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