/*

 * 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

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 */

#ifndef SHARE_GC_SHARED_SATBMARKQUEUE_HPP

#define SHARE_GC_SHARED_SATBMARKQUEUE_HPP

#include "gc/shared/ptrQueue.hpp"

#include "memory/allocation.hpp"

#include "memory/padded.hpp"

class Thread;

class Monitor;

class SATBMarkQueueSet;

// Base class for processing the contents of a SATB buffer.

class SATBBufferClosure : public StackObj {

protected:

  ~SATBBufferClosure() { }

public:

  // Process the SATB entries in the designated buffer range.

  virtual void do_buffer(void** buffer, size_t size) = 0;

};

// A PtrQueue whose elements are (possibly stale) pointers to object heads.

class SATBMarkQueue: public PtrQueue {

  friend class SATBMarkQueueSet;

private:

  // Filter out unwanted entries from the buffer.

  inline void filter();

  // Removes entries from the buffer that are no longer needed.

  template<typename Filter>

  inline void apply_filter(Filter filter_out);

protected:

  virtual void handle_completed_buffer();

public:

  SATBMarkQueue(SATBMarkQueueSet* qset);

  // Process queue entries and free resources.

  void flush();

  inline SATBMarkQueueSet* satb_qset() const;

  // Apply cl to the active part of the buffer.

  // Prerequisite: Must be at a safepoint.

  void apply_closure_and_empty(SATBBufferClosure* cl);

#ifndef PRODUCT

  // Helpful for debugging

  void print(const char* name);

#endif // PRODUCT

  // Compiler support.

  static ByteSize byte_offset_of_index() {

    return PtrQueue::byte_offset_of_index<SATBMarkQueue>();

  }

  using PtrQueue::byte_width_of_index;

  static ByteSize byte_offset_of_buf() {

    return PtrQueue::byte_offset_of_buf<SATBMarkQueue>();

  }

  using PtrQueue::byte_width_of_buf;

  static ByteSize byte_offset_of_active() {

    return PtrQueue::byte_offset_of_active<SATBMarkQueue>();

  }

  using PtrQueue::byte_width_of_active;

};

class SATBMarkQueueSet: public PtrQueueSet {

  DEFINE_PAD_MINUS_SIZE(1, DEFAULT_CACHE_LINE_SIZE, 0);

  PaddedEnd<BufferNode::Stack> _list;

  volatile size_t _count_and_process_flag;

  // These are rarely (if ever) changed, so same cache line as count.

  size_t _process_completed_buffers_threshold;

  size_t _buffer_enqueue_threshold;

  DEFINE_PAD_MINUS_SIZE(2, DEFAULT_CACHE_LINE_SIZE, 3 * sizeof(size_t));

  BufferNode* get_completed_buffer();

  void abandon_completed_buffers();

#ifdef ASSERT

  void dump_active_states(bool expected_active);

  void verify_active_states(bool expected_active);

#endif // ASSERT

protected:

  ~SATBMarkQueueSet();

  template<typename Filter>

  void apply_filter(Filter filter, SATBMarkQueue* queue) {

    queue->apply_filter(filter);

  }

public:

  virtual SATBMarkQueue& satb_queue_for_thread(Thread* const t) const = 0;

  // Apply "set_active(active)" to all SATB queues in the set. It should be

  // called only with the world stopped. The method will assert that the

  // SATB queues of all threads it visits, as well as the SATB queue

  // set itself, has an active value same as expected_active.

  void set_active_all_threads(bool active, bool expected_active);

  size_t buffer_enqueue_threshold() const { return _buffer_enqueue_threshold; }

  virtual void filter(SATBMarkQueue* queue) = 0;

  // If there exists some completed buffer, pop and process it, and

  // return true.  Otherwise return false.  Processing a buffer

  // consists of applying the closure to the active range of the

  // buffer; the leading entries may be excluded due to filtering.

  bool apply_closure_to_completed_buffer(SATBBufferClosure* cl);

  virtual void enqueue_completed_buffer(BufferNode* node);

  // The number of buffers in the list.  Racy and not updated atomically

  // with the set of completed buffers.

  size_t completed_buffers_num() const {

    return _count_and_process_flag >> 1;

  }

  // Return true if completed buffers should be processed.

  bool process_completed_buffers() const {

    return (_count_and_process_flag & 1) != 0;

  }

#ifndef PRODUCT

  // Helpful for debugging

  void print_all(const char* msg);

#endif // PRODUCT

  // If a marking is being abandoned, reset any unprocessed log buffers.

  void abandon_partial_marking();

};

inline SATBMarkQueueSet* SATBMarkQueue::satb_qset() const {

  return static_cast<SATBMarkQueueSet*>(qset());

}

inline void SATBMarkQueue::filter() {

  satb_qset()->filter(this);

}

// Removes entries from the buffer that are no longer needed, as

// determined by filter. If e is a void* entry in the buffer,

// filter_out(e) must be a valid expression whose value is convertible

// to bool. Entries are removed (filtered out) if the result is true,

// retained if false.

template<typename Filter>

inline void SATBMarkQueue::apply_filter(Filter filter_out) {

  void** buf = this->_buf;

  if (buf == NULL) {

    // nothing to do

    return;

  }

  // Two-fingered compaction toward the end.

  void** src = &buf[this->index()];

  void** dst = &buf[this->capacity()];

  assert(src <= dst, "invariant");

  for ( ; src < dst; ++src) {

    // Search low to high for an entry to keep.

    void* entry = *src;

    if (!filter_out(entry)) {

      // Found keeper.  Search high to low for an entry to discard.

      while (src < --dst) {

        if (filter_out(*dst)) {

          *dst = entry;         // Replace discard with keeper.

          break;

        }

      }

      // If discard search failed (src == dst), the outer loop will also end.

    }

  }

  // dst points to the lowest retained entry, or the end of the buffer

  // if all the entries were filtered out.

  this->set_index(dst - buf);

}

#endif // SHARE_GC_SHARED_SATBMARKQUEUE_HPP