/*

 * Copyright (c) 2001, 2015, 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

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 */

#ifndef SHARE_VM_GC_G1_BUFFERINGOOPCLOSURE_HPP

#define SHARE_VM_GC_G1_BUFFERINGOOPCLOSURE_HPP

#include "memory/iterator.hpp"

#include "oops/oopsHierarchy.hpp"

#include "runtime/os.hpp"

#include "utilities/debug.hpp"

// A BufferingOops closure tries to separate out the cost of finding roots

// from the cost of applying closures to them.  It maintains an array of

// ref-containing locations.  Until the array is full, applying the closure

// to an oop* merely records that location in the array.  Since this

// closure app cost is small, an elapsed timer can approximately attribute

// all of this cost to the cost of finding the roots.  When the array fills

// up, the wrapped closure is applied to all elements, keeping track of

// this elapsed time of this process, and leaving the array empty.

// The caller must be sure to call "done" to process any unprocessed

// buffered entries.

class BufferingOopClosure: public OopClosure {

  friend class BufferingOopClosureTest;

protected:

  static const size_t BufferLength = 1024;

  // We need to know if the buffered addresses contain oops or narrowOops.

  // We can't tag the addresses the way StarTask does, because we need to

  // be able to handle unaligned addresses coming from oops embedded in code.

  //

  // The addresses for the full-sized oops are filled in from the bottom,

  // while the addresses for the narrowOops are filled in from the top.

  OopOrNarrowOopStar  _buffer[BufferLength];

  OopOrNarrowOopStar* _oop_top;

  OopOrNarrowOopStar* _narrowOop_bottom;

  OopClosure* _oc;

  double      _closure_app_seconds;

  bool is_buffer_empty() {

    return _oop_top == _buffer && _narrowOop_bottom == (_buffer + BufferLength - 1);

  }

  bool is_buffer_full() {

    return _narrowOop_bottom < _oop_top;

  }

  // Process addresses containing full-sized oops.

  void process_oops() {

    for (OopOrNarrowOopStar* curr = _buffer; curr < _oop_top; ++curr) {

      _oc->do_oop((oop*)(*curr));

    }

    _oop_top = _buffer;

  }

  // Process addresses containing narrow oops.

  void process_narrowOops() {

    for (OopOrNarrowOopStar* curr = _buffer + BufferLength - 1; curr > _narrowOop_bottom; --curr) {

      _oc->do_oop((narrowOop*)(*curr));

    }

    _narrowOop_bottom = _buffer + BufferLength - 1;

  }

  // Apply the closure to all oops and clear the buffer.

  // Accumulate the time it took.

  void process_buffer() {

    double start = os::elapsedTime();

    process_oops();

    process_narrowOops();

    _closure_app_seconds += (os::elapsedTime() - start);

  }

  void process_buffer_if_full() {

    if (is_buffer_full()) {

      process_buffer();

    }

  }

  void add_narrowOop(narrowOop* p) {

    assert(!is_buffer_full(), "Buffer should not be full");

    *_narrowOop_bottom = (OopOrNarrowOopStar)p;

    _narrowOop_bottom--;

  }

  void add_oop(oop* p) {

    assert(!is_buffer_full(), "Buffer should not be full");

    *_oop_top = (OopOrNarrowOopStar)p;

    _oop_top++;

  }

public:

  virtual void do_oop(narrowOop* p) {

    process_buffer_if_full();

    add_narrowOop(p);

  }

  virtual void do_oop(oop* p)       {

    process_buffer_if_full();

    add_oop(p);

  }

  void done() {

    if (!is_buffer_empty()) {

      process_buffer();

    }

  }

  double closure_app_seconds() {

    return _closure_app_seconds;

  }

  BufferingOopClosure(OopClosure *oc) :

    _oc(oc),

    _oop_top(_buffer),

    _narrowOop_bottom(_buffer + BufferLength - 1),

    _closure_app_seconds(0.0) { }

};

#endif // SHARE_VM_GC_G1_BUFFERINGOOPCLOSURE_HPP