1 /*
   2  * Copyright (c) 2002, 2015, 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.utilities;
  26 
  27 import java.io.*;
  28 import java.util.*;
  29 import sun.jvm.hotspot.debugger.*;
  30 import sun.jvm.hotspot.gc.shared.*;
  31 import sun.jvm.hotspot.memory.*;
  32 import sun.jvm.hotspot.oops.*;
  33 import sun.jvm.hotspot.runtime.*;
  34 import sun.jvm.hotspot.utilities.*;
  35 
  36 /** For a set of known roots, descends recursively into the object
  37     graph, for each object recording those objects (and their fields)
  38     which point to it. NOTE: currently only a subset of the roots
  39     known to the VM is exposed to the SA: objects on the stack, static
  40     fields in classes, and JNI handles. These should be most of the
  41     user-level roots keeping objects alive. */
  42 
  43 public class ReversePtrsAnalysis {
  44   // Used for debugging this code
  45   private static final boolean DEBUG = false;
  46 
  47   public ReversePtrsAnalysis() {
  48   }
  49 
  50   /** Sets an optional progress thunk */
  51   public void setHeapProgressThunk(HeapProgressThunk thunk) {
  52     progressThunk = thunk;
  53   }
  54 
  55 
  56   /** Runs the analysis algorithm */
  57   public void run() {
  58     if (VM.getVM().getRevPtrs() != null) {
  59       return; // Assume already done
  60     }
  61 
  62     VM vm = VM.getVM();
  63     rp = new ReversePtrs();
  64     vm.setRevPtrs(rp);
  65     Universe universe = vm.getUniverse();
  66     CollectedHeap collHeap = universe.heap();
  67     usedSize = collHeap.used();
  68     visitedSize = 0;
  69 
  70     // Note that an experiment to iterate the heap linearly rather
  71     // than in recursive-descent order has been done. It turns out
  72     // that the recursive-descent algorithm is nearly twice as fast
  73     // due to the fact that it scans only live objects and (currently)
  74     // only a fraction of the perm gen, namely the static fields
  75     // contained in instanceKlasses. (Iterating the heap linearly
  76     // would also change the semantics of the result so that
  77     // ReversePtrs.get() would return a non-null value even for dead
  78     // objects.) Nonetheless, the reverse pointer computation is still
  79     // quite slow and optimization in field iteration of objects
  80     // should be done.
  81 
  82     if (progressThunk != null) {
  83       // Get it started
  84       progressThunk.heapIterationFractionUpdate(0);
  85     }
  86 
  87     // Allocate mark bits for heap
  88     markBits = new MarkBits(collHeap);
  89 
  90     // Get a hold of the object heap
  91     heap = vm.getObjectHeap();
  92 
  93     // Do each thread's roots
  94     for (JavaThread thread = VM.getVM().getThreads().first();
  95          thread != null;
  96          thread = thread.next()) {
  97       ByteArrayOutputStream bos = new ByteArrayOutputStream();
  98       thread.printThreadIDOn(new PrintStream(bos));
  99       String threadDesc =
 100         " in thread \"" + thread.getThreadName() +
 101         "\" (id " + bos.toString() + ")";
 102       doStack(thread,
 103               new RootVisitor("Stack root" + threadDesc));
 104       doJNIHandleBlock(thread.activeHandles(),
 105                        new RootVisitor("JNI handle root" + threadDesc));
 106     }
 107 
 108     // Do global JNI handles
 109     JNIHandles handles = VM.getVM().getJNIHandles();
 110     doJNIHandleBlock(handles.globalHandles(),
 111                      new RootVisitor("Global JNI handle root"));
 112     doJNIHandleBlock(handles.weakGlobalHandles(),
 113                      new RootVisitor("Weak global JNI handle root"));
 114 
 115     // Do Java-level static fields
 116     SystemDictionary sysDict = VM.getVM().getSystemDictionary();
 117     sysDict.allClassesDo(new SystemDictionary.ClassVisitor() {
 118 
 119             public void visit(Klass k) {
 120                 if (k instanceof InstanceKlass) {
 121                     final InstanceKlass ik = (InstanceKlass)k;
 122             ik.iterateStaticFields(
 123                new DefaultOopVisitor() {
 124                    public void doOop(OopField field, boolean isVMField) {
 125                      Oop next = field.getValue(getObj());
 126                                                    NamedFieldIdentifier nfi = new NamedFieldIdentifier("Static field \"" +
 127                                                 field.getID().getName() +
 128                                                 "\" in class \"" +
 129                                                                                                        ik.getName().asString() + "\"");
 130                                                    LivenessPathElement lp = new LivenessPathElement(null, nfi);
 131                      rp.put(lp, next);
 132                      try {
 133                        markAndTraverse(next);
 134                      } catch (AddressException e) {
 135                        System.err.print("RevPtrs analysis: WARNING: AddressException at 0x" +
 136                                         Long.toHexString(e.getAddress()) +
 137                                         " while traversing static fields of InstanceKlass ");
 138                        ik.printValueOn(System.err);
 139                        System.err.println();
 140                      } catch (UnknownOopException e) {
 141                        System.err.println("RevPtrs analysis: WARNING: UnknownOopException while " +
 142                                           "traversing static fields of InstanceKlass ");
 143                        ik.printValueOn(System.err);
 144                        System.err.println();
 145                      }
 146                    }
 147                  });
 148           }
 149         }
 150       });
 151 
 152     if (progressThunk != null) {
 153       progressThunk.heapIterationComplete();
 154     }
 155 
 156     // Clear out markBits
 157     markBits = null;
 158   }
 159 
 160 
 161   //---------------------------------------------------------------------------
 162   // Internals only below this point
 163   //
 164   private HeapProgressThunk   progressThunk;
 165   private long                usedSize;
 166   private long                visitedSize;
 167   private double              lastNotificationFraction;
 168   private static final double MINIMUM_NOTIFICATION_FRACTION = 0.01;
 169   private ObjectHeap          heap;
 170   private MarkBits            markBits;
 171   private int                 depth; // Debugging only
 172   private ReversePtrs         rp;
 173 
 174   private void markAndTraverse(OopHandle handle) {
 175     try {
 176       markAndTraverse(heap.newOop(handle));
 177     } catch (AddressException e) {
 178       System.err.println("RevPtrs analysis: WARNING: AddressException at 0x" +
 179                          Long.toHexString(e.getAddress()) +
 180                          " while traversing oop at " + handle);
 181     } catch (UnknownOopException e) {
 182       System.err.println("RevPtrs analysis: WARNING: UnknownOopException for " +
 183                          "oop at " + handle);
 184     }
 185   }
 186 
 187   private void printHeader() {
 188     for (int i = 0; i < depth; i++) {
 189       System.err.print(" ");
 190     }
 191   }
 192 
 193   private void markAndTraverse(final Oop obj) {
 194 
 195     // End of path
 196     if (obj == null) {
 197       return;
 198     }
 199 
 200     // Visited object
 201     if (!markBits.mark(obj)) {
 202       return;
 203     }
 204 
 205     // Root of work list for objects to be visited.  A simple
 206     // stack for saving new objects to be analyzed.
 207 
 208     final Stack workList = new Stack();
 209 
 210     // Next object to be visited.
 211     Oop next = obj;
 212 
 213     try {
 214       // Node in the list currently being visited.
 215 
 216       while (true) {
 217         final Oop currObj = next;
 218 
 219         // For the progress meter
 220         if (progressThunk != null) {
 221           visitedSize += currObj.getObjectSize();
 222           double curFrac = (double) visitedSize / (double) usedSize;
 223           if (curFrac >
 224               lastNotificationFraction + MINIMUM_NOTIFICATION_FRACTION) {
 225             progressThunk.heapIterationFractionUpdate(curFrac);
 226             lastNotificationFraction = curFrac;
 227           }
 228         }
 229 
 230         if (DEBUG) {
 231           ++depth;
 232           printHeader();
 233           System.err.println("ReversePtrs.markAndTraverse(" +
 234               currObj.getHandle() + ")");
 235         }
 236 
 237         // Iterate over the references in the object.  Do the
 238         // reverse pointer analysis for each reference.
 239         // Add the reference to the work-list so that its
 240         // references will be visited.
 241         currObj.iterate(new DefaultOopVisitor() {
 242           public void doOop(OopField field, boolean isVMField) {
 243             // "field" refers to a reference in currObj
 244             Oop next = field.getValue(currObj);
 245             rp.put(new LivenessPathElement(currObj, field.getID()), next);
 246             if ((next != null) && markBits.mark(next)) {
 247               workList.push(next);
 248             }
 249           }
 250         }, false);
 251 
 252         if (DEBUG) {
 253           --depth;
 254         }
 255 
 256         // Get the next object to visit.
 257         next = (Oop) workList.pop();
 258       }
 259     } catch (EmptyStackException e) {
 260       // Done
 261     } catch (NullPointerException e) {
 262       System.err.println("ReversePtrs: WARNING: " + e +
 263         " during traversal");
 264     } catch (Exception e) {
 265       System.err.println("ReversePtrs: WARNING: " + e +
 266         " during traversal");
 267     }
 268   }
 269 
 270 
 271   class RootVisitor implements AddressVisitor {
 272     RootVisitor(String baseRootDescription) {
 273       this.baseRootDescription = baseRootDescription;
 274     }
 275 
 276     public void visitAddress(Address addr) {
 277       Oop next = heap.newOop(addr.getOopHandleAt(0));
 278       LivenessPathElement lp = new LivenessPathElement(null,
 279                                         new NamedFieldIdentifier(baseRootDescription +
 280                                                                  " @ " + addr));
 281       rp.put(lp, next);
 282       markAndTraverse(next);
 283     }
 284 
 285     public void visitCompOopAddress(Address addr) {
 286       Oop next = heap.newOop(addr.getCompOopHandleAt(0));
 287       LivenessPathElement lp = new LivenessPathElement(null,
 288                                         new NamedFieldIdentifier(baseRootDescription +
 289                                                                  " @ " + addr));
 290       rp.put(lp, next);
 291       markAndTraverse(next);
 292     }
 293 
 294     private String baseRootDescription;
 295   }
 296 
 297   // Traverse the roots on a given thread's stack
 298   private void doStack(JavaThread thread, AddressVisitor oopVisitor) {
 299     for (StackFrameStream fst = new StackFrameStream(thread); !fst.isDone(); fst.next()) {
 300       fst.getCurrent().oopsDo(oopVisitor, fst.getRegisterMap());
 301     }
 302   }
 303 
 304   // Traverse a JNIHandleBlock
 305   private void doJNIHandleBlock(JNIHandleBlock handles, AddressVisitor oopVisitor) {
 306     handles.oopsDo(oopVisitor);
 307   }
 308 }