/* * Copyright (c) 2018, 2019, Oracle and/or its affiliates. All rights reserved. * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. * * This code is free software; you can redistribute it and/or modify it * under the terms of the GNU General Public License version 2 only, as * published by the Free Software Foundation. * * This code is distributed in the hope that it will be useful, but WITHOUT * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License * version 2 for more details (a copy is included in the LICENSE file that * accompanied this code). * * You should have received a copy of the GNU General Public License version * 2 along with this work; if not, write to the Free Software Foundation, * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. * * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA * or visit www.oracle.com if you need additional information or have any * questions. * */ #include "precompiled.hpp" #include "gc/shared/oopStorage.inline.hpp" #include "gc/shared/oopStorageParState.inline.hpp" #include "logging/log.hpp" #include "logging/logStream.hpp" #include "memory/allocation.inline.hpp" #include "runtime/atomic.hpp" #include "runtime/globals.hpp" #include "runtime/handles.inline.hpp" #include "runtime/interfaceSupport.inline.hpp" #include "runtime/mutex.hpp" #include "runtime/mutexLocker.hpp" #include "runtime/orderAccess.hpp" #include "runtime/os.hpp" #include "runtime/safepoint.hpp" #include "runtime/stubRoutines.hpp" #include "runtime/thread.hpp" #include "utilities/align.hpp" #include "utilities/count_trailing_zeros.hpp" #include "utilities/debug.hpp" #include "utilities/globalDefinitions.hpp" #include "utilities/macros.hpp" #include "utilities/ostream.hpp" OopStorage::AllocationListEntry::AllocationListEntry() : _prev(NULL), _next(NULL) {} OopStorage::AllocationListEntry::~AllocationListEntry() { assert(_prev == NULL, "deleting attached block"); assert(_next == NULL, "deleting attached block"); } OopStorage::AllocationList::AllocationList() : _head(NULL), _tail(NULL) {} OopStorage::AllocationList::~AllocationList() { // ~OopStorage() empties its lists before destroying them. assert(_head == NULL, "deleting non-empty block list"); assert(_tail == NULL, "deleting non-empty block list"); } void OopStorage::AllocationList::push_front(const Block& block) { const Block* old = _head; if (old == NULL) { assert(_tail == NULL, "invariant"); _head = _tail = █ } else { block.allocation_list_entry()._next = old; old->allocation_list_entry()._prev = █ _head = █ } } void OopStorage::AllocationList::push_back(const Block& block) { const Block* old = _tail; if (old == NULL) { assert(_head == NULL, "invariant"); _head = _tail = █ } else { old->allocation_list_entry()._next = █ block.allocation_list_entry()._prev = old; _tail = █ } } void OopStorage::AllocationList::unlink(const Block& block) { const AllocationListEntry& block_entry = block.allocation_list_entry(); const Block* prev_blk = block_entry._prev; const Block* next_blk = block_entry._next; block_entry._prev = NULL; block_entry._next = NULL; if ((prev_blk == NULL) && (next_blk == NULL)) { assert(_head == &block, "invariant"); assert(_tail == &block, "invariant"); _head = _tail = NULL; } else if (prev_blk == NULL) { assert(_head == &block, "invariant"); next_blk->allocation_list_entry()._prev = NULL; _head = next_blk; } else if (next_blk == NULL) { assert(_tail == &block, "invariant"); prev_blk->allocation_list_entry()._next = NULL; _tail = prev_blk; } else { next_blk->allocation_list_entry()._prev = prev_blk; prev_blk->allocation_list_entry()._next = next_blk; } } OopStorage::ActiveArray::ActiveArray(size_t size) : _size(size), _block_count(0), _refcount(0) {} OopStorage::ActiveArray::~ActiveArray() { assert(_refcount == 0, "precondition"); } OopStorage::ActiveArray* OopStorage::ActiveArray::create(size_t size, AllocFailType alloc_fail) { size_t size_in_bytes = blocks_offset() + sizeof(Block*) * size; void* mem = NEW_C_HEAP_ARRAY3(char, size_in_bytes, mtGC, CURRENT_PC, alloc_fail); if (mem == NULL) return NULL; return new (mem) ActiveArray(size); } void OopStorage::ActiveArray::destroy(ActiveArray* ba) { ba->~ActiveArray(); FREE_C_HEAP_ARRAY(char, ba); } size_t OopStorage::ActiveArray::size() const { return _size; } size_t OopStorage::ActiveArray::block_count() const { return _block_count; } size_t OopStorage::ActiveArray::block_count_acquire() const { return Atomic::load_acquire(&_block_count); } void OopStorage::ActiveArray::increment_refcount() const { int new_value = Atomic::add(&_refcount, 1); assert(new_value >= 1, "negative refcount %d", new_value - 1); } bool OopStorage::ActiveArray::decrement_refcount() const { int new_value = Atomic::sub(&_refcount, 1); assert(new_value >= 0, "negative refcount %d", new_value); return new_value == 0; } bool OopStorage::ActiveArray::push(Block* block) { size_t index = _block_count; if (index < _size) { block->set_active_index(index); *block_ptr(index) = block; // Use a release_store to ensure all the setup is complete before // making the block visible. Atomic::release_store(&_block_count, index + 1); return true; } else { return false; } } void OopStorage::ActiveArray::remove(Block* block) { assert(_block_count > 0, "array is empty"); size_t index = block->active_index(); assert(*block_ptr(index) == block, "block not present"); size_t last_index = _block_count - 1; Block* last_block = *block_ptr(last_index); last_block->set_active_index(index); *block_ptr(index) = last_block; _block_count = last_index; } void OopStorage::ActiveArray::copy_from(const ActiveArray* from) { assert(_block_count == 0, "array must be empty"); size_t count = from->_block_count; assert(count <= _size, "precondition"); Block* const* from_ptr = from->block_ptr(0); Block** to_ptr = block_ptr(0); for (size_t i = 0; i < count; ++i) { Block* block = *from_ptr++; assert(block->active_index() == i, "invariant"); *to_ptr++ = block; } _block_count = count; } // Blocks start with an array of BitsPerWord oop entries. That array // is divided into conceptual BytesPerWord sections of BitsPerByte // entries. Blocks are allocated aligned on section boundaries, for // the convenience of mapping from an entry to the containing block; // see block_for_ptr(). Aligning on section boundary rather than on // the full _data wastes a lot less space, but makes for a bit more // work in block_for_ptr(). const unsigned section_size = BitsPerByte; const unsigned section_count = BytesPerWord; const unsigned block_alignment = sizeof(oop) * section_size; OopStorage::Block::Block(const OopStorage* owner, void* memory) : _data(), _allocated_bitmask(0), _owner_address(reinterpret_cast(owner)), _memory(memory), _active_index(0), _allocation_list_entry(), _deferred_updates_next(NULL), _release_refcount(0) { STATIC_ASSERT(_data_pos == 0); STATIC_ASSERT(section_size * section_count == ARRAY_SIZE(_data)); assert(offset_of(Block, _data) == _data_pos, "invariant"); assert(owner != NULL, "NULL owner"); assert(is_aligned(this, block_alignment), "misaligned block"); } OopStorage::Block::~Block() { assert(_release_refcount == 0, "deleting block while releasing"); assert(_deferred_updates_next == NULL, "deleting block with deferred update"); // Clear fields used by block_for_ptr and entry validation, which // might help catch bugs. Volatile to prevent dead-store elimination. const_cast(_allocated_bitmask) = 0; const_cast(_owner_address) = 0; } size_t OopStorage::Block::allocation_size() { // _data must be first member, so aligning Block aligns _data. STATIC_ASSERT(_data_pos == 0); return sizeof(Block) + block_alignment - sizeof(void*); } size_t OopStorage::Block::allocation_alignment_shift() { return exact_log2(block_alignment); } inline bool is_full_bitmask(uintx bitmask) { return ~bitmask == 0; } inline bool is_empty_bitmask(uintx bitmask) { return bitmask == 0; } bool OopStorage::Block::is_full() const { return is_full_bitmask(allocated_bitmask()); } bool OopStorage::Block::is_empty() const { return is_empty_bitmask(allocated_bitmask()); } uintx OopStorage::Block::bitmask_for_entry(const oop* ptr) const { return bitmask_for_index(get_index(ptr)); } // An empty block is not yet deletable if either: // (1) There is a release() operation currently operating on it. // (2) It is in the deferred updates list. // For interaction with release(), these must follow the empty check, // and the order of these checks is important. bool OopStorage::Block::is_safe_to_delete() const { assert(is_empty(), "precondition"); OrderAccess::loadload(); return (Atomic::load_acquire(&_release_refcount) == 0) && (Atomic::load_acquire(&_deferred_updates_next) == NULL); } OopStorage::Block* OopStorage::Block::deferred_updates_next() const { return _deferred_updates_next; } void OopStorage::Block::set_deferred_updates_next(Block* block) { _deferred_updates_next = block; } bool OopStorage::Block::contains(const oop* ptr) const { const oop* base = get_pointer(0); return (base <= ptr) && (ptr < (base + ARRAY_SIZE(_data))); } size_t OopStorage::Block::active_index() const { return _active_index; } void OopStorage::Block::set_active_index(size_t index) { _active_index = index; } size_t OopStorage::Block::active_index_safe(const Block* block) { STATIC_ASSERT(sizeof(intptr_t) == sizeof(block->_active_index)); assert(CanUseSafeFetchN(), "precondition"); return SafeFetchN((intptr_t*)&block->_active_index, 0); } unsigned OopStorage::Block::get_index(const oop* ptr) const { assert(contains(ptr), PTR_FORMAT " not in block " PTR_FORMAT, p2i(ptr), p2i(this)); return static_cast(ptr - get_pointer(0)); } oop* OopStorage::Block::allocate() { // Use CAS loop because release may change bitmask outside of lock. uintx allocated = allocated_bitmask(); while (true) { assert(!is_full_bitmask(allocated), "attempt to allocate from full block"); unsigned index = count_trailing_zeros(~allocated); uintx new_value = allocated | bitmask_for_index(index); uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, allocated); if (fetched == allocated) { return get_pointer(index); // CAS succeeded; return entry for index. } allocated = fetched; // CAS failed; retry with latest value. } } OopStorage::Block* OopStorage::Block::new_block(const OopStorage* owner) { // _data must be first member: aligning block => aligning _data. STATIC_ASSERT(_data_pos == 0); size_t size_needed = allocation_size(); void* memory = NEW_C_HEAP_ARRAY_RETURN_NULL(char, size_needed, mtGC); if (memory == NULL) { return NULL; } void* block_mem = align_up(memory, block_alignment); assert(sizeof(Block) + pointer_delta(block_mem, memory, 1) <= size_needed, "allocated insufficient space for aligned block"); return ::new (block_mem) Block(owner, memory); } void OopStorage::Block::delete_block(const Block& block) { void* memory = block._memory; block.Block::~Block(); FREE_C_HEAP_ARRAY(char, memory); } // This can return a false positive if ptr is not contained by some // block. For some uses, it is a precondition that ptr is valid, // e.g. contained in some block in owner's _active_array. Other uses // require additional validation of the result. OopStorage::Block* OopStorage::Block::block_for_ptr(const OopStorage* owner, const oop* ptr) { assert(CanUseSafeFetchN(), "precondition"); STATIC_ASSERT(_data_pos == 0); // Const-ness of ptr is not related to const-ness of containing block. // Blocks are allocated section-aligned, so get the containing section. oop* section_start = align_down(const_cast(ptr), block_alignment); // Start with a guess that the containing section is the last section, // so the block starts section_count-1 sections earlier. oop* section = section_start - (section_size * (section_count - 1)); // Walk up through the potential block start positions, looking for // the owner in the expected location. If we're below the actual block // start position, the value at the owner position will be some oop // (possibly NULL), which can never match the owner. intptr_t owner_addr = reinterpret_cast(owner); for (unsigned i = 0; i < section_count; ++i, section += section_size) { Block* candidate = reinterpret_cast(section); if (SafeFetchN(&candidate->_owner_address, 0) == owner_addr) { return candidate; } } return NULL; } ////////////////////////////////////////////////////////////////////////////// // Allocation // // Allocation involves the _allocation_list, which contains a subset of the // blocks owned by a storage object. This is a doubly-linked list, linked // through dedicated fields in the blocks. Full blocks are removed from this // list, though they are still present in the _active_array. Empty blocks are // kept at the end of the _allocation_list, to make it easy for empty block // deletion to find them. // // allocate(), and delete_empty_blocks() lock the // _allocation_mutex while performing any list and array modifications. // // allocate() and release() update a block's _allocated_bitmask using CAS // loops. This prevents loss of updates even though release() performs // its updates without any locking. // // allocate() obtains the entry from the first block in the _allocation_list, // and updates that block's _allocated_bitmask to indicate the entry is in // use. If this makes the block full (all entries in use), the block is // removed from the _allocation_list so it won't be considered by future // allocations until some entries in it are released. // // release() is performed lock-free. (Note: This means it can't notify the // service thread of pending cleanup work. It must be lock-free because // it is called in all kinds of contexts where even quite low ranked locks // may be held.) release() first looks up the block for // the entry, using address alignment to find the enclosing block (thereby // avoiding iteration over the _active_array). Once the block has been // determined, its _allocated_bitmask needs to be updated, and its position in // the _allocation_list may need to be updated. There are two cases: // // (a) If the block is neither full nor would become empty with the release of // the entry, only its _allocated_bitmask needs to be updated. But if the CAS // update fails, the applicable case may change for the retry. // // (b) Otherwise, the _allocation_list also needs to be modified. This requires // locking the _allocation_mutex. To keep the release() operation lock-free, // rather than updating the _allocation_list itself, it instead performs a // lock-free push of the block onto the _deferred_updates list. Entries on // that list are processed by allocate() and delete_empty_blocks(), while // they already hold the necessary lock. That processing makes the block's // list state consistent with its current _allocated_bitmask. The block is // added to the _allocation_list if not already present and the bitmask is not // full. The block is moved to the end of the _allocation_list if the bitmask // is empty, for ease of empty block deletion processing. oop* OopStorage::allocate() { MutexLocker ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); Block* block = block_for_allocation(); if (block == NULL) return NULL; // Block allocation failed. assert(!block->is_full(), "invariant"); if (block->is_empty()) { // Transitioning from empty to not empty. log_trace(oopstorage, blocks)("%s: block not empty " PTR_FORMAT, name(), p2i(block)); } oop* result = block->allocate(); assert(result != NULL, "allocation failed"); assert(!block->is_empty(), "postcondition"); Atomic::inc(&_allocation_count); // release updates outside lock. if (block->is_full()) { // Transitioning from not full to full. // Remove full blocks from consideration by future allocates. log_trace(oopstorage, blocks)("%s: block full " PTR_FORMAT, name(), p2i(block)); _allocation_list.unlink(*block); } log_trace(oopstorage, ref)("%s: allocated " PTR_FORMAT, name(), p2i(result)); return result; } bool OopStorage::try_add_block() { assert_lock_strong(_allocation_mutex); Block* block; { MutexUnlocker ul(_allocation_mutex, Mutex::_no_safepoint_check_flag); block = Block::new_block(this); } if (block == NULL) return false; // Add new block to the _active_array, growing if needed. if (!_active_array->push(block)) { if (expand_active_array()) { guarantee(_active_array->push(block), "push failed after expansion"); } else { log_debug(oopstorage, blocks)("%s: failed active array expand", name()); Block::delete_block(*block); return false; } } // Add to end of _allocation_list. The mutex release allowed other // threads to add blocks to the _allocation_list. We prefer to // allocate from non-empty blocks, to allow empty blocks to be // deleted. But we don't bother notifying about the empty block // because we're (probably) about to allocate an entry from it. _allocation_list.push_back(*block); log_debug(oopstorage, blocks)("%s: new block " PTR_FORMAT, name(), p2i(block)); return true; } OopStorage::Block* OopStorage::block_for_allocation() { assert_lock_strong(_allocation_mutex); while (true) { // Use the first block in _allocation_list for the allocation. Block* block = _allocation_list.head(); if (block != NULL) { return block; } else if (reduce_deferred_updates()) { // Might have added a block to the _allocation_list, so retry. } else if (try_add_block()) { // Successfully added a new block to the list, so retry. assert(_allocation_list.chead() != NULL, "invariant"); } else if (_allocation_list.chead() != NULL) { // Trying to add a block failed, but some other thread added to the // list while we'd dropped the lock over the new block allocation. } else if (!reduce_deferred_updates()) { // Once more before failure. // Attempt to add a block failed, no other thread added a block, // and no deferred updated added a block, then allocation failed. log_info(oopstorage, blocks)("%s: failed block allocation", name()); return NULL; } } } // Create a new, larger, active array with the same content as the // current array, and then replace, relinquishing the old array. // Return true if the array was successfully expanded, false to // indicate allocation failure. bool OopStorage::expand_active_array() { assert_lock_strong(_allocation_mutex); ActiveArray* old_array = _active_array; size_t new_size = 2 * old_array->size(); log_debug(oopstorage, blocks)("%s: expand active array " SIZE_FORMAT, name(), new_size); ActiveArray* new_array = ActiveArray::create(new_size, AllocFailStrategy::RETURN_NULL); if (new_array == NULL) return false; new_array->copy_from(old_array); replace_active_array(new_array); relinquish_block_array(old_array); return true; } // Make new_array the _active_array. Increments new_array's refcount // to account for the new reference. The assignment is atomic wrto // obtain_active_array; once this function returns, it is safe for the // caller to relinquish the old array. void OopStorage::replace_active_array(ActiveArray* new_array) { // Caller has the old array that is the current value of _active_array. // Update new_array refcount to account for the new reference. new_array->increment_refcount(); // Install new_array, ensuring its initialization is complete first. Atomic::release_store(&_active_array, new_array); // Wait for any readers that could read the old array from _active_array. // Can't use GlobalCounter here, because this is called from allocate(), // which may be called in the scope of a GlobalCounter critical section // when inserting a StringTable entry. _protect_active.synchronize(); // All obtain critical sections that could see the old array have // completed, having incremented the refcount of the old array. The // caller can now safely relinquish the old array. } // Atomically (wrto replace_active_array) get the active array and // increment its refcount. This provides safe access to the array, // even if an allocate operation expands and replaces the value of // _active_array. The caller must relinquish the array when done // using it. OopStorage::ActiveArray* OopStorage::obtain_active_array() const { SingleWriterSynchronizer::CriticalSection cs(&_protect_active); ActiveArray* result = Atomic::load_acquire(&_active_array); result->increment_refcount(); return result; } // Decrement refcount of array and destroy if refcount is zero. void OopStorage::relinquish_block_array(ActiveArray* array) const { if (array->decrement_refcount()) { assert(array != _active_array, "invariant"); ActiveArray::destroy(array); } } class OopStorage::WithActiveArray : public StackObj { const OopStorage* _storage; ActiveArray* _active_array; public: WithActiveArray(const OopStorage* storage) : _storage(storage), _active_array(storage->obtain_active_array()) {} ~WithActiveArray() { _storage->relinquish_block_array(_active_array); } ActiveArray& active_array() const { return *_active_array; } }; OopStorage::Block* OopStorage::find_block_or_null(const oop* ptr) const { assert(ptr != NULL, "precondition"); return Block::block_for_ptr(this, ptr); } static void log_release_transitions(uintx releasing, uintx old_allocated, const OopStorage* owner, const void* block) { LogTarget(Trace, oopstorage, blocks) lt; if (lt.is_enabled()) { LogStream ls(lt); if (is_full_bitmask(old_allocated)) { ls.print_cr("%s: block not full " PTR_FORMAT, owner->name(), p2i(block)); } if (releasing == old_allocated) { ls.print_cr("%s: block empty " PTR_FORMAT, owner->name(), p2i(block)); } } } void OopStorage::Block::release_entries(uintx releasing, OopStorage* owner) { assert(releasing != 0, "preconditon"); // Prevent empty block deletion when transitioning to empty. Atomic::inc(&_release_refcount); // Atomically update allocated bitmask. uintx old_allocated = _allocated_bitmask; while (true) { assert((releasing & ~old_allocated) == 0, "releasing unallocated entries"); uintx new_value = old_allocated ^ releasing; uintx fetched = Atomic::cmpxchg(new_value, &_allocated_bitmask, old_allocated); if (fetched == old_allocated) break; // Successful update. old_allocated = fetched; // Retry with updated bitmask. } // Now that the bitmask has been updated, if we have a state transition // (updated bitmask is empty or old bitmask was full), atomically push // this block onto the deferred updates list. Some future call to // reduce_deferred_updates will make any needed changes related to this // block and _allocation_list. This deferral avoids _allocation_list // updates and the associated locking here. if ((releasing == old_allocated) || is_full_bitmask(old_allocated)) { // Log transitions. Both transitions are possible in a single update. log_release_transitions(releasing, old_allocated, owner, this); // Attempt to claim responsibility for adding this block to the deferred // list, by setting the link to non-NULL by self-looping. If this fails, // then someone else has made such a claim and the deferred update has not // yet been processed and will include our change, so we don't need to do // anything further. if (Atomic::replace_if_null(this, &_deferred_updates_next)) { // Successfully claimed. Push, with self-loop for end-of-list. Block* head = owner->_deferred_updates; while (true) { _deferred_updates_next = (head == NULL) ? this : head; Block* fetched = Atomic::cmpxchg(this, &owner->_deferred_updates, head); if (fetched == head) break; // Successful update. head = fetched; // Retry with updated head. } // Only request cleanup for to-empty transitions, not for from-full. // There isn't any rush to process from-full transitions. Allocation // will reduce deferrals before allocating new blocks, so may process // some. And the service thread will drain the entire deferred list // if there are any pending to-empty transitions. if (releasing == old_allocated) { owner->record_needs_cleanup(); } log_trace(oopstorage, blocks)("%s: deferred update " PTR_FORMAT, owner->name(), p2i(this)); } } // Release hold on empty block deletion. Atomic::dec(&_release_refcount); } // Process one available deferred update. Returns true if one was processed. bool OopStorage::reduce_deferred_updates() { assert_lock_strong(_allocation_mutex); // Atomically pop a block off the list, if any available. // No ABA issue because this is only called by one thread at a time. // The atomicity is wrto pushes by release(). Block* block = Atomic::load_acquire(&_deferred_updates); while (true) { if (block == NULL) return false; // Try atomic pop of block from list. Block* tail = block->deferred_updates_next(); if (block == tail) tail = NULL; // Handle self-loop end marker. Block* fetched = Atomic::cmpxchg(tail, &_deferred_updates, block); if (fetched == block) break; // Update successful. block = fetched; // Retry with updated block. } block->set_deferred_updates_next(NULL); // Clear tail after updating head. // Ensure bitmask read after pop is complete, including clearing tail, for // ordering with release(). Without this, we may be processing a stale // bitmask state here while blocking a release() operation from recording // the deferred update needed for its bitmask change. OrderAccess::fence(); // Process popped block. uintx allocated = block->allocated_bitmask(); // Make membership in list consistent with bitmask state. if ((_allocation_list.ctail() != NULL) && ((_allocation_list.ctail() == block) || (_allocation_list.next(*block) != NULL))) { // Block is in the _allocation_list. assert(!is_full_bitmask(allocated), "invariant"); } else if (!is_full_bitmask(allocated)) { // Block is not in the _allocation_list, but now should be. _allocation_list.push_front(*block); } // Else block is full and not in list, which is correct. // Move empty block to end of list, for possible deletion. if (is_empty_bitmask(allocated)) { _allocation_list.unlink(*block); _allocation_list.push_back(*block); } log_trace(oopstorage, blocks)("%s: processed deferred update " PTR_FORMAT, name(), p2i(block)); return true; // Processed one pending update. } inline void check_release_entry(const oop* entry) { assert(entry != NULL, "Releasing NULL"); assert(*entry == NULL, "Releasing uncleared entry: " PTR_FORMAT, p2i(entry)); } void OopStorage::release(const oop* ptr) { check_release_entry(ptr); Block* block = find_block_or_null(ptr); assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptr)); log_trace(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptr)); block->release_entries(block->bitmask_for_entry(ptr), this); Atomic::dec(&_allocation_count); } void OopStorage::release(const oop* const* ptrs, size_t size) { size_t i = 0; while (i < size) { check_release_entry(ptrs[i]); Block* block = find_block_or_null(ptrs[i]); assert(block != NULL, "%s: invalid release " PTR_FORMAT, name(), p2i(ptrs[i])); log_trace(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptrs[i])); size_t count = 0; uintx releasing = 0; for ( ; i < size; ++i) { const oop* entry = ptrs[i]; check_release_entry(entry); // If entry not in block, finish block and resume outer loop with entry. if (!block->contains(entry)) break; // Add entry to releasing bitmap. log_trace(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(entry)); uintx entry_bitmask = block->bitmask_for_entry(entry); assert((releasing & entry_bitmask) == 0, "Duplicate entry: " PTR_FORMAT, p2i(entry)); releasing |= entry_bitmask; ++count; } // Release the contiguous entries that are in block. block->release_entries(releasing, this); Atomic::sub(&_allocation_count, count); } } const size_t initial_active_array_size = 8; OopStorage::OopStorage(const char* name, Mutex* allocation_mutex, Mutex* active_mutex) : _name(os::strdup(name)), _active_array(ActiveArray::create(initial_active_array_size)), _allocation_list(), _deferred_updates(NULL), _allocation_mutex(allocation_mutex), _active_mutex(active_mutex), _allocation_count(0), _concurrent_iteration_count(0), _needs_cleanup(false) { _active_array->increment_refcount(); assert(_active_mutex->rank() < _allocation_mutex->rank(), "%s: active_mutex must have lower rank than allocation_mutex", _name); assert(Service_lock->rank() < _active_mutex->rank(), "%s: active_mutex must have higher rank than Service_lock", _name); assert(_active_mutex->_safepoint_check_required == Mutex::_safepoint_check_never, "%s: active mutex requires never safepoint check", _name); assert(_allocation_mutex->_safepoint_check_required == Mutex::_safepoint_check_never, "%s: allocation mutex requires never safepoint check", _name); } void OopStorage::delete_empty_block(const Block& block) { assert(block.is_empty(), "discarding non-empty block"); log_debug(oopstorage, blocks)("%s: delete empty block " PTR_FORMAT, name(), p2i(&block)); Block::delete_block(block); } OopStorage::~OopStorage() { Block* block; while ((block = _deferred_updates) != NULL) { _deferred_updates = block->deferred_updates_next(); block->set_deferred_updates_next(NULL); } while ((block = _allocation_list.head()) != NULL) { _allocation_list.unlink(*block); } bool unreferenced = _active_array->decrement_refcount(); assert(unreferenced, "deleting storage while _active_array is referenced"); for (size_t i = _active_array->block_count(); 0 < i; ) { block = _active_array->at(--i); Block::delete_block(*block); } ActiveArray::destroy(_active_array); os::free(const_cast(_name)); } // Managing service thread notifications. // // We don't want cleanup work to linger indefinitely, but we also don't want // to run the service thread too often. We're also very limited in what we // can do in a release operation, where cleanup work is created. // // When a release operation changes a block's state to empty, it records the // need for cleanup in both the associated storage object and in the global // request state. A safepoint cleanup task notifies the service thread when // there may be cleanup work for any storage object, based on the global // request state. But that notification is deferred if the service thread // has run recently, and we also avoid duplicate notifications. The service // thread updates the timestamp and resets the state flags on every iteration. // Global cleanup request state. static volatile bool needs_cleanup_requested = false; // Flag for avoiding duplicate notifications. static bool needs_cleanup_triggered = false; // Time after which a notification can be made. static jlong cleanup_trigger_permit_time = 0; // Minimum time since last service thread check before notification is // permitted. The value of 500ms was an arbitrary choice; frequent, but not // too frequent. const jlong cleanup_trigger_defer_period = 500 * NANOSECS_PER_MILLISEC; void OopStorage::trigger_cleanup_if_needed() { MonitorLocker ml(Service_lock, Monitor::_no_safepoint_check_flag); if (Atomic::load(&needs_cleanup_requested) && !needs_cleanup_triggered && (os::javaTimeNanos() > cleanup_trigger_permit_time)) { needs_cleanup_triggered = true; ml.notify_all(); } } bool OopStorage::has_cleanup_work_and_reset() { assert_lock_strong(Service_lock); cleanup_trigger_permit_time = os::javaTimeNanos() + cleanup_trigger_defer_period; needs_cleanup_triggered = false; // Set the request flag false and return its old value. // Needs to be atomic to avoid dropping a concurrent request. // Can't use Atomic::xchg, which may not support bool. return Atomic::cmpxchg(false, &needs_cleanup_requested, true); } // Record that cleanup is needed, without notifying the Service thread. // Used by release(), where we can't lock even Service_lock. void OopStorage::record_needs_cleanup() { // Set local flag first, else service thread could wake up and miss // the request. This order may instead (rarely) unnecessarily notify. Atomic::release_store(&_needs_cleanup, true); Atomic::release_store_fence(&needs_cleanup_requested, true); } bool OopStorage::delete_empty_blocks() { // Service thread might have oopstorage work, but not for this object. // Check for deferred updates even though that's not a service thread // trigger; since we're here, we might as well process them. if (!Atomic::load_acquire(&_needs_cleanup) && (Atomic::load_acquire(&_deferred_updates) == NULL)) { return false; } MutexLocker ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); // Clear the request before processing. Atomic::release_store_fence(&_needs_cleanup, false); // Other threads could be adding to the empty block count or the // deferred update list while we're working. Set an upper bound on // how many updates we'll process and blocks we'll try to release, // so other threads can't cause an unbounded stay in this function. // We add a bit of slop because the reduce_deferred_updates clause // can cause blocks to be double counted. If there are few blocks // and many of them are deferred and empty, we might hit the limit // and spin the caller without doing very much work. Otherwise, // we don't normally hit the limit anyway, instead running out of // work to do. size_t limit = block_count() + 10; for (size_t i = 0; i < limit; ++i) { // Process deferred updates, which might make empty blocks available. // Continue checking once deletion starts, since additional updates // might become available while we're working. if (reduce_deferred_updates()) { // Be safepoint-polite while looping. MutexUnlocker ul(_allocation_mutex, Mutex::_no_safepoint_check_flag); ThreadBlockInVM tbiv(JavaThread::current()); } else { Block* block = _allocation_list.tail(); if ((block == NULL) || !block->is_empty()) { return false; } else if (!block->is_safe_to_delete()) { // Look for other work while waiting for block to be deletable. break; } // Try to delete the block. First, try to remove from _active_array. { MutexLocker aml(_active_mutex, Mutex::_no_safepoint_check_flag); // Don't interfere with an active concurrent iteration. // Instead, give up immediately. There is more work to do, // but don't re-notify, to avoid useless spinning of the // service thread. Instead, iteration completion notifies. if (_concurrent_iteration_count > 0) return true; _active_array->remove(block); } // Remove block from _allocation_list and delete it. _allocation_list.unlink(*block); // Be safepoint-polite while deleting and looping. MutexUnlocker ul(_allocation_mutex, Mutex::_no_safepoint_check_flag); delete_empty_block(*block); ThreadBlockInVM tbiv(JavaThread::current()); } } // Exceeded work limit or can't delete last block. This will // cause the service thread to loop, giving other subtasks an // opportunity to run too. There's no need for a notification, // because we are part of the service thread (unless gtesting). record_needs_cleanup(); return true; } OopStorage::EntryStatus OopStorage::allocation_status(const oop* ptr) const { const Block* block = find_block_or_null(ptr); if (block != NULL) { // Prevent block deletion and _active_array modification. MutexLocker ml(_allocation_mutex, Mutex::_no_safepoint_check_flag); // Block could be a false positive, so get index carefully. size_t index = Block::active_index_safe(block); if ((index < _active_array->block_count()) && (block == _active_array->at(index)) && block->contains(ptr)) { if ((block->allocated_bitmask() & block->bitmask_for_entry(ptr)) != 0) { return ALLOCATED_ENTRY; } else { return UNALLOCATED_ENTRY; } } } return INVALID_ENTRY; } size_t OopStorage::allocation_count() const { return _allocation_count; } size_t OopStorage::block_count() const { WithActiveArray wab(this); // Count access is racy, but don't care. return wab.active_array().block_count(); } size_t OopStorage::total_memory_usage() const { size_t total_size = sizeof(OopStorage); total_size += strlen(name()) + 1; total_size += sizeof(ActiveArray); WithActiveArray wab(this); const ActiveArray& blocks = wab.active_array(); // Count access is racy, but don't care. total_size += blocks.block_count() * Block::allocation_size(); total_size += blocks.size() * sizeof(Block*); return total_size; } // Parallel iteration support uint OopStorage::BasicParState::default_estimated_thread_count(bool concurrent) { uint configured = concurrent ? ConcGCThreads : ParallelGCThreads; return MAX2(1u, configured); // Never estimate zero threads. } OopStorage::BasicParState::BasicParState(const OopStorage* storage, uint estimated_thread_count, bool concurrent) : _storage(storage), _active_array(_storage->obtain_active_array()), _block_count(0), // initialized properly below _next_block(0), _estimated_thread_count(estimated_thread_count), _concurrent(concurrent) { assert(estimated_thread_count > 0, "estimated thread count must be positive"); update_concurrent_iteration_count(1); // Get the block count *after* iteration state updated, so concurrent // empty block deletion is suppressed and can't reduce the count. But // ensure the count we use was written after the block with that count // was fully initialized; see ActiveArray::push. _block_count = _active_array->block_count_acquire(); } OopStorage::BasicParState::~BasicParState() { _storage->relinquish_block_array(_active_array); update_concurrent_iteration_count(-1); if (_concurrent) { // We may have deferred some cleanup work. const_cast(_storage)->record_needs_cleanup(); } } void OopStorage::BasicParState::update_concurrent_iteration_count(int value) { if (_concurrent) { MutexLocker ml(_storage->_active_mutex, Mutex::_no_safepoint_check_flag); _storage->_concurrent_iteration_count += value; assert(_storage->_concurrent_iteration_count >= 0, "invariant"); } } bool OopStorage::BasicParState::claim_next_segment(IterationData* data) { data->_processed += data->_segment_end - data->_segment_start; size_t start = Atomic::load_acquire(&_next_block); if (start >= _block_count) { return finish_iteration(data); // No more blocks available. } // Try to claim several at a time, but not *too* many. We want to // avoid deciding there are many available and selecting a large // quantity, get delayed, and then end up claiming most or all of // the remaining largish amount of work, leaving nothing for other // threads to do. But too small a step can lead to contention // over _next_block, esp. when the work per block is small. size_t max_step = 10; size_t remaining = _block_count - start; size_t step = MIN2(max_step, 1 + (remaining / _estimated_thread_count)); // Atomic::add with possible overshoot. This can perform better // than a CAS loop on some platforms when there is contention. // We can cope with the uncertainty by recomputing start/end from // the result of the add, and dealing with potential overshoot. size_t end = Atomic::add(&_next_block, step); // _next_block may have changed, so recompute start from result of add. start = end - step; // _next_block may have changed so much that end has overshot. end = MIN2(end, _block_count); // _next_block may have changed so much that even start has overshot. if (start < _block_count) { // Record claimed segment for iteration. data->_segment_start = start; data->_segment_end = end; return true; // Success. } else { // No more blocks to claim. return finish_iteration(data); } } bool OopStorage::BasicParState::finish_iteration(const IterationData* data) const { log_info(oopstorage, blocks, stats) ("Parallel iteration on %s: blocks = " SIZE_FORMAT ", processed = " SIZE_FORMAT " (%2.f%%)", _storage->name(), _block_count, data->_processed, percent_of(data->_processed, _block_count)); return false; } const char* OopStorage::name() const { return _name; } #ifndef PRODUCT void OopStorage::print_on(outputStream* st) const { size_t allocations = _allocation_count; size_t blocks = _active_array->block_count(); double data_size = section_size * section_count; double alloc_percentage = percent_of((double)allocations, blocks * data_size); st->print("%s: " SIZE_FORMAT " entries in " SIZE_FORMAT " blocks (%.F%%), " SIZE_FORMAT " bytes", name(), allocations, blocks, alloc_percentage, total_memory_usage()); if (_concurrent_iteration_count > 0) { st->print(", concurrent iteration active"); } } #endif // !PRODUCT