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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13 * accompanied this code).
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25 #include "precompiled.hpp"
26 #include "gc_implementation/g1/g1MMUTracker.hpp"
27 #include "runtime/mutexLocker.hpp"
28 #include "utilities/ostream.hpp"
30 #define _DISABLE_MMU 0
32 // can't rely on comparing doubles with tolerating a small margin for error
33 #define SMALL_MARGIN 0.0000001
34 #define is_double_leq_0(_value) ( (_value) < SMALL_MARGIN )
35 #define is_double_leq(_val1, _val2) is_double_leq_0((_val1) - (_val2))
36 #define is_double_geq(_val1, _val2) is_double_leq_0((_val2) - (_val1))
38 /***** ALL TIMES ARE IN SECS!!!!!!! *****/
40 G1MMUTracker::G1MMUTracker(double time_slice, double max_gc_time) :
41 _time_slice(time_slice),
42 _max_gc_time(max_gc_time) { }
44 G1MMUTrackerQueue::G1MMUTrackerQueue(double time_slice, double max_gc_time) :
45 G1MMUTracker(time_slice, max_gc_time),
46 _head_index(0),
47 _tail_index(trim_index(_head_index+1)),
48 _no_entries(0) { }
50 void G1MMUTrackerQueue::remove_expired_entries(double current_time) {
51 double limit = current_time - _time_slice;
52 while (_no_entries > 0) {
53 if (is_double_geq(limit, _array[_tail_index].end_time())) {
54 _tail_index = trim_index(_tail_index + 1);
55 --_no_entries;
56 } else
57 return;
58 }
59 guarantee(_no_entries == 0, "should have no entries in the array");
60 }
62 double G1MMUTrackerQueue::calculate_gc_time(double current_time) {
63 double gc_time = 0.0;
64 double limit = current_time - _time_slice;
65 for (int i = 0; i < _no_entries; ++i) {
66 int index = trim_index(_tail_index + i);
67 G1MMUTrackerQueueElem *elem = &_array[index];
68 if (elem->end_time() > limit) {
69 if (elem->start_time() > limit)
70 gc_time += elem->duration();
71 else
72 gc_time += elem->end_time() - limit;
73 }
74 }
75 return gc_time;
76 }
78 void G1MMUTrackerQueue::add_pause(double start, double end, bool gc_thread) {
79 double longest_allowed = longest_pause_internal(start);
80 if (longest_allowed < 0.0)
81 longest_allowed = 0.0;
82 double duration = end - start;
84 remove_expired_entries(end);
85 if (_no_entries == QueueLength) {
86 // OK, we've filled up the queue. There are a few ways
87 // of dealing with this "gracefully"
88 // increase the array size (:-)
89 // remove the oldest entry (this might allow more GC time for
90 // the time slice than what's allowed) - this is what we
91 // currently do
92 // consolidate the two entries with the minimum gap between them
93 // (this might allow less GC time than what's allowed)
95 // In the case where ScavengeALot is true, such overflow is not
96 // uncommon; in such cases, we can, without much loss of precision
97 // or performance (we are GC'ing most of the time anyway!),
98 // simply overwrite the oldest entry in the tracker.
100 if (G1PolicyVerbose > 1) {
101 warning("MMU Tracker Queue overflow. Replacing earliest entry.");
102 }
104 _head_index = trim_index(_head_index + 1);
105 assert(_head_index == _tail_index, "Because we have a full circular buffer");
106 _tail_index = trim_index(_tail_index + 1);
107 } else {
108 _head_index = trim_index(_head_index + 1);
109 ++_no_entries;
110 }
111 _array[_head_index] = G1MMUTrackerQueueElem(start, end);
112 }
114 // basically the _internal call does not remove expired entries
115 // this is for trying things out in the future and a couple
116 // of other places (debugging)
118 double G1MMUTrackerQueue::longest_pause(double current_time) {
119 if (_DISABLE_MMU)
120 return _max_gc_time;
122 MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);
123 remove_expired_entries(current_time);
125 return longest_pause_internal(current_time);
126 }
128 double G1MMUTrackerQueue::longest_pause_internal(double current_time) {
129 double target_time = _max_gc_time;
131 while( 1 ) {
132 double gc_time =
133 calculate_gc_time(current_time + target_time);
134 double diff = target_time + gc_time - _max_gc_time;
135 if (!is_double_leq_0(diff)) {
136 target_time -= diff;
137 if (is_double_leq_0(target_time)) {
138 target_time = -1.0;
139 break;
140 }
141 } else {
142 break;
143 }
144 }
146 return target_time;
147 }
149 // basically the _internal call does not remove expired entries
150 // this is for trying things out in the future and a couple
151 // of other places (debugging)
153 double G1MMUTrackerQueue::when_sec(double current_time, double pause_time) {
154 if (_DISABLE_MMU)
155 return 0.0;
157 MutexLockerEx x(MMUTracker_lock, Mutex::_no_safepoint_check_flag);
158 remove_expired_entries(current_time);
160 return when_internal(current_time, pause_time);
161 }
163 double G1MMUTrackerQueue::when_internal(double current_time,
164 double pause_time) {
165 // if the pause is over the maximum, just assume that it's the maximum
166 double adjusted_pause_time =
167 (pause_time > max_gc_time()) ? max_gc_time() : pause_time;
168 double earliest_end = current_time + adjusted_pause_time;
169 double limit = earliest_end - _time_slice;
170 double gc_time = calculate_gc_time(earliest_end);
171 double diff = gc_time + adjusted_pause_time - max_gc_time();
172 if (is_double_leq_0(diff))
173 return 0.0;
175 int index = _tail_index;
176 while ( 1 ) {
177 G1MMUTrackerQueueElem *elem = &_array[index];
178 if (elem->end_time() > limit) {
179 if (elem->start_time() > limit)
180 diff -= elem->duration();
181 else
182 diff -= elem->end_time() - limit;
183 if (is_double_leq_0(diff))
184 return elem->end_time() + diff + _time_slice - adjusted_pause_time - current_time;
185 }
186 index = trim_index(index+1);
187 guarantee(index != trim_index(_head_index + 1), "should not go past head");
188 }
189 }