/*

 * Copyright (c) 2018, 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 "memory/resourceArea.hpp"

#include "runtime/atomic.hpp"

#include "runtime/handles.inline.hpp"

#include "runtime/mutex.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/orderAccess.inline.hpp"

#include "runtime/safepoint.hpp"

#include "runtime/stubRoutines.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::BlockEntry::BlockEntry() : _prev(NULL), _next(NULL) {}

OopStorage::BlockEntry::~BlockEntry() {

  assert(_prev == NULL, "deleting attached block");

  assert(_next == NULL, "deleting attached block");

}

OopStorage::BlockList::BlockList(const BlockEntry& (*get_entry)(const Block& block)) :

  _head(NULL), _tail(NULL), _get_entry(get_entry)

{}

OopStorage::BlockList::~BlockList() {

  // ~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::BlockList::push_front(const Block& block) {

  const Block* old = _head;

  if (old == NULL) {

    assert(_tail == NULL, "invariant");

    _head = _tail = █

  } else {

    _get_entry(block)._next = old;

    _get_entry(*old)._prev = █

    _head = █

  }

}

void OopStorage::BlockList::push_back(const Block& block) {

  const Block* old = _tail;

  if (old == NULL) {

    assert(_head == NULL, "invariant");

    _head = _tail = █

  } else {

    _get_entry(*old)._next = █

    _get_entry(block)._prev = old;

    _tail = █

  }

}

void OopStorage::BlockList::unlink(const Block& block) {

  const BlockEntry& block_entry = _get_entry(block);

  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");

    _get_entry(*next_blk)._prev = NULL;

    _head = next_blk;

  } else if (next_blk == NULL) {

    assert(_tail == &block, "invariant");

    _get_entry(*prev_blk)._next = NULL;

    _tail = prev_blk;

  } else {

    _get_entry(*next_blk)._prev = prev_blk;

    _get_entry(*prev_blk)._next = next_blk;

  }

}

// 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(owner),

  _memory(memory),

  _active_entry(),

  _allocate_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<uintx volatile&>(_allocated_bitmask) = 0;

  const_cast<OopStorage* volatile&>(_owner) = NULL;

}

const OopStorage::BlockEntry& OopStorage::Block::get_active_entry(const Block& block) {

  return block._active_entry;

}

const OopStorage::BlockEntry& OopStorage::Block::get_allocate_entry(const Block& block) {

  return block._allocate_entry;

}

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));

}

// A block is deletable if

// (1) It is empty.

// (2) There is not a release() operation currently operating on it.

// (3) It is not in the deferred updates list.

// The order of tests is important for proper interaction between release()

// and concurrent deletion.

bool OopStorage::Block::is_deletable() const {

  return (OrderAccess::load_acquire(&_allocated_bitmask) == 0) &&

         (OrderAccess::load_acquire(&_release_refcount) == 0) &&

         (OrderAccess::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)));

}

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<unsigned>(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_list.  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<oop*>(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<intptr_t>(owner);

  for (unsigned i = 0; i < section_count; ++i, section += section_size) {

    Block* candidate = reinterpret_cast<Block*>(section);

    intptr_t* candidate_owner_addr

      = reinterpret_cast<intptr_t*>(&candidate->_owner);

    if (SafeFetchN(candidate_owner_addr, 0) == owner_addr) {

      return candidate;

    }

  }

  return NULL;

}

//////////////////////////////////////////////////////////////////////////////

// Allocation

//

// Allocation involves the _allocate_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_list.  Empty blocks are

// kept at the end of the _allocate_list, to make it easy for empty block

// deletion to find them.

//

// allocate(), and delete_empty_blocks_concurrent() lock the

// _allocate_mutex while performing any list 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 _allocate_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 _allocate_list so it won't be considered by future

// allocations until some entries in it are released.

//

// release() is performed lock-free. release() first looks up the block for

// the entry, using address alignment to find the enclosing block (thereby

// avoiding iteration over the _active_list).  Once the block has been

// determined, its _allocated_bitmask needs to be updated, and its position in

// the _allocate_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 _allocate_list also needs to be modified.  This requires

// locking the _allocate_mutex.  To keep the release() operation lock-free,

// rather than updating the _allocate_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_XXX(), 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 _allocate_list if not already present and the bitmask is not

// full.  The block is moved to the end of the _allocated_list if the bitmask

// is empty, for ease of empty block deletion processing.

oop* OopStorage::allocate() {

  MutexLockerEx ml(_allocate_mutex, Mutex::_no_safepoint_check_flag);

  // Do some deferred update processing every time we allocate.

  // Continue processing deferred updates if _allocate_list is empty,

  // in the hope that we'll get a block from that, rather than

  // allocating a new block.

  while (reduce_deferred_updates() && (_allocate_list.head() == NULL)) {}

  // Use the first block in _allocate_list for the allocation.

  Block* block = _allocate_list.head();

  if (block == NULL) {

    // No available blocks; make a new one, and add to storage.

    {

      MutexUnlockerEx mul(_allocate_mutex, Mutex::_no_safepoint_check_flag);

      block = Block::new_block(this);

    }

    if (block == NULL) {

      while (_allocate_list.head() == NULL) {

        if (!reduce_deferred_updates()) {

          // Failed to make new block, no other thread made a block

          // available while the mutex was released, and didn't get

          // one from a deferred update either, so return failure.

          log_info(oopstorage, ref)("%s: failed allocation", name());

          return NULL;

        }

      }

    } else {

      // Add new block to storage.

      log_info(oopstorage, blocks)("%s: new block " PTR_FORMAT, name(), p2i(block));

      // Add to end of _allocate_list.  The mutex release allowed

      // other threads to add blocks to the _allocate_list.  We prefer

      // to allocate from non-empty blocks, to allow empty blocks to

      // be deleted.

      _allocate_list.push_back(*block);

      // Add to front of _active_list, and then record as the head

      // block, for concurrent iteration protocol.

      _active_list.push_front(*block);

      ++_block_count;

      // Ensure all setup of block is complete before making it visible.

      OrderAccess::release_store(&_active_head, block);

    }

    block = _allocate_list.head();

  }

  // Allocate from first block.

  assert(block != NULL, "invariant");

  assert(!block->is_full(), "invariant");

  if (block->is_empty()) {

    // Transitioning from empty to not empty.

    log_debug(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_debug(oopstorage, blocks)("%s: block full " PTR_FORMAT, name(), p2i(block));

    _allocate_list.unlink(*block);

  }

  log_info(oopstorage, ref)("%s: allocated " PTR_FORMAT, name(), p2i(result));

  return result;

}

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) {

  ResourceMark rm;

  Log(oopstorage, blocks) log;

  LogStream ls(log.debug());

  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, Block* volatile* deferred_list) {

  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 _allocate_list.  This deferral avoids 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.

    if (log_is_enabled(Debug, oopstorage, blocks)) {

      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 = *deferred_list;

      while (true) {

        _deferred_updates_next = (head == NULL) ? this : head;

        Block* fetched = Atomic::cmpxchg(this, deferred_list, head);

        if (fetched == head) break; // Successful update.

        head = fetched;             // Retry with updated head.

      }

      log_debug(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_locked_or_safepoint(_allocate_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 = OrderAccess::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::storeload();

  // Process popped block.

  uintx allocated = block->allocated_bitmask();

  // Make membership in list consistent with bitmask state.

  if ((_allocate_list.ctail() != NULL) &&

      ((_allocate_list.ctail() == block) ||

       (_allocate_list.next(*block) != NULL))) {

    // Block is in the allocate list.

    assert(!is_full_bitmask(allocated), "invariant");

  } else if (!is_full_bitmask(allocated)) {

    // Block is not in the allocate list, but now should be.

    _allocate_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)) {

    _allocate_list.unlink(*block);

    _allocate_list.push_back(*block);

  }

  log_debug(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_info(oopstorage, ref)("%s: released " PTR_FORMAT, name(), p2i(ptr));

  block->release_entries(block->bitmask_for_entry(ptr), &_deferred_updates);

  Atomic::dec(&_allocation_count);

}