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/satbQueue.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 ObjPtrQueue::ObjPtrQueue(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 ObjPtrQueue::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_raw(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 ObjPtrQueue::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 ObjPtrQueue::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 sz = _sz;
176 size_t all_entries = sz / sizeof(void*);
177 size_t retained_entries = (sz - _index) / sizeof(void*);
178 size_t perc = retained_entries * 100 / all_entries;
179 bool should_enqueue = perc > (size_t) G1SATBBufferEnqueueingThresholdPercent;
180 return should_enqueue;
181 }
182
183 void ObjPtrQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
184 assert(SafepointSynchronize::is_at_safepoint(),
185 "SATB queues must only be processed at safepoints");
186 if (_buf != NULL) {
187 assert(_index % sizeof(void*) == 0, "invariant");
188 assert(_sz % sizeof(void*) == 0, "invariant");
189 assert(_index <= _sz, "invariant");
190 cl->do_buffer(_buf + byte_index_to_index(_index),
191 byte_index_to_index(_sz - _index));
192 _index = _sz;
193 }
194 }
195
196 #ifndef PRODUCT
197 // Helpful for debugging
198
199 void ObjPtrQueue::print(const char* name) {
200 print(name, _buf, _index, _sz);
201 }
202
203 void ObjPtrQueue::print(const char* name,
204 void** buf, size_t index, size_t sz) {
205 gclog_or_tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " "
206 "index: " SIZE_FORMAT " sz: " SIZE_FORMAT,
207 name, p2i(buf), index, sz);
208 }
209 #endif // PRODUCT
210
211 #ifdef _MSC_VER // the use of 'this' below gets a warning, make it go away
212 #pragma warning( disable:4355 ) // 'this' : used in base member initializer list
213 #endif // _MSC_VER
214
215 SATBMarkQueueSet::SATBMarkQueueSet() :
216 PtrQueueSet(),
217 _shared_satb_queue(this, true /*perm*/) { }
218
219 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock,
220 int process_completed_threshold,
221 Mutex* lock) {
222 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1);
223 _shared_satb_queue.set_lock(lock);
224 }
225
226 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) {
227 t->satb_mark_queue().handle_zero_index();
228 }
229
230 #ifdef ASSERT
231 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
232 gclog_or_tty->print_cr("Expected SATB active state: %s",
233 expected_active ? "ACTIVE" : "INACTIVE");
234 gclog_or_tty->print_cr("Actual SATB active states:");
235 gclog_or_tty->print_cr(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
236 for (JavaThread* t = Threads::first(); t; t = t->next()) {
237 gclog_or_tty->print_cr(" Thread \"%s\" queue: %s", t->name(),
238 t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE");
239 }
240 gclog_or_tty->print_cr(" Shared queue: %s",
241 shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE");
242 }
243
244 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
245 // Verify queue set state
246 if (is_active() != expected_active) {
247 dump_active_states(expected_active);
248 guarantee(false, "SATB queue set has an unexpected active state");
249 }
250
251 // Verify thread queue states
252 for (JavaThread* t = Threads::first(); t; t = t->next()) {
253 if (t->satb_mark_queue().is_active() != expected_active) {
254 dump_active_states(expected_active);
255 guarantee(false, "Thread SATB queue has an unexpected active state");
256 }
257 }
258
259 // Verify shared queue state
260 if (shared_satb_queue()->is_active() != expected_active) {
261 dump_active_states(expected_active);
262 guarantee(false, "Shared SATB queue has an unexpected active state");
263 }
264 }
265 #endif // ASSERT
266
267 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
268 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
269 #ifdef ASSERT
270 verify_active_states(expected_active);
271 #endif // ASSERT
272 _all_active = active;
273 for (JavaThread* t = Threads::first(); t; t = t->next()) {
274 t->satb_mark_queue().set_active(active);
275 }
276 shared_satb_queue()->set_active(active);
277 }
278
279 void SATBMarkQueueSet::filter_thread_buffers() {
280 for(JavaThread* t = Threads::first(); t; t = t->next()) {
281 t->satb_mark_queue().filter();
282 }
283 shared_satb_queue()->filter();
284 }
285
286 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
287 BufferNode* nd = NULL;
288 {
289 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
290 if (_completed_buffers_head != NULL) {
291 nd = _completed_buffers_head;
292 _completed_buffers_head = nd->next();
293 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL;
294 _n_completed_buffers--;
295 if (_n_completed_buffers == 0) _process_completed = false;
296 }
297 }
298 if (nd != NULL) {
299 void **buf = BufferNode::make_buffer_from_node(nd);
300 // Skip over NULL entries at beginning (e.g. push end) of buffer.
301 // Filtering can result in non-full completed buffers; see
302 // should_enqueue_buffer.
303 assert(_sz % sizeof(void*) == 0, "invariant");
304 size_t limit = ObjPtrQueue::byte_index_to_index(_sz);
305 for (size_t i = 0; i < limit; ++i) {
306 if (buf[i] != NULL) {
307 // Found the end of the block of NULLs; process the remainder.
308 cl->do_buffer(buf + i, limit - i);
309 break;
310 }
311 }
312 deallocate_buffer(buf);
313 return true;
314 } else {
315 return false;
316 }
317 }
318
319 #ifndef PRODUCT
320 // Helpful for debugging
321
322 #define SATB_PRINTER_BUFFER_SIZE 256
323
324 void SATBMarkQueueSet::print_all(const char* msg) {
325 char buffer[SATB_PRINTER_BUFFER_SIZE];
326 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
327
328 gclog_or_tty->cr();
329 gclog_or_tty->print_cr("SATB BUFFERS [%s]", msg);
330
331 BufferNode* nd = _completed_buffers_head;
332 int i = 0;
333 while (nd != NULL) {
334 void** buf = BufferNode::make_buffer_from_node(nd);
335 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
336 ObjPtrQueue::print(buffer, buf, 0, _sz);
337 nd = nd->next();
338 i += 1;
339 }
340
341 for (JavaThread* t = Threads::first(); t; t = t->next()) {
342 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
343 t->satb_mark_queue().print(buffer);
344 }
345
346 shared_satb_queue()->print("Shared");
347
348 gclog_or_tty->cr();
349 }
350 #endif // PRODUCT
351
352 void SATBMarkQueueSet::abandon_partial_marking() {
353 BufferNode* buffers_to_delete = NULL;
354 {
355 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);
356 while (_completed_buffers_head != NULL) {
357 BufferNode* nd = _completed_buffers_head;
358 _completed_buffers_head = nd->next();
359 nd->set_next(buffers_to_delete);
360 buffers_to_delete = nd;
361 }
362 _completed_buffers_tail = NULL;
363 _n_completed_buffers = 0;
364 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked());
365 }
366 while (buffers_to_delete != NULL) {
367 BufferNode* nd = buffers_to_delete;
368 buffers_to_delete = nd->next();
369 deallocate_buffer(BufferNode::make_buffer_from_node(nd));
370 }
371 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
372 // So we can safely manipulate these queues.
373 for (JavaThread* t = Threads::first(); t; t = t->next()) {
374 t->satb_mark_queue().reset();
375 }
376 shared_satb_queue()->reset();
377 }