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