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