1 /* 2 * Copyright (c) 2001, 2016, 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 inline bool retain_entry(const void* entry, G1CollectedHeap* heap) { 104 return requires_marking(entry, heap) && !heap->isMarkedNext((oop)entry); 105 } 106 107 // This method removes entries from a SATB buffer that will not be 108 // useful to the concurrent marking threads. Entries are retained if 109 // they require marking and are not already marked. Retained entries 110 // are compacted toward the top of the buffer. 111 112 void SATBMarkQueue::filter() { 113 G1CollectedHeap* g1h = G1CollectedHeap::heap(); 114 void** buf = _buf; 115 116 if (buf == NULL) { 117 // nothing to do 118 return; 119 } 120 121 assert(_index <= _sz, "invariant"); 122 123 // Two-fingered compaction toward the end. 124 void** src = &buf[byte_index_to_index(_index)]; 125 void** dst = &buf[byte_index_to_index(_sz)]; 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 _index = pointer_delta(dst, buf, 1); 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 percent_used = ((_sz - _index) * 100) / _sz; 165 bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent; 166 return should_enqueue; 167 } 168 169 void SATBMarkQueue::apply_closure_and_empty(SATBBufferClosure* cl) { 170 assert(SafepointSynchronize::is_at_safepoint(), 171 "SATB queues must only be processed at safepoints"); 172 if (_buf != NULL) { 173 assert(_index % sizeof(void*) == 0, "invariant"); 174 assert(_sz % sizeof(void*) == 0, "invariant"); 175 assert(_index <= _sz, "invariant"); 176 cl->do_buffer(_buf + byte_index_to_index(_index), 177 byte_index_to_index(_sz - _index)); 178 _index = _sz; 179 } 180 } 181 182 #ifndef PRODUCT 183 // Helpful for debugging 184 185 void SATBMarkQueue::print(const char* name) { 186 print(name, _buf, _index, _sz); 187 } 188 189 void SATBMarkQueue::print(const char* name, 190 void** buf, size_t index, size_t sz) { 191 tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT " sz: " SIZE_FORMAT, 192 name, p2i(buf), index, sz); 193 } 194 #endif // PRODUCT 195 196 SATBMarkQueueSet::SATBMarkQueueSet() : 197 PtrQueueSet(), 198 _shared_satb_queue(this, true /* permanent */) { } 199 200 void SATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock, 201 int process_completed_threshold, 202 Mutex* lock) { 203 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1); 204 _shared_satb_queue.set_lock(lock); 205 } 206 207 void SATBMarkQueueSet::handle_zero_index_for_thread(JavaThread* t) { 208 t->satb_mark_queue().handle_zero_index(); 209 } 210 211 #ifdef ASSERT 212 void SATBMarkQueueSet::dump_active_states(bool expected_active) { 213 log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE"); 214 log_error(gc, verify)("Actual SATB active states:"); 215 log_error(gc, verify)(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE"); 216 for (JavaThread* t = Threads::first(); t; t = t->next()) { 217 log_error(gc, verify)(" Thread \"%s\" queue: %s", t->name(), t->satb_mark_queue().is_active() ? "ACTIVE" : "INACTIVE"); 218 } 219 log_error(gc, verify)(" Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE"); 220 } 221 222 void SATBMarkQueueSet::verify_active_states(bool expected_active) { 223 // Verify queue set state 224 if (is_active() != expected_active) { 225 dump_active_states(expected_active); 226 guarantee(false, "SATB queue set has an unexpected active state"); 227 } 228 229 // Verify thread queue states 230 for (JavaThread* t = Threads::first(); t; t = t->next()) { 231 if (t->satb_mark_queue().is_active() != expected_active) { 232 dump_active_states(expected_active); 233 guarantee(false, "Thread SATB queue has an unexpected active state"); 234 } 235 } 236 237 // Verify shared queue state 238 if (shared_satb_queue()->is_active() != expected_active) { 239 dump_active_states(expected_active); 240 guarantee(false, "Shared SATB queue has an unexpected active state"); 241 } 242 } 243 #endif // ASSERT 244 245 void SATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) { 246 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint."); 247 #ifdef ASSERT 248 verify_active_states(expected_active); 249 #endif // ASSERT 250 _all_active = active; 251 for (JavaThread* t = Threads::first(); t; t = t->next()) { 252 t->satb_mark_queue().set_active(active); 253 } 254 shared_satb_queue()->set_active(active); 255 } 256 257 void SATBMarkQueueSet::filter_thread_buffers() { 258 for(JavaThread* t = Threads::first(); t; t = t->next()) { 259 t->satb_mark_queue().filter(); 260 } 261 shared_satb_queue()->filter(); 262 } 263 264 bool SATBMarkQueueSet::apply_closure_to_completed_buffer(SATBBufferClosure* cl) { 265 BufferNode* nd = NULL; 266 { 267 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag); 268 if (_completed_buffers_head != NULL) { 269 nd = _completed_buffers_head; 270 _completed_buffers_head = nd->next(); 271 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL; 272 _n_completed_buffers--; 273 if (_n_completed_buffers == 0) _process_completed = false; 274 } 275 } 276 if (nd != NULL) { 277 void **buf = BufferNode::make_buffer_from_node(nd); 278 size_t index = SATBMarkQueue::byte_index_to_index(nd->index()); 279 size_t size = SATBMarkQueue::byte_index_to_index(_sz); 280 assert(index <= size, "invariant"); 281 cl->do_buffer(buf + index, size - index); 282 deallocate_buffer(nd); 283 return true; 284 } else { 285 return false; 286 } 287 } 288 289 #ifndef PRODUCT 290 // Helpful for debugging 291 292 #define SATB_PRINTER_BUFFER_SIZE 256 293 294 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 = _completed_buffers_head; 302 int i = 0; 303 while (nd != NULL) { 304 void** buf = BufferNode::make_buffer_from_node(nd); 305 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i); 306 SATBMarkQueue::print(buffer, buf, 0, _sz); 307 nd = nd->next(); 308 i += 1; 309 } 310 311 for (JavaThread* t = Threads::first(); t; t = t->next()) { 312 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name()); 313 t->satb_mark_queue().print(buffer); 314 } 315 316 shared_satb_queue()->print("Shared"); 317 318 tty->cr(); 319 } 320 #endif // PRODUCT 321 322 void SATBMarkQueueSet::abandon_partial_marking() { 323 BufferNode* buffers_to_delete = NULL; 324 { 325 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag); 326 while (_completed_buffers_head != NULL) { 327 BufferNode* nd = _completed_buffers_head; 328 _completed_buffers_head = nd->next(); 329 nd->set_next(buffers_to_delete); 330 buffers_to_delete = nd; 331 } 332 _completed_buffers_tail = NULL; 333 _n_completed_buffers = 0; 334 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked()); 335 } 336 while (buffers_to_delete != NULL) { 337 BufferNode* nd = buffers_to_delete; 338 buffers_to_delete = nd->next(); 339 deallocate_buffer(nd); 340 } 341 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint."); 342 // So we can safely manipulate these queues. 343 for (JavaThread* t = Threads::first(); t; t = t->next()) { 344 t->satb_mark_queue().reset(); 345 } 346 shared_satb_queue()->reset(); 347 }