Mercurial > hg > graal-compiler
comparison agent/src/share/classes/sun/jvm/hotspot/utilities/LivenessAnalysis.java @ 0:a61af66fc99e jdk7-b24
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author | duke |
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date | Sat, 01 Dec 2007 00:00:00 +0000 |
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children | c18cbe5936b8 |
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1 /* | |
2 * Copyright 2001-2006 Sun Microsystems, Inc. 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, | |
20 * CA 95054 USA or visit www.sun.com if you need additional information or | |
21 * have any 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 | |
35 /** Finds all paths from roots to the specified set of objects. NOTE: | |
36 currently only a subset of the roots known to the VM is exposed to | |
37 the SA: objects on the stack, static fields in classes, and JNI | |
38 handles. These should be most of the user-level roots keeping | |
39 objects alive. */ | |
40 | |
41 public class LivenessAnalysis { | |
42 // Used for debugging this code | |
43 private static final boolean DEBUG = false; | |
44 | |
45 private LivenessAnalysis() {} | |
46 | |
47 public static LivenessPathList computeAllLivenessPaths(Oop target) { | |
48 LivenessPathList list = computeAllLivenessPaths(target, true); | |
49 if ((list == null) || (list.size() == 0)) { | |
50 // Dead object | |
51 return null; | |
52 } | |
53 return list; | |
54 } | |
55 | |
56 //--------------------------------------------------------------------------- | |
57 // Internals only below this point | |
58 // | |
59 | |
60 // Returns true if a new path was completed, otherwise false | |
61 // indicating there were no more paths to complete. | |
62 // | |
63 // The trimPathsThroughPopularObjects flag alters the behavior of | |
64 // the returned results. If true, then if multiple paths to | |
65 // different roots all go through a particular popular object, those | |
66 // paths will be truncated and only one (arbitrary one) will be be | |
67 // returned. On the other hand, if the target object itself is | |
68 // popular and there are multiple distinct paths to it (indicating | |
69 // that there are multiple objects pointing directly to it) then all | |
70 // of those paths will be reported. | |
71 private static LivenessPathList computeAllLivenessPaths(Oop target, boolean trimPathsThroughPopularObjects) { | |
72 ReversePtrs rev = VM.getVM().getRevPtrs(); | |
73 if (rev == null) { | |
74 throw new RuntimeException("LivenessAnalysis requires ReversePtrs to have been computed"); | |
75 } | |
76 | |
77 // Currently the reverse pointer analysis returns non-null results | |
78 // only for live objects | |
79 if (rev.get(target) == null) { | |
80 // Object is dead | |
81 return null; | |
82 } | |
83 | |
84 // HashSet of Oops acting as a bit mask indicating which ones have | |
85 // already been traversed | |
86 Set/*<Oop>*/ visitedOops = new HashSet/*<Oop>*/(); | |
87 | |
88 // IdentityHashMap of LivenessElements acting as a bit mask | |
89 // indicating which roots have already been traversed | |
90 Map/*<LivenessElement, LivenessElement>*/ visitedRoots = | |
91 new IdentityHashMap/*<LivenessElement, LivenessElement>*/(); | |
92 | |
93 visitedOops.add(target); | |
94 | |
95 // Construct the initial LivenessPath | |
96 LivenessPathList list = new LivenessPathList(); | |
97 { | |
98 LivenessPath path = new LivenessPath(); | |
99 path.push(new LivenessPathElement(target, null)); | |
100 list.add(path); | |
101 } | |
102 | |
103 // Iterate until done | |
104 while (true) { | |
105 // See if there are any incomplete paths left | |
106 LivenessPath path = null; | |
107 | |
108 for (int i = list.size() - 1; i >= 0; i--) { | |
109 LivenessPath tmp = list.get(i); | |
110 if (!tmp.isComplete()) { | |
111 path = tmp; | |
112 break; | |
113 } | |
114 } | |
115 | |
116 // If no incomplete paths left, return | |
117 if (path == null) { | |
118 return list; | |
119 } | |
120 | |
121 // Try to complete this path | |
122 | |
123 // Remove the path from the list of reported ones in | |
124 // anticipation of completing it | |
125 list.remove(path); | |
126 | |
127 try { | |
128 // Fetch next set of reverse pointers for the last object on | |
129 // the list | |
130 ArrayList/*<LivenessPathElement>*/ nextPtrs = | |
131 rev.get(path.peek().getObj()); | |
132 | |
133 // Depending on exactly what the reverse pointers analysis | |
134 // yields, these results may be null, although currently they | |
135 // won't be | |
136 if (nextPtrs != null) { | |
137 // Iterate these | |
138 for (Iterator iter = nextPtrs.iterator(); iter.hasNext(); ) { | |
139 LivenessPathElement nextElement = (LivenessPathElement) iter.next(); | |
140 // See whether we've visited this element yet | |
141 if ((nextElement.isRoot() && (visitedRoots.get(nextElement) == null)) || | |
142 (!nextElement.isRoot() && !visitedOops.contains(nextElement.getObj()))) { | |
143 // Show we've visited this one | |
144 if (nextElement.isRoot()) { | |
145 visitedRoots.put(nextElement, nextElement); | |
146 } else { | |
147 visitedOops.add(nextElement.getObj()); | |
148 } | |
149 | |
150 // Create a new LivenessPath for each one | |
151 LivenessPath nextPath = path.copy(); | |
152 nextPath.push(nextElement); | |
153 | |
154 // Regardless of whether we found a root, put the | |
155 // original path back on the list because we're going to | |
156 // do depth-first searching rather than breadth-first | |
157 list.add(path); | |
158 list.add(nextPath); | |
159 | |
160 // See whether this path is complete (i.e., it | |
161 // terminates in a root) | |
162 if (trimPathsThroughPopularObjects && nextElement.isRoot()) { | |
163 // Go back through the path list and remove all | |
164 // incomplete paths ending in any of the intermediate | |
165 // (non-root and non-terminal) nodes in this path. | |
166 // This has the effect of removing multiple paths | |
167 // going through popular objects. | |
168 for (int i = 1; i < nextPath.size() - 1; i++) { | |
169 LivenessPathElement el = nextPath.get(i); | |
170 int j = 0; | |
171 while (j < list.size()) { | |
172 LivenessPath curPath = list.get(j); | |
173 // We can use an object identity since these | |
174 // intermediate nodes are canonicalized via the | |
175 // ReversePtrsAnalysis | |
176 if (curPath.peek() == el) { | |
177 list.remove(curPath); | |
178 } else { | |
179 j++; | |
180 } | |
181 } | |
182 } | |
183 } | |
184 | |
185 // Do depth-first searching, not breadth-first | |
186 break; | |
187 } | |
188 } | |
189 } | |
190 } catch (Exception e) { | |
191 System.err.println("LivenessAnalysis: WARNING: " + e + | |
192 " during traversal"); | |
193 } | |
194 } | |
195 } | |
196 } |