/*

 * Copyright (c) 2001, 2012, 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_implementation/g1/ptrQueue.hpp"

#include "memory/allocation.hpp"

#include "memory/allocation.inline.hpp"

#include "runtime/mutex.hpp"

#include "runtime/mutexLocker.hpp"

#include "runtime/thread.inline.hpp"

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

  _qset(qset), _buf(NULL), _index(0), _active(active),

  _perm(perm), _lock(NULL)

{}

void PtrQueue::flush() {

  if (!_perm && _buf != NULL) {

    if (_index == _sz) {

      // No work to do.

      qset()->deallocate_buffer(_buf);

    } else {

      // We must NULL out the unused entries, then enqueue.

      for (size_t i = 0; i < _index; i += oopSize) {

        _buf[byte_index_to_index((int)i)] = NULL;

      }

      qset()->enqueue_complete_buffer(_buf);

    }

    _buf = NULL;

    _index = 0;

  }

}

void PtrQueue::enqueue_known_active(void* ptr) {

  assert(0 <= _index && _index <= _sz, "Invariant.");

  assert(_index == 0 || _buf != NULL, "invariant");

  while (_index == 0) {

    handle_zero_index();

  }

  assert(_index > 0, "postcondition");

  _index -= oopSize;

  _buf[byte_index_to_index((int)_index)] = ptr;

  assert(0 <= _index && _index <= _sz, "Invariant.");

}

void PtrQueue::locking_enqueue_completed_buffer(void** buf) {

  assert(_lock->owned_by_self(), "Required.");

  // We have to unlock _lock (which may be Shared_DirtyCardQ_lock) before

  // we acquire DirtyCardQ_CBL_mon inside enqeue_complete_buffer as they

  // have the same rank and we may get the "possible deadlock" message

  _lock->unlock();

  qset()->enqueue_complete_buffer(buf);

  // We must relock only because the caller will unlock, for the normal

  // case.

  _lock->lock_without_safepoint_check();

}

PtrQueueSet::PtrQueueSet(bool notify_when_complete) :

  _max_completed_queue(0),

  _cbl_mon(NULL), _fl_lock(NULL),

  _notify_when_complete(notify_when_complete),

  _sz(0),

  _completed_buffers_head(NULL),

  _completed_buffers_tail(NULL),

  _n_completed_buffers(0),

  _process_completed_threshold(0), _process_completed(false),

  _buf_free_list(NULL), _buf_free_list_sz(0)

{

  _fl_owner = this;

}

void** PtrQueueSet::allocate_buffer() {

  assert(_sz > 0, "Didn't set a buffer size.");

  MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);

  if (_fl_owner->_buf_free_list != NULL) {

    void** res = BufferNode::make_buffer_from_node(_fl_owner->_buf_free_list);

    _fl_owner->_buf_free_list = _fl_owner->_buf_free_list->next();

    _fl_owner->_buf_free_list_sz--;

    return res;

  } else {

    // Allocate space for the BufferNode in front of the buffer.

    char *b =  NEW_C_HEAP_ARRAY(char, _sz + BufferNode::aligned_size(), mtGC);

    return BufferNode::make_buffer_from_block(b);

  }

}

void PtrQueueSet::deallocate_buffer(void** buf) {

  assert(_sz > 0, "Didn't set a buffer size.");

  MutexLockerEx x(_fl_owner->_fl_lock, Mutex::_no_safepoint_check_flag);

  BufferNode *node = BufferNode::make_node_from_buffer(buf);

  node->set_next(_fl_owner->_buf_free_list);

  _fl_owner->_buf_free_list = node;

  _fl_owner->_buf_free_list_sz++;

}

void PtrQueueSet::reduce_free_list() {

  assert(_fl_owner == this, "Free list reduction is allowed only for the owner");

  // For now we'll adopt the strategy of deleting half.

  MutexLockerEx x(_fl_lock, Mutex::_no_safepoint_check_flag);

  size_t n = _buf_free_list_sz / 2;

  while (n > 0) {

    assert(_buf_free_list != NULL, "_buf_free_list_sz must be wrong.");

    void* b = BufferNode::make_block_from_node(_buf_free_list);

    _buf_free_list = _buf_free_list->next();

    FREE_C_HEAP_ARRAY(char, b, mtGC);

    _buf_free_list_sz --;

    n--;

  }

}

void PtrQueue::handle_zero_index() {

  assert(_index == 0, "Precondition.");

  // This thread records the full buffer and allocates a new one (while

  // holding the lock if there is one).

  if (_buf != NULL) {

    if (!should_enqueue_buffer()) {

      assert(_index > 0, "the buffer can only be re-used if it's not full");

      return;

    }

    if (_lock) {

      assert(_lock->owned_by_self(), "Required.");

      // The current PtrQ may be the shared dirty card queue and

      // may be being manipulated by more than one worker thread

      // during a pause. Since the enqueuing of the completed

      // buffer unlocks the Shared_DirtyCardQ_lock more than one

      // worker thread can 'race' on reading the shared queue attributes

      // (_buf and _index) and multiple threads can call into this

      // routine for the same buffer. This will cause the completed

      // buffer to be added to the CBL multiple times.

      // We "claim" the current buffer by caching value of _buf in

      // a local and clearing the field while holding _lock. When

      // _lock is released (while enqueueing the completed buffer)

      // the thread that acquires _lock will skip this code,

      // preventing the subsequent the multiple enqueue, and

      // install a newly allocated buffer below.

      void** buf = _buf;   // local pointer to completed buffer

      _buf = NULL;         // clear shared _buf field

      locking_enqueue_completed_buffer(buf);  // enqueue completed buffer

      // While the current thread was enqueuing the buffer another thread

      // may have a allocated a new buffer and inserted it into this pointer

      // queue. If that happens then we just return so that the current

      // thread doesn't overwrite the buffer allocated by the other thread

      // and potentially losing some dirtied cards.

      if (_buf != NULL) return;

    } else {

      if (qset()->process_or_enqueue_complete_buffer(_buf)) {

        // Recycle the buffer. No allocation.

        _sz = qset()->buffer_size();

        _index = _sz;

        return;

      }

    }

  }

  // Reallocate the buffer

  _buf = qset()->allocate_buffer();

  _sz = qset()->buffer_size();

  _index = _sz;

  assert(0 <= _index && _index <= _sz, "Invariant.");

}

bool PtrQueueSet::process_or_enqueue_complete_buffer(void** buf) {

  if (Thread::current()->is_Java_thread()) {

    // We don't lock. It is fine to be epsilon-precise here.

    if (_max_completed_queue == 0 || _max_completed_queue > 0 &&

        _n_completed_buffers >= _max_completed_queue + _completed_queue_padding) {

      bool b = mut_process_buffer(buf);

      if (b) {

        // True here means that the buffer hasn't been deallocated and the caller may reuse it.

        return true;

      }

    }

  }

  // The buffer will be enqueued. The caller will have to get a new one.

  enqueue_complete_buffer(buf);

  return false;

}

void PtrQueueSet::enqueue_complete_buffer(void** buf, size_t index) {

  MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

  BufferNode* cbn = BufferNode::new_from_buffer(buf);

  cbn->set_index(index);

  if (_completed_buffers_tail == NULL) {

    assert(_completed_buffers_head == NULL, "Well-formedness");

    _completed_buffers_head = cbn;

    _completed_buffers_tail = cbn;

  } else {

    _completed_buffers_tail->set_next(cbn);

    _completed_buffers_tail = cbn;

  }

  _n_completed_buffers++;

  if (!_process_completed && _process_completed_threshold >= 0 &&

      _n_completed_buffers >= _process_completed_threshold) {

    _process_completed = true;

    if (_notify_when_complete)

      _cbl_mon->notify();

  }

  debug_only(assert_completed_buffer_list_len_correct_locked());

}

int PtrQueueSet::completed_buffers_list_length() {

  int n = 0;

  BufferNode* cbn = _completed_buffers_head;

  while (cbn != NULL) {

    n++;

    cbn = cbn->next();

  }

  return n;

}

void PtrQueueSet::assert_completed_buffer_list_len_correct() {

  MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

  assert_completed_buffer_list_len_correct_locked();

}

void PtrQueueSet::assert_completed_buffer_list_len_correct_locked() {

  guarantee(completed_buffers_list_length() ==  _n_completed_buffers,

            "Completed buffer length is wrong.");

}

void PtrQueueSet::set_buffer_size(size_t sz) {

  assert(_sz == 0 && sz > 0, "Should be called only once.");

  _sz = sz * oopSize;

}

// Merge lists of buffers. Notify the processing threads.

// The source queue is emptied as a result. The queues

// must share the monitor.

void PtrQueueSet::merge_bufferlists(PtrQueueSet *src) {

  assert(_cbl_mon == src->_cbl_mon, "Should share the same lock");

  MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

  if (_completed_buffers_tail == NULL) {

    assert(_completed_buffers_head == NULL, "Well-formedness");

    _completed_buffers_head = src->_completed_buffers_head;

    _completed_buffers_tail = src->_completed_buffers_tail;

  } else {

    assert(_completed_buffers_head != NULL, "Well formedness");

    if (src->_completed_buffers_head != NULL) {

      _completed_buffers_tail->set_next(src->_completed_buffers_head);

      _completed_buffers_tail = src->_completed_buffers_tail;

    }

  }

  _n_completed_buffers += src->_n_completed_buffers;

  src->_n_completed_buffers = 0;

  src->_completed_buffers_head = NULL;

  src->_completed_buffers_tail = NULL;

  assert(_completed_buffers_head == NULL && _completed_buffers_tail == NULL ||

         _completed_buffers_head != NULL && _completed_buffers_tail != NULL,

         "Sanity");

}

void PtrQueueSet::notify_if_necessary() {

  MutexLockerEx x(_cbl_mon, Mutex::_no_safepoint_check_flag);

  if (_n_completed_buffers >= _process_completed_threshold || _max_completed_queue == 0) {

    _process_completed = true;

    if (_notify_when_complete)

      _cbl_mon->notify();

  }

}