src/hotspot/share/oops/markWord.hpp - openjdk/jdk25u - Git at Google

 /*
  * Copyright (c) 1997, 2024, 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
  * or visit www.oracle.com if you need additional information or have any
  * questions.
  *
  */

 #ifndef SHARE_OOPS_MARKWORD_HPP
 #define SHARE_OOPS_MARKWORD_HPP

 #include "metaprogramming/primitiveConversions.hpp"
 #include "oops/compressedKlass.hpp"
 #include "oops/oopsHierarchy.hpp"
 #include "runtime/globals.hpp"

 #include <type_traits>

 // The markWord describes the header of an object.
 //
 // Bit-format of an object header (most significant first, big endian layout below):
 //
 //  32 bits:
 //  --------
 //             hash:25 ------------>| age:4  self-fwd:1  lock:2 (normal object)
 //
 //  64 bits:
 //  --------
 //  unused:22 hash:31 -->| unused_gap:4  age:4  self-fwd:1  lock:2 (normal object)
 //
 //  64 bits (with compact headers):
 //  -------------------------------
 //  klass:22  hash:31 -->| unused_gap:4  age:4  self-fwd:1  lock:2 (normal object)
 //
 //  - hash contains the identity hash value: largest value is
 //    31 bits, see os::random().  Also, 64-bit vm's require
 //    a hash value no bigger than 32 bits because they will not
 //    properly generate a mask larger than that: see library_call.cpp
 //
 //  - the two lock bits are used to describe three states: locked/unlocked and monitor.
 //
 //    [ptr             | 00]  locked             ptr points to real header on stack (stack-locking in use)
 //    [header          | 00]  locked             locked regular object header (fast-locking in use)
 //    [header          | 01]  unlocked           regular object header
 //    [ptr             | 10]  monitor            inflated lock (header is swapped out, UseObjectMonitorTable == false)
 //    [header          | 10]  monitor            inflated lock (UseObjectMonitorTable == true)
 //    [ptr             | 11]  marked             used to mark an object
 //    [0 ............ 0| 00]  inflating          inflation in progress (stack-locking in use)
 //
 //    We assume that stack/thread pointers have the lowest two bits cleared.
 //
 //  - INFLATING() is a distinguished markword value of all zeros that is
 //    used when inflating an existing stack-lock into an ObjectMonitor.
 //    See below for is_being_inflated() and INFLATING().

 class BasicLock;
 class ObjectMonitor;
 class JavaThread;
 class outputStream;

 class markWord {
  private:
   uintptr_t _value;

  public:
   explicit markWord(uintptr_t value) : _value(value) {}

   markWord() = default;         // Doesn't initialize _value.

   // It is critical for performance that this class be trivially
   // destructable, copyable, and assignable.
   ~markWord() = default;
   markWord(const markWord&) = default;
   markWord& operator=(const markWord&) = default;

   static markWord from_pointer(void* ptr) {
     return markWord((uintptr_t)ptr);
   }
   void* to_pointer() const {
     return (void*)_value;
   }

   bool operator==(const markWord& other) const {
     return _value == other._value;
   }
   bool operator!=(const markWord& other) const {
     return !operator==(other);
   }

   // Conversion
   uintptr_t value() const { return _value; }

   // Constants
   static const int age_bits                       = 4;
   static const int lock_bits                      = 2;
   static const int self_fwd_bits                  = 1;
   static const int max_hash_bits                  = BitsPerWord - age_bits - lock_bits - self_fwd_bits;
   static const int hash_bits                      = max_hash_bits > 31 ? 31 : max_hash_bits;
   static const int unused_gap_bits                = LP64_ONLY(4) NOT_LP64(0); // Reserved for Valhalla.

   static const int lock_shift                     = 0;
   static const int self_fwd_shift                 = lock_shift + lock_bits;
   static const int age_shift                      = self_fwd_shift + self_fwd_bits;
   static const int hash_shift                     = age_shift + age_bits + unused_gap_bits;

   static const uintptr_t lock_mask                = right_n_bits(lock_bits);
   static const uintptr_t lock_mask_in_place       = lock_mask << lock_shift;
   static const uintptr_t self_fwd_mask            = right_n_bits(self_fwd_bits);
   static const uintptr_t self_fwd_mask_in_place   = self_fwd_mask << self_fwd_shift;
   static const uintptr_t age_mask                 = right_n_bits(age_bits);
   static const uintptr_t age_mask_in_place        = age_mask << age_shift;
   static const uintptr_t hash_mask                = right_n_bits(hash_bits);
   static const uintptr_t hash_mask_in_place       = hash_mask << hash_shift;

 #ifdef _LP64
   // Used only with compact headers:
   // We store the (narrow) Klass* in the bits 43 to 64.

   // These are for bit-precise extraction of the narrow Klass* from the 64-bit Markword
   static constexpr int klass_offset_in_bytes      = 4;
   static constexpr int klass_shift                = hash_shift + hash_bits;
   static constexpr int klass_shift_at_offset      = klass_shift - klass_offset_in_bytes * BitsPerByte;
   static constexpr int klass_bits                 = 22;
   static constexpr uintptr_t klass_mask           = right_n_bits(klass_bits);
   static constexpr uintptr_t klass_mask_in_place  = klass_mask << klass_shift;
 #endif


   static const uintptr_t locked_value             = 0;
   static const uintptr_t unlocked_value           = 1;
   static const uintptr_t monitor_value            = 2;
   static const uintptr_t marked_value             = 3;

   static const uintptr_t no_hash                  = 0 ;  // no hash value assigned
   static const uintptr_t no_hash_in_place         = (uintptr_t)no_hash << hash_shift;
   static const uintptr_t no_lock_in_place         = unlocked_value;

   static const uint max_age                       = age_mask;

   // Creates a markWord with all bits set to zero.
   static markWord zero() { return markWord(uintptr_t(0)); }

   // lock accessors (note that these assume lock_shift == 0)
   bool is_locked()   const {
     return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
   }
   bool is_unlocked() const {
     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
   }
   bool is_marked()   const {
     return (mask_bits(value(), lock_mask_in_place) == marked_value);
   }
   bool is_forwarded() const {
     // Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
     return mask_bits(value(), lock_mask_in_place | self_fwd_mask_in_place) >= static_cast<intptr_t>(marked_value);
   }
   bool is_neutral()  const {  // Not locked, or marked - a "clean" neutral state
     return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
   }

   // Special temporary state of the markWord while being inflated.
   // Code that looks at mark outside a lock need to take this into account.
   bool is_being_inflated() const { return (value() == 0); }

   // Distinguished markword value - used when inflating over
   // an existing stack-lock.  0 indicates the markword is "BUSY".
   // Lockword mutators that use a LD...CAS idiom should always
   // check for and avoid overwriting a 0 value installed by some
   // other thread.  (They should spin or block instead.  The 0 value
   // is transient and *should* be short-lived).
   // Fast-locking does not use INFLATING.
   static markWord INFLATING() { return zero(); }    // inflate-in-progress

   // Should this header be preserved during GC?
   bool must_be_preserved() const {
     return (!is_unlocked() || !has_no_hash());
   }

   // WARNING: The following routines are used EXCLUSIVELY by
   // synchronization functions. They are not really gc safe.
   // They must get updated if markWord layout get changed.
   markWord set_unlocked() const {
     return markWord(value() | unlocked_value);
   }
   bool has_locker() const {
     assert(LockingMode == LM_LEGACY, "should only be called with legacy stack locking");
     return (value() & lock_mask_in_place) == locked_value;
   }
   BasicLock* locker() const {
     assert(has_locker(), "check");
     return (BasicLock*) value();
   }

   bool is_fast_locked() const {
     assert(LockingMode == LM_LIGHTWEIGHT, "should only be called with new lightweight locking");
     return (value() & lock_mask_in_place) == locked_value;
   }
   markWord set_fast_locked() const {
     // Clear the lock_mask_in_place bits to set locked_value:
     return markWord(value() & ~lock_mask_in_place);
   }

   bool has_monitor() const {
     return ((value() & lock_mask_in_place) == monitor_value);
   }
   ObjectMonitor* monitor() const {
     assert(has_monitor(), "check");
     assert(!UseObjectMonitorTable, "Lightweight locking with OM table does not use markWord for monitors");
     // Use xor instead of &~ to provide one extra tag-bit check.
     return (ObjectMonitor*) (value() ^ monitor_value);
   }
   bool has_displaced_mark_helper() const {
     intptr_t lockbits = value() & lock_mask_in_place;
     if (LockingMode == LM_LIGHTWEIGHT) {
       return !UseObjectMonitorTable && lockbits == monitor_value;
     }
     // monitor (0b10) | stack-locked (0b00)?
     return (lockbits & unlocked_value) == 0;
   }
   markWord displaced_mark_helper() const;
   void set_displaced_mark_helper(markWord m) const;
   markWord copy_set_hash(intptr_t hash) const {
     uintptr_t tmp = value() & (~hash_mask_in_place);
     tmp |= ((hash & hash_mask) << hash_shift);
     return markWord(tmp);
   }
   // it is only used to be stored into BasicLock as the
   // indicator that the lock is using heavyweight monitor
   static markWord unused_mark() {
     return markWord(marked_value);
   }
   // the following two functions create the markWord to be
   // stored into object header, it encodes monitor info
   static markWord encode(BasicLock* lock) {
     return from_pointer(lock);
   }
   static markWord encode(ObjectMonitor* monitor) {
     assert(!UseObjectMonitorTable, "Lightweight locking with OM table does not use markWord for monitors");
     uintptr_t tmp = (uintptr_t) monitor;
     return markWord(tmp | monitor_value);
   }

   markWord set_has_monitor() const {
     return markWord((value() & ~lock_mask_in_place) | monitor_value);
   }

   // used to encode pointers during GC
   markWord clear_lock_bits() const { return markWord(value() & ~lock_mask_in_place); }

   // age operations
   markWord set_marked()   { return markWord((value() & ~lock_mask_in_place) | marked_value); }
   markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) | unlocked_value); }

   uint     age()           const { return (uint) mask_bits(value() >> age_shift, age_mask); }
   markWord set_age(uint v) const {
     assert((v & ~age_mask) == 0, "shouldn't overflow age field");
     return markWord((value() & ~age_mask_in_place) | ((v & age_mask) << age_shift));
   }
   markWord incr_age()      const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }

   // hash operations
   intptr_t hash() const {
     return mask_bits(value() >> hash_shift, hash_mask);
   }

   bool has_no_hash() const {
     return hash() == no_hash;
   }

   inline Klass* klass() const;
   inline Klass* klass_or_null() const;
   inline Klass* klass_without_asserts() const;
   inline narrowKlass narrow_klass() const;
   inline markWord set_narrow_klass(narrowKlass narrow_klass) const;

   // Prototype mark for initialization
   static markWord prototype() {
     return markWord( no_hash_in_place | no_lock_in_place );
   }

   // Debugging
   void print_on(outputStream* st, bool print_monitor_info = true) const;

   // Prepare address of oop for placement into mark
   inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }

   // Recover address of oop from encoded form used in mark
   inline void* decode_pointer() const { return (void*)clear_lock_bits().value(); }

   inline bool is_self_forwarded() const {
     NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
     return mask_bits(value(), self_fwd_mask_in_place) != 0;
   }

   inline markWord set_self_forwarded() const {
     NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
     return markWord(value() | self_fwd_mask_in_place);
   }

   inline markWord unset_self_forwarded() const {
     NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
     return markWord(value() & ~self_fwd_mask_in_place);
   }

   inline oop forwardee() const {
     return cast_to_oop(decode_pointer());
   }
 };

 // Support atomic operations.
 template<>
 struct PrimitiveConversions::Translate<markWord> : public std::true_type {
   typedef markWord Value;
   typedef uintptr_t Decayed;

   static Decayed decay(const Value& x) { return x.value(); }
   static Value recover(Decayed x) { return Value(x); }
 };

 #endif // SHARE_OOPS_MARKWORD_HPP
	/*
	* Copyright (c) 1997, 2024, 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
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*
	*/

	#ifndef SHARE_OOPS_MARKWORD_HPP
	#define SHARE_OOPS_MARKWORD_HPP

	#include "metaprogramming/primitiveConversions.hpp"
	#include "oops/compressedKlass.hpp"
	#include "oops/oopsHierarchy.hpp"
	#include "runtime/globals.hpp"

	#include <type_traits>

	// The markWord describes the header of an object.
	//
	// Bit-format of an object header (most significant first, big endian layout below):
	//
	// 32 bits:
	// --------
	// hash:25 ------------>\| age:4 self-fwd:1 lock:2 (normal object)
	//
	// 64 bits:
	// --------
	// unused:22 hash:31 -->\| unused_gap:4 age:4 self-fwd:1 lock:2 (normal object)
	//
	// 64 bits (with compact headers):
	// -------------------------------
	// klass:22 hash:31 -->\| unused_gap:4 age:4 self-fwd:1 lock:2 (normal object)
	//
	// - hash contains the identity hash value: largest value is
	// 31 bits, see os::random(). Also, 64-bit vm's require
	// a hash value no bigger than 32 bits because they will not
	// properly generate a mask larger than that: see library_call.cpp
	//
	// - the two lock bits are used to describe three states: locked/unlocked and monitor.
	//
	// [ptr \| 00] locked ptr points to real header on stack (stack-locking in use)
	// [header \| 00] locked locked regular object header (fast-locking in use)
	// [header \| 01] unlocked regular object header
	// [ptr \| 10] monitor inflated lock (header is swapped out, UseObjectMonitorTable == false)
	// [header \| 10] monitor inflated lock (UseObjectMonitorTable == true)
	// [ptr \| 11] marked used to mark an object
	// [0 ............ 0\| 00] inflating inflation in progress (stack-locking in use)
	//
	// We assume that stack/thread pointers have the lowest two bits cleared.
	//
	// - INFLATING() is a distinguished markword value of all zeros that is
	// used when inflating an existing stack-lock into an ObjectMonitor.
	// See below for is_being_inflated() and INFLATING().

	class BasicLock;
	class ObjectMonitor;
	class JavaThread;
	class outputStream;

	class markWord {
	private:
	uintptr_t _value;

	public:
	explicit markWord(uintptr_t value) : _value(value) {}

	markWord() = default; // Doesn't initialize _value.

	// It is critical for performance that this class be trivially
	// destructable, copyable, and assignable.
	~markWord() = default;
	markWord(const markWord&) = default;
	markWord& operator=(const markWord&) = default;

	static markWord from_pointer(void* ptr) {
	return markWord((uintptr_t)ptr);
	}
	void* to_pointer() const {
	return (void*)_value;
	}

	bool operator==(const markWord& other) const {
	return _value == other._value;
	}
	bool operator!=(const markWord& other) const {
	return !operator==(other);
	}

	// Conversion
	uintptr_t value() const { return _value; }

	// Constants
	static const int age_bits = 4;
	static const int lock_bits = 2;
	static const int self_fwd_bits = 1;
	static const int max_hash_bits = BitsPerWord - age_bits - lock_bits - self_fwd_bits;
	static const int hash_bits = max_hash_bits > 31 ? 31 : max_hash_bits;
	static const int unused_gap_bits = LP64_ONLY(4) NOT_LP64(0); // Reserved for Valhalla.

	static const int lock_shift = 0;
	static const int self_fwd_shift = lock_shift + lock_bits;
	static const int age_shift = self_fwd_shift + self_fwd_bits;
	static const int hash_shift = age_shift + age_bits + unused_gap_bits;

	static const uintptr_t lock_mask = right_n_bits(lock_bits);
	static const uintptr_t lock_mask_in_place = lock_mask << lock_shift;
	static const uintptr_t self_fwd_mask = right_n_bits(self_fwd_bits);
	static const uintptr_t self_fwd_mask_in_place = self_fwd_mask << self_fwd_shift;
	static const uintptr_t age_mask = right_n_bits(age_bits);
	static const uintptr_t age_mask_in_place = age_mask << age_shift;
	static const uintptr_t hash_mask = right_n_bits(hash_bits);
	static const uintptr_t hash_mask_in_place = hash_mask << hash_shift;

	#ifdef _LP64
	// Used only with compact headers:
	// We store the (narrow) Klass* in the bits 43 to 64.

	// These are for bit-precise extraction of the narrow Klass* from the 64-bit Markword
	static constexpr int klass_offset_in_bytes = 4;
	static constexpr int klass_shift = hash_shift + hash_bits;
	static constexpr int klass_shift_at_offset = klass_shift - klass_offset_in_bytes * BitsPerByte;
	static constexpr int klass_bits = 22;
	static constexpr uintptr_t klass_mask = right_n_bits(klass_bits);
	static constexpr uintptr_t klass_mask_in_place = klass_mask << klass_shift;
	#endif


	static const uintptr_t locked_value = 0;
	static const uintptr_t unlocked_value = 1;
	static const uintptr_t monitor_value = 2;
	static const uintptr_t marked_value = 3;

	static const uintptr_t no_hash = 0 ; // no hash value assigned
	static const uintptr_t no_hash_in_place = (uintptr_t)no_hash << hash_shift;
	static const uintptr_t no_lock_in_place = unlocked_value;

	static const uint max_age = age_mask;

	// Creates a markWord with all bits set to zero.
	static markWord zero() { return markWord(uintptr_t(0)); }

	// lock accessors (note that these assume lock_shift == 0)
	bool is_locked() const {
	return (mask_bits(value(), lock_mask_in_place) != unlocked_value);
	}
	bool is_unlocked() const {
	return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
	}
	bool is_marked() const {
	return (mask_bits(value(), lock_mask_in_place) == marked_value);
	}
	bool is_forwarded() const {
	// Returns true for normal forwarded (0b011) and self-forwarded (0b1xx).
	return mask_bits(value(), lock_mask_in_place \| self_fwd_mask_in_place) >= static_cast<intptr_t>(marked_value);
	}
	bool is_neutral() const { // Not locked, or marked - a "clean" neutral state
	return (mask_bits(value(), lock_mask_in_place) == unlocked_value);
	}

	// Special temporary state of the markWord while being inflated.
	// Code that looks at mark outside a lock need to take this into account.
	bool is_being_inflated() const { return (value() == 0); }

	// Distinguished markword value - used when inflating over
	// an existing stack-lock. 0 indicates the markword is "BUSY".
	// Lockword mutators that use a LD...CAS idiom should always
	// check for and avoid overwriting a 0 value installed by some
	// other thread. (They should spin or block instead. The 0 value
	// is transient and should be short-lived).
	// Fast-locking does not use INFLATING.
	static markWord INFLATING() { return zero(); } // inflate-in-progress

	// Should this header be preserved during GC?
	bool must_be_preserved() const {
	return (!is_unlocked() \|\| !has_no_hash());
	}

	// WARNING: The following routines are used EXCLUSIVELY by
	// synchronization functions. They are not really gc safe.
	// They must get updated if markWord layout get changed.
	markWord set_unlocked() const {
	return markWord(value() \| unlocked_value);
	}
	bool has_locker() const {
	assert(LockingMode == LM_LEGACY, "should only be called with legacy stack locking");
	return (value() & lock_mask_in_place) == locked_value;
	}
	BasicLock* locker() const {
	assert(has_locker(), "check");
	return (BasicLock*) value();
	}

	bool is_fast_locked() const {
	assert(LockingMode == LM_LIGHTWEIGHT, "should only be called with new lightweight locking");
	return (value() & lock_mask_in_place) == locked_value;
	}
	markWord set_fast_locked() const {
	// Clear the lock_mask_in_place bits to set locked_value:
	return markWord(value() & ~lock_mask_in_place);
	}

	bool has_monitor() const {
	return ((value() & lock_mask_in_place) == monitor_value);
	}
	ObjectMonitor* monitor() const {
	assert(has_monitor(), "check");
	assert(!UseObjectMonitorTable, "Lightweight locking with OM table does not use markWord for monitors");
	// Use xor instead of &~ to provide one extra tag-bit check.
	return (ObjectMonitor*) (value() ^ monitor_value);
	}
	bool has_displaced_mark_helper() const {
	intptr_t lockbits = value() & lock_mask_in_place;
	if (LockingMode == LM_LIGHTWEIGHT) {
	return !UseObjectMonitorTable && lockbits == monitor_value;
	}
	// monitor (0b10) \| stack-locked (0b00)?
	return (lockbits & unlocked_value) == 0;
	}
	markWord displaced_mark_helper() const;
	void set_displaced_mark_helper(markWord m) const;
	markWord copy_set_hash(intptr_t hash) const {
	uintptr_t tmp = value() & (~hash_mask_in_place);
	tmp \|= ((hash & hash_mask) << hash_shift);
	return markWord(tmp);
	}
	// it is only used to be stored into BasicLock as the
	// indicator that the lock is using heavyweight monitor
	static markWord unused_mark() {
	return markWord(marked_value);
	}
	// the following two functions create the markWord to be
	// stored into object header, it encodes monitor info
	static markWord encode(BasicLock* lock) {
	return from_pointer(lock);
	}
	static markWord encode(ObjectMonitor* monitor) {
	assert(!UseObjectMonitorTable, "Lightweight locking with OM table does not use markWord for monitors");
	uintptr_t tmp = (uintptr_t) monitor;
	return markWord(tmp \| monitor_value);
	}

	markWord set_has_monitor() const {
	return markWord((value() & ~lock_mask_in_place) \| monitor_value);
	}

	// used to encode pointers during GC
	markWord clear_lock_bits() const { return markWord(value() & ~lock_mask_in_place); }

	// age operations
	markWord set_marked() { return markWord((value() & ~lock_mask_in_place) \| marked_value); }
	markWord set_unmarked() { return markWord((value() & ~lock_mask_in_place) \| unlocked_value); }

	uint age() const { return (uint) mask_bits(value() >> age_shift, age_mask); }
	markWord set_age(uint v) const {
	assert((v & ~age_mask) == 0, "shouldn't overflow age field");
	return markWord((value() & ~age_mask_in_place) \| ((v & age_mask) << age_shift));
	}
	markWord incr_age() const { return age() == max_age ? markWord(_value) : set_age(age() + 1); }

	// hash operations
	intptr_t hash() const {
	return mask_bits(value() >> hash_shift, hash_mask);
	}

	bool has_no_hash() const {
	return hash() == no_hash;
	}

	inline Klass* klass() const;
	inline Klass* klass_or_null() const;
	inline Klass* klass_without_asserts() const;
	inline narrowKlass narrow_klass() const;
	inline markWord set_narrow_klass(narrowKlass narrow_klass) const;

	// Prototype mark for initialization
	static markWord prototype() {
	return markWord( no_hash_in_place \| no_lock_in_place );
	}

	// Debugging
	void print_on(outputStream* st, bool print_monitor_info = true) const;

	// Prepare address of oop for placement into mark
	inline static markWord encode_pointer_as_mark(void* p) { return from_pointer(p).set_marked(); }

	// Recover address of oop from encoded form used in mark
	inline void* decode_pointer() const { return (void*)clear_lock_bits().value(); }

	inline bool is_self_forwarded() const {
	NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
	return mask_bits(value(), self_fwd_mask_in_place) != 0;
	}

	inline markWord set_self_forwarded() const {
	NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
	return markWord(value() \| self_fwd_mask_in_place);
	}

	inline markWord unset_self_forwarded() const {
	NOT_LP64(assert(LockingMode != LM_LEGACY, "incorrect with LM_LEGACY on 32 bit");)
	return markWord(value() & ~self_fwd_mask_in_place);
	}

	inline oop forwardee() const {
	return cast_to_oop(decode_pointer());
	}
	};

	// Support atomic operations.
	template<>
	struct PrimitiveConversions::Translate<markWord> : public std::true_type {
	typedef markWord Value;
	typedef uintptr_t Decayed;

	static Decayed decay(const Value& x) { return x.value(); }
	static Value recover(Decayed x) { return Value(x); }
	};

	#endif // SHARE_OOPS_MARKWORD_HPP