Java example source code file (ObjectHeap.java)

This example Java source code file (ObjectHeap.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Learn more about this Java project at its project page.

Java - Java tags/keywords

address, concurrentmarksweepgeneration, debug, g1collectedheap, gencollectedheap, klass, list, liveregionscollector, memregion, objectfilter, parallelscavengeheap, runtimeexception, typearrayklass, unknownoopexception, util

The ObjectHeap.java Java example source code

/*
 * Copyright (c) 2000, 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

//
// The ObjectHeap is an abstraction over all generations in the VM
// It gives access to all present objects and classes.
//

package sun.jvm.hotspot.oops;

import java.util.*;

import sun.jvm.hotspot.debugger.*;
import sun.jvm.hotspot.gc_interface.*;
import sun.jvm.hotspot.gc_implementation.g1.*;
import sun.jvm.hotspot.gc_implementation.parallelScavenge.*;
import sun.jvm.hotspot.memory.*;
import sun.jvm.hotspot.runtime.*;
import sun.jvm.hotspot.types.*;
import sun.jvm.hotspot.utilities.*;

public class ObjectHeap {

  private static final boolean DEBUG;

  static {
    DEBUG = System.getProperty("sun.jvm.hotspot.oops.ObjectHeap.DEBUG") != null;
  }

  private Address              boolArrayKlassHandle;
  private Address              byteArrayKlassHandle;
  private Address              charArrayKlassHandle;
  private Address              intArrayKlassHandle;
  private Address              shortArrayKlassHandle;
  private Address              longArrayKlassHandle;
  private Address              singleArrayKlassHandle;
  private Address              doubleArrayKlassHandle;

  private TypeArrayKlass         boolArrayKlassObj;
  private TypeArrayKlass         byteArrayKlassObj;
  private TypeArrayKlass         charArrayKlassObj;
  private TypeArrayKlass         intArrayKlassObj;
  private TypeArrayKlass         shortArrayKlassObj;
  private TypeArrayKlass         longArrayKlassObj;
  private TypeArrayKlass         singleArrayKlassObj;
  private TypeArrayKlass         doubleArrayKlassObj;

  public void initialize(TypeDataBase db) throws WrongTypeException {
    // Lookup the roots in the object hierarchy.
    Type universeType = db.lookupType("Universe");

    boolArrayKlassHandle      = universeType.getAddressField("_boolArrayKlassObj").getValue();
    boolArrayKlassObj         = new TypeArrayKlass(boolArrayKlassHandle);

    byteArrayKlassHandle      = universeType.getAddressField("_byteArrayKlassObj").getValue();
    byteArrayKlassObj         = new TypeArrayKlass(byteArrayKlassHandle);

    charArrayKlassHandle      = universeType.getAddressField("_charArrayKlassObj").getValue();
    charArrayKlassObj         = new TypeArrayKlass(charArrayKlassHandle);

    intArrayKlassHandle       = universeType.getAddressField("_intArrayKlassObj").getValue();
    intArrayKlassObj          = new TypeArrayKlass(intArrayKlassHandle);

    shortArrayKlassHandle     = universeType.getAddressField("_shortArrayKlassObj").getValue();
    shortArrayKlassObj        = new TypeArrayKlass(shortArrayKlassHandle);

    longArrayKlassHandle      = universeType.getAddressField("_longArrayKlassObj").getValue();
    longArrayKlassObj         = new TypeArrayKlass(longArrayKlassHandle);

    singleArrayKlassHandle    = universeType.getAddressField("_singleArrayKlassObj").getValue();
    singleArrayKlassObj       = new TypeArrayKlass(singleArrayKlassHandle);

    doubleArrayKlassHandle    = universeType.getAddressField("_doubleArrayKlassObj").getValue();
    doubleArrayKlassObj       = new TypeArrayKlass(doubleArrayKlassHandle);
  }

  public ObjectHeap(TypeDataBase db) throws WrongTypeException {
    // Get commonly used sizes of basic types
    oopSize     = VM.getVM().getOopSize();
    byteSize    = db.getJByteType().getSize();
    charSize    = db.getJCharType().getSize();
    booleanSize = db.getJBooleanType().getSize();
    intSize     = db.getJIntType().getSize();
    shortSize   = db.getJShortType().getSize();
    longSize    = db.getJLongType().getSize();
    floatSize   = db.getJFloatType().getSize();
    doubleSize  = db.getJDoubleType().getSize();

    initialize(db);
  }

  /** Comparison operation for oops, either or both of which may be null */
  public boolean equal(Oop o1, Oop o2) {
    if (o1 != null) return o1.equals(o2);
    return (o2 == null);
  }

  // Cached sizes of basic types
  private long oopSize;
  private long byteSize;
  private long charSize;
  private long booleanSize;
  private long intSize;
  private long shortSize;
  private long longSize;
  private long floatSize;
  private long doubleSize;

  public long getOopSize()     { return oopSize;     }
  public long getByteSize()    { return byteSize;    }
  public long getCharSize()    { return charSize;    }
  public long getBooleanSize() { return booleanSize; }
  public long getIntSize()     { return intSize;     }
  public long getShortSize()   { return shortSize;   }
  public long getLongSize()    { return longSize;    }
  public long getFloatSize()   { return floatSize;   }
  public long getDoubleSize()  { return doubleSize;  }

  // Accessors for well-known system classes (from Universe)
  public TypeArrayKlass         getBoolArrayKlassObj()         { return boolArrayKlassObj; }
  public TypeArrayKlass         getByteArrayKlassObj()         { return byteArrayKlassObj; }
  public TypeArrayKlass         getCharArrayKlassObj()         { return charArrayKlassObj; }
  public TypeArrayKlass         getIntArrayKlassObj()          { return intArrayKlassObj; }
  public TypeArrayKlass         getShortArrayKlassObj()        { return shortArrayKlassObj; }
  public TypeArrayKlass         getLongArrayKlassObj()         { return longArrayKlassObj; }
  public TypeArrayKlass         getSingleArrayKlassObj()       { return singleArrayKlassObj; }
  public TypeArrayKlass         getDoubleArrayKlassObj()       { return doubleArrayKlassObj; }

  /** Takes a BasicType and returns the corresponding primitive array
      klass */
  public Klass typeArrayKlassObj(int t) {
    if (t == BasicType.getTBoolean()) return getBoolArrayKlassObj();
    if (t == BasicType.getTChar())    return getCharArrayKlassObj();
    if (t == BasicType.getTFloat())   return getSingleArrayKlassObj();
    if (t == BasicType.getTDouble())  return getDoubleArrayKlassObj();
    if (t == BasicType.getTByte())    return getByteArrayKlassObj();
    if (t == BasicType.getTShort())   return getShortArrayKlassObj();
    if (t == BasicType.getTInt())     return getIntArrayKlassObj();
    if (t == BasicType.getTLong())    return getLongArrayKlassObj();
    throw new RuntimeException("Illegal basic type " + t);
  }

  /** an interface to filter objects while walking heap */
  public static interface ObjectFilter {
    public boolean canInclude(Oop obj);
  }

  /** The base heap iteration mechanism */
  public void iterate(HeapVisitor visitor) {
    iterateLiveRegions(collectLiveRegions(), visitor, null);
  }

  /** iterate objects satisfying a specified ObjectFilter */
  public void iterate(HeapVisitor visitor, ObjectFilter of) {
    iterateLiveRegions(collectLiveRegions(), visitor, of);
  }

  /** iterate objects of given Klass. param 'includeSubtypes' tells whether to
   *  include objects of subtypes or not */
  public void iterateObjectsOfKlass(HeapVisitor visitor, final Klass k, boolean includeSubtypes) {
    if (includeSubtypes) {
      if (k.isFinal()) {
        // do the simpler "exact" klass loop
        iterateExact(visitor, k);
      } else {
        iterateSubtypes(visitor, k);
      }
    } else {
      // there can no object of abstract classes and interfaces
      if (!k.isAbstract() && !k.isInterface()) {
        iterateExact(visitor, k);
      }
    }
  }

  /** iterate objects of given Klass (objects of subtypes included) */
  public void iterateObjectsOfKlass(HeapVisitor visitor, final Klass k) {
    iterateObjectsOfKlass(visitor, k, true);
  }

  /** This routine can be used to iterate through the heap at an
      extremely low level (stepping word-by-word) to provide the
      ability to do very low-level debugging */
  public void iterateRaw(RawHeapVisitor visitor) {
    List liveRegions = collectLiveRegions();

    // Summarize size
    long totalSize = 0;
    for (int i = 0; i < liveRegions.size(); i += 2) {
      Address bottom = (Address) liveRegions.get(i);
      Address top    = (Address) liveRegions.get(i+1);
      totalSize += top.minus(bottom);
    }
    visitor.prologue(totalSize);

    for (int i = 0; i < liveRegions.size(); i += 2) {
      Address bottom = (Address) liveRegions.get(i);
      Address top    = (Address) liveRegions.get(i+1);

      // Traverses the space from bottom to top
      while (bottom.lessThan(top)) {
        visitor.visitAddress(bottom);
        bottom = bottom.addOffsetTo(VM.getVM().getAddressSize());
      }
    }

    visitor.epilogue();
  }

  public boolean isValidMethod(Address handle) {
    try {
      Method m = (Method)Metadata.instantiateWrapperFor(handle);
      return true;
    } catch (Exception e) {
      return false;
  }
  }

  // Creates an instance from the Oop hierarchy based based on the handle
  public Oop newOop(OopHandle handle) {
    // The only known way to detect the right type of an oop is
    // traversing the class chain until a well-known klass is recognized.
    // A more direct solution would require the klasses to expose
    // the C++ vtbl structure.

    // Handle the null reference
    if (handle == null) return null;

    // Then check if obj.klass() is one of the root objects
    Klass klass = Oop.getKlassForOopHandle(handle);
    if (klass != null) {
      if (klass instanceof TypeArrayKlass) return new TypeArray(handle, this);
      if (klass instanceof ObjArrayKlass) return new ObjArray(handle, this);
      if (klass instanceof InstanceKlass) return new Instance(handle, this);
    }

    if (DEBUG) {
      System.err.println("Unknown oop at " + handle);
      System.err.println("Oop's klass is " + klass);
    }

    throw new UnknownOopException();
  }

  // Print all objects in the object heap
  public void print() {
    HeapPrinter printer = new HeapPrinter(System.out);
    iterate(printer);
  }

  //---------------------------------------------------------------------------
  // Internals only below this point
  //

  private void iterateExact(HeapVisitor visitor, final Klass k) {
    iterateLiveRegions(collectLiveRegions(), visitor, new ObjectFilter() {
          public boolean canInclude(Oop obj) {
            Klass tk = obj.getKlass();
            // null Klass is seen sometimes!
            return (tk != null && tk.equals(k));
          }
        });
  }

  private void iterateSubtypes(HeapVisitor visitor, final Klass k) {
    iterateLiveRegions(collectLiveRegions(), visitor, new ObjectFilter() {
          public boolean canInclude(Oop obj) {
            Klass tk = obj.getKlass();
            // null Klass is seen sometimes!
            return (tk != null && tk.isSubtypeOf(k));
          }
        });
  }

  private void iterateLiveRegions(List liveRegions, HeapVisitor visitor, ObjectFilter of) {
    // Summarize size
    long totalSize = 0;
    for (int i = 0; i < liveRegions.size(); i += 2) {
      Address bottom = (Address) liveRegions.get(i);
      Address top    = (Address) liveRegions.get(i+1);
      totalSize += top.minus(bottom);
    }
    visitor.prologue(totalSize);

    CompactibleFreeListSpace cmsSpaceOld = null;
    CollectedHeap heap = VM.getVM().getUniverse().heap();

    if (heap instanceof GenCollectedHeap) {
      GenCollectedHeap genHeap = (GenCollectedHeap) heap;
      Generation genOld = genHeap.getGen(1);
      if (genOld instanceof ConcurrentMarkSweepGeneration) {
          ConcurrentMarkSweepGeneration concGen = (ConcurrentMarkSweepGeneration)genOld;
          cmsSpaceOld = concGen.cmsSpace();
      }
    }

    for (int i = 0; i < liveRegions.size(); i += 2) {
      Address bottom = (Address) liveRegions.get(i);
      Address top    = (Address) liveRegions.get(i+1);

      try {
        // Traverses the space from bottom to top
        OopHandle handle = bottom.addOffsetToAsOopHandle(0);

        while (handle.lessThan(top)) {
        Oop obj = null;

          try {
            obj = newOop(handle);
          } catch (UnknownOopException exp) {
            if (DEBUG) {
              throw new RuntimeException(" UnknownOopException  " + exp);
            }
          }
          if (obj == null) {
             //Find the object size using Printezis bits and skip over
             long size = 0;

             if ( (cmsSpaceOld != null) && cmsSpaceOld.contains(handle) ){
                 size = cmsSpaceOld.collector().blockSizeUsingPrintezisBits(handle);
             }

             if (size <= 0) {
                //Either Printezis bits not set or handle is not in cms space.
                throw new UnknownOopException();
             }

             handle = handle.addOffsetToAsOopHandle(CompactibleFreeListSpace.adjustObjectSizeInBytes(size));
             continue;
          }
          if (of == null || of.canInclude(obj)) {
                  if (visitor.doObj(obj)) {
                         // doObj() returns true to abort this loop.
                          break;
                  }
          }
          if ( (cmsSpaceOld != null) && cmsSpaceOld.contains(handle)) {
              handle = handle.addOffsetToAsOopHandle(CompactibleFreeListSpace.adjustObjectSizeInBytes(obj.getObjectSize()) );
          } else {
              handle = handle.addOffsetToAsOopHandle(obj.getObjectSize());
          }
        }
      }
      catch (AddressException e) {
        // This is okay at the top of these regions
          }
      catch (UnknownOopException e) {
        // This is okay at the top of these regions
      }
    }

    visitor.epilogue();
  }

  private void addLiveRegions(String name, List input, List output) {
     for (Iterator itr = input.iterator(); itr.hasNext();) {
        MemRegion reg = (MemRegion) itr.next();
        Address top = reg.end();
        Address bottom = reg.start();
        if (Assert.ASSERTS_ENABLED) {
           Assert.that(top != null, "top address in a live region should not be null");
        }
        if (Assert.ASSERTS_ENABLED) {
           Assert.that(bottom != null, "bottom address in a live region should not be null");
        }
        output.add(top);
        output.add(bottom);
        if (DEBUG) {
          System.err.println("Live region: " + name + ": " + bottom + ", " + top);
        }
     }
  }

  private class LiveRegionsCollector implements SpaceClosure {
     LiveRegionsCollector(List l) {
        liveRegions = l;
     }

     public void doSpace(Space s) {
        addLiveRegions(s.toString(), s.getLiveRegions(), liveRegions);
     }
     private List liveRegions;
  }

  // Returns a List<Address> where the addresses come in pairs. These
  // designate the live regions of the heap.
  private List collectLiveRegions() {
    // We want to iterate through all live portions of the heap, but
    // do not want to abort the heap traversal prematurely if we find
    // a problem (like an allocated but uninitialized object at the
    // top of a generation). To do this we enumerate all generations'
    // bottom and top regions, and factor in TLABs if necessary.

    // List<Address>. Addresses come in pairs.
    List liveRegions = new ArrayList();
    LiveRegionsCollector lrc = new LiveRegionsCollector(liveRegions);

    CollectedHeap heap = VM.getVM().getUniverse().heap();

    if (heap instanceof GenCollectedHeap) {
       GenCollectedHeap genHeap = (GenCollectedHeap) heap;
       // Run through all generations, obtaining bottom-top pairs.
       for (int i = 0; i < genHeap.nGens(); i++) {
         Generation gen = genHeap.getGen(i);
         gen.spaceIterate(lrc, true);
       }
    } else if (heap instanceof ParallelScavengeHeap) {
       ParallelScavengeHeap psh = (ParallelScavengeHeap) heap;
       PSYoungGen youngGen = psh.youngGen();
       // Add eden space
       addLiveRegions("eden", youngGen.edenSpace().getLiveRegions(), liveRegions);
       // Add from-space but not to-space
       addLiveRegions("from", youngGen.fromSpace().getLiveRegions(), liveRegions);
       PSOldGen oldGen = psh.oldGen();
       addLiveRegions("old ", oldGen.objectSpace().getLiveRegions(), liveRegions);
    } else if (heap instanceof G1CollectedHeap) {
        G1CollectedHeap g1h = (G1CollectedHeap) heap;
        g1h.heapRegionIterate(lrc);
    } else {
       if (Assert.ASSERTS_ENABLED) {
          Assert.that(false, "Expecting GenCollectedHeap, G1CollectedHeap, " +
                      "or ParallelScavengeHeap, but got " +
                      heap.getClass().getName());
       }
    }

    // If UseTLAB is enabled, snip out regions associated with TLABs'
    // dead regions. Note that TLABs can be present in any generation.

    // FIXME: consider adding fewer boundaries to live region list.
    // Theoretically only need to stop at TLAB's top and resume at its
    // end.

    if (VM.getVM().getUseTLAB()) {
      for (JavaThread thread = VM.getVM().getThreads().first(); thread != null; thread = thread.next()) {
        ThreadLocalAllocBuffer tlab = thread.tlab();
        if (tlab.start() != null) {
          if ((tlab.top() == null) || (tlab.end() == null)) {
            System.err.print("Warning: skipping invalid TLAB for thread ");
            thread.printThreadIDOn(System.err);
            System.err.println();
          } else {
            if (DEBUG) {
              System.err.print("TLAB for " + thread.getThreadName() + ", #");
              thread.printThreadIDOn(System.err);
              System.err.print(": ");
              tlab.printOn(System.err);
            }
            // Go from:
            //  - below start() to start()
            //  - start() to top()
            //  - end() and above
            liveRegions.add(tlab.start());
            liveRegions.add(tlab.start());
            liveRegions.add(tlab.top());
            liveRegions.add(tlab.hardEnd());
          }
        }
      }
    }

    // Now sort live regions
    sortLiveRegions(liveRegions);

    if (Assert.ASSERTS_ENABLED) {
      Assert.that(liveRegions.size() % 2 == 0, "Must have even number of region boundaries");
    }

    if (DEBUG) {
      System.err.println("liveRegions:");
      for (int i = 0; i < liveRegions.size(); i += 2) {
          Address bottom = (Address) liveRegions.get(i);
          Address top    = (Address) liveRegions.get(i+1);
          System.err.println(" " + bottom + " - " + top);
      }
    }

    return liveRegions;
  }

  private void sortLiveRegions(List liveRegions) {
    Collections.sort(liveRegions, new Comparator() {
        public int compare(Object o1, Object o2) {
          Address a1 = (Address) o1;
          Address a2 = (Address) o2;
          if (AddressOps.lt(a1, a2)) {
            return -1;
          } else if (AddressOps.gt(a1, a2)) {
            return 1;
          }
          return 0;
        }
      });
  }
}