1 /*
2 * Copyright (c) 2001, 2019, 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/shared/satbMarkQueue.hpp"
27 #include "gc/shared/collectedHeap.hpp"
28 #include "logging/log.hpp"
29 #include "memory/allocation.inline.hpp"
30 #include "oops/oop.inline.hpp"
31 #include "runtime/atomic.hpp"
32 #include "runtime/mutexLocker.hpp"
33 #include "runtime/os.hpp"
34 #include "runtime/safepoint.hpp"
35 #include "runtime/thread.hpp"
36 #include "runtime/threadSMR.hpp"
37 #include "runtime/vmThread.hpp"
38 #include "utilities/globalCounter.inline.hpp"
39
SATBMarkQueue(SATBMarkQueueSet * qset)40 SATBMarkQueue::SATBMarkQueue(SATBMarkQueueSet* qset) :
41 // SATB queues are only active during marking cycles. We create
42 // them with their active field set to false. If a thread is
43 // created during a cycle and its SATB queue needs to be activated
44 // before the thread starts running, we'll need to set its active
45 // field to true. This must be done in the collector-specific
46 // BarrierSet thread attachment protocol.
47 PtrQueue(qset, false /* active */)
48 { }
49
flush()50 void SATBMarkQueue::flush() {
51 // Filter now to possibly save work later. If filtering empties the
52 // buffer then flush_impl can deallocate the buffer.
53 filter();
54 flush_impl();
55 }
56
57 // This method will first apply filtering to the buffer. If filtering
58 // retains a small enough collection in the buffer, we can continue to
59 // use the buffer as-is, instead of enqueueing and replacing it.
60
handle_completed_buffer()61 void SATBMarkQueue::handle_completed_buffer() {
62 // This method should only be called if there is a non-NULL buffer
63 // that is full.
64 assert(index() == 0, "pre-condition");
65 assert(_buf != NULL, "pre-condition");
66
67 filter();
68
69 size_t threshold = satb_qset()->buffer_enqueue_threshold();
70 // Ensure we'll enqueue completely full buffers.
71 assert(threshold > 0, "enqueue threshold = 0");
72 // Ensure we won't enqueue empty buffers.
73 assert(threshold <= capacity(),
74 "enqueue threshold " SIZE_FORMAT " exceeds capacity " SIZE_FORMAT,
75 threshold, capacity());
76
77 if (index() < threshold) {
78 // Buffer is sufficiently full; enqueue and allocate a new one.
79 enqueue_completed_buffer();
80 } // Else continue to accumulate in buffer.
81 }
82
apply_closure_and_empty(SATBBufferClosure * cl)83 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) {
84 assert(SafepointSynchronize::is_at_safepoint(),
85 "SATB queues must only be processed at safepoints");
86 if (_buf != NULL) {
87 cl->do_buffer(&_buf[index()], size());
88 reset();
89 }
90 }
91
92 #ifndef PRODUCT
93 // Helpful for debugging
94
print_satb_buffer(const char * name,void ** buf,size_t index,size_t capacity)95 static void print_satb_buffer(const char* name,
96 void** buf,
97 size_t index,
98 size_t capacity) {
99 tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT
100 " capacity: " SIZE_FORMAT,
101 name, p2i(buf), index, capacity);
102 }
103
print(const char * name)104 void SATBMarkQueue::print(const char* name) {
105 print_satb_buffer(name, _buf, index(), capacity());
106 }
107
108 #endif // PRODUCT
109
SATBMarkQueueSet(BufferNode::Allocator * allocator)110 SATBMarkQueueSet::SATBMarkQueueSet(BufferNode::Allocator* allocator) :
111 PtrQueueSet(allocator),
112 _list(),
113 _count_and_process_flag(0),
114 _process_completed_buffers_threshold(SIZE_MAX),
115 _buffer_enqueue_threshold(0)
116 {}
117
~SATBMarkQueueSet()118 SATBMarkQueueSet::~SATBMarkQueueSet() {
119 abandon_completed_buffers();
120 }
121
122 // _count_and_process_flag has flag in least significant bit, count in
123 // remaining bits. _process_completed_buffers_threshold is scaled
124 // accordingly, with the lsbit set, so a _count_and_process_flag value
125 // is directly comparable with the recorded threshold value. The
126 // process flag is set whenever the count exceeds the threshold, and
127 // remains set until the count is reduced to zero.
128
129 // Increment count. If count > threshold, set flag, else maintain flag.
increment_count(volatile size_t * cfptr,size_t threshold)130 static void increment_count(volatile size_t* cfptr, size_t threshold) {
131 size_t old;
132 size_t value = Atomic::load(cfptr);
133 do {
134 old = value;
135 value += 2;
136 assert(value > old, "overflow");
137 if (value > threshold) value |= 1;
138 value = Atomic::cmpxchg(cfptr, old, value);
139 } while (value != old);
140 }
141
142 // Decrement count. If count == 0, clear flag, else maintain flag.
decrement_count(volatile size_t * cfptr)143 static void decrement_count(volatile size_t* cfptr) {
144 size_t old;
145 size_t value = Atomic::load(cfptr);
146 do {
147 assert((value >> 1) != 0, "underflow");
148 old = value;
149 value -= 2;
150 if (value <= 1) value = 0;
151 value = Atomic::cmpxchg(cfptr, old, value);
152 } while (value != old);
153 }
154
set_process_completed_buffers_threshold(size_t value)155 void SATBMarkQueueSet::set_process_completed_buffers_threshold(size_t value) {
156 // Scale requested threshold to align with count field. If scaling
157 // overflows, just use max value. Set process flag field to make
158 // comparison in increment_count exact.
159 size_t scaled_value = value << 1;
160 if ((scaled_value >> 1) != value) {
161 scaled_value = SIZE_MAX;
162 }
163 _process_completed_buffers_threshold = scaled_value | 1;
164 }
165
set_buffer_enqueue_threshold_percentage(uint value)166 void SATBMarkQueueSet::set_buffer_enqueue_threshold_percentage(uint value) {
167 // Minimum threshold of 1 ensures enqueuing of completely full buffers.
168 size_t size = buffer_size();
169 size_t enqueue_qty = (size * value) / 100;
170 _buffer_enqueue_threshold = MAX2(size - enqueue_qty, (size_t)1);
171 }
172
173 #ifdef ASSERT
dump_active_states(bool expected_active)174 void SATBMarkQueueSet::dump_active_states(bool expected_active) {
175 log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE");
176 log_error(gc, verify)("Actual SATB active states:");
177 log_error(gc, verify)(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE");
178
179 class DumpThreadStateClosure : public ThreadClosure {
180 SATBMarkQueueSet* _qset;
181 public:
182 DumpThreadStateClosure(SATBMarkQueueSet* qset) : _qset(qset) {}
183 virtual void do_thread(Thread* t) {
184 SATBMarkQueue& queue = _qset->satb_queue_for_thread(t);
185 log_error(gc, verify)(" Thread \"%s\" queue: %s",
186 t->name(),
187 queue.is_active() ? "ACTIVE" : "INACTIVE");
188 }
189 } closure(this);
190 Threads::threads_do(&closure);
191 }
192
verify_active_states(bool expected_active)193 void SATBMarkQueueSet::verify_active_states(bool expected_active) {
194 // Verify queue set state
195 if (is_active() != expected_active) {
196 dump_active_states(expected_active);
197 fatal("SATB queue set has an unexpected active state");
198 }
199
200 // Verify thread queue states
201 class VerifyThreadStatesClosure : public ThreadClosure {
202 SATBMarkQueueSet* _qset;
203 bool _expected_active;
204 public:
205 VerifyThreadStatesClosure(SATBMarkQueueSet* qset, bool expected_active) :
206 _qset(qset), _expected_active(expected_active) {}
207 virtual void do_thread(Thread* t) {
208 if (_qset->satb_queue_for_thread(t).is_active() != _expected_active) {
209 _qset->dump_active_states(_expected_active);
210 fatal("Thread SATB queue has an unexpected active state");
211 }
212 }
213 } closure(this, expected_active);
214 Threads::threads_do(&closure);
215 }
216 #endif // ASSERT
217
set_active_all_threads(bool active,bool expected_active)218 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) {
219 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
220 #ifdef ASSERT
221 verify_active_states(expected_active);
222 #endif // ASSERT
223 // Update the global state, synchronized with threads list management.
224 {
225 MutexLocker ml(NonJavaThreadsList_lock, Mutex::_no_safepoint_check_flag);
226 _all_active = active;
227 }
228
229 class SetThreadActiveClosure : public ThreadClosure {
230 SATBMarkQueueSet* _qset;
231 bool _active;
232 public:
233 SetThreadActiveClosure(SATBMarkQueueSet* qset, bool active) :
234 _qset(qset), _active(active) {}
235 virtual void do_thread(Thread* t) {
236 _qset->satb_queue_for_thread(t).set_active(_active);
237 }
238 } closure(this, active);
239 Threads::threads_do(&closure);
240 }
241
apply_closure_to_completed_buffer(SATBBufferClosure * cl)242 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) {
243 BufferNode* nd = get_completed_buffer();
244 if (nd != NULL) {
245 void **buf = BufferNode::make_buffer_from_node(nd);
246 size_t index = nd->index();
247 size_t size = buffer_size();
248 assert(index <= size, "invariant");
249 cl->do_buffer(buf + index, size - index);
250 deallocate_buffer(nd);
251 return true;
252 } else {
253 return false;
254 }
255 }
256
257 // SATB buffer life-cycle - Per-thread queues obtain buffers from the
258 // qset's buffer allocator, fill them, and push them onto the qset's
259 // list. The GC concurrently pops buffers from the qset, processes
260 // them, and returns them to the buffer allocator for re-use. Both
261 // the allocator and the qset use lock-free stacks. The ABA problem
262 // is solved by having both allocation pops and GC pops performed
263 // within GlobalCounter critical sections, while the return of buffers
264 // to the allocator performs a GlobalCounter synchronize before
265 // pushing onto the allocator's list.
266
enqueue_completed_buffer(BufferNode * node)267 void SATBMarkQueueSet::enqueue_completed_buffer(BufferNode* node) {
268 assert(node != NULL, "precondition");
269 // Increment count and update flag appropriately. Done before
270 // pushing buffer so count is always at least the actual number in
271 // the list, and decrement never underflows.
272 increment_count(&_count_and_process_flag, _process_completed_buffers_threshold);
273 _list.push(*node);
274 }
275
get_completed_buffer()276 BufferNode* SATBMarkQueueSet::get_completed_buffer() {
277 BufferNode* node;
278 {
279 GlobalCounter::CriticalSection cs(Thread::current());
280 node = _list.pop();
281 }
282 if (node != NULL) {
283 // Got a buffer so decrement count and update flag appropriately.
284 decrement_count(&_count_and_process_flag);
285 }
286 return node;
287 }
288
289 #ifndef PRODUCT
290 // Helpful for debugging
291
292 #define SATB_PRINTER_BUFFER_SIZE 256
293
print_all(const char * msg)294 void SATBMarkQueueSet::print_all(const char* msg) {
295 char buffer[SATB_PRINTER_BUFFER_SIZE];
296 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
297
298 tty->cr();
299 tty->print_cr("SATB BUFFERS [%s]", msg);
300
301 BufferNode* nd = _list.top();
302 int i = 0;
303 while (nd != NULL) {
304 void** buf = BufferNode::make_buffer_from_node(nd);
305 os::snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i);
306 print_satb_buffer(buffer, buf, nd->index(), buffer_size());
307 nd = nd->next();
308 i += 1;
309 }
310
311 class PrintThreadClosure : public ThreadClosure {
312 SATBMarkQueueSet* _qset;
313 char* _buffer;
314
315 public:
316 PrintThreadClosure(SATBMarkQueueSet* qset, char* buffer) :
317 _qset(qset), _buffer(buffer) {}
318
319 virtual void do_thread(Thread* t) {
320 os::snprintf(_buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name());
321 _qset->satb_queue_for_thread(t).print(_buffer);
322 }
323 } closure(this, buffer);
324 Threads::threads_do(&closure);
325
326 tty->cr();
327 }
328 #endif // PRODUCT
329
abandon_completed_buffers()330 void SATBMarkQueueSet::abandon_completed_buffers() {
331 Atomic::store(&_count_and_process_flag, size_t(0));
332 BufferNode* buffers_to_delete = _list.pop_all();
333 while (buffers_to_delete != NULL) {
334 BufferNode* bn = buffers_to_delete;
335 buffers_to_delete = bn->next();
336 bn->set_next(NULL);
337 deallocate_buffer(bn);
338 }
339 }
340
abandon_partial_marking()341 void SATBMarkQueueSet::abandon_partial_marking() {
342 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint.");
343 abandon_completed_buffers();
344
345 class AbandonThreadQueueClosure : public ThreadClosure {
346 SATBMarkQueueSet* _qset;
347 public:
348 AbandonThreadQueueClosure(SATBMarkQueueSet* qset) : _qset(qset) {}
349 virtual void do_thread(Thread* t) {
350 _qset->satb_queue_for_thread(t).reset();
351 }
352 } closure(this);
353 Threads::threads_do(&closure);
354 }
355