1 /* 2 * Copyright (c) 2018, 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/oopStorage.inline.hpp" 27 #include "gc/shared/oopStorageParState.inline.hpp" 28 #include "logging/log.hpp" 29 #include "logging/logStream.hpp" 30 #include "memory/allocation.inline.hpp" 31 #include "runtime/atomic.hpp" 32 #include "runtime/globals.hpp" 33 #include "runtime/handles.inline.hpp" 34 #include "runtime/mutex.hpp" 35 #include "runtime/mutexLocker.hpp" 36 #include "runtime/orderAccess.hpp" 37 #include "runtime/safepoint.hpp" 38 #include "runtime/stubRoutines.hpp" 39 #include "runtime/thread.hpp" 40 #include "utilities/align.hpp" 41 #include "utilities/count_trailing_zeros.hpp" 42 #include "utilities/debug.hpp" 43 #include "utilities/globalDefinitions.hpp" 44 #include "utilities/macros.hpp" 45 #include "utilities/ostream.hpp" 46 #include "utilities/spinYield.hpp" 47 48 OopStorage::AllocationListEntry::AllocationListEntry() : _prev(NULL), _next(NULL) {} 49 50 OopStorage::AllocationListEntry::~AllocationListEntry() { 51 assert(_prev == NULL, "deleting attached block"); 52 assert(_next == NULL, "deleting attached block"); 53 } 54 55 OopStorage::AllocationList::AllocationList() : _head(NULL), _tail(NULL) {} 56 57 OopStorage::AllocationList::~AllocationList() { 58 // ~OopStorage() empties its lists before destroying them. 59 assert(_head == NULL, "deleting non-empty block list"); 60 assert(_tail == NULL, "deleting non-empty block list"); 61 } 62 63 void OopStorage::AllocationList::push_front(const Block& block) { 64 const Block* old = _head; 65 if (old == NULL) { 66 assert(_tail == NULL, "invariant"); 67 _head = _tail = █ 68 } else { 69 block.allocation_list_entry()._next = old; 70 old->allocation_list_entry()._prev = █ 71 _head = █ 72 } 73 } 74 75 void OopStorage::AllocationList::push_back(const Block& block) { 76 const Block* old = _tail; 77 if (old == NULL) { 78 assert(_head == NULL, "invariant"); 79 _head = _tail = █ 80 } else { 81 old->allocation_list_entry()._next = █ 82 block.allocation_list_entry()._prev = old; 83 _tail = █ 84 } 85 } 86 87 void OopStorage::AllocationList::unlink(const Block& block) { 88 const AllocationListEntry& block_entry = block.allocation_list_entry(); 89 const Block* prev_blk = block_entry._prev; 90 const Block* next_blk = block_entry._next; 91 block_entry._prev = NULL; 92 block_entry._next = NULL; 93 if ((prev_blk == NULL) && (next_blk == NULL)) { 94 assert(_head == &block, "invariant"); 95 assert(_tail == &block, "invariant"); 96 _head = _tail = NULL; 97 } else if (prev_blk == NULL) { 98 assert(_head == &block, "invariant"); 99 next_blk->allocation_list_entry()._prev = NULL; 100 _head = next_blk; 101 } else if (next_blk == NULL) { 102 assert(_tail == &block, "invariant"); 103 prev_blk->allocation_list_entry()._next = NULL; 104 _tail = prev_blk; 105 } else { 106 next_blk->allocation_list_entry()._prev = prev_blk; 107 prev_blk->allocation_list_entry()._next = next_blk; 108 } 109 } 110 111 OopStorage::ActiveArray::ActiveArray(size_t size) : 112 _size(size), 113 _block_count(0), 114 _refcount(0) 115 {} 116 117 OopStorage::ActiveArray::~ActiveArray() { 118 assert(_refcount == 0, "precondition"); 119 } 120 121 OopStorage::ActiveArray* OopStorage::ActiveArray::create(size_t size, AllocFailType alloc_fail) { 122 size_t size_in_bytes = blocks_offset() + sizeof(Block*) * size; 123 void* mem = NEW_C_HEAP_ARRAY3(char, size_in_bytes, mtGC, CURRENT_PC, alloc_fail); 124 if (mem == NULL) return NULL; 125 return new (mem) ActiveArray(size); 126 } 127 128 void OopStorage::ActiveArray::destroy(ActiveArray* ba) { 129 ba->~ActiveArray(); 130 FREE_C_HEAP_ARRAY(char, ba); 131 } 132 133 size_t OopStorage::ActiveArray::size() const { 134 return _size; 135 } 136 137 size_t OopStorage::ActiveArray::block_count() const { 138 return _block_count; 139 } 140 141 size_t OopStorage::ActiveArray::block_count_acquire() const { 142 return OrderAccess::load_acquire(&_block_count); 143 } 144 145 void OopStorage::ActiveArray::increment_refcount() const { 146 int new_value = Atomic::add(1, &_refcount); 147 assert(new_value >= 1, "negative refcount %d", new_value - 1); 148 } 149 150 bool OopStorage::ActiveArray::decrement_refcount() const { 151 int new_value = Atomic::sub(1, &_refcount); 152 assert(new_value >= 0, "negative refcount %d", new_value); 153 return new_value == 0; 154 } 155 156 bool OopStorage::ActiveArray::push(Block* block) { 157 size_t index = _block_count; 158 if (index < _size) { 159 block->set_active_index(index); 160 *block_ptr(index) = block; 161 // Use a release_store to ensure all the setup is complete before 162 // making the block visible. 163 OrderAccess::release_store(&_block_count, index + 1); 164 return true; 165 } else { 166 return false; 167 } 168 } 169 170 void OopStorage::ActiveArray::remove(Block* block) { 171 assert(_block_count > 0, "array is empty"); 172 size_t index = block->active_index(); 173 assert(*block_ptr(index) == block, "block not present"); 174 size_t last_index = _block_count - 1; 175 Block* last_block = *block_ptr(last_index); 176 last_block->set_active_index(index); 177 *block_ptr(index) = last_block; 178 _block_count = last_index; 179 } 180 181 void OopStorage::ActiveArray::copy_from(const ActiveArray* from) { 182 assert(_block_count == 0, "array must be empty"); 183 size_t count = from->_block_count; 184 assert(count <= _size, "precondition"); 185 Block* const* from_ptr = from->block_ptr(0); 186 Block** to_ptr = block_ptr(0); 187 for (size_t i = 0; i < count; ++i) { 188 Block* block = *from_ptr++; 189 assert(block->active_index() == i, "invariant"); 190 *to_ptr++ = block; 191 } 192 _block_count = count; 193 } 194 195 // Blocks start with an array of BitsPerWord oop entries. That array 196 // is divided into conceptual BytesPerWord sections of BitsPerByte 197 // entries. Blocks are allocated aligned on section boundaries, for 198 // the convenience of mapping from an entry to the containing block; 199 // see block_for_ptr(). Aligning on section boundary rather than on 200 // the full _data wastes a lot less space, but makes for a bit more 201 // work in block_for_ptr(). 202 203 const unsigned section_size = BitsPerByte; 204 const unsigned section_count = BytesPerWord; 205 const unsigned block_alignment = sizeof(oop) * section_size; 206 207 OopStorage::Block::Block(const OopStorage* owner, void* memory) : 208 _data(), 209 _allocated_bitmask(0), 210 _owner(owner), 211 _memory(memory), 212 _active_index(0), 213 _allocation_list_entry(), 214 _deferred_updates_next(NULL), 215 _release_refcount(0) 216 { 217 STATIC_ASSERT(_data_pos == 0); 218 STATIC_ASSERT(section_size * section_count == ARRAY_SIZE(_data)); 219 assert(offset_of(Block, _data) == _data_pos, "invariant"); 220 assert(owner != NULL, "NULL owner"); 221 assert(is_aligned(this, block_alignment), "misaligned block"); 222 } 223 224 OopStorage::Block::~Block() { 225 assert(_release_refcount == 0, "deleting block while releasing"); 226 assert(_deferred_updates_next == NULL, "deleting block with deferred update"); 227 // Clear fields used by block_for_ptr and entry validation, which 228 // might help catch bugs. Volatile to prevent dead-store elimination. 229 const_cast<uintx volatile&>(_allocated_bitmask) = 0; 230 const_cast<OopStorage* volatile&>(_owner) = NULL; 231 } 232 233 size_t OopStorage::Block::allocation_size() { 234 // _data must be first member, so aligning Block aligns _data. 235 STATIC_ASSERT(_data_pos == 0); 236 return sizeof(Block) + block_alignment - sizeof(void*); 237 } 238 239 size_t OopStorage::Block::allocation_alignment_shift() { 240 return exact_log2(block_alignment); 241 } 242 243 inline bool is_full_bitmask(uintx bitmask) { return ~bitmask == 0; } 244 inline bool is_empty_bitmask(uintx bitmask) { return bitmask == 0; } 245 246 bool OopStorage::Block::is_full() const { 247 return is_full_bitmask(allocated_bitmask()); 248 } 249 250 bool OopStorage::Block::is_empty() const { 251 return is_empty_bitmask(allocated_bitmask()); 252 } 253 254 uintx OopStorage::Block::bitmask_for_entry(const oop* ptr) const { 255 return bitmask_for_index(get_index(ptr)); 256 } 257 258 // A block is deletable if 259 // (1) It is empty. 260 // (2) There is not a release() operation currently operating on it. 261 // (3) It is not in the deferred updates list. 262 // The order of tests is important for proper interaction between release() 263 // and concurrent deletion. 264 bool OopStorage::Block::is_deletable() const { 265 return (OrderAccess::load_acquire(&_allocated_bitmask) == 0) && 266 (OrderAccess::load_acquire(&_release_refcount) == 0) && 267 (OrderAccess::load_acquire(&_deferred_updates_next) == NULL); 268 } 269 270 OopStorage::Block* OopStorage::Block::deferred_updates_next() const { 271 return _deferred_updates_next; 272 } 273 274 void OopStorage::Block::set_deferred_updates_next(Block* block) { 275 _deferred_updates_next = block; 276 } 277 278 bool OopStorage::Block::contains(const oop* ptr) const { 279 const oop* base = get_pointer(0); 280 return (base <= ptr) && (ptr < (base + ARRAY_SIZE(_data))); 281 } 282 283 size_t OopStorage::Block::active_index() const { 284 return _active_index; 285 } 286 287 void OopStorage::Block::set_active_index(size_t index) { 288 _active_index = index; 289 } 290 291 size_t OopStorage::Block::active_index_safe(const Block* block) { 292 STATIC_ASSERT(sizeof(intptr_t) == sizeof(block->_active_index)); 293 assert(CanUseSafeFetchN(), "precondition"); 294 return SafeFetchN((intptr_t*)&block->_active_index, 0); 295 } 296 297 unsigned OopStorage::Block::get_index(const oop* ptr) const { 298 assert(contains(ptr), PTR_FORMAT " not in block " PTR_FORMAT, p2i(ptr), p2i(this)); 299 return static_cast<unsigned>(ptr - get_pointer(0)); 300 } 301 302 oop* OopStorage::Block::allocate() { 303 // Use CAS loop because release may change bitmask outside of lock. 304 uintx allocated = allocated_bitmask(); 305 while (true) { 306 assert(!is_full_bitmask(allocated), "attempt to allocate from full block"); 307 unsigned index = count_trailing_zeros(~allocated); 308 uintx new_value = allocated | bitmask_for_index(index); 309 uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, allocated); 310 if (fetched == allocated) { 311 return get_pointer(index); // CAS succeeded; return entry for index. 312 } 313 allocated = fetched; // CAS failed; retry with latest value. 314 } 315 } 316 317 OopStorage::Block* OopStorage::Block::new_block(const OopStorage* owner) { 318 // _data must be first member: aligning block => aligning _data. 319 STATIC_ASSERT(_data_pos == 0); 320 size_t size_needed = allocation_size(); 321 void* memory = NEW_C_HEAP_ARRAY_RETURN_NULL(char, size_needed, mtGC); 322 if (memory == NULL) { 323 return NULL; 324 } 325 void* block_mem = align_up(memory, block_alignment); 326 assert(sizeof(Block) + pointer_delta(block_mem, memory, 1) <= size_needed, 327 "allocated insufficient space for aligned block"); 328 return ::new (block_mem) Block(owner, memory); 329 } 330 331 void OopStorage::Block::delete_block(const Block& block) { 332 void* memory = block._memory; 333 block.Block::~Block(); 334 FREE_C_HEAP_ARRAY(char, memory); 335 } 336 337 // This can return a false positive if ptr is not contained by some 338 // block. For some uses, it is a precondition that ptr is valid, 339 // e.g. contained in some block in owner's _active_array. Other uses 340 // require additional validation of the result. 341 OopStorage::Block* 342 OopStorage::Block::block_for_ptr(const OopStorage* owner, const oop* ptr) { 343 assert(CanUseSafeFetchN(), "precondition"); 344 STATIC_ASSERT(_data_pos == 0); 345 // Const-ness of ptr is not related to const-ness of containing block. 346 // Blocks are allocated section-aligned, so get the containing section. 347 oop* section_start = align_down(const_cast<oop*>(ptr), block_alignment); 348 // Start with a guess that the containing section is the last section, 349 // so the block starts section_count-1 sections earlier. 350 oop* section = section_start - (section_size * (section_count - 1)); 351 // Walk up through the potential block start positions, looking for 352 // the owner in the expected location. If we're below the actual block 353 // start position, the value at the owner position will be some oop 354 // (possibly NULL), which can never match the owner. 355 intptr_t owner_addr = reinterpret_cast<intptr_t>(owner); 356 for (unsigned i = 0; i < section_count; ++i, section += section_size) { 357 Block* candidate = reinterpret_cast<Block*>(section); 358 intptr_t* candidate_owner_addr 359 = reinterpret_cast<intptr_t*>(&candidate->_owner); 360 if (SafeFetchN(candidate_owner_addr, 0) == owner_addr) { 361 return candidate; 362 } 363 } 364 return NULL; 365 } 366 367 ////////////////////////////////////////////////////////////////////////////// 368 // Allocation 369 // 370 // Allocation involves the _allocation_list, which contains a subset of the 371 // blocks owned by a storage object. This is a doubly-linked list, linked 372 // through dedicated fields in the blocks. Full blocks are removed from this 373 // list, though they are still present in the _active_array. Empty blocks are 374 // kept at the end of the _allocation_list, to make it easy for empty block 375 // deletion to find them. 376 // 377 // allocate(), and delete_empty_blocks_concurrent() lock the 378 // _allocation_mutex while performing any list and array modifications. 379 // 380 // allocate() and release() update a block's _allocated_bitmask using CAS 381 // loops. This prevents loss of updates even though release() performs 382 // its updates without any locking. 383 // 384 // allocate() obtains the entry from the first block in the _allocation_list, 385 // and updates that block's _allocated_bitmask to indicate the entry is in 386 // use. If this makes the block full (all entries in use), the block is 387 // removed from the _allocation_list so it won't be considered by future 388 // allocations until some entries in it are released. 389 // 390 // release() is performed lock-free. release() first looks up the block for 391 // the entry, using address alignment to find the enclosing block (thereby 392 // avoiding iteration over the _active_array). Once the block has been 393 // determined, its _allocated_bitmask needs to be updated, and its position in 394 // the _allocation_list may need to be updated. There are two cases: 395 // 396 // (a) If the block is neither full nor would become empty with the release of 397 // the entry, only its _allocated_bitmask needs to be updated. But if the CAS 398 // update fails, the applicable case may change for the retry. 399 // 400 // (b) Otherwise, the _allocation_list also needs to be modified. This requires 401 // locking the _allocation_mutex. To keep the release() operation lock-free, 402 // rather than updating the _allocation_list itself, it instead performs a 403 // lock-free push of the block onto the _deferred_updates list. Entries on 404 // that list are processed by allocate() and delete_empty_blocks_XXX(), while 405 // they already hold the necessary lock. That processing makes the block's 406 // list state consistent with its current _allocated_bitmask. The block is 407 // added to the _allocation_list if not already present and the bitmask is not 408 // full. The block is moved to the end of the _allocation_list if the bitmask 409 // is empty, for ease of empty block deletion processing. 410 411 oop* OopStorage::allocate() { 412 MutexLockerEx ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); 413 // Do some deferred update processing every time we allocate. 414 // Continue processing deferred updates if _allocation_list is empty, 415 // in the hope that we'll get a block from that, rather than 416 // allocating a new block. 417 while (reduce_deferred_updates() && (_allocation_list.head() == NULL)) {} 418 419 // Use the first block in _allocation_list for the allocation. 420 Block* block = _allocation_list.head(); 421 if (block == NULL) { 422 // No available blocks; make a new one, and add to storage. 423 { 424 MutexUnlockerEx mul(_allocation_mutex, Mutex::_no_safepoint_check_flag); 425 block = Block::new_block(this); 426 } 427 if (block == NULL) { 428 while (_allocation_list.head() == NULL) { 429 if (!reduce_deferred_updates()) { 430 // Failed to make new block, no other thread made a block 431 // available while the mutex was released, and didn't get 432 // one from a deferred update either, so return failure. 433 log_info(oopstorage, ref)("%s: failed block allocation", name()); 434 return NULL; 435 } 436 } 437 } else { 438 // Add new block to storage. 439 log_info(oopstorage, blocks)("%s: new block " PTR_FORMAT, name(), p2i(block)); 440 441 // Add new block to the _active_array, growing if needed. 442 if (!_active_array->push(block)) { 443 if (expand_active_array()) { 444 guarantee(_active_array->push(block), "push failed after expansion"); 445 } else { 446 log_info(oopstorage, blocks)("%s: failed active array expand", name()); 447 Block::delete_block(*block); 448 return NULL; 449 } 450 } 451 // Add to end of _allocation_list. The mutex release allowed 452 // other threads to add blocks to the _allocation_list. We prefer 453 // to allocate from non-empty blocks, to allow empty blocks to 454 // be deleted. 455 _allocation_list.push_back(*block); 456 } 457 block = _allocation_list.head(); 458 } 459 // Allocate from first block. 460 assert(block != NULL, "invariant"); 461 assert(!block->is_full(), "invariant"); 462 if (block->is_empty()) { 463 // Transitioning from empty to not empty. 464 log_debug(oopstorage, blocks)("%s: block not empty " PTR_FORMAT, name(), p2i(block)); 465 } 466 oop* result = block->allocate(); 467 assert(result != NULL, "allocation failed"); 468 assert(!block->is_empty(), "postcondition"); 469 Atomic::inc(&_allocation_count); // release updates outside lock. 470 if (block->is_full()) { 471 // Transitioning from not full to full. 472 // Remove full blocks from consideration by future allocates. 473 log_debug(oopstorage, blocks)("%s: block full " PTR_FORMAT, name(), p2i(block)); 474 _allocation_list.unlink(*block); 475 } 476 log_info(oopstorage, ref)("%s: allocated " PTR_FORMAT, name(), p2i(result)); 477 return result; 478 } 479 480 // Create a new, larger, active array with the same content as the 481 // current array, and then replace, relinquishing the old array. 482 // Return true if the array was successfully expanded, false to 483 // indicate allocation failure. 484 bool OopStorage::expand_active_array() { 485 assert_lock_strong(_allocation_mutex); 486 ActiveArray* old_array = _active_array; 487 size_t new_size = 2 * old_array->size(); 488 log_info(oopstorage, blocks)("%s: expand active array " SIZE_FORMAT, 489 name(), new_size); 490 ActiveArray* new_array = ActiveArray::create(new_size, AllocFailStrategy::RETURN_NULL); 491 if (new_array == NULL) return false; 492 new_array->copy_from(old_array); 493 replace_active_array(new_array); 494 relinquish_block_array(old_array); 495 return true; 496 } 497 498 OopStorage::ProtectActive::ProtectActive() : _enter(0), _exit() {} 499 500 // Begin read-side critical section. 501 uint OopStorage::ProtectActive::read_enter() { 502 return Atomic::add(2u, &_enter); 503 } 504 505 // End read-side critical section. 506 void OopStorage::ProtectActive::read_exit(uint enter_value) { 507 Atomic::add(2u, &_exit[enter_value & 1]); 508 } 509 510 // Wait until all readers that entered the critical section before 511 // synchronization have exited that critical section. 512 void OopStorage::ProtectActive::write_synchronize() { 513 SpinYield spinner; 514 // Determine old and new exit counters, based on bit0 of the 515 // on-entry _enter counter. 516 uint value = OrderAccess::load_acquire(&_enter); 517 volatile uint* new_ptr = &_exit[(value + 1) & 1]; 518 // Atomically change the in-use exit counter to the new counter, by 519 // adding 1 to the _enter counter (flipping bit0 between 0 and 1) 520 // and initializing the new exit counter to that enter value. Note: 521 // The new exit counter is not being used by read operations until 522 // this change succeeds. 523 uint old; 524 do { 525 old = value; 526 *new_ptr = ++value; 527 value = Atomic::cmpxchg(value, &_enter, old); 528 } while (old != value); 529 // Readers that entered the critical section before we changed the 530 // selected exit counter will use the old exit counter. Readers 531 // entering after the change will use the new exit counter. Wait 532 // for all the critical sections started before the change to 533 // complete, e.g. for the value of old_ptr to catch up with old. 534 volatile uint* old_ptr = &_exit[old & 1]; 535 while (old != OrderAccess::load_acquire(old_ptr)) { 536 spinner.wait(); 537 } 538 } 539 540 // Make new_array the _active_array. Increments new_array's refcount 541 // to account for the new reference. The assignment is atomic wrto 542 // obtain_active_array; once this function returns, it is safe for the 543 // caller to relinquish the old array. 544 void OopStorage::replace_active_array(ActiveArray* new_array) { 545 // Caller has the old array that is the current value of _active_array. 546 // Update new_array refcount to account for the new reference. 547 new_array->increment_refcount(); 548 // Install new_array, ensuring its initialization is complete first. 549 OrderAccess::release_store(&_active_array, new_array); 550 // Wait for any readers that could read the old array from _active_array. 551 _protect_active.write_synchronize(); 552 // All obtain critical sections that could see the old array have 553 // completed, having incremented the refcount of the old array. The 554 // caller can now safely relinquish the old array. 555 } 556 557 // Atomically (wrto replace_active_array) get the active array and 558 // increment its refcount. This provides safe access to the array, 559 // even if an allocate operation expands and replaces the value of 560 // _active_array. The caller must relinquish the array when done 561 // using it. 562 OopStorage::ActiveArray* OopStorage::obtain_active_array() const { 563 uint enter_value = _protect_active.read_enter(); 564 ActiveArray* result = OrderAccess::load_acquire(&_active_array); 565 result->increment_refcount(); 566 _protect_active.read_exit(enter_value); 567 return result; 568 } 569 570 // Decrement refcount of array and destroy if refcount is zero. 571 void OopStorage::relinquish_block_array(ActiveArray* array) const { 572 if (array->decrement_refcount()) { 573 assert(array != _active_array, "invariant"); 574 ActiveArray::destroy(array); 575 } 576 } 577 578 class OopStorage::WithActiveArray : public StackObj { 579 const OopStorage* _storage; 580 ActiveArray* _active_array; 581 582 public: 583 WithActiveArray(const OopStorage* storage) : 584 _storage(storage), 585 _active_array(storage->obtain_active_array()) 586 {} 587 588 ~WithActiveArray() { 589 _storage->relinquish_block_array(_active_array); 590 } 591 592 ActiveArray& active_array() const { 593 return *_active_array; 594 } 595 }; 596 597 OopStorage::Block* OopStorage::find_block_or_null(const oop* ptr) const { 598 assert(ptr != NULL, "precondition"); 599 return Block::block_for_ptr(this, ptr); 600 } 601 602 static void log_release_transitions(uintx releasing, 603 uintx old_allocated, 604 const OopStorage* owner, 605 const void* block) { 606 Log(oopstorage, blocks) log; 607 LogStream ls(log.debug()); 608 if (is_full_bitmask(old_allocated)) { 609 ls.print_cr("%s: block not full " PTR_FORMAT, owner->name(), p2i(block)); 610 } 611 if (releasing == old_allocated) { 612 ls.print_cr("%s: block empty " PTR_FORMAT, owner->name(), p2i(block)); 613 } 614 } 615 616 void OopStorage::Block::release_entries(uintx releasing, Block* volatile* deferred_list) { 617 assert(releasing != 0, "preconditon"); 618 // Prevent empty block deletion when transitioning to empty. 619 Atomic::inc(&_release_refcount); 620 621 // Atomically update allocated bitmask. 622 uintx old_allocated = _allocated_bitmask; 623 while (true) { 624 assert((releasing & ~old_allocated) == 0, "releasing unallocated entries"); 625 uintx new_value = old_allocated ^ releasing; 626 uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, old_allocated); 627 if (fetched == old_allocated) break; // Successful update. 628 old_allocated = fetched; // Retry with updated bitmask. 629 } 630 631 // Now that the bitmask has been updated, if we have a state transition 632 // (updated bitmask is empty or old bitmask was full), atomically push 633 // this block onto the deferred updates list. Some future call to 634 // reduce_deferred_updates will make any needed changes related to this 635 // block and _allocation_list. This deferral avoids list updates and the 636 // associated locking here. 637 if ((releasing == old_allocated) || is_full_bitmask(old_allocated)) { 638 // Log transitions. Both transitions are possible in a single update. 639 if (log_is_enabled(Debug, oopstorage, blocks)) { 640 log_release_transitions(releasing, old_allocated, _owner, this); 641 } 642 // Attempt to claim responsibility for adding this block to the deferred 643 // list, by setting the link to non-NULL by self-looping. If this fails, 644 // then someone else has made such a claim and the deferred update has not 645 // yet been processed and will include our change, so we don't need to do 646 // anything further. 647 if (Atomic::replace_if_null(this, &_deferred_updates_next)) { 648 // Successfully claimed. Push, with self-loop for end-of-list. 649 Block* head = *deferred_list; 650 while (true) { 651 _deferred_updates_next = (head == NULL) ? this : head; 652 Block* fetched = Atomic::cmpxchg(this, deferred_list, head); 653 if (fetched == head) break; // Successful update. 654 head = fetched; // Retry with updated head. 655 } 656 log_debug(oopstorage, blocks)("%s: deferred update " PTR_FORMAT, 657 _owner->name(), p2i(this)); 658 } 659 } 660 // Release hold on empty block deletion. 661 Atomic::dec(&_release_refcount); 662 } 663 664 // Process one available deferred update. Returns true if one was processed. 665 bool OopStorage::reduce_deferred_updates() { 666 assert_locked_or_safepoint(_allocation_mutex); 667 // Atomically pop a block off the list, if any available. 668 // No ABA issue because this is only called by one thread at a time. 669 // The atomicity is wrto pushes by release(). 670 Block* block = OrderAccess::load_acquire(&_deferred_updates); 671 while (true) { 672 if (block == NULL) return false; 673 // Try atomic pop of block from list. 674 Block* tail = block->deferred_updates_next(); 675 if (block == tail) tail = NULL; // Handle self-loop end marker. 676 Block* fetched = Atomic::cmpxchg(tail, &_deferred_updates, block); 677 if (fetched == block) break; // Update successful. 678 block = fetched; // Retry with updated block. 679 } 680 block->set_deferred_updates_next(NULL); // Clear tail after updating head. 681 // Ensure bitmask read after pop is complete, including clearing tail, for 682 // ordering with release(). Without this, we may be processing a stale 683 // bitmask state here while blocking a release() operation from recording 684 // the deferred update needed for its bitmask change. 685 OrderAccess::storeload(); 686 // Process popped block. 687 uintx allocated = block->allocated_bitmask(); 688 689 // Make membership in list consistent with bitmask state. 690 if ((_allocation_list.ctail() != NULL) && 691 ((_allocation_list.ctail() == block) || 692 (_allocation_list.next(*block) != NULL))) { 693 // Block is in the _allocation_list. 694 assert(!is_full_bitmask(allocated), "invariant"); 695 } else if (!is_full_bitmask(allocated)) { 696 // Block is not in the _allocation_list, but now should be. 697 _allocation_list.push_front(*block); 698 } // Else block is full and not in list, which is correct. 699 700 // Move empty block to end of list, for possible deletion. 701 if (is_empty_bitmask(allocated)) { 702 _allocation_list.unlink(*block); 703 _allocation_list.push_back(*block); 704 } 705 706 log_debug(oopstorage, blocks)("%s: processed deferred update " PTR_FORMAT, 707 name(), p2i(block)); 708 return true; // Processed one pending update. 709 } 710 711 inline void check_release_entry(const oop* entry) { 712 assert(entry != NULL, "Releasing NULL"); 713 assert(*entry == NULL, "Releasing uncleared entry: " PTR_FORMAT, p2i(entry)); 714 } 715 716 void OopStorage::release(const oop* ptr) { 717 check_release_entry(ptr); 718 Block* block = find_block_or_null(ptr); 719 assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptr)); 720 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptr)); 721 block->release_entries(block->bitmask_for_entry(ptr), &_deferred_updates); 722 Atomic::dec(&_allocation_count); 723 } 724 725 void OopStorage::release(const oop* const* ptrs, size_t size) { 726 size_t i = 0; 727 while (i < size) { 728 check_release_entry(ptrs[i]); 729 Block* block = find_block_or_null(ptrs[i]); 730 assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptrs[i])); 731 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptrs[i])); 732 size_t count = 0; 733 uintx releasing = 0; 734 for ( ; i < size; ++i) { 735 const oop* entry = ptrs[i]; 736 check_release_entry(entry); 737 // If entry not in block, finish block and resume outer loop with entry. 738 if (!block->contains(entry)) break; 739 // Add entry to releasing bitmap. 740 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(entry)); 741 uintx entry_bitmask = block->bitmask_for_entry(entry); 742 assert((releasing & entry_bitmask) == 0, 743 "Duplicate entry: " PTR_FORMAT, p2i(entry)); 744 releasing |= entry_bitmask; 745 ++count; 746 } 747 // Release the contiguous entries that are in block. 748 block->release_entries(releasing, &_deferred_updates); 749 Atomic::sub(count, &_allocation_count); 750 } 751 } 752 753 const char* dup_name(const char* name) { 754 char* dup = NEW_C_HEAP_ARRAY(char, strlen(name) + 1, mtGC); 755 strcpy(dup, name); 756 return dup; 757 } 758 759 const size_t initial_active_array_size = 8; 760 761 OopStorage::OopStorage(const char* name, 762 Mutex* allocation_mutex, 763 Mutex* active_mutex) : 764 _name(dup_name(name)), 765 _active_array(ActiveArray::create(initial_active_array_size)), 766 _allocation_list(), 767 _deferred_updates(NULL), 768 _allocation_mutex(allocation_mutex), 769 _active_mutex(active_mutex), 770 _allocation_count(0), 771 _concurrent_iteration_active(false) 772 { 773 _active_array->increment_refcount(); 774 assert(_active_mutex->rank() < _allocation_mutex->rank(), 775 "%s: active_mutex must have lower rank than allocation_mutex", _name); 776 assert(_active_mutex->_safepoint_check_required != Mutex::_safepoint_check_always, 777 "%s: active mutex requires safepoint check", _name); 778 assert(_allocation_mutex->_safepoint_check_required != Mutex::_safepoint_check_always, 779 "%s: allocation mutex requires safepoint check", _name); 780 } 781 782 void OopStorage::delete_empty_block(const Block& block) { 783 assert(block.is_empty(), "discarding non-empty block"); 784 log_info(oopstorage, blocks)("%s: delete empty block " PTR_FORMAT, name(), p2i(&block)); 785 Block::delete_block(block); 786 } 787 788 OopStorage::~OopStorage() { 789 Block* block; 790 while ((block = _deferred_updates) != NULL) { 791 _deferred_updates = block->deferred_updates_next(); 792 block->set_deferred_updates_next(NULL); 793 } 794 while ((block = _allocation_list.head()) != NULL) { 795 _allocation_list.unlink(*block); 796 } 797 bool unreferenced = _active_array->decrement_refcount(); 798 assert(unreferenced, "deleting storage while _active_array is referenced"); 799 for (size_t i = _active_array->block_count(); 0 < i; ) { 800 block = _active_array->at(--i); 801 Block::delete_block(*block); 802 } 803 ActiveArray::destroy(_active_array); 804 FREE_C_HEAP_ARRAY(char, _name); 805 } 806 807 void OopStorage::delete_empty_blocks_safepoint() { 808 assert_at_safepoint(); 809 // Process any pending release updates, which may make more empty 810 // blocks available for deletion. 811 while (reduce_deferred_updates()) {} 812 // Don't interfere with a concurrent iteration. 813 if (_concurrent_iteration_active) return; 814 // Delete empty (and otherwise deletable) blocks from end of _allocation_list. 815 for (Block* block = _allocation_list.tail(); 816 (block != NULL) && block->is_deletable(); 817 block = _allocation_list.tail()) { 818 _active_array->remove(block); 819 _allocation_list.unlink(*block); 820 delete_empty_block(*block); 821 } 822 } 823 824 void OopStorage::delete_empty_blocks_concurrent() { 825 MutexLockerEx ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); 826 // Other threads could be adding to the empty block count while we 827 // release the mutex across the block deletions. Set an upper bound 828 // on how many blocks we'll try to release, so other threads can't 829 // cause an unbounded stay in this function. 830 size_t limit = block_count(); 831 832 for (size_t i = 0; i < limit; ++i) { 833 // Additional updates might become available while we dropped the 834 // lock. But limit number processed to limit lock duration. 835 reduce_deferred_updates(); 836 837 Block* block = _allocation_list.tail(); 838 if ((block == NULL) || !block->is_deletable()) { 839 // No block to delete, so done. There could be more pending 840 // deferred updates that could give us more work to do; deal with 841 // that in some later call, to limit lock duration here. 842 return; 843 } 844 845 { 846 MutexLockerEx aml(_active_mutex, Mutex::_no_safepoint_check_flag); 847 // Don't interfere with a concurrent iteration. 848 if (_concurrent_iteration_active) return; 849 _active_array->remove(block); 850 } 851 // Remove block from _allocation_list and delete it. 852 _allocation_list.unlink(*block); 853 // Release mutex while deleting block. 854 MutexUnlockerEx ul(_allocation_mutex, Mutex::_no_safepoint_check_flag); 855 delete_empty_block(*block); 856 } 857 } 858 859 OopStorage::EntryStatus OopStorage::allocation_status(const oop* ptr) const { 860 const Block* block = find_block_or_null(ptr); 861 if (block != NULL) { 862 // Prevent block deletion and _active_array modification. 863 MutexLockerEx ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); 864 // Block could be a false positive, so get index carefully. 865 size_t index = Block::active_index_safe(block); 866 if ((index < _active_array->block_count()) && 867 (block == _active_array->at(index)) && 868 block->contains(ptr)) { 869 if ((block->allocated_bitmask() & block->bitmask_for_entry(ptr)) != 0) { 870 return ALLOCATED_ENTRY; 871 } else { 872 return UNALLOCATED_ENTRY; 873 } 874 } 875 } 876 return INVALID_ENTRY; 877 } 878 879 size_t OopStorage::allocation_count() const { 880 return _allocation_count; 881 } 882 883 size_t OopStorage::block_count() const { 884 WithActiveArray wab(this); 885 // Count access is racy, but don't care. 886 return wab.active_array().block_count(); 887 } 888 889 size_t OopStorage::total_memory_usage() const { 890 size_t total_size = sizeof(OopStorage); 891 total_size += strlen(name()) + 1; 892 total_size += sizeof(ActiveArray); 893 WithActiveArray wab(this); 894 const ActiveArray& blocks = wab.active_array(); 895 // Count access is racy, but don't care. 896 total_size += blocks.block_count() * Block::allocation_size(); 897 total_size += blocks.size() * sizeof(Block*); 898 return total_size; 899 } 900 901 // Parallel iteration support 902 903 uint OopStorage::BasicParState::default_estimated_thread_count(bool concurrent) { 904 uint configured = concurrent ? ConcGCThreads : ParallelGCThreads; 905 return MAX2(1u, configured); // Never estimate zero threads. 906 } 907 908 OopStorage::BasicParState::BasicParState(const OopStorage* storage, 909 uint estimated_thread_count, 910 bool concurrent) : 911 _storage(storage), 912 _active_array(_storage->obtain_active_array()), 913 _block_count(0), // initialized properly below 914 _next_block(0), 915 _estimated_thread_count(estimated_thread_count), 916 _concurrent(concurrent) 917 { 918 assert(estimated_thread_count > 0, "estimated thread count must be positive"); 919 update_iteration_state(true); 920 // Get the block count *after* iteration state updated, so concurrent 921 // empty block deletion is suppressed and can't reduce the count. But 922 // ensure the count we use was written after the block with that count 923 // was fully initialized; see ActiveArray::push. 924 _block_count = _active_array->block_count_acquire(); 925 } 926 927 OopStorage::BasicParState::~BasicParState() { 928 _storage->relinquish_block_array(_active_array); 929 update_iteration_state(false); 930 } 931 932 void OopStorage::BasicParState::update_iteration_state(bool value) { 933 if (_concurrent) { 934 MutexLockerEx ml(_storage->_active_mutex, Mutex::_no_safepoint_check_flag); 935 assert(_storage->_concurrent_iteration_active != value, "precondition"); 936 _storage->_concurrent_iteration_active = value; 937 } 938 } 939 940 bool OopStorage::BasicParState::claim_next_segment(IterationData* data) { 941 data->_processed += data->_segment_end - data->_segment_start; 942 size_t start = OrderAccess::load_acquire(&_next_block); 943 if (start >= _block_count) { 944 return finish_iteration(data); // No more blocks available. 945 } 946 // Try to claim several at a time, but not *too* many. We want to 947 // avoid deciding there are many available and selecting a large 948 // quantity, get delayed, and then end up claiming most or all of 949 // the remaining largish amount of work, leaving nothing for other 950 // threads to do. But too small a step can lead to contention 951 // over _next_block, esp. when the work per block is small. 952 size_t max_step = 10; 953 size_t remaining = _block_count - start; 954 size_t step = MIN2(max_step, 1 + (remaining / _estimated_thread_count)); 955 // Atomic::add with possible overshoot. This can perform better 956 // than a CAS loop on some platforms when there is contention. 957 // We can cope with the uncertainty by recomputing start/end from 958 // the result of the add, and dealing with potential overshoot. 959 size_t end = Atomic::add(step, &_next_block); 960 // _next_block may have changed, so recompute start from result of add. 961 start = end - step; 962 // _next_block may have changed so much that end has overshot. 963 end = MIN2(end, _block_count); 964 // _next_block may have changed so much that even start has overshot. 965 if (start < _block_count) { 966 // Record claimed segment for iteration. 967 data->_segment_start = start; 968 data->_segment_end = end; 969 return true; // Success. 970 } else { 971 // No more blocks to claim. 972 return finish_iteration(data); 973 } 974 } 975 976 bool OopStorage::BasicParState::finish_iteration(const IterationData* data) const { 977 log_debug(oopstorage, blocks, stats) 978 ("Parallel iteration on %s: blocks = " SIZE_FORMAT 979 ", processed = " SIZE_FORMAT " (%2.f%%)", 980 _storage->name(), _block_count, data->_processed, 981 percent_of(data->_processed, _block_count)); 982 return false; 983 } 984 985 const char* OopStorage::name() const { return _name; } 986 987 #ifndef PRODUCT 988 989 void OopStorage::print_on(outputStream* st) const { 990 size_t allocations = _allocation_count; 991 size_t blocks = _active_array->block_count(); 992 993 double data_size = section_size * section_count; 994 double alloc_percentage = percent_of((double)allocations, blocks * data_size); 995 996 st->print("%s: " SIZE_FORMAT " entries in " SIZE_FORMAT " blocks (%.F%%), " SIZE_FORMAT " bytes", 997 name(), allocations, blocks, alloc_percentage, total_memory_usage()); 998 if (_concurrent_iteration_active) { 999 st->print(", concurrent iteration active"); 1000 } 1001 } 1002 1003 #endif // !PRODUCT