1 /*
2 * Copyright (c) 2001, 2015, 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
21 * questions.
22 *
23 */
24
25 #include "precompiled.hpp"
26 #include "gc/g1/g1CollectedHeap.inline.hpp"
27 #include "gc/g1/satbMarkQueue.hpp"
28 #include "gc/shared/collectedHeap.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/mutexLocker.hpp"
32 #include "runtime/safepoint.hpp"
33 #include "runtime/thread.hpp"
34 #include "runtime/vmThread.hpp"
35
36 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
37 // SATB queues are only active during marking cycles. We create
38 // them with their active field set to false. If a thread is
39 // created during a cycle and its SATB queue needs to be activated
40 // before the thread starts running, we'll need to set its active
41 // field to true. This is done in JavaThread::initialize_queues().
42 PtrQueue(qset, permanent, false /* active */)
43 { }
44
45 void SATBMarkQueue::flush() {
46 // Filter now to possibly save work later. If filtering empties the
47 // buffer then flush_impl can deallocate the buffer.
48 filter();
49 flush_impl();
50 }
51
52 // Return true if a SATB buffer entry refers to an object that
53 // requires marking.
54 //
55 // The entry must point into the G1 heap. In particular, it must not
56 // be a NULL pointer. NULL pointers are pre-filtered and never
57 // inserted into a SATB buffer.
58 //
59 // An entry that is below the NTAMS pointer for the containing heap
60 // region requires marking. Such an entry must point to a valid object.
61 //
62 // An entry that is at least the NTAMS pointer for the containing heap
63 // region might be any of the following, none of which should be marked.
64 //
65 // * A reference to an object allocated since marking started.
66 // According to SATB, such objects are implicitly kept live and do
67 // not need to be dealt with via SATB buffer processing.
68 //
69 // * A reference to a young generation object. Young objects are
70 // handled separately and are not marked by concurrent marking.
71 //
72 // * A stale reference to a young generation object. If a young
73 // generation object reference is recorded and not filtered out
74 // before being moved by a young collection, the reference becomes
75 // stale.
76 //
77 // * A stale reference to an eagerly reclaimed humongous object. If a
78 // humongous object is recorded and then reclaimed, the reference
79 // becomes stale.
80 //
81 // The stale reference cases are implicitly handled by the NTAMS
82 // comparison. Because of the possibility of stale references, buffer
83 // processing must be somewhat circumspect and not assume entries
84 // in an unfiltered buffer refer to valid objects.
85
86 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
87 // Includes rejection of NULL pointers.
88 assert(heap->is_in_reserved(entry),
89 "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
90
91 HeapRegion* region = heap->heap_region_containing(entry);
92 assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
93 if (entry >= region->next_top_at_mark_start()) {
94 return false;
95 }
96
97 assert(((oop)entry)->is_oop(true /* ignore mark word */),
98 "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
99
100 return true;
101 }
102
103 // This method removes entries from a SATB buffer that will not be
104 // useful to the concurrent marking threads. Entries are retained if
105 // they require marking and are not already marked. Retained entries
106 // are compacted toward the top of the buffer.
107
108 void SATBMarkQueue::filter() {
109 G1CollectedHeap* g1h = G1CollectedHeap::heap();
110 void** buf = _buf;
111
112 if (buf == NULL) {
113 // nothing to do
114 return;
115 }
116
117 // Used for sanity checking at the end of the loop.
118 DEBUG_ONLY(size_t entries = 0; size_t retained = 0;)
119
120 assert(_index <= _sz, "invariant");
121 void** limit = &buf[byte_index_to_index(_index)];
122 void** src = &buf[byte_index_to_index(_sz)];
123 void** dst = src;
124
125 while (limit < src) {
126 DEBUG_ONLY(entries += 1;)
127 --src;
128 void* entry = *src;
129 // NULL the entry so that unused parts of the buffer contain NULLs
130 // at the end. If we are going to retain it we will copy it to its
131 // final place. If we have retained all entries we have visited so
132 // far, we'll just end up copying it to the same place.
133 *src = NULL;
134
135 if (requires_marking(entry, g1h) && !g1h->isMarkedNext((oop)entry)) {
136 --dst;
137 assert(*dst == NULL, "filtering destination should be clear");
138 *dst = entry;
139 DEBUG_ONLY(retained += 1;);
140 }
141 }
142 size_t new_index = pointer_delta(dst, buf, 1);
143
144 #ifdef ASSERT
145 size_t entries_calc = (_sz - _index) / sizeof(void*);
146 assert(entries == entries_calc, "the number of entries we counted "
147 "should match the number of entries we calculated");
148 size_t retained_calc = (_sz - new_index) / sizeof(void*);
149 assert(retained == retained_calc, "the number of retained entries we counted "
150 "should match the number of retained entries we calculated");
151 #endif // ASSERT
152
153 _index = new_index;
154 }
155
156 // This method will first apply the above filtering to the buffer. If
157 // post-filtering a large enough chunk of the buffer has been cleared
158 // we can re-use the buffer (instead of enqueueing it) and we can just
159 // allow the mutator to carry on executing using the same buffer
160 // instead of replacing it.
161
162 bool SATBMarkQueue::should_enqueue_buffer() {
163 assert(_lock == NULL || _lock->owned_by_self(),
164 "we should have taken the lock before calling this");
165
166 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
167
168 // This method should only be called if there is a non-NULL buffer
169 // that is full.
170 assert(_index == 0, "pre-condition");
171 assert(_buf != NULL, "pre-condition");
172
173 filter();
174
175 size_t percent_used = ((_sz - _index) * 100) / _sz;
176 bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
177 return should_enqueue;
178 }
179
180 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
181 assert(SafepointSynchronize::is_at_safepoint(),
182 "SATB queues must only be processed at safepoints");
183 if (_buf != NULL) {
184 assert(_index % sizeof(void*) == 0, "invariant");
185 assert(_sz % sizeof(void*) == 0, "invariant");
186 assert(_index <= _sz, "invariant");
187 cl->do_buffer(_buf + byte_index_to_index(_index),
188 byte_index_to_index(_sz - _index));
189 _index = _sz;
190 }
191 }
192
193 #ifndef PRODUCT
194 // Helpful for debugging
195
196 void SATBMarkQueue::print(const char* name) {
197 print(name, _buf, _index, _sz);
198 }
199
200 void SATBMarkQueue::print(const char* name,
201 void** buf, size_t index, size_t sz) {
202 gclog_or_tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " "
203 "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,
204 name, p2i(buf), index, sz);
205 }
206 #endif // PRODUCT
207
208 SATBMarkQueueSet::SATBMarkQueueSet() :
209 PtrQueueSet(),
210 _shared_satb_queue(this, true /* permanent */) { }
211
212 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
213 int process_completed_threshold,
214 Mutex* lock) {
215 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
216 _shared_satb_queue.set_lock(lock);
217 }
218
219 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
220 t->satb_mark_queue().handle_zero_index();
221 }
222
223 #ifdef ASSERT
224 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
225 gclog_or_tty->print_cr("Expected SATB active state: %s",
226 expected_active ? "ACTIVE" : "INACTIVE");
227 gclog_or_tty->print_cr("Actual SATB active states:");
228 gclog_or_tty->print_cr(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
229 for (JavaThread* t = Threads::first(); t; t = t->next()) {
230 gclog_or_tty->print_cr(" Thread \"%s\" queue: %s", t->name(),
231 t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
232 }
233 gclog_or_tty->print_cr(" Shared queue: %s",
234 shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
235 }
236
237 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
238 // Verify queue set state
239 if (is_active() != expected_active) {
240 dump_active_states(expected_active);
241 guarantee(false, "SATB queue set has an unexpected active state");
242 }
243
244 // Verify thread queue states
245 for (JavaThread* t = Threads::first(); t; t = t->next()) {
246 if (t->satb_mark_queue().is_active() != expected_active) {
247 dump_active_states(expected_active);
248 guarantee(false, "Thread SATB queue has an unexpected active state");
249 }
250 }
251
252 // Verify shared queue state
253 if (shared_satb_queue()->is_active() != expected_active) {
254 dump_active_states(expected_active);
255 guarantee(false, "Shared SATB queue has an unexpected active state");
256 }
257 }
258 #endif // ASSERT
259
260 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
261 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
262 #ifdef ASSERT
263 verify_active_states(expected_active);
264 #endif // ASSERT
265 _all_active = active;
266 for (JavaThread* t = Threads::first(); t; t = t->next()) {
267 t->satb_mark_queue().set_active(active);
268 }
269 shared_satb_queue()->set_active(active);
270 }
271
272 void SATBMarkQueueSet::filter_thread_buffers() {
273 for(JavaThread* t = Threads::first(); t; t = t->next()) {
274 t->satb_mark_queue().filter();
275 }
276 shared_satb_queue()->filter();
277 }
278
279 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
280 BufferNode* nd = NULL;
281 {
282 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
283 if (_completed_buffers_head != NULL) {
284 nd = _completed_buffers_head;
285 _completed_buffers_head = nd->next();
286 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
287 _n_completed_buffers--;
288 if (_n_completed_buffers == 0) _process_completed = false;
289 }
290 }
291 if (nd != NULL) {
292 void **buf = BufferNode::make_buffer_from_node(nd);
293 // Skip over NULL entries at beginning (e.g. push end) of buffer.
294 // Filtering can result in non-full completed buffers; see
295 // should_enqueue_buffer.
296 assert(_sz % sizeof(void*) == 0, "invariant");
297 size_t limit = SATBMarkQueue::byte_index_to_index(_sz);
298 for (size_t i = 0; i < limit; ++i) {
299 if (buf[i] != NULL) {
300 // Found the end of the block of NULLs; process the remainder.
301 cl->do_buffer(buf + i, limit - i);
302 break;
303 }
304 }
305 deallocate_buffer(buf);
306 return true;
307 } else {
308 return false;
309 }
310 }
311
312 #ifndef PRODUCT
313 // Helpful for debugging
314
315 #define SATB_PRINTER_BUFFER_SIZE 256
316
317 void SATBMarkQueueSet::print_all(const char* msg) {
318 char buffer[SATB_PRINTER_BUFFER_SIZE];
319 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
320
321 gclog_or_tty->cr();
322 gclog_or_tty->print_cr("SATB BUFFERS [%s]", msg);
323
324 BufferNode* nd = _completed_buffers_head;
325 int i = 0;
326 while (nd != NULL) {
327 void** buf = BufferNode::make_buffer_from_node(nd);
328 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
329 SATBMarkQueue::print(buffer, buf, 0, _sz);
330 nd = nd->next();
331 i += 1;
332 }
333
334 for (JavaThread* t = Threads::first(); t; t = t->next()) {
335 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
336 t->satb_mark_queue().print(buffer);
337 }
338
339 shared_satb_queue()->print("Shared");
340
341 gclog_or_tty->cr();
342 }
343 #endif // PRODUCT
344
345 void SATBMarkQueueSet::abandon_partial_marking() {
346 BufferNode* buffers_to_delete = NULL;
347 {
348 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
349 while (_completed_buffers_head != NULL) {
350 BufferNode* nd = _completed_buffers_head;
351 _completed_buffers_head = nd->next();
352 nd->set_next(buffers_to_delete);
353 buffers_to_delete = nd;
354 }
355 _completed_buffers_tail = NULL;
356 _n_completed_buffers = 0;
357 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
358 }
359 while (buffers_to_delete != NULL) {
360 BufferNode* nd = buffers_to_delete;
361 buffers_to_delete = nd->next();
362 deallocate_buffer(BufferNode::make_buffer_from_node(nd));
363 }
364 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
365 // So we can safely manipulate these queues.
366 for (JavaThread* t = Threads::first(); t; t = t->next()) {
367 t->satb_mark_queue().reset();
368 }
369 shared_satb_queue()->reset();
370 }