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 #include "precompiled.hpp"
26 #include "oops/markOop.hpp"
27 #ifdef TARGET_OS_FAMILY_linux
28 # include "thread_linux.inline.hpp"
29 #endif
30 #ifdef TARGET_OS_FAMILY_solaris
31 # include "thread_solaris.inline.hpp"
32 #endif
33 #ifdef TARGET_OS_FAMILY_windows
34 # include "thread_windows.inline.hpp"
35 #endif
38 void markOopDesc::print_on(outputStream* st) const {
39 if (is_locked()) {
40 st->print("locked(0x%lx)->", value());
41 markOop(*(markOop*)value())->print_on(st);
42 } else {
43 assert(is_unlocked() || has_bias_pattern(), "just checking");
44 st->print("mark(");
45 if (has_bias_pattern()) st->print("biased,");
46 st->print("hash %#lx,", hash());
47 st->print("age %d)", age());
48 }
49 }
52 // Give advice about whether the oop that contains this markOop
53 // should be cached or not.
54 bool markOopDesc::should_not_be_cached() const {
55 // the cast is because decode_pointer() isn't marked const
56 if (is_marked() && ((markOopDesc *)this)->decode_pointer() != NULL) {
57 // If the oop containing this markOop is being forwarded, then
58 // we are in the middle of GC and we do not want the containing
59 // oop to be added to a cache. We have no way of knowing whether
60 // the cache has already been visited by the current GC phase so
61 // we don't know whether the forwarded oop will be properly
62 // processed in this phase. If the forwarded oop is not properly
63 // processed, then we'll see strange crashes or asserts during
64 // the next GC run because the markOop will contain an unexpected
65 // value.
66 //
67 // This situation has been seen when we are GC'ing a methodOop
68 // because we use the methodOop while we're GC'ing it. Scary
69 // stuff. Some of the uses the methodOop cause the methodOop to
70 // be added to the OopMapCache in the instanceKlass as a side
71 // effect. This check lets the cache maintainer know when a
72 // cache addition would not be safe.
73 return true;
74 }
76 // caching the containing oop should be just fine
77 return false;
78 }