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 "memory/resourceArea.hpp"
32 #include "runtime/atomic.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 "utilities/align.hpp"
40 #include "utilities/count_trailing_zeros.hpp"
41 #include "utilities/debug.hpp"
42 #include "utilities/globalDefinitions.hpp"
43 #include "utilities/macros.hpp"
44 #include "utilities/ostream.hpp"
45
46 OopStorage::BlockEntry::BlockEntry() : _prev(NULL), _next(NULL) {}
47
48 OopStorage::BlockEntry::~BlockEntry() {
49 assert(_prev == NULL, "deleting attached block");
50 assert(_next == NULL, "deleting attached block");
51 }
52
53 OopStorage::BlockList::BlockList(const BlockEntry& (*get_entry)(const Block& block)) :
54 _head(NULL), _tail(NULL), _get_entry(get_entry)
55 {}
56
57 OopStorage::BlockList::~BlockList() {
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::BlockList::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 _get_entry(block)._next = old;
70 _get_entry(*old)._prev = █
71 _head = █
72 }
73 }
74
75 void OopStorage::BlockList::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 _get_entry(*old)._next = █
82 _get_entry(block)._prev = old;
83 _tail = █
84 }
85 }
86
87 void OopStorage::BlockList::unlink(const Block& block) {
88 const BlockEntry& block_entry = _get_entry(block);
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 _get_entry(*next_blk)._prev = NULL;
100 _head = next_blk;
101 } else if (next_blk == NULL) {
102 assert(_tail == &block, "invariant");
103 _get_entry(*prev_blk)._next = NULL;
104 _tail = prev_blk;
105 } else {
106 _get_entry(*next_blk)._prev = prev_blk;
107 _get_entry(*prev_blk)._next = next_blk;
108 }
109 }
110
111 // Blocks start with an array of BitsPerWord oop entries. That array
112 // is divided into conceptual BytesPerWord sections of BitsPerByte
113 // entries. Blocks are allocated aligned on section boundaries, for
114 // the convenience of mapping from an entry to the containing block;
115 // see block_for_ptr(). Aligning on section boundary rather than on
116 // the full _data wastes a lot less space, but makes for a bit more
117 // work in block_for_ptr().
118
119 const unsigned section_size = BitsPerByte;
120 const unsigned section_count = BytesPerWord;
121 const unsigned block_alignment = sizeof(oop) * section_size;
122
123 // VS2013 warns (C4351) that elements of _data will be *correctly* default
124 // initialized, unlike earlier versions that *incorrectly* did not do so.
125 #ifdef _WINDOWS
126 #pragma warning(push)
127 #pragma warning(disable: 4351)
128 #endif // _WINDOWS
129 OopStorage::Block::Block(const OopStorage* owner, void* memory) :
130 _data(),
131 _allocated_bitmask(0),
132 _owner(owner),
133 _memory(memory),
134 _active_entry(),
135 _allocate_entry(),
136 _deferred_updates_next(NULL),
137 _release_refcount(0)
138 {
139 STATIC_ASSERT(_data_pos == 0);
140 STATIC_ASSERT(section_size * section_count == ARRAY_SIZE(_data));
141 assert(offset_of(Block, _data) == _data_pos, "invariant");
142 assert(owner != NULL, "NULL owner");
143 assert(is_aligned(this, block_alignment), "misaligned block");
144 }
145 #ifdef _WINDOWS
146 #pragma warning(pop)
147 #endif
148
149 OopStorage::Block::~Block() {
150 assert(_release_refcount == 0, "deleting block while releasing");
151 assert(_deferred_updates_next == NULL, "deleting block with deferred update");
152 // Clear fields used by block_for_ptr and entry validation, which
153 // might help catch bugs. Volatile to prevent dead-store elimination.
154 const_cast<uintx volatile&>(_allocated_bitmask) = 0;
155 const_cast<OopStorage* volatile&>(_owner) = NULL;
156 }
157
158 const OopStorage::BlockEntry& OopStorage::Block::get_active_entry(const Block& block) {
159 return block._active_entry;
160 }
161
162 const OopStorage::BlockEntry& OopStorage::Block::get_allocate_entry(const Block& block) {
163 return block._allocate_entry;
164 }
165
166 size_t OopStorage::Block::allocation_size() {
167 // _data must be first member, so aligning Block aligns _data.
168 STATIC_ASSERT(_data_pos == 0);
169 return sizeof(Block) + block_alignment - sizeof(void*);
170 }
171
172 size_t OopStorage::Block::allocation_alignment_shift() {
173 return exact_log2(block_alignment);
174 }
175
176 inline bool is_full_bitmask(uintx bitmask) { return ~bitmask == 0; }
177 inline bool is_empty_bitmask(uintx bitmask) { return bitmask == 0; }
178
179 bool OopStorage::Block::is_full() const {
180 return is_full_bitmask(allocated_bitmask());
181 }
182
183 bool OopStorage::Block::is_empty() const {
184 return is_empty_bitmask(allocated_bitmask());
185 }
186
187 uintx OopStorage::Block::bitmask_for_entry(const oop* ptr) const {
188 return bitmask_for_index(get_index(ptr));
189 }
190
191 // A block is deletable if
192 // (1) It is empty.
193 // (2) There is not a release() operation currently operating on it.
194 // (3) It is not in the deferred updates list.
195 // The order of tests is important for proper interaction between release()
196 // and concurrent deletion.
197 bool OopStorage::Block::is_deletable() const {
198 return (OrderAccess::load_acquire(&_allocated_bitmask) == 0) &&
199 (OrderAccess::load_acquire(&_release_refcount) == 0) &&
200 (OrderAccess::load_acquire(&_deferred_updates_next) == NULL);
201 }
202
203 OopStorage::Block* OopStorage::Block::deferred_updates_next() const {
204 return _deferred_updates_next;
205 }
206
207 void OopStorage::Block::set_deferred_updates_next(Block* block) {
208 _deferred_updates_next = block;
209 }
210
211 bool OopStorage::Block::contains(const oop* ptr) const {
212 const oop* base = get_pointer(0);
213 return (base <= ptr) && (ptr < (base + ARRAY_SIZE(_data)));
214 }
215
216 unsigned OopStorage::Block::get_index(const oop* ptr) const {
217 assert(contains(ptr), PTR_FORMAT " not in block " PTR_FORMAT, p2i(ptr), p2i(this));
218 return static_cast<unsigned>(ptr - get_pointer(0));
219 }
220
221 oop* OopStorage::Block::allocate() {
222 // Use CAS loop because release may change bitmask outside of lock.
223 uintx allocated = allocated_bitmask();
224 while (true) {
225 assert(!is_full_bitmask(allocated), "attempt to allocate from full block");
226 unsigned index = count_trailing_zeros(~allocated);
227 uintx new_value = allocated | bitmask_for_index(index);
228 uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, allocated);
229 if (fetched == allocated) {
230 return get_pointer(index); // CAS succeeded; return entry for index.
231 }
232 allocated = fetched; // CAS failed; retry with latest value.
233 }
234 }
235
236 OopStorage::Block* OopStorage::Block::new_block(const OopStorage* owner) {
237 // _data must be first member: aligning block => aligning _data.
238 STATIC_ASSERT(_data_pos == 0);
239 size_t size_needed = allocation_size();
240 void* memory = NEW_C_HEAP_ARRAY_RETURN_NULL(char, size_needed, mtGC);
241 if (memory == NULL) {
242 return NULL;
243 }
244 void* block_mem = align_up(memory, block_alignment);
245 assert(sizeof(Block) + pointer_delta(block_mem, memory, 1) <= size_needed,
246 "allocated insufficient space for aligned block");
247 return ::new (block_mem) Block(owner, memory);
248 }
249
250 void OopStorage::Block::delete_block(const Block& block) {
251 void* memory = block._memory;
252 block.Block::~Block();
253 FREE_C_HEAP_ARRAY(char, memory);
254 }
255
256 // This can return a false positive if ptr is not contained by some
257 // block. For some uses, it is a precondition that ptr is valid,
258 // e.g. contained in some block in owner's _active_list. Other uses
259 // require additional validation of the result.
260 OopStorage::Block*
261 OopStorage::Block::block_for_ptr(const OopStorage* owner, const oop* ptr) {
262 assert(CanUseSafeFetchN(), "precondition");
263 STATIC_ASSERT(_data_pos == 0);
264 // Const-ness of ptr is not related to const-ness of containing block.
265 // Blocks are allocated section-aligned, so get the containing section.
266 oop* section_start = align_down(const_cast<oop*>(ptr), block_alignment);
267 // Start with a guess that the containing section is the last section,
268 // so the block starts section_count-1 sections earlier.
269 oop* section = section_start - (section_size * (section_count - 1));
270 // Walk up through the potential block start positions, looking for
271 // the owner in the expected location. If we're below the actual block
272 // start position, the value at the owner position will be some oop
273 // (possibly NULL), which can never match the owner.
274 intptr_t owner_addr = reinterpret_cast<intptr_t>(owner);
275 for (unsigned i = 0; i < section_count; ++i, section += section_size) {
276 Block* candidate = reinterpret_cast<Block*>(section);
277 intptr_t* candidate_owner_addr
278 = reinterpret_cast<intptr_t*>(&candidate->_owner);
279 if (SafeFetchN(candidate_owner_addr, 0) == owner_addr) {
280 return candidate;
281 }
282 }
283 return NULL;
284 }
285
286 //////////////////////////////////////////////////////////////////////////////
287 // Allocation
288 //
289 // Allocation involves the _allocate_list, which contains a subset of the
290 // blocks owned by a storage object. This is a doubly-linked list, linked
291 // through dedicated fields in the blocks. Full blocks are removed from this
292 // list, though they are still present in the _active_list. Empty blocks are
293 // kept at the end of the _allocate_list, to make it easy for empty block
294 // deletion to find them.
295 //
296 // allocate(), and delete_empty_blocks_concurrent() lock the
297 // _allocate_mutex while performing any list modifications.
298 //
299 // allocate() and release() update a block's _allocated_bitmask using CAS
300 // loops. This prevents loss of updates even though release() performs
301 // its updates without any locking.
302 //
303 // allocate() obtains the entry from the first block in the _allocate_list,
304 // and updates that block's _allocated_bitmask to indicate the entry is in
305 // use. If this makes the block full (all entries in use), the block is
306 // removed from the _allocate_list so it won't be considered by future
307 // allocations until some entries in it are released.
308 //
309 // release() is performed lock-free. release() first looks up the block for
310 // the entry, using address alignment to find the enclosing block (thereby
311 // avoiding iteration over the _active_list). Once the block has been
312 // determined, its _allocated_bitmask needs to be updated, and its position in
313 // the _allocate_list may need to be updated. There are two cases:
314 //
315 // (a) If the block is neither full nor would become empty with the release of
316 // the entry, only its _allocated_bitmask needs to be updated. But if the CAS
317 // update fails, the applicable case may change for the retry.
318 //
319 // (b) Otherwise, the _allocate_list also needs to be modified. This requires
320 // locking the _allocate_mutex. To keep the release() operation lock-free,
321 // rather than updating the _allocate_list itself, it instead performs a
322 // lock-free push of the block onto the _deferred_updates list. Entries on
323 // that list are processed by allocate() and delete_empty_blocks_XXX(), while
324 // they already hold the necessary lock. That processing makes the block's
325 // list state consistent with its current _allocated_bitmask. The block is
326 // added to the _allocate_list if not already present and the bitmask is not
327 // full. The block is moved to the end of the _allocated_list if the bitmask
328 // is empty, for ease of empty block deletion processing.
329
330 oop* OopStorage::allocate() {
331 MutexLockerEx ml(_allocate_mutex, Mutex::_no_safepoint_check_flag);
332 // Do some deferred update processing every time we allocate.
333 // Continue processing deferred updates if _allocate_list is empty,
334 // in the hope that we'll get a block from that, rather than
335 // allocating a new block.
336 while (reduce_deferred_updates() && (_allocate_list.head() == NULL)) {}
337
338 // Use the first block in _allocate_list for the allocation.
339 Block* block = _allocate_list.head();
340 if (block == NULL) {
341 // No available blocks; make a new one, and add to storage.
342 {
343 MutexUnlockerEx mul(_allocate_mutex, Mutex::_no_safepoint_check_flag);
344 block = Block::new_block(this);
345 }
346 if (block == NULL) {
347 while (_allocate_list.head() == NULL) {
348 if (!reduce_deferred_updates()) {
349 // Failed to make new block, no other thread made a block
350 // available while the mutex was released, and didn't get
351 // one from a deferred update either, so return failure.
352 log_info(oopstorage, ref)("%s: failed allocation", name());
353 return NULL;
354 }
355 }
356 } else {
357 // Add new block to storage.
358 log_info(oopstorage, blocks)("%s: new block " PTR_FORMAT, name(), p2i(block));
359
360 // Add to end of _allocate_list. The mutex release allowed
361 // other threads to add blocks to the _allocate_list. We prefer
362 // to allocate from non-empty blocks, to allow empty blocks to
363 // be deleted.
364 _allocate_list.push_back(*block);
365 // Add to front of _active_list, and then record as the head
366 // block, for concurrent iteration protocol.
367 _active_list.push_front(*block);
368 ++_block_count;
369 // Ensure all setup of block is complete before making it visible.
370 OrderAccess::release_store(&_active_head, block);
371 }
372 block = _allocate_list.head();
373 }
374 // Allocate from first block.
375 assert(block != NULL, "invariant");
376 assert(!block->is_full(), "invariant");
377 if (block->is_empty()) {
378 // Transitioning from empty to not empty.
379 log_debug(oopstorage, blocks)("%s: block not empty " PTR_FORMAT, name(), p2i(block));
380 }
381 oop* result = block->allocate();
382 assert(result != NULL, "allocation failed");
383 assert(!block->is_empty(), "postcondition");
384 Atomic::inc(&_allocation_count); // release updates outside lock.
385 if (block->is_full()) {
386 // Transitioning from not full to full.
387 // Remove full blocks from consideration by future allocates.
388 log_debug(oopstorage, blocks)("%s: block full " PTR_FORMAT, name(), p2i(block));
389 _allocate_list.unlink(*block);
390 }
391 log_info(oopstorage, ref)("%s: allocated " PTR_FORMAT, name(), p2i(result));
392 return result;
393 }
394
395 OopStorage::Block* OopStorage::find_block_or_null(const oop* ptr) const {
396 assert(ptr != NULL, "precondition");
397 return Block::block_for_ptr(this, ptr);
398 }
399
400 static void log_release_transitions(uintx releasing,
401 uintx old_allocated,
402 const OopStorage* owner,
403 const void* block) {
404 ResourceMark rm;
405 Log(oopstorage, blocks) log;
406 LogStream ls(log.debug());
407 if (is_full_bitmask(old_allocated)) {
408 ls.print_cr("%s: block not full " PTR_FORMAT, owner->name(), p2i(block));
409 }
410 if (releasing == old_allocated) {
411 ls.print_cr("%s: block empty " PTR_FORMAT, owner->name(), p2i(block));
412 }
413 }
414
415 void OopStorage::Block::release_entries(uintx releasing, Block* volatile* deferred_list) {
416 assert(releasing != 0, "preconditon");
417 // Prevent empty block deletion when transitioning to empty.
418 Atomic::inc(&_release_refcount);
419
420 // Atomically update allocated bitmask.
421 uintx old_allocated = _allocated_bitmask;
422 while (true) {
423 assert((releasing & ~old_allocated) == 0, "releasing unallocated entries");
424 uintx new_value = old_allocated ^ releasing;
425 uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, old_allocated);
426 if (fetched == old_allocated) break; // Successful update.
427 old_allocated = fetched; // Retry with updated bitmask.
428 }
429
430 // Now that the bitmask has been updated, if we have a state transition
431 // (updated bitmask is empty or old bitmask was full), atomically push
432 // this block onto the deferred updates list. Some future call to
433 // reduce_deferred_updates will make any needed changes related to this
434 // block and _allocate_list. This deferral avoids list updates and the
435 // associated locking here.
436 if ((releasing == old_allocated) || is_full_bitmask(old_allocated)) {
437 // Log transitions. Both transitions are possible in a single update.
438 if (log_is_enabled(Debug, oopstorage, blocks)) {
439 log_release_transitions(releasing, old_allocated, _owner, this);
440 }
441 // Attempt to claim responsibility for adding this block to the deferred
442 // list, by setting the link to non-NULL by self-looping. If this fails,
443 // then someone else has made such a claim and the deferred update has not
444 // yet been processed and will include our change, so we don't need to do
445 // anything further.
446 if (Atomic::replace_if_null(this, &_deferred_updates_next)) {
447 // Successfully claimed. Push, with self-loop for end-of-list.
448 Block* head = *deferred_list;
449 while (true) {
450 _deferred_updates_next = (head == NULL) ? this : head;
451 Block* fetched = Atomic::cmpxchg(this, deferred_list, head);
452 if (fetched == head) break; // Successful update.
453 head = fetched; // Retry with updated head.
454 }
455 log_debug(oopstorage, blocks)("%s: deferred update " PTR_FORMAT,
456 _owner->name(), p2i(this));
457 }
458 }
459 // Release hold on empty block deletion.
460 Atomic::dec(&_release_refcount);
461 }
462
463 // Process one available deferred update. Returns true if one was processed.
464 bool OopStorage::reduce_deferred_updates() {
465 assert_locked_or_safepoint(_allocate_mutex);
466 // Atomically pop a block off the list, if any available.
467 // No ABA issue because this is only called by one thread at a time.
468 // The atomicity is wrto pushes by release().
469 Block* block = OrderAccess::load_acquire(&_deferred_updates);
470 while (true) {
471 if (block == NULL) return false;
472 // Try atomic pop of block from list.
473 Block* tail = block->deferred_updates_next();
474 if (block == tail) tail = NULL; // Handle self-loop end marker.
475 Block* fetched = Atomic::cmpxchg(tail, &_deferred_updates, block);
476 if (fetched == block) break; // Update successful.
477 block = fetched; // Retry with updated block.
478 }
479 block->set_deferred_updates_next(NULL); // Clear tail after updating head.
480 // Ensure bitmask read after pop is complete, including clearing tail, for
481 // ordering with release(). Without this, we may be processing a stale
482 // bitmask state here while blocking a release() operation from recording
483 // the deferred update needed for its bitmask change.
484 OrderAccess::storeload();
485 // Process popped block.
486 uintx allocated = block->allocated_bitmask();
487
488 // Make membership in list consistent with bitmask state.
489 if ((_allocate_list.ctail() != NULL) &&
490 ((_allocate_list.ctail() == block) ||
491 (_allocate_list.next(*block) != NULL))) {
492 // Block is in the allocate list.
493 assert(!is_full_bitmask(allocated), "invariant");
494 } else if (!is_full_bitmask(allocated)) {
495 // Block is not in the allocate list, but now should be.
496 _allocate_list.push_front(*block);
497 } // Else block is full and not in list, which is correct.
498
499 // Move empty block to end of list, for possible deletion.
500 if (is_empty_bitmask(allocated)) {
501 _allocate_list.unlink(*block);
502 _allocate_list.push_back(*block);
503 }
504
505 log_debug(oopstorage, blocks)("%s: processed deferred update " PTR_FORMAT,
506 name(), p2i(block));
507 return true; // Processed one pending update.
508 }
509
510 inline void check_release_entry(const oop* entry) {
511 assert(entry != NULL, "Releasing NULL");
512 assert(*entry == NULL, "Releasing uncleared entry: " PTR_FORMAT, p2i(entry));
513 }
514
515 void OopStorage::release(const oop* ptr) {
516 check_release_entry(ptr);
517 Block* block = find_block_or_null(ptr);
518 assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptr));
519 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptr));
520 block->release_entries(block->bitmask_for_entry(ptr), &_deferred_updates);
521 Atomic::dec(&_allocation_count);
522 }
523
524 void OopStorage::release(const oop* const* ptrs, size_t size) {
525 size_t i = 0;
526 while (i < size) {
527 check_release_entry(ptrs[i]);
528 Block* block = find_block_or_null(ptrs[i]);
529 assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptrs[i]));
530 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptrs[i]));
531 size_t count = 0;
532 uintx releasing = 0;
533 for ( ; i < size; ++i) {
534 const oop* entry = ptrs[i];
535 check_release_entry(entry);
536 // If entry not in block, finish block and resume outer loop with entry.
537 if (!block->contains(entry)) break;
538 // Add entry to releasing bitmap.
539 log_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(entry));
540 uintx entry_bitmask = block->bitmask_for_entry(entry);
541 assert((releasing & entry_bitmask) == 0,
542 "Duplicate entry: " PTR_FORMAT, p2i(entry));
543 releasing |= entry_bitmask;
544 ++count;
545 }
546 // Release the contiguous entries that are in block.
547 block->release_entries(releasing, &_deferred_updates);
548 Atomic::sub(count, &_allocation_count);
549 }
550 }
551
552 const char* dup_name(const char* name) {
553 char* dup = NEW_C_HEAP_ARRAY(char, strlen(name) + 1, mtGC);
554 strcpy(dup, name);
555 return dup;
556 }
557
558 OopStorage::OopStorage(const char* name,
559 Mutex* allocate_mutex,
560 Mutex* active_mutex) :
561 _name(dup_name(name)),
562 _active_list(&Block::get_active_entry),
563 _allocate_list(&Block::get_allocate_entry),
564 _active_head(NULL),
565 _deferred_updates(NULL),
566 _allocate_mutex(allocate_mutex),
567 _active_mutex(active_mutex),
568 _allocation_count(0),
569 _block_count(0),
570 _concurrent_iteration_active(false)
571 {
572 assert(_active_mutex->rank() < _allocate_mutex->rank(),
573 "%s: active_mutex must have lower rank than allocate_mutex", _name);
574 assert(_active_mutex->_safepoint_check_required != Mutex::_safepoint_check_always,
575 "%s: active mutex requires safepoint check", _name);
576 assert(_allocate_mutex->_safepoint_check_required != Mutex::_safepoint_check_always,
577 "%s: allocate mutex requires safepoint check", _name);
578 }
579
580 void OopStorage::delete_empty_block(const Block& block) {
581 assert(block.is_empty(), "discarding non-empty block");
582 log_info(oopstorage, blocks)("%s: delete empty block " PTR_FORMAT, name(), p2i(&block));
583 Block::delete_block(block);
584 }
585
586 OopStorage::~OopStorage() {
587 Block* block;
588 while ((block = _deferred_updates) != NULL) {
589 _deferred_updates = block->deferred_updates_next();
590 block->set_deferred_updates_next(NULL);
591 }
592 while ((block = _allocate_list.head()) != NULL) {
593 _allocate_list.unlink(*block);
594 }
595 while ((block = _active_list.head()) != NULL) {
596 _active_list.unlink(*block);
597 Block::delete_block(*block);
598 }
599 FREE_C_HEAP_ARRAY(char, _name);
600 }
601
602 void OopStorage::delete_empty_blocks_safepoint() {
603 assert_at_safepoint();
604 // Process any pending release updates, which may make more empty
605 // blocks available for deletion.
606 while (reduce_deferred_updates()) {}
607 // Don't interfere with a concurrent iteration.
608 if (_concurrent_iteration_active) return;
609 // Delete empty (and otherwise deletable) blocks from end of _allocate_list.
610 for (const Block* block = _allocate_list.ctail();
611 (block != NULL) && block->is_deletable();
612 block = _allocate_list.ctail()) {
613 _active_list.unlink(*block);
614 _allocate_list.unlink(*block);
615 delete_empty_block(*block);
616 --_block_count;
617 }
618 // Update _active_head, in case current value was in deleted set.
619 _active_head = _active_list.head();
620 }
621
622 void OopStorage::delete_empty_blocks_concurrent() {
623 MutexLockerEx ml(_allocate_mutex, Mutex::_no_safepoint_check_flag);
624 // Other threads could be adding to the empty block count while we
625 // release the mutex across the block deletions. Set an upper bound
626 // on how many blocks we'll try to release, so other threads can't
627 // cause an unbounded stay in this function.
628 size_t limit = _block_count;
629
630 for (size_t i = 0; i < limit; ++i) {
631 // Additional updates might become available while we dropped the
632 // lock. But limit number processed to limit lock duration.
633 reduce_deferred_updates();
634
635 const Block* block = _allocate_list.ctail();
636 if ((block == NULL) || !block->is_deletable()) {
637 // No block to delete, so done. There could be more pending
638 // deferred updates that could give us more work to do; deal with
639 // that in some later call, to limit lock duration here.
640 return;
641 }
642
643 {
644 MutexLockerEx aml(_active_mutex, Mutex::_no_safepoint_check_flag);
645 // Don't interfere with a concurrent iteration.
646 if (_concurrent_iteration_active) return;
647 // Remove block from _active_list, updating head if needed.
648 _active_list.unlink(*block);
649 --_block_count;
650 if (block == _active_head) {
651 _active_head = _active_list.head();
652 }
653 }
654 // Remove block from _allocate_list and delete it.
655 _allocate_list.unlink(*block);
656 // Release mutex while deleting block.
657 MutexUnlockerEx ul(_allocate_mutex, Mutex::_no_safepoint_check_flag);
658 delete_empty_block(*block);
659 }
660 }
661
662 OopStorage::EntryStatus OopStorage::allocation_status(const oop* ptr) const {
663 const Block* block = find_block_or_null(ptr);
664 if (block != NULL) {
665 // Verify block is a real block. For now, simple linear search.
666 // Do something more clever if this is a performance bottleneck.
667 MutexLockerEx ml(_allocate_mutex, Mutex::_no_safepoint_check_flag);
668 for (const Block* check_block = _active_list.chead();
669 check_block != NULL;
670 check_block = _active_list.next(*check_block)) {
671 if (check_block == block) {
672 if ((block->allocated_bitmask() & block->bitmask_for_entry(ptr)) != 0) {
673 return ALLOCATED_ENTRY;
674 } else {
675 return UNALLOCATED_ENTRY;
676 }
677 }
678 }
679 }
680 return INVALID_ENTRY;
681 }
682
683 size_t OopStorage::allocation_count() const {
684 return _allocation_count;
685 }
686
687 size_t OopStorage::block_count() const {
688 return _block_count;
689 }
690
691 size_t OopStorage::total_memory_usage() const {
692 size_t total_size = sizeof(OopStorage);
693 total_size += strlen(name()) + 1;
694 total_size += block_count() * Block::allocation_size();
695 return total_size;
696 }
697
698 // Parallel iteration support
699 #if INCLUDE_ALL_GCS
700
701 static char* not_started_marker_dummy = NULL;
702 static void* const not_started_marker = ¬_started_marker_dummy;
703
704 OopStorage::BasicParState::BasicParState(OopStorage* storage, bool concurrent) :
705 _storage(storage),
706 _next_block(not_started_marker),
707 _concurrent(concurrent)
708 {
709 update_iteration_state(true);
710 }
711
712 OopStorage::BasicParState::~BasicParState() {
713 update_iteration_state(false);
714 }
715
716 void OopStorage::BasicParState::update_iteration_state(bool value) {
717 if (_concurrent) {
718 MutexLockerEx ml(_storage->_active_mutex, Mutex::_no_safepoint_check_flag);
719 assert(_storage->_concurrent_iteration_active != value, "precondition");
720 _storage->_concurrent_iteration_active = value;
721 }
722 }
723
724 void OopStorage::BasicParState::ensure_iteration_started() {
725 if (!_concurrent) {
726 assert_at_safepoint();
727 }
728 assert(!_concurrent || _storage->_concurrent_iteration_active, "invariant");
729 // Ensure _next_block is not the not_started_marker, setting it to
730 // the _active_head to start the iteration if necessary.
731 if (OrderAccess::load_acquire(&_next_block) == not_started_marker) {
732 Atomic::cmpxchg(_storage->_active_head, &_next_block, not_started_marker);
733 }
734 assert(_next_block != not_started_marker, "postcondition");
735 }
736
737 OopStorage::Block* OopStorage::BasicParState::claim_next_block() {
738 assert(_next_block != not_started_marker, "Iteration not started");
739 void* next = _next_block;
740 while (next != NULL) {
741 void* new_next = _storage->_active_list.next(*static_cast<Block*>(next));
742 void* fetched = Atomic::cmpxchg(new_next, &_next_block, next);
743 if (fetched == next) break; // Claimed.
744 next = fetched;
745 }
746 return static_cast<Block*>(next);
747 }
748
749 #endif // INCLUDE_ALL_GCS
750
751 const char* OopStorage::name() const { return _name; }
752
753 #ifndef PRODUCT
754
755 void OopStorage::print_on(outputStream* st) const {
756 size_t allocations = _allocation_count;
757 size_t blocks = _block_count;
758
759 double data_size = section_size * section_count;
760 double alloc_percentage = percent_of((double)allocations, blocks * data_size);
761
762 st->print("%s: " SIZE_FORMAT " entries in " SIZE_FORMAT " blocks (%.F%%), " SIZE_FORMAT " bytes",
763 name(), allocations, blocks, alloc_percentage, total_memory_usage());
764 if (_concurrent_iteration_active) {
765 st->print(", concurrent iteration active");
766 }
767 }
768
769 #endif // !PRODUCT