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 /*
2 * Copyright (c) 2001, 2011, Oracle and/or its affiliates. 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
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23 */
25 #ifndef SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTG1REFINE_HPP
26 #define SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTG1REFINE_HPP
28 #include "memory/allocation.hpp"
29 #include "memory/cardTableModRefBS.hpp"
30 #include "runtime/thread.hpp"
31 #include "utilities/globalDefinitions.hpp"
33 // Forward decl
34 class ConcurrentG1RefineThread;
35 class G1RemSet;
37 class ConcurrentG1Refine: public CHeapObj {
38 ConcurrentG1RefineThread** _threads;
39 int _n_threads;
40 int _n_worker_threads;
41 /*
42 * The value of the update buffer queue length falls into one of 3 zones:
43 * green, yellow, red. If the value is in [0, green) nothing is
44 * done, the buffers are left unprocessed to enable the caching effect of the
45 * dirtied cards. In the yellow zone [green, yellow) the concurrent refinement
46 * threads are gradually activated. In [yellow, red) all threads are
47 * running. If the length becomes red (max queue length) the mutators start
48 * processing the buffers.
49 *
50 * There are some interesting cases (when G1UseAdaptiveConcRefinement
51 * is turned off):
52 * 1) green = yellow = red = 0. In this case the mutator will process all
53 * buffers. Except for those that are created by the deferred updates
54 * machinery during a collection.
55 * 2) green = 0. Means no caching. Can be a good way to minimize the
56 * amount of time spent updating rsets during a collection.
57 */
58 int _green_zone;
59 int _yellow_zone;
60 int _red_zone;
62 int _thread_threshold_step;
64 // Reset the threshold step value based of the current zone boundaries.
65 void reset_threshold_step();
67 // The cache for card refinement.
68 bool _use_cache;
69 bool _def_use_cache;
71 size_t _n_periods; // Used as clearing epoch
73 // An evicting cache of the number of times each card
74 // is accessed. Reduces, but does not eliminate, the amount
75 // of duplicated processing of dirty cards.
77 enum SomePrivateConstants {
78 epoch_bits = 32,
79 card_num_shift = epoch_bits,
80 epoch_mask = AllBits,
81 card_num_mask = AllBits,
83 // The initial cache size is approximately this fraction
84 // of a maximal cache (i.e. the size needed for all cards
85 // in the heap)
86 InitialCacheFraction = 512
87 };
89 const static julong card_num_mask_in_place =
90 (julong) card_num_mask << card_num_shift;
92 typedef struct {
93 julong _value; // | card_num | epoch |
94 } CardEpochCacheEntry;
96 julong make_epoch_entry(unsigned int card_num, unsigned int epoch) {
97 assert(0 <= card_num && card_num < _max_cards, "Bounds");
98 assert(0 <= epoch && epoch <= _n_periods, "must be");
100 return ((julong) card_num << card_num_shift) | epoch;
101 }
103 unsigned int extract_epoch(julong v) {
104 return (v & epoch_mask);
105 }
107 unsigned int extract_card_num(julong v) {
108 return (v & card_num_mask_in_place) >> card_num_shift;
109 }
111 typedef struct {
112 unsigned char _count;
113 unsigned char _evict_count;
114 } CardCountCacheEntry;
116 CardCountCacheEntry* _card_counts;
117 CardEpochCacheEntry* _card_epochs;
119 // The current number of buckets in the card count cache
120 size_t _n_card_counts;
122 // The number of cards for the entire reserved heap
123 size_t _max_cards;
125 // The max number of buckets for the card counts and epochs caches.
126 // This is the maximum that the counts and epochs will grow to.
127 // It is specified as a fraction or percentage of _max_cards using
128 // G1MaxHotCardCountSizePercent.
129 size_t _max_n_card_counts;
131 // Possible sizes of the cache: odd primes that roughly double in size.
132 // (See jvmtiTagMap.cpp).
133 enum {
134 MAX_CC_CACHE_INDEX = 15 // maximum index into the cache size array.
135 };
137 static size_t _cc_cache_sizes[MAX_CC_CACHE_INDEX];
139 // The index in _cc_cache_sizes corresponding to the size of
140 // _card_counts.
141 int _cache_size_index;
143 bool _expand_card_counts;
145 const jbyte* _ct_bot;
147 jbyte** _hot_cache;
148 int _hot_cache_size;
149 int _n_hot;
150 int _hot_cache_idx;
152 int _hot_cache_par_chunk_size;
153 volatile int _hot_cache_par_claimed_idx;
155 // Needed to workaround 6817995
156 CardTableModRefBS* _ct_bs;
157 G1CollectedHeap* _g1h;
159 // Helper routine for expand_card_count_cache().
160 // The arrays used to hold the card counts and the epochs must have
161 // a 1:1 correspondence. Hence they are allocated and freed together.
162 // Returns true if the allocations of both the counts and epochs
163 // were successful; false otherwise.
164 bool allocate_card_count_cache(size_t n,
165 CardCountCacheEntry** counts,
166 CardEpochCacheEntry** epochs);
168 // Expands the arrays that hold the card counts and epochs
169 // to the cache size at index. Returns true if the expansion/
170 // allocation was successful; false otherwise.
171 bool expand_card_count_cache(int index);
173 // hash a given key (index of card_ptr) with the specified size
174 static unsigned int hash(size_t key, size_t size) {
175 return (unsigned int) key % size;
176 }
178 // hash a given key (index of card_ptr)
179 unsigned int hash(size_t key) {
180 return hash(key, _n_card_counts);
181 }
183 unsigned ptr_2_card_num(jbyte* card_ptr) {
184 return (unsigned) (card_ptr - _ct_bot);
185 }
187 jbyte* card_num_2_ptr(unsigned card_num) {
188 return (jbyte*) (_ct_bot + card_num);
189 }
191 // Returns the count of this card after incrementing it.
192 jbyte* add_card_count(jbyte* card_ptr, int* count, bool* defer);
194 // Returns true if this card is in a young region
195 bool is_young_card(jbyte* card_ptr);
197 public:
198 ConcurrentG1Refine();
199 ~ConcurrentG1Refine();
201 void init(); // Accomplish some initialization that has to wait.
202 void stop();
204 void reinitialize_threads();
206 // Iterate over the conc refine threads
207 void threads_do(ThreadClosure *tc);
209 // If this is the first entry for the slot, writes into the cache and
210 // returns NULL. If it causes an eviction, returns the evicted pointer.
211 // Otherwise, its a cache hit, and returns NULL.
212 jbyte* cache_insert(jbyte* card_ptr, bool* defer);
214 // Process the cached entries.
215 void clean_up_cache(int worker_i, G1RemSet* g1rs, DirtyCardQueue* into_cset_dcq);
217 // Set up for parallel processing of the cards in the hot cache
218 void clear_hot_cache_claimed_index() {
219 _hot_cache_par_claimed_idx = 0;
220 }
222 // Discard entries in the hot cache.
223 void clear_hot_cache() {
224 _hot_cache_idx = 0; _n_hot = 0;
225 }
227 bool hot_cache_is_empty() { return _n_hot == 0; }
229 bool use_cache() { return _use_cache; }
230 void set_use_cache(bool b) {
231 if (b) _use_cache = _def_use_cache;
232 else _use_cache = false;
233 }
235 void clear_and_record_card_counts();
237 static int thread_num();
239 void print_worker_threads_on(outputStream* st) const;
241 void set_green_zone(int x) { _green_zone = x; }
242 void set_yellow_zone(int x) { _yellow_zone = x; }
243 void set_red_zone(int x) { _red_zone = x; }
245 int green_zone() const { return _green_zone; }
246 int yellow_zone() const { return _yellow_zone; }
247 int red_zone() const { return _red_zone; }
249 int total_thread_num() const { return _n_threads; }
250 int worker_thread_num() const { return _n_worker_threads; }
252 int thread_threshold_step() const { return _thread_threshold_step; }
253 };
255 #endif // SHARE_VM_GC_IMPLEMENTATION_G1_CONCURRENTG1REFINE_HPP