1 /*
2 * Copyright (c) 2002, 2018, 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.classfile.*;
31 import sun.jvm.hotspot.gc.shared.*;
32 import sun.jvm.hotspot.memory.*;
33 import sun.jvm.hotspot.oops.*;
34 import sun.jvm.hotspot.runtime.*;
35 import sun.jvm.hotspot.utilities.*;
36
37 /** For a set of known roots, descends recursively into the object
38 graph, for each object recording those objects (and their fields)
39 which point to it. NOTE: currently only a subset of the roots
40 known to the VM is exposed to the SA: objects on the stack, static
41 fields in classes, and JNI handles. These should be most of the
42 user-level roots keeping objects alive. */
43
44 public class ReversePtrsAnalysis {
45 // Used for debugging this code
46 private static final boolean DEBUG = false;
47
48 public ReversePtrsAnalysis() {
49 }
50
51 /** Sets an optional progress thunk */
52 public void setHeapProgressThunk(HeapProgressThunk thunk) {
53 progressThunk = thunk;
54 }
55
56
57 /** Runs the analysis algorithm */
58 public void run() {
59 if (VM.getVM().getRevPtrs() != null) {
60 return; // Assume already done
61 }
62
63 VM vm = VM.getVM();
64 rp = new ReversePtrs();
65 vm.setRevPtrs(rp);
66 Universe universe = vm.getUniverse();
67 CollectedHeap collHeap = universe.heap();
68 usedSize = collHeap.used();
69 visitedSize = 0;
70
71 // Note that an experiment to iterate the heap linearly rather
72 // than in recursive-descent order has been done. It turns out
73 // that the recursive-descent algorithm is nearly twice as fast
74 // due to the fact that it scans only live objects and (currently)
75 // only a fraction of the perm gen, namely the static fields
76 // contained in instanceKlasses. (Iterating the heap linearly
77 // would also change the semantics of the result so that
78 // ReversePtrs.get() would return a non-null value even for dead
79 // objects.) Nonetheless, the reverse pointer computation is still
80 // quite slow and optimization in field iteration of objects
81 // should be done.
82
83 if (progressThunk != null) {
84 // Get it started
85 progressThunk.heapIterationFractionUpdate(0);
86 }
87
88 // Allocate mark bits for heap
89 markBits = new MarkBits(collHeap);
90
91 // Get a hold of the object heap
92 heap = vm.getObjectHeap();
93
94 // Do each thread's roots
95 VM.getVM().getThreads().doJavaThreads((thread) -> {
96 ByteArrayOutputStream bos = new ByteArrayOutputStream();
97 thread.printThreadIDOn(new PrintStream(bos));
98 String threadDesc =
99 " in thread \"" + thread.getThreadName() +
100 "\" (id " + bos.toString() + ")";
101 doStack(thread,
102 new RootVisitor("Stack root" + threadDesc));
103 doJNIHandleBlock(thread.activeHandles(),
104 new RootVisitor("JNI handle root" + threadDesc));
105 });
106
107 // Do global JNI handles
108 JNIHandles handles = VM.getVM().getJNIHandles();
109 doOopStorage(handles.globalHandles(),
110 new RootVisitor("Global JNI handle root"));
111 doOopStorage(handles.weakGlobalHandles(),
112 new RootVisitor("Weak global JNI handle root"));
113
114 // Do Java-level static fields
115 ClassLoaderDataGraph cldg = VM.getVM().getClassLoaderDataGraph();
116 cldg.classesDo(new ClassLoaderDataGraph.ClassVisitor() {
117
118 public void visit(Klass k) {
119 if (k instanceof InstanceKlass) {
120 final InstanceKlass ik = (InstanceKlass)k;
121 ik.iterateStaticFields(
122 new DefaultOopVisitor() {
123 public void doOop(OopField field, boolean isVMField) {
124 Oop next = field.getValue(getObj());
125 NamedFieldIdentifier nfi = new NamedFieldIdentifier("Static field \"" +
126 field.getID().getName() +
127 "\" in class \"" +
128 ik.getName().asString() + "\"");
129 LivenessPathElement lp = new LivenessPathElement(null, nfi);
130 rp.put(lp, next);
131 try {
132 markAndTraverse(next);
133 } catch (AddressException e) {
134 System.err.print("RevPtrs analysis: WARNING: AddressException at 0x" +
135 Long.toHexString(e.getAddress()) +
136 " while traversing static fields of InstanceKlass ");
137 ik.printValueOn(System.err);
138 System.err.println();
139 } catch (UnknownOopException e) {
140 System.err.println("RevPtrs analysis: WARNING: UnknownOopException while " +
141 "traversing static fields of InstanceKlass ");
142 ik.printValueOn(System.err);
143 System.err.println();
144 }
145 }
146 });
147 }
148 }
149 });
150
151 if (progressThunk != null) {
152 progressThunk.heapIterationComplete();
153 }
154
155 // Clear out markBits
156 markBits = null;
157 }
158
159
160 //---------------------------------------------------------------------------
161 // Internals only below this point
162 //
163 private HeapProgressThunk progressThunk;
164 private long usedSize;
165 private long visitedSize;
166 private double lastNotificationFraction;
167 private static final double MINIMUM_NOTIFICATION_FRACTION = 0.01;
168 private ObjectHeap heap;
169 private MarkBits markBits;
170 private int depth; // Debugging only
171 private ReversePtrs rp;
172
173 private void markAndTraverse(OopHandle handle) {
174 try {
175 markAndTraverse(heap.newOop(handle));
176 } catch (AddressException e) {
177 System.err.println("RevPtrs analysis: WARNING: AddressException at 0x" +
178 Long.toHexString(e.getAddress()) +
179 " while traversing oop at " + handle);
180 } catch (UnknownOopException e) {
181 System.err.println("RevPtrs analysis: WARNING: UnknownOopException for " +
182 "oop at " + handle);
183 }
184 }
185
186 private void printHeader() {
187 for (int i = 0; i < depth; i++) {
188 System.err.print(" ");
189 }
190 }
191
192 private void markAndTraverse(final Oop obj) {
193
194 // End of path
195 if (obj == null) {
196 return;
197 }
198
199 // Visited object
200 if (!markBits.mark(obj)) {
201 return;
202 }
203
204 // Root of work list for objects to be visited. A simple
205 // stack for saving new objects to be analyzed.
206
207 final Stack workList = new Stack();
208
209 // Next object to be visited.
210 Oop next = obj;
211
212 try {
213 // Node in the list currently being visited.
214
215 while (true) {
216 final Oop currObj = next;
217
218 // For the progress meter
219 if (progressThunk != null) {
220 visitedSize += currObj.getObjectSize();
221 double curFrac = (double) visitedSize / (double) usedSize;
222 if (curFrac >
223 lastNotificationFraction + MINIMUM_NOTIFICATION_FRACTION) {
224 progressThunk.heapIterationFractionUpdate(curFrac);
225 lastNotificationFraction = curFrac;
226 }
227 }
228
229 if (DEBUG) {
230 ++depth;
231 printHeader();
232 System.err.println("ReversePtrs.markAndTraverse(" +
233 currObj.getHandle() + ")");
234 }
235
236 // Iterate over the references in the object. Do the
237 // reverse pointer analysis for each reference.
238 // Add the reference to the work-list so that its
239 // references will be visited.
240 currObj.iterate(new DefaultOopVisitor() {
241 public void doOop(OopField field, boolean isVMField) {
242 // "field" refers to a reference in currObj
243 Oop next = field.getValue(currObj);
244 rp.put(new LivenessPathElement(currObj, field.getID()), next);
245 if ((next != null) && markBits.mark(next)) {
246 workList.push(next);
247 }
248 }
249 }, false);
250
251 if (DEBUG) {
252 --depth;
253 }
254
255 // Get the next object to visit.
256 next = (Oop) workList.pop();
257 }
258 } catch (EmptyStackException e) {
259 // Done
260 } catch (NullPointerException e) {
261 System.err.println("ReversePtrs: WARNING: " + e +
262 " during traversal");
263 } catch (Exception e) {
264 System.err.println("ReversePtrs: WARNING: " + e +
265 " during traversal");
266 }
267 }
268
269
270 class RootVisitor implements AddressVisitor {
271 RootVisitor(String baseRootDescription) {
272 this.baseRootDescription = baseRootDescription;
273 }
274
275 public void visitAddress(Address addr) {
276 Oop next = heap.newOop(addr.getOopHandleAt(0));
277 LivenessPathElement lp = new LivenessPathElement(null,
278 new NamedFieldIdentifier(baseRootDescription +
279 " @ " + addr));
280 rp.put(lp, next);
281 markAndTraverse(next);
282 }
283
284 public void visitCompOopAddress(Address addr) {
285 Oop next = heap.newOop(addr.getCompOopHandleAt(0));
286 LivenessPathElement lp = new LivenessPathElement(null,
287 new NamedFieldIdentifier(baseRootDescription +
288 " @ " + addr));
289 rp.put(lp, next);
290 markAndTraverse(next);
291 }
292
293 private String baseRootDescription;
294 }
295
296 // Traverse the roots on a given thread's stack
297 private void doStack(JavaThread thread, AddressVisitor oopVisitor) {
298 for (StackFrameStream fst = new StackFrameStream(thread); !fst.isDone(); fst.next()) {
299 fst.getCurrent().oopsDo(oopVisitor, fst.getRegisterMap());
300 }
301 }
302
303 // Traverse a JNIHandleBlock
304 private void doJNIHandleBlock(JNIHandleBlock handles, AddressVisitor oopVisitor) {
305 handles.oopsDo(oopVisitor);
306 }
307
308 // Traverse jobjects in global JNIHandles
309 private void doOopStorage(OopStorage oopSet, AddressVisitor oopVisitor) {
310 oopSet.oopsDo(oopVisitor);
311 }
312 }