1 /*
  2  * Copyright (c) 2001, 2021, Oracle and/or its affiliates. All rights reserved.
  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.
  8  *
  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  *
 15  * You should have received a copy of the GNU General Public License version
 16  * 2 along with this work; if not, write to the Free Software Foundation,
 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
 21  * questions.
 22  *
 23  */
 24 
 25 package sun.jvm.hotspot.oops;
 26 
 27 import java.io.*;
 28 import java.util.*;
 29 
 30 import sun.jvm.hotspot.debugger.*;
 31 import sun.jvm.hotspot.runtime.*;
 32 import sun.jvm.hotspot.types.*;
 33 import sun.jvm.hotspot.utilities.*;
 34 import sun.jvm.hotspot.utilities.Observable;
 35 import sun.jvm.hotspot.utilities.Observer;
 36 
 37 public class Mark extends VMObject {
 38   static {
 39     VM.registerVMInitializedObserver(new Observer() {
 40         public void update(Observable o, Object data) {
 41           initialize(VM.getVM().getTypeDataBase());
 42         }
 43       });
 44   }
 45 
 46   private static synchronized void initialize(TypeDataBase db) throws WrongTypeException {
 47     Type type  = db.lookupType("oopDesc");
 48     markField  = type.getCIntegerField("_mark");
 49 
 50     ageBits             = db.lookupLongConstant("markWord::age_bits").longValue();
 51     lockBits            = db.lookupLongConstant("markWord::lock_bits").longValue();
 52     maxHashBits         = db.lookupLongConstant("markWord::max_hash_bits").longValue();
 53     hashBits            = db.lookupLongConstant("markWord::hash_bits").longValue();
 54     lockShift           = db.lookupLongConstant("markWord::lock_shift").longValue();
 55     ageShift            = db.lookupLongConstant("markWord::age_shift").longValue();
 56     hashShift           = db.lookupLongConstant("markWord::hash_shift").longValue();
 57     lockMask            = db.lookupLongConstant("markWord::lock_mask").longValue();
 58     lockMaskInPlace     = db.lookupLongConstant("markWord::lock_mask_in_place").longValue();
 59     ageMask             = db.lookupLongConstant("markWord::age_mask").longValue();
 60     ageMaskInPlace      = db.lookupLongConstant("markWord::age_mask_in_place").longValue();
 61     hashMask            = db.lookupLongConstant("markWord::hash_mask").longValue();
 62     hashMaskInPlace     = db.lookupLongConstant("markWord::hash_mask_in_place").longValue();
 63     lockedValue         = db.lookupLongConstant("markWord::locked_value").longValue();
 64     unlockedValue       = db.lookupLongConstant("markWord::unlocked_value").longValue();
 65     monitorValue        = db.lookupLongConstant("markWord::monitor_value").longValue();
 66     markedValue         = db.lookupLongConstant("markWord::marked_value").longValue();
 67     noHash              = db.lookupLongConstant("markWord::no_hash").longValue();
 68     noHashInPlace       = db.lookupLongConstant("markWord::no_hash_in_place").longValue();
 69     noLockInPlace       = db.lookupLongConstant("markWord::no_lock_in_place").longValue();
 70     maxAge              = db.lookupLongConstant("markWord::max_age").longValue();
 71   }
 72 
 73   // Field accessors
 74   private static CIntegerField markField;
 75 
 76   // Constants -- read from VM
 77   private static long ageBits;
 78   private static long lockBits;
 79   private static long maxHashBits;
 80   private static long hashBits;
 81 
 82   private static long lockShift;
 83   private static long ageShift;
 84   private static long hashShift;
 85 
 86   private static long lockMask;
 87   private static long lockMaskInPlace;
 88   private static long ageMask;
 89   private static long ageMaskInPlace;
 90   private static long hashMask;
 91   private static long hashMaskInPlace;
 92 
 93   private static long lockedValue;
 94   private static long unlockedValue;
 95   private static long monitorValue;
 96   private static long markedValue;
 97 
 98   private static long noHash;
 99 
100   private static long noHashInPlace;
101   private static long noLockInPlace;
102 
103   private static long maxAge;
104 
105   /* Constants in markWord used by CMS. */
106   private static long cmsShift;
107   private static long cmsMask;
108   private static long sizeShift;
109 
110   public Mark(Address addr) {
111     super(addr);
112   }
113 
114   public long value() {
115     return markField.getValue(addr);
116   }
117 
118   public Address valueAsAddress() {
119     return addr.getAddressAt(markField.getOffset());
120   }
121 
122   // lock accessors (note that these assume lock_shift == 0)
123   public boolean isLocked() {
124     return (Bits.maskBitsLong(value(), lockMaskInPlace) != unlockedValue);
125   }
126   public boolean isUnlocked() {
127     return (Bits.maskBitsLong(value(), lockMaskInPlace) == unlockedValue);
128   }
129   public boolean isMarked() {
130     return (Bits.maskBitsLong(value(), lockMaskInPlace) == markedValue);
131   }
132 
133   // Special temporary state of the markWord while being inflated.
134   // Code that looks at mark outside a lock need to take this into account.
135   public boolean isBeingInflated() {
136     return (value() == 0);
137   }
138 
139   // Should this header be preserved during GC?
140   public boolean mustBePreserved() {
141      return (!isUnlocked() || !hasNoHash());
142   }
143 
144   // WARNING: The following routines are used EXCLUSIVELY by
145   // synchronization functions. They are not really gc safe.
146   // They must get updated if markWord layout get changed.
147 
148   public boolean hasLocker() {
149     return ((value() & lockMaskInPlace) == lockedValue);
150   }
151   public boolean hasMonitor() {
152     return ((value() & monitorValue) != 0);
153   }
154   public ObjectMonitor monitor() {
155     if (Assert.ASSERTS_ENABLED) {
156       Assert.that(hasMonitor(), "check");
157     }
158     // Use xor instead of &~ to provide one extra tag-bit check.
159     Address monAddr = valueAsAddress().xorWithMask(monitorValue);
160     return new ObjectMonitor(monAddr);
161   }
162   public boolean hasDisplacedMarkHelper() {
163     return ((value() & unlockedValue) == 0);
164   }
165   public Mark displacedMarkHelper() {
166     if (Assert.ASSERTS_ENABLED) {
167       Assert.that(hasDisplacedMarkHelper(), "check");
168     }
169     Address addr = valueAsAddress().andWithMask(~monitorValue);
170     return new Mark(addr.getAddressAt(0));
171   }
172   public int age() { return (int) Bits.maskBitsLong(value() >> ageShift, ageMask); }
173 
174   // hash operations
175   public long hash() {
176     return Bits.maskBitsLong(value() >> hashShift, hashMask);
177   }
178 
179   public boolean hasNoHash() {
180     return hash() == noHash;
181   }
182 
183   // Debugging
184   public void printOn(PrintStream tty) {
185     if (isLocked()) {
186       tty.print("locked(0x" +
187                 Long.toHexString(value()) + ")->");
188       displacedMarkHelper().printOn(tty);
189     } else {
190       if (Assert.ASSERTS_ENABLED) {
191         Assert.that(isUnlocked(), "just checking");
192       }
193       tty.print("mark(");
194       tty.print("hash " + Long.toHexString(hash()) + ",");
195       tty.print("age " + age() + ")");
196     }
197   }
198 
199   public long getSize() { return (long)(value() >> sizeShift); }
200 }