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1   /*
2    * Copyright (c) 2002, 2012, 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_interface.*;
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 }