 private:

  void      AddWaiter(ObjectWaiter* waiter);

  void      INotify(Thread* self);

  ObjectWaiter* DequeueWaiter();

  void      DequeueSpecificWaiter(ObjectWaiter* waiter);

  void      EnterI(TRAPS);

  void      ReenterI(Thread* self, ObjectWaiter* self_node);

  void      UnlinkAfterAcquire(Thread* self, ObjectWaiter* self_node);

  int       TryLock(Thread* self);

  int       NotRunnable(Thread* self, Thread * Owner);

  int       TrySpin(Thread* self);

  void      ExitEpilog(Thread* self, ObjectWaiter* Wakee);

  bool      ExitSuspendEquivalent(JavaThread* self);

};

#endif // SHARE_RUNTIME_OBJECTMONITOR_HPP