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 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 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 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 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 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 } 103 104 void SATBMarkQueue::print(const char* name) { 105 print_satb_buffer(name, _buf, index(), capacity()); 106 } 107 108 #endif // PRODUCT 109 110 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 {} 117 118 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. 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. 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 } 154 155 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 } 165 166 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 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 } 192 193 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 217 218 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 } 241 242 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. 266 267 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 } 275 276 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 256 293 294 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 329 330 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 } 340 341 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 }