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 "jvm.h" 27 #include "gc/shared/collectedHeap.hpp" 28 #include "memory/allocation.inline.hpp" 29 #include "oops/oop.inline.hpp" 30 #include "runtime/mutexLocker.hpp" 31 #include "runtime/safepoint.hpp" 32 #include "runtime/thread.hpp" 33 #include "runtime/threadSMR.hpp" 34 #include "runtime/vmThread.hpp" 35 #include "utilities/macros.hpp" 36 #include "gc/shenandoah/shenandoahHeap.inline.hpp" 37 #include "gc/shenandoah/shenandoahSATBMarkQueue.hpp" 38 #include "gc/shenandoah/shenandoahThreadLocalData.hpp" 39 40 ShenandoahSATBMarkQueue::ShenandoahSATBMarkQueue(ShenandoahSATBMarkQueueSet* qset, bool permanent) : 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 is done in G1SBarrierSet::on_thread_attach(). 46 PtrQueue(qset, permanent, false /* active */) 47 { } 48 49 void ShenandoahSATBMarkQueue::flush() { 50 // Filter now to possibly save work later. If filtering empties the 51 // buffer then flush_impl can deallocate the buffer. 52 filter(); 53 flush_impl(); 54 } 55 56 // Return true if a SATB buffer entry refers to an object that 57 // requires marking. 58 // 59 // The entry must point into the Shenandoah heap. In particular, it must not 60 // be a NULL pointer. NULL pointers are pre-filtered and never 61 // inserted into a SATB buffer. 62 // 63 // An entry that is below the NTAMS pointer for the containing heap 64 // region requires marking. Such an entry must point to a valid object. 65 // 66 // An entry that is at least the NTAMS pointer for the containing heap 67 // region might be any of the following, none of which should be marked. 68 // 69 // * A reference to an object allocated since marking started. 70 // According to SATB, such objects are implicitly kept live and do 71 // not need to be dealt with via SATB buffer processing. 72 // 73 // * A reference to a young generation object. Young objects are 74 // handled separately and are not marked by concurrent marking. 75 // 76 // * A stale reference to a young generation object. If a young 77 // generation object reference is recorded and not filtered out 78 // before being moved by a young collection, the reference becomes 79 // stale. 80 // 81 // * A stale reference to an eagerly reclaimed humongous object. If a 82 // humongous object is recorded and then reclaimed, the reference 83 // becomes stale. 84 // 85 // The stale reference cases are implicitly handled by the NTAMS 86 // comparison. Because of the possibility of stale references, buffer 87 // processing must be somewhat circumspect and not assume entries 88 // in an unfiltered buffer refer to valid objects. 89 90 inline bool retain_entry(const void* entry, ShenandoahHeap* heap) { 91 return heap->requires_marking(entry); 92 } 93 94 // This method removes entries from a SATB buffer that will not be 95 // useful to the concurrent marking threads. Entries are retained if 96 // they require marking and are not already marked. Retained entries 97 // are compacted toward the top of the buffer. 98 99 void ShenandoahSATBMarkQueue::filter() { 100 ShenandoahHeap* heap = ShenandoahHeap::heap(); 101 void** buf = _buf; 102 103 if (buf == NULL) { 104 // nothing to do 105 return; 106 } 107 108 // Two-fingered compaction toward the end. 109 void** src = &buf[index()]; 110 void** dst = &buf[capacity()]; 111 assert(src <= dst, "invariant"); 112 for ( ; src < dst; ++src) { 113 // Search low to high for an entry to keep. 114 void* entry = *src; 115 if (retain_entry(entry, heap)) { 116 // Found keeper. Search high to low for an entry to discard. 117 while (src < --dst) { 118 if (!retain_entry(*dst, heap)) { 119 *dst = entry; // Replace discard with keeper. 120 break; 121 } 122 } 123 // If discard search failed (src == dst), the outer loop will also end. 124 } 125 } 126 // dst points to the lowest retained entry, or the end of the buffer 127 // if all the entries were filtered out. 128 set_index(dst - buf); 129 } 130 131 // This method will first apply the above filtering to the buffer. If 132 // post-filtering a large enough chunk of the buffer has been cleared 133 // we can re-use the buffer (instead of enqueueing it) and we can just 134 // allow the mutator to carry on executing using the same buffer 135 // instead of replacing it. 136 137 bool ShenandoahSATBMarkQueue::should_enqueue_buffer() { 138 assert(_lock == NULL || _lock->owned_by_self(), 139 "we should have taken the lock before calling this"); 140 141 // If G1SATBBufferEnqueueingThresholdPercent == 0 we could skip filtering. 142 143 // This method should only be called if there is a non-NULL buffer 144 // that is full. 145 assert(index() == 0, "pre-condition"); 146 assert(_buf != NULL, "pre-condition"); 147 148 filter(); 149 150 size_t cap = capacity(); 151 size_t percent_used = ((cap - index()) * 100) / cap; 152 bool should_enqueue = percent_used > G1SATBBufferEnqueueingThresholdPercent; 153 154 Thread* t = Thread::current(); 155 if (ShenandoahThreadLocalData::is_force_satb_flush(t)) { 156 if (!should_enqueue && cap != index()) { 157 // Non-empty buffer is compacted, and we decided not to enqueue it. 158 // We still want to know about leftover work in that buffer eventually. 159 // This avoid dealing with these leftovers during the final-mark, after 160 // the buffers are drained completely. See JDK-8205353 for more discussion. 161 should_enqueue = true; 162 } 163 ShenandoahThreadLocalData::set_force_satb_flush(t, false); 164 } 165 return should_enqueue; 166 } 167 168 void ShenandoahSATBMarkQueue::apply_closure_and_empty(ShenandoahSATBBufferClosure* cl) { 169 assert(SafepointSynchronize::is_at_safepoint(), 170 "SATB queues must only be processed at safepoints"); 171 if (_buf != NULL) { 172 cl->do_buffer(&_buf[index()], size()); 173 reset(); 174 } 175 } 176 177 #ifndef PRODUCT 178 // Helpful for debugging 179 180 static void print_satb_buffer(const char* name, 181 void** buf, 182 size_t index, 183 size_t capacity) { 184 tty->print_cr(" SATB BUFFER [%s] buf: " PTR_FORMAT " index: " SIZE_FORMAT 185 " capacity: " SIZE_FORMAT, 186 name, p2i(buf), index, capacity); 187 } 188 189 void ShenandoahSATBMarkQueue::print(const char* name) { 190 print_satb_buffer(name, _buf, index(), capacity()); 191 } 192 193 #endif // PRODUCT 194 195 ShenandoahSATBMarkQueueSet::ShenandoahSATBMarkQueueSet() : 196 PtrQueueSet(), 197 _shared_satb_queue(this, true /* permanent */) { } 198 199 void ShenandoahSATBMarkQueueSet::initialize(Monitor* cbl_mon, Mutex* fl_lock, 200 int process_completed_threshold, 201 Mutex* lock) { 202 PtrQueueSet::initialize(cbl_mon, fl_lock, process_completed_threshold, -1); 203 _shared_satb_queue.set_lock(lock); 204 } 205 206 #ifdef ASSERT 207 void ShenandoahSATBMarkQueueSet::dump_active_states(bool expected_active) { 208 log_error(gc, verify)("Expected SATB active state: %s", expected_active ? "ACTIVE" : "INACTIVE"); 209 log_error(gc, verify)("Actual SATB active states:"); 210 log_error(gc, verify)(" Queue set: %s", is_active() ? "ACTIVE" : "INACTIVE"); 211 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 212 log_error(gc, verify)(" Thread \"%s\" queue: %s", t->name(), satb_queue_for_thread(t).is_active() ? "ACTIVE" : "INACTIVE"); 213 } 214 log_error(gc, verify)(" Shared queue: %s", shared_satb_queue()->is_active() ? "ACTIVE" : "INACTIVE"); 215 } 216 217 void ShenandoahSATBMarkQueueSet::verify_active_states(bool expected_active) { 218 // Verify queue set state 219 if (is_active() != expected_active) { 220 dump_active_states(expected_active); 221 guarantee(false, "SATB queue set has an unexpected active state"); 222 } 223 224 // Verify thread queue states 225 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 226 if (satb_queue_for_thread(t).is_active() != expected_active) { 227 dump_active_states(expected_active); 228 guarantee(false, "Thread SATB queue has an unexpected active state"); 229 } 230 } 231 232 // Verify shared queue state 233 if (shared_satb_queue()->is_active() != expected_active) { 234 dump_active_states(expected_active); 235 guarantee(false, "Shared SATB queue has an unexpected active state"); 236 } 237 } 238 #endif // ASSERT 239 240 void ShenandoahSATBMarkQueueSet::set_active_all_threads(bool active, bool expected_active) { 241 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint."); 242 #ifdef ASSERT 243 verify_active_states(expected_active); 244 #endif // ASSERT 245 _all_active = active; 246 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 247 satb_queue_for_thread(t).set_active(active); 248 } 249 shared_satb_queue()->set_active(active); 250 } 251 252 void ShenandoahSATBMarkQueueSet::filter_thread_buffers() { 253 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 254 satb_queue_for_thread(t).filter(); 255 } 256 shared_satb_queue()->filter(); 257 } 258 259 bool ShenandoahSATBMarkQueueSet::apply_closure_to_completed_buffer(ShenandoahSATBBufferClosure* cl) { 260 BufferNode* nd = NULL; 261 { 262 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag); 263 if (_completed_buffers_head != NULL) { 264 nd = _completed_buffers_head; 265 _completed_buffers_head = nd->next(); 266 if (_completed_buffers_head == NULL) _completed_buffers_tail = NULL; 267 _n_completed_buffers--; 268 if (_n_completed_buffers == 0) _process_completed = false; 269 } 270 } 271 if (nd != NULL) { 272 void **buf = BufferNode::make_buffer_from_node(nd); 273 size_t index = nd->index(); 274 size_t size = buffer_size(); 275 assert(index <= size, "invariant"); 276 cl->do_buffer(buf + index, size - index); 277 deallocate_buffer(nd); 278 return true; 279 } else { 280 return false; 281 } 282 } 283 284 #ifndef PRODUCT 285 // Helpful for debugging 286 287 #define SATB_PRINTER_BUFFER_SIZE 256 288 289 void ShenandoahSATBMarkQueueSet::print_all(const char* msg) { 290 char buffer[SATB_PRINTER_BUFFER_SIZE]; 291 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint."); 292 293 tty->cr(); 294 tty->print_cr("SATB BUFFERS [%s]", msg); 295 296 BufferNode* nd = _completed_buffers_head; 297 int i = 0; 298 while (nd != NULL) { 299 void** buf = BufferNode::make_buffer_from_node(nd); 300 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Enqueued: %d", i); 301 print_satb_buffer(buffer, buf, nd->index(), buffer_size()); 302 nd = nd->next(); 303 i += 1; 304 } 305 306 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 307 jio_snprintf(buffer, SATB_PRINTER_BUFFER_SIZE, "Thread: %s", t->name()); 308 satb_queue_for_thread(t).print(buffer); 309 } 310 311 shared_satb_queue()->print("Shared"); 312 313 tty->cr(); 314 } 315 #endif // PRODUCT 316 317 void ShenandoahSATBMarkQueueSet::abandon_partial_marking() { 318 BufferNode* buffers_to_delete = NULL; 319 { 320 MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag); 321 while (_completed_buffers_head != NULL) { 322 BufferNode* nd = _completed_buffers_head; 323 _completed_buffers_head = nd->next(); 324 nd->set_next(buffers_to_delete); 325 buffers_to_delete = nd; 326 } 327 _completed_buffers_tail = NULL; 328 _n_completed_buffers = 0; 329 DEBUG_ONLY(assert_completed_buffer_list_len_correct_locked()); 330 } 331 while (buffers_to_delete != NULL) { 332 BufferNode* nd = buffers_to_delete; 333 buffers_to_delete = nd->next(); 334 deallocate_buffer(nd); 335 } 336 assert(SafepointSynchronize::is_at_safepoint(), "Must be at safepoint."); 337 // So we can safely manipulate these queues. 338 for (JavaThreadIteratorWithHandle jtiwh; JavaThread *t = jtiwh.next(); ) { 339 satb_queue_for_thread(t).reset(); 340 } 341 shared_satb_queue()->reset(); 342 } 343 344 ShenandoahSATBMarkQueue& ShenandoahSATBMarkQueueSet::satb_queue_for_thread(Thread* t) { 345 return ShenandoahThreadLocalData::satb_mark_queue(t); 346 } 347