24
25 package sun.jvm.hotspot.utilities;
26
27 import sun.jvm.hotspot.debugger.*;
28 import sun.jvm.hotspot.gc.shared.*;
29 import sun.jvm.hotspot.memory.*;
30 import sun.jvm.hotspot.oops.*;
31 import sun.jvm.hotspot.runtime.*;
32
33 /** Helper class which covers the reserved area of the heap with an
34 (object-external) set of mark bits, used for GC-like scans through
35 the heap like liveness analysis. */
36
37 public class MarkBits {
38 public MarkBits(CollectedHeap heap) {
39 MemRegion reserved = heap.reservedRegion();
40 // Must cover "reserved" with one bit for each OopHandle
41 start = reserved.start();
42 end = reserved.end();
43 long numOopHandles = end.minus(start) / VM.getVM().getOopSize();
44 // FIXME: will have trouble with larger heap sizes
45 bits = new BitMap((int) numOopHandles);
46 }
47
48 public void clear() {
49 bits.clear();
50 }
51
52 /** Returns true if a mark was newly placed for the given Oop, or
53 false if the Oop was already marked. If the Oop happens to lie
54 outside the heap (should not happen), prints a warning and
55 returns false. */
56 public boolean mark(Oop obj) {
57 if (obj == null) {
58 System.err.println("MarkBits: WARNING: null object, ignoring");
59 return false;
60 }
61
62 OopHandle handle = obj.getHandle();
63 // FIXME: will have trouble with larger heap sizes
64 long idx = handle.minus(start) / VM.getVM().getOopSize();
65 if ((idx < 0) || (idx >= bits.size())) {
66 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring");
67 return false;
68 }
69 int intIdx = (int) idx;
70 if (bits.at(intIdx)) {
71 return false; // already marked
72 }
73 bits.atPut(intIdx, true);
74 return true;
75 }
76
77 /** Forces clearing of a given mark bit. */
78 public void clear(Oop obj) {
79 OopHandle handle = obj.getHandle();
80 // FIXME: will have trouble with larger heap sizes
81 long idx = handle.minus(start) / VM.getVM().getOopSize();
82 if ((idx < 0) || (idx >= bits.size())) {
83 System.err.println("MarkBits: WARNING: object " + handle + " outside of heap, ignoring");
84 return;
85 }
86 int intIdx = (int) idx;
87 bits.atPut(intIdx, false);
88 }
89
90 private BitMap bits;
91 private Address start;
92 private Address end;
93 }
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24
25 package sun.jvm.hotspot.utilities;
26
27 import sun.jvm.hotspot.debugger.*;
28 import sun.jvm.hotspot.gc.shared.*;
29 import sun.jvm.hotspot.memory.*;
30 import sun.jvm.hotspot.oops.*;
31 import sun.jvm.hotspot.runtime.*;
32
33 /** Helper class which covers the reserved area of the heap with an
34 (object-external) set of mark bits, used for GC-like scans through
35 the heap like liveness analysis. */
36
37 public class MarkBits {
38 public MarkBits(CollectedHeap heap) {
39 MemRegion reserved = heap.reservedRegion();
40 // Must cover "reserved" with one bit for each OopHandle
41 start = reserved.start();
42 end = reserved.end();
43 long numOopHandles = end.minus(start) / VM.getVM().getOopSize();
44 bits = heap.createBitMap(numOopHandles);
45 }
46
47 public void clear() {
48 bits.clear();
49 }
50
51 /** Returns true if a mark was newly placed for the given Oop, or
52 false if the Oop was already marked. If the Oop happens to lie
53 outside the heap (should not happen), prints a warning and
54 returns false. */
55 public boolean mark(Oop obj) {
56 if (obj == null) {
57 System.err.println("MarkBits: WARNING: null object, ignoring");
58 return false;
59 }
60
61 OopHandle handle = obj.getHandle();
62 long idx = handle.minus(start) / VM.getVM().getOopSize();
63 if (bits.at(idx)) {
64 return false; // already marked
65 }
66 bits.atPut(idx, true);
67 return true;
68 }
69
70 /** Forces clearing of a given mark bit. */
71 public void clear(Oop obj) {
72 OopHandle handle = obj.getHandle();
73 long idx = handle.minus(start) / VM.getVM().getOopSize();
74 bits.atPut(idx, false);
75 }
76
77 private BitMapInterface bits;
78 private Address start;
79 private Address end;
80 }
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