Thu, 07 Apr 2011 09:53:20 -0700
7009266: G1: assert(obj->is_oop_or_null(true )) failed: Error
Summary: A referent object that is only weakly reachable at the start of concurrent marking but is re-attached to the strongly reachable object graph during marking may not be marked as live. This can cause the reference object to be processed prematurely and leave dangling pointers to the referent object. Implement a read barrier for the java.lang.ref.Reference::referent field by intrinsifying the Reference.get() method, and intercepting accesses though JNI, reflection, and Unsafe, so that when a non-null referent object is read it is also logged in an SATB buffer.
Reviewed-by: kvn, iveresov, never, tonyp, dholmes
1 /*
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25 #ifndef SHARE_VM_OOPS_MARKOOP_INLINE_HPP
26 #define SHARE_VM_OOPS_MARKOOP_INLINE_HPP
28 #include "oops/klass.hpp"
29 #include "oops/klassOop.hpp"
30 #include "oops/markOop.hpp"
31 #include "runtime/globals.hpp"
33 // Should this header be preserved during GC (when biased locking is enabled)?
34 inline bool markOopDesc::must_be_preserved_with_bias(oop obj_containing_mark) const {
35 assert(UseBiasedLocking, "unexpected");
36 if (has_bias_pattern()) {
37 // Will reset bias at end of collection
38 // Mark words of biased and currently locked objects are preserved separately
39 return false;
40 }
41 markOop prototype_header = prototype_for_object(obj_containing_mark);
42 if (prototype_header->has_bias_pattern()) {
43 // Individual instance which has its bias revoked; must return
44 // true for correctness
45 return true;
46 }
47 return (!is_unlocked() || !has_no_hash());
48 }
50 // Should this header be preserved during GC?
51 inline bool markOopDesc::must_be_preserved(oop obj_containing_mark) const {
52 if (!UseBiasedLocking)
53 return (!is_unlocked() || !has_no_hash());
54 return must_be_preserved_with_bias(obj_containing_mark);
55 }
57 // Should this header be preserved in the case of a promotion failure
58 // during scavenge (when biased locking is enabled)?
59 inline bool markOopDesc::must_be_preserved_with_bias_for_promotion_failure(oop obj_containing_mark) const {
60 assert(UseBiasedLocking, "unexpected");
61 // We don't explicitly save off the mark words of biased and
62 // currently-locked objects during scavenges, so if during a
63 // promotion failure we encounter either a biased mark word or a
64 // klass which still has a biasable prototype header, we have to
65 // preserve the mark word. This results in oversaving, but promotion
66 // failures are rare, and this avoids adding more complex logic to
67 // the scavengers to call new variants of
68 // BiasedLocking::preserve_marks() / restore_marks() in the middle
69 // of a scavenge when a promotion failure has first been detected.
70 if (has_bias_pattern() ||
71 prototype_for_object(obj_containing_mark)->has_bias_pattern()) {
72 return true;
73 }
74 return (!is_unlocked() || !has_no_hash());
75 }
77 // Should this header be preserved in the case of a promotion failure
78 // during scavenge?
79 inline bool markOopDesc::must_be_preserved_for_promotion_failure(oop obj_containing_mark) const {
80 if (!UseBiasedLocking)
81 return (!is_unlocked() || !has_no_hash());
82 return must_be_preserved_with_bias_for_promotion_failure(obj_containing_mark);
83 }
86 // Same as must_be_preserved_with_bias_for_promotion_failure() except that
87 // it takes a klassOop argument, instead of the object of which this is the mark word.
88 inline bool markOopDesc::must_be_preserved_with_bias_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const {
89 assert(UseBiasedLocking, "unexpected");
90 // CMS scavenges preserve mark words in similar fashion to promotion failures; see above
91 if (has_bias_pattern() ||
92 klass_of_obj_containing_mark->klass_part()->prototype_header()->has_bias_pattern()) {
93 return true;
94 }
95 return (!is_unlocked() || !has_no_hash());
96 }
98 // Same as must_be_preserved_for_promotion_failure() except that
99 // it takes a klassOop argument, instead of the object of which this is the mark word.
100 inline bool markOopDesc::must_be_preserved_for_cms_scavenge(klassOop klass_of_obj_containing_mark) const {
101 if (!UseBiasedLocking)
102 return (!is_unlocked() || !has_no_hash());
103 return must_be_preserved_with_bias_for_cms_scavenge(klass_of_obj_containing_mark);
104 }
106 inline markOop markOopDesc::prototype_for_object(oop obj) {
107 #ifdef ASSERT
108 markOop prototype_header = obj->klass()->klass_part()->prototype_header();
109 assert(prototype_header == prototype() || prototype_header->has_bias_pattern(), "corrupt prototype header");
110 #endif
111 return obj->klass()->klass_part()->prototype_header();
112 }
114 #endif // SHARE_VM_OOPS_MARKOOP_INLINE_HPP