/*

 * Copyright (c) 2001, 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/ptrQueue.hpp"

#include "logging/log.hpp"

#include "memory/allocation.hpp"

#include "memory/allocation.inline.hpp"

#include "runtime/atomic.hpp"

#include "runtime/mutex.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/thread.inline.hpp"

#include "utilities/globalCounter.inline.hpp"

#include <new>

PtrQueue::PtrQueue(PtrQueueSet* qset, bool active) :

  _qset(qset),

  _active(active),

  _index(0),

  _capacity_in_bytes(index_to_byte_index(qset->buffer_size())),

  _buf(NULL)

{}

PtrQueue::~PtrQueue() {

  assert(_buf == NULL, "queue must be flushed before delete");

}

void PtrQueue::flush_impl() {

  if (_buf != NULL) {

    BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());

    if (is_empty()) {

      // No work to do.

      qset()->deallocate_buffer(node);

    } else {

      qset()->enqueue_completed_buffer(node);

    }

    _buf = NULL;

    set_index(0);

  }

}

void PtrQueue::enqueue_known_active(void* ptr) {

  while (_index == 0) {

    handle_zero_index();

  }

  assert(_buf != NULL, "postcondition");

  assert(index() > 0, "postcondition");

  assert(index() <= capacity(), "invariant");

  _index -= _element_size;

  _buf[index()] = ptr;

}

void PtrQueue::handle_zero_index() {

  assert(index() == 0, "precondition");

  if (_buf != NULL) {

    handle_completed_buffer();

  } else {

    allocate_buffer();

  }

}

void PtrQueue::allocate_buffer() {

  _buf = qset()->allocate_buffer();

  reset();

}

void PtrQueue::enqueue_completed_buffer() {

  assert(_buf != NULL, "precondition");

  BufferNode* node = BufferNode::make_node_from_buffer(_buf, index());

  qset()->enqueue_completed_buffer(node);

  allocate_buffer();

}

BufferNode* BufferNode::allocate(size_t size) {

  size_t byte_size = size * sizeof(void*);

  void* data = NEW_C_HEAP_ARRAY(char, buffer_offset() + byte_size, mtGC);

  return new (data) BufferNode;

}

void BufferNode::deallocate(BufferNode* node) {

  node->~BufferNode();

  FREE_C_HEAP_ARRAY(char, node);

}

BufferNode::Allocator::Allocator(const char* name, size_t buffer_size) :

  _buffer_size(buffer_size),

  _pending_list(),

  _free_list(),

  _pending_count(0),

  _free_count(0),

  _transfer_lock(false)

{

  strncpy(_name, name, sizeof(_name) - 1);

  _name[sizeof(_name) - 1] = '\0';

}

BufferNode::Allocator::~Allocator() {

  delete_list(_free_list.pop_all());

  delete_list(_pending_list.pop_all());

}

void BufferNode::Allocator::delete_list(BufferNode* list) {

  while (list != NULL) {

    BufferNode* next = list->next();

    DEBUG_ONLY(list->set_next(NULL);)

    BufferNode::deallocate(list);

    list = next;

  }

}

size_t BufferNode::Allocator::free_count() const {

  return Atomic::load(&_free_count);

}

BufferNode* BufferNode::Allocator::allocate() {

  BufferNode* node;

  {

    // Protect against ABA; see release().

    GlobalCounter::CriticalSection cs(Thread::current());

    node = _free_list.pop();

  }

  if (node == NULL) {

    node = BufferNode::allocate(_buffer_size);

  } else {

    // Decrement count after getting buffer from free list.  This, along

    // with incrementing count before adding to free list, ensures count

    // never underflows.

    size_t count = Atomic::sub(&_free_count, 1u);

    assert((count + 1) != 0, "_free_count underflow");

  }

  return node;

}

// To solve the ABA problem for lock-free stack pop, allocate does the

// pop inside a critical section, and release synchronizes on the

// critical sections before adding to the _free_list.  But we don't

// want to make every release have to do a synchronize.  Instead, we

// initially place released nodes on the _pending_list, and transfer

// them to the _free_list in batches.  Only one transfer at a time is

// permitted, with a lock bit to control access to that phase.  A

// transfer takes all the nodes from the _pending_list, synchronizes on

// the _free_list pops, and then adds the former pending nodes to the

// _free_list.  While that's happening, other threads might be adding

// other nodes to the _pending_list, to be dealt with by some later

// transfer.

void BufferNode::Allocator::release(BufferNode* node) {

  assert(node != NULL, "precondition");

  assert(node->next() == NULL, "precondition");

  // Desired minimum transfer batch size.  There is relatively little

  // importance to the specific number.  It shouldn't be too big, else

  // we're wasting space when the release rate is low.  If the release

  // rate is high, we might accumulate more than this before being

  // able to start a new transfer, but that's okay.  Also note that

  // the allocation rate and the release rate are going to be fairly

  // similar, due to how the buffers are used.

  const size_t trigger_transfer = 10;

  // Add to pending list. Update count first so no underflow in transfer.

  size_t pending_count = Atomic::add(&_pending_count, 1u);

  _pending_list.push(*node);

  if (pending_count > trigger_transfer) {

    try_transfer_pending();

  }

}

// Try to transfer nodes from _pending_list to _free_list, with a

// synchronization delay for any in-progress pops from the _free_list,

// to solve ABA there.  Return true if performed a (possibly empty)

// transfer, false if blocked from doing so by some other thread's

// in-progress transfer.

bool BufferNode::Allocator::try_transfer_pending() {

  // Attempt to claim the lock.

  if (Atomic::load(&_transfer_lock) || // Skip CAS if likely to fail.

      Atomic::cmpxchg(&_transfer_lock, false, true)) {

    return false;

  }

  // Have the lock; perform the transfer.

  // Claim all the pending nodes.

  BufferNode* first = _pending_list.pop_all();

  if (first != NULL) {

    // Prepare to add the claimed nodes, and update _pending_count.

    BufferNode* last = first;

    size_t count = 1;

    for (BufferNode* next = first->next(); next != NULL; next = next->next()) {

      last = next;

      ++count;

    }

    Atomic::sub(&_pending_count, count);

    // Wait for any in-progress pops, to avoid ABA for them.

    GlobalCounter::write_synchronize();

    // Add synchronized nodes to _free_list.

    // Update count first so no underflow in allocate().

    Atomic::add(&_free_count, count);

    _free_list.prepend(*first, *last);

    log_trace(gc, ptrqueue, freelist)

             ("Transferred %s pending to free: " SIZE_FORMAT, name(), count);

  }

  Atomic::release_store(&_transfer_lock, false);

  return true;

}

size_t BufferNode::Allocator::reduce_free_list(size_t remove_goal) {

  try_transfer_pending();

  size_t removed = 0;

  for ( ; removed < remove_goal; ++removed) {

    BufferNode* node = _free_list.pop();

    if (node == NULL) break;

    BufferNode::deallocate(node);

  }

  size_t new_count = Atomic::sub(&_free_count, removed);

  log_debug(gc, ptrqueue, freelist)

           ("Reduced %s free list by " SIZE_FORMAT " to " SIZE_FORMAT,

            name(), removed, new_count);

  return removed;

}

PtrQueueSet::PtrQueueSet(BufferNode::Allocator* allocator) :

  _allocator(allocator),

  _all_active(false)

{}

PtrQueueSet::~PtrQueueSet() {}

void** PtrQueueSet::allocate_buffer() {

  BufferNode* node = _allocator->allocate();

  return BufferNode::make_buffer_from_node(node);

}

void PtrQueueSet::deallocate_buffer(BufferNode* node) {

  _allocator->release(node);

}