vm/runtime/objectMonitor.hpp

/*
 * Copyright (c) 1998, 2013, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * 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).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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#ifndef SHARE_VM_RUNTIME_OBJECTMONITOR_HPP
#define SHARE_VM_RUNTIME_OBJECTMONITOR_HPP

#include "runtime/os.hpp"
#include "runtime/park.hpp"
#include "runtime/perfData.hpp"

// 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 };
  enum Sorted  { PREPEND, APPEND, SORTED };
  ObjectWaiter * volatile _next;
  ObjectWaiter * volatile _prev;
  Thread*       _thread;
  jlong         _notifier_tid;
  ParkEvent *   _event;
  volatile int  _notified;
  volatile TStates TState;
  Sorted        _Sorted;           // List placement disposition
  bool          _active;           // Contention monitoring is enabled
 public:
  ObjectWaiter(Thread* thread);

  void wait_reenter_begin(ObjectMonitor *mon);
  void wait_reenter_end(ObjectMonitor *mon);
};

// forward declaration to avoid include tracing.hpp
class EventJavaMonitorWait;

// WARNING:
//   This is a very sensitive and fragile class. DO NOT make any
// change unless you are fully aware of the underlying semantics.

//   This class can not inherit from any other class, because I have
// to let the displaced header be the very first word. Otherwise I
// have to let markOop include this file, which would export the
// monitor data structure to everywhere.
//
// The ObjectMonitor class is used to implement JavaMonitors which have
// transformed from the lightweight structure of the thread stack to a
// heavy weight lock due to contention

// It is also used as RawMonitor by the JVMTI


class ObjectMonitor {
 public:
  enum {
    OM_OK,                    // no error
    OM_SYSTEM_ERROR,          // operating system error
    OM_ILLEGAL_MONITOR_STATE, // IllegalMonitorStateException
    OM_INTERRUPTED,           // Thread.interrupt()
    OM_TIMED_OUT              // Object.wait() timed out
  };

 public:
  // 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 count_offset_in_bytes()       { return offset_of(ObjectMonitor, _count);      }
  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);  }
  static int FreeNext_offset_in_bytes()    { return offset_of(ObjectMonitor, FreeNext);    }
  static int WaitSet_offset_in_bytes()     { return offset_of(ObjectMonitor, _WaitSet);   }
  static int Responsible_offset_in_bytes() { return offset_of(ObjectMonitor, _Responsible); }
  static int Spinner_offset_in_bytes()     { return offset_of(ObjectMonitor, _Spinner);    }

 public:
  // Eventually we'll make provisions for multiple callbacks, but
  // now one will suffice.
  static int (*SpinCallbackFunction)(intptr_t, int);
  static intptr_t SpinCallbackArgument;


 public:
  markOop   header() const;
  void      set_header(markOop hdr);

  intptr_t is_busy() const {
    // TODO-FIXME: merge _count and _waiters.
    // TODO-FIXME: assert _owner == null implies _recursions = 0
    // TODO-FIXME: assert _WaitSet != null implies _count > 0
    return _count|_waiters|intptr_t(_owner)|intptr_t(_cxq)|intptr_t(_EntryList);
  }

  intptr_t  is_entered(Thread* current) const;

  void*     owner() const;
  void      set_owner(void* owner);

  intptr_t  waiters() const;

  intptr_t  count() const;
  void      set_count(intptr_t count);
  intptr_t  contentions() const;
  intptr_t  recursions() const                                         { return _recursions; }

  // JVM/DI GetMonitorInfo() needs this
  ObjectWaiter* first_waiter()                                         { return _WaitSet; }
  ObjectWaiter* next_waiter(ObjectWaiter* o)                           { return o->_next; }
  Thread* thread_of_waiter(ObjectWaiter* o)                            { return o->_thread; }

  // initialize the monitor, exception the semaphore, all other fields
  // are simple integers or pointers
  ObjectMonitor() {
    _header       = NULL;
    _count        = 0;
    _waiters      = 0,
    _recursions   = 0;
    _object       = NULL;
    _owner        = NULL;
    _WaitSet      = NULL;
    _WaitSetLock  = 0;
    _Responsible  = NULL;
    _succ         = NULL;
    _cxq          = NULL;
    FreeNext      = NULL;
    _EntryList    = NULL;
    _SpinFreq     = 0;
    _SpinClock    = 0;
    OwnerIsThread = 0;
    _previous_owner_tid = 0;
  }

  ~ObjectMonitor() {
   // TODO: Add asserts ...
   // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
   // _count == 0 _EntryList  == NULL etc
  }

private:
  void Recycle() {
    // TODO: add stronger asserts ...
    // _cxq == 0 _succ == NULL _owner == NULL _waiters == 0
    // _count == 0 EntryList  == NULL
    // _recursions == 0 _WaitSet == NULL
    // TODO: assert (is_busy()|_recursions) == 0
    _succ          = NULL;
    _EntryList     = NULL;
    _cxq           = NULL;
    _WaitSet       = NULL;
    _recursions    = 0;
    _SpinFreq      = 0;
    _SpinClock     = 0;
    OwnerIsThread  = 0;
  }

public:

  void*     object() const;
  void*     object_addr();
  void      set_object(void* obj);

  bool      check(TRAPS);       // true if the thread owns the monitor.
  void      check_slow(TRAPS);
  void      clear();
#ifndef PRODUCT
  void      verify();
  void      print();
#endif

  bool      try_enter(TRAPS);
  void      enter(TRAPS);
  void      exit(bool not_suspended, TRAPS);
  void      wait(jlong millis, bool interruptable, TRAPS);
  void      notify(TRAPS);
  void      notifyAll(TRAPS);

// Use the following at your own risk
  intptr_t  complete_exit(TRAPS);
  void      reenter(intptr_t recursions, TRAPS);

 private:
  void      AddWaiter(ObjectWaiter * waiter);
  static    void DeferredInitialize();

  ObjectWaiter * DequeueWaiter();
  void      DequeueSpecificWaiter(ObjectWaiter * waiter);
  void      EnterI(TRAPS);
  void      ReenterI(Thread * Self, ObjectWaiter * SelfNode);
  void      UnlinkAfterAcquire(Thread * Self, ObjectWaiter * SelfNode);
  int       TryLock(Thread * Self);
  int       NotRunnable(Thread * Self, Thread * Owner);
  int       TrySpin_Fixed(Thread * Self);
  int       TrySpin_VaryFrequency(Thread * Self);
  int       TrySpin_VaryDuration(Thread * Self);
  void      ctAsserts();
  void      ExitEpilog(Thread * Self, ObjectWaiter * Wakee);
  bool      ExitSuspendEquivalent(JavaThread * Self);
  void      post_monitor_wait_event(EventJavaMonitorWait * event,
                                                   jlong notifier_tid,
                                                   jlong timeout,
                                                   bool timedout);

 private:
  friend class ObjectSynchronizer;
  friend class ObjectWaiter;
  friend class VMStructs;

  // WARNING: this must be the very first word of ObjectMonitor
  // This means this class can't use any virtual member functions.
  // TODO-FIXME: assert that offsetof(_header) is 0 or get rid of the
  // implicit 0 offset in emitted code.

  volatile markOop   _header;       // displaced object header word - mark
  void*     volatile _object;       // backward object pointer - strong root

  double SharingPad[1];           // temp to reduce false sharing

  // All the following fields must be machine word aligned
  // The VM assumes write ordering wrt these fields, which can be
  // read from other threads.

 protected:                         // protected for jvmtiRawMonitor
  void *  volatile _owner;          // pointer to owning thread OR BasicLock
  volatile jlong _previous_owner_tid; // thread id of the previous owner of the monitor
  volatile intptr_t  _recursions;   // recursion count, 0 for first entry
 private:
  int OwnerIsThread;               // _owner is (Thread *) vs SP/BasicLock
  ObjectWaiter * volatile _cxq;    // LL of recently-arrived threads blocked on entry.
                                    // The list is actually composed of WaitNodes, acting
                                    // as proxies for Threads.
 protected:
  ObjectWaiter * volatile _EntryList;     // Threads blocked on entry or reentry.
 private:
  Thread * volatile _succ;          // Heir presumptive thread - used for futile wakeup throttling
  Thread * volatile _Responsible;
  int _PromptDrain;                // rqst to drain cxq into EntryList ASAP

  volatile int _Spinner;           // for exit->spinner handoff optimization
  volatile int _SpinFreq;          // Spin 1-out-of-N attempts: success rate
  volatile int _SpinClock;
  volatile int _SpinDuration;
  volatile intptr_t _SpinState;    // MCS/CLH list of spinners

  // TODO-FIXME: _count, _waiters and _recursions should be of
  // type int, or int32_t but not intptr_t.  There's no reason
  // to use 64-bit fields for these variables on a 64-bit JVM.

  volatile intptr_t  _count;        // reference count to prevent reclamation/deflation
                                    // at stop-the-world time.  See deflate_idle_monitors().
                                    // _count is approximately |_WaitSet| + |_EntryList|
 protected:
  volatile intptr_t  _waiters;      // number of waiting threads
 private:
 protected:
  ObjectWaiter * volatile _WaitSet; // LL of threads wait()ing on the monitor
 private:
  volatile int _WaitSetLock;        // protects Wait Queue - simple spinlock

 public:
  int _QMix;                       // Mixed prepend queue discipline
  ObjectMonitor * FreeNext;        // Free list linkage
  intptr_t StatA, StatsB;

 public:
  static void Initialize();
  static PerfCounter * _sync_ContendedLockAttempts;
  static PerfCounter * _sync_FutileWakeups;
  static PerfCounter * _sync_Parks;
  static PerfCounter * _sync_EmptyNotifications;
  static PerfCounter * _sync_Notifications;
  static PerfCounter * _sync_SlowEnter;
  static PerfCounter * _sync_SlowExit;
  static PerfCounter * _sync_SlowNotify;
  static PerfCounter * _sync_SlowNotifyAll;
  static PerfCounter * _sync_FailedSpins;
  static PerfCounter * _sync_SuccessfulSpins;
  static PerfCounter * _sync_PrivateA;
  static PerfCounter * _sync_PrivateB;
  static PerfCounter * _sync_MonInCirculation;
  static PerfCounter * _sync_MonScavenged;
  static PerfCounter * _sync_Inflations;
  static PerfCounter * _sync_Deflations;
  static PerfLongVariable * _sync_MonExtant;

 public:
  static int Knob_Verbose;
  static int Knob_SpinLimit;
  void* operator new (size_t size) throw() {
    return AllocateHeap(size, mtInternal);
  }
  void* operator new[] (size_t size) throw() {
    return operator new (size);
  }
  void operator delete(void* p) {
    FreeHeap(p, mtInternal);
  }
  void operator delete[] (void *p) {
    operator delete(p);
  }
};

#undef TEVENT
#define TEVENT(nom) {if (SyncVerbose) FEVENT(nom); }

#define FEVENT(nom) { static volatile int ctr = 0; int v = ++ctr; if ((v & (v-1)) == 0) { ::printf (#nom " : %d \n", v); ::fflush(stdout); }}

#undef  TEVENT
#define TEVENT(nom) {;}


#endif // SHARE_VM_RUNTIME_OBJECTMONITOR_HPP