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 }