1 /*
2 * Copyright (c) 2001, 2017, 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 "jvm.h"
27 #include "gc/g1/g1CollectedHeap.inline.hpp"
28 #include "gc/g1/satbMarkQueue.hpp"
29 #include "gc/shared/collectedHeap.hpp"
30 #include "memory/allocation.inline.hpp"
31 #include "oops/oop.inline.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/safepoint.hpp"
34 #include "runtime/thread.hpp"
35 #include "runtime/threadSMR.hpp"
36 #include "runtime/vmThread.hpp"
37
38 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset, bool permanent) :
39 // SATB queues are only active during marking cycles. We create
40 // them with their active field set to false. If a thread is
41 // created during a cycle and its SATB queue needs to be activated
42 // before the thread starts running, we'll need to set its active
43 // field to true. This is done in JavaThread::initialize_queues().
44 PtrQueue(qset, permanent, false /* active */)
45 { }
46
47 void SATBMarkQueue::flush() {
48 // Filter now to possibly save work later. If filtering empties the
49 // buffer then flush_impl can deallocate the buffer.
50 filter();
51 flush_impl();
52 }
53
54 // Return true if a SATB buffer entry refers to an object that
55 // requires marking.
56 //
57 // The entry must point into the G1 heap. In particular, it must not
58 // be a NULL pointer. NULL pointers are pre-filtered and never
59 // inserted into a SATB buffer.
60 //
61 // An entry that is below the NTAMS pointer for the containing heap
62 // region requires marking. Such an entry must point to a valid object.
63 //
64 // An entry that is at least the NTAMS pointer for the containing heap
65 // region might be any of the following, none of which should be marked.
66 //
67 // * A reference to an object allocated since marking started.
68 // According to SATB, such objects are implicitly kept live and do
69 // not need to be dealt with via SATB buffer processing.
70 //
71 // * A reference to a young generation object. Young objects are
72 // handled separately and are not marked by concurrent marking.
73 //
74 // * A stale reference to a young generation object. If a young
75 // generation object reference is recorded and not filtered out
76 // before being moved by a young collection, the reference becomes
77 // stale.
78 //
79 // * A stale reference to an eagerly reclaimed humongous object. If a
80 // humongous object is recorded and then reclaimed, the reference
81 // becomes stale.
82 //
83 // The stale reference cases are implicitly handled by the NTAMS
84 // comparison. Because of the possibility of stale references, buffer
85 // processing must be somewhat circumspect and not assume entries
86 // in an unfiltered buffer refer to valid objects.
87
88 inline bool requires_marking(const void* entry, G1CollectedHeap* heap) {
89 // Includes rejection of NULL pointers.
90 assert(heap->is_in_reserved(entry),
91 "Non-heap pointer in SATB buffer: " PTR_FORMAT, p2i(entry));
92
93 HeapRegion* region = heap->heap_region_containing(entry);
94 assert(region != NULL, "No region for " PTR_FORMAT, p2i(entry));
95 if (entry >= region->next_top_at_mark_start()) {
96 return false;
97 }
98
99 assert(oopDesc::is_oop(oop(entry), true /* ignore mark word */),
100 "Invalid oop in SATB buffer: " PTR_FORMAT, p2i(entry));
101
102 return true;
103 }
104
105 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) {
106 return requires_marking(entry, heap) && !heap->isMarkedNext((oop)entry);
107 }
108
109 // This method removes entries from a SATB buffer that will not be
110 // useful to the concurrent marking threads. Entries are retained if
111 // they require marking and are not already marked. Retained entries
112 // are compacted toward the top of the buffer.
113
114 void SATBMarkQueue::filter() {
115 G1CollectedHeap* g1h = G1CollectedHeap::heap();
116 void** buf = _buf;
117
118 if (buf == NULL) {
119 // nothing to do
120 return;
121 }
122
123 // Two-fingered compaction toward the end.
124 void** src = &buf[index()];
125 void** dst = &buf[capacity()];
126 assert(src <= dst, "invariant");
127 for ( ; src < dst; ++src) {
128 // Search low to high for an entry to keep.
129 void* entry = *src;
130 if (retain_entry(entry, g1h)) {
131 // Found keeper. Search high to low for an entry to discard.
132 while (src < --dst) {
133 if (!retain_entry(*dst, g1h)) {
134 *dst = entry; // Replace discard with keeper.
135 break;
136 }
137 }
138 // If discard search failed (src == dst), the outer loop will also end.
139 }
140 }
141 // dst points to the lowest retained entry, or the end of the buffer
142 // if all the entries were filtered out.
143 set_index(dst - buf);
144 }
145
146 // This method will first apply the above filtering to the buffer. If
147 // post-filtering a large enough chunk of the buffer has been cleared
148 // we can re-use the buffer (instead of enqueueing it) and we can just
149 // allow the mutator to carry on executing using the same buffer
150 // instead of replacing it.
151
152 bool SATBMarkQueue::should_enqueue_buffer() {
153 assert(_lock == NULL || _lock->owned_by_self(),
154 "we should have taken the lock before calling this");
155
156 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering.
157
158 // This method should only be called if there is a non-NULL buffer
159 // that is full.
160 assert(index() == 0, "pre-condition");
161 assert(_buf != NULL, "pre-condition");
162
163 filter();
164
165 size_t cap = capacity();
166 size_t percent_used = ((cap - index()) * 100) / cap;
167 bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent;
168 return should_enqueue;
169 }
170
171 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
172 assert(SafepointSynchronize::is_at_safepoint(),
173 "SATB queues must only be processed at safepoints");
174 if (_buf != NULL) {
175 cl->do_buffer(&_buf[index()], size());
176 reset();
177 }
178 }
179
180 #ifndef PRODUCT
181 // Helpful for debugging
182
183 static void print_satb_buffer(const char* name,
184 void** buf,
185 size_t index,
186 size_t capacity) {
187 tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
188 " capacity: " SIZE_FORMAT,
189 name, p2i(buf), index, capacity);
190 }
191
192 void SATBMarkQueue::print(const char* name) {
193 print_satb_buffer(name, _buf, index(), capacity());
194 }
195
196 #endif // PRODUCT
197
198 SATBMarkQueueSet::SATBMarkQueueSet() :
199 PtrQueueSet(),
200 _shared_satb_queue(this, true /* permanent */) { }
201
202 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
203 int process_completed_threshold,
204 Mutex* lock) {
205 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
206 _shared_satb_queue.set_lock(lock);
207 }
208
209 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
210 t->satb_mark_queue().handle_zero_index();
211 }
212
213 #ifdef ASSERT
214 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
215 log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
216 log_error(gc, verify)("Actual SATB active states:");
217 log_error(gc, verify)(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
218 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
219 log_error(gc, verify)(" Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
220 }
221 log_error(gc, verify)(" Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
222 }
223
224 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
225 // Verify queue set state
226 if (is_active() != expected_active) {
227 dump_active_states(expected_active);
228 guarantee(false, "SATB queue set has an unexpected active state");
229 }
230
231 // Verify thread queue states
232 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
233 if (t->satb_mark_queue().is_active() != expected_active) {
234 dump_active_states(expected_active);
235 guarantee(false, "Thread SATB queue has an unexpected active state");
236 }
237 }
238
239 // Verify shared queue state
240 if (shared_satb_queue()->is_active() != expected_active) {
241 dump_active_states(expected_active);
242 guarantee(false, "Shared SATB queue has an unexpected active state");
243 }
244 }
245 #endif // ASSERT
246
247 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
248 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
249 #ifdef ASSERT
250 verify_active_states(expected_active);
251 #endif // ASSERT
252 _all_active = active;
253 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
254 t->satb_mark_queue().set_active(active);
255 }
256 shared_satb_queue()->set_active(active);
257 }
258
259 void SATBMarkQueueSet::filter_thread_buffers() {
260 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
261 t->satb_mark_queue().filter();
262 }
263 shared_satb_queue()->filter();
264 }
265
266 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
267 BufferNode* nd = NULL;
268 {
269 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
270 if (_completed_buffers_head != NULL) {
271 nd = _completed_buffers_head;
272 _completed_buffers_head = nd->next();
273 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
274 _n_completed_buffers--;
275 if (_n_completed_buffers == 0) _process_completed = false;
276 }
277 }
278 if (nd != NULL) {
279 void **buf = BufferNode::make_buffer_from_node(nd);
280 size_t index = nd->index();
281 size_t size = buffer_size();
282 assert(index <= size, "invariant");
283 cl->do_buffer(buf + index, size - index);
284 deallocate_buffer(nd);
285 return true;
286 } else {
287 return false;
288 }
289 }
290
291 #ifndef PRODUCT
292 // Helpful for debugging
293
294 #define SATB_PRINTER_BUFFER_SIZE 256
295
296 void SATBMarkQueueSet::print_all(const char* msg) {
297 char buffer[SATB_PRINTER_BUFFER_SIZE];
298 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
299
300 tty->cr();
301 tty->print_cr("SATB BUFFERS [%s]", msg);
302
303 BufferNode* nd = _completed_buffers_head;
304 int i = 0;
305 while (nd != NULL) {
306 void** buf = BufferNode::make_buffer_from_node(nd);
307 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
308 print_satb_buffer(buffer, buf, nd->index(), buffer_size());
309 nd = nd->next();
310 i += 1;
311 }
312
313 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
314 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
315 t->satb_mark_queue().print(buffer);
316 }
317
318 shared_satb_queue()->print("Shared");
319
320 tty->cr();
321 }
322 #endif // PRODUCT
323
324 void SATBMarkQueueSet::abandon_partial_marking() {
325 BufferNode* buffers_to_delete = NULL;
326 {
327 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
328 while (_completed_buffers_head != NULL) {
329 BufferNode* nd = _completed_buffers_head;
330 _completed_buffers_head = nd->next();
331 nd->set_next(buffers_to_delete);
332 buffers_to_delete = nd;
333 }
334 _completed_buffers_tail = NULL;
335 _n_completed_buffers = 0;
336 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
337 }
338 while (buffers_to_delete != NULL) {
339 BufferNode* nd = buffers_to_delete;
340 buffers_to_delete = nd->next();
341 deallocate_buffer(nd);
342 }
343 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
344 // So we can safely manipulate these queues.
345 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) {
346 t->satb_mark_queue().reset();
347 }
348 shared_satb_queue()->reset();
349 }