/*

 * Copyright (c) 2001, 2016, 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.

 *

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 */

#ifndef SHARE_VM_GC_G1_PTRQUEUE_HPP

#define SHARE_VM_GC_G1_PTRQUEUE_HPP

#include "memory/allocation.hpp"

#include "utilities/sizes.hpp"

// There are various techniques that require threads to be able to log

// addresses.  For example, a generational write barrier might log

// the addresses of modified old-generation objects.  This type supports

// this operation.

class PtrQueueSet;

class PtrQueue VALUE_OBJ_CLASS_SPEC {

  friend class VMStructs;

  // Noncopyable - not defined.

  PtrQueue(const PtrQueue&);

  PtrQueue& operator=(const PtrQueue&);

  // The ptr queue set to which this queue belongs.

  PtrQueueSet* const _qset;

  // Whether updates should be logged.

  bool _active;

  // If true, the queue is permanent, and doesn't need to deallocate

  // its buffer in the destructor (since that obtains a lock which may not

  // be legally locked by then.

  const bool _permanent;

protected:

  // The buffer.

  void** _buf;

  // The (byte) index at which an object was last enqueued.  Starts at "_sz"

  // (indicating an empty buffer) and goes towards zero.

  size_t _index;

  // The (byte) size of the buffer.

  size_t _sz;

  // If there is a lock associated with this buffer, this is that lock.

  Mutex* _lock;

  PtrQueueSet* qset() { return _qset; }

  bool is_permanent() const { return _permanent; }

  // Process queue entries and release resources, if not permanent.

  void flush_impl();

  // Initialize this queue to contain a null buffer, and be part of the

  // given PtrQueueSet.

  PtrQueue(PtrQueueSet* qset, bool permanent = false, bool active = false);

  // Requires queue flushed or permanent.

  ~PtrQueue();

public:

  // Associate a lock with a ptr queue.

  void set_lock(Mutex* lock) { _lock = lock; }

  void reset() { if (_buf != NULL) _index = _sz; }

  void enqueue(volatile void* ptr) {

    enqueue((void*)(ptr));

  }

  // Enqueues the given "obj".

  void enqueue(void* ptr) {

    if (!_active) return;

    else enqueue_known_active(ptr);

  }

  // This method is called when we're doing the zero index handling

  // and gives a chance to the queues to do any pre-enqueueing

  // processing they might want to do on the buffer. It should return

  // true if the buffer should be enqueued, or false if enough

  // entries were cleared from it so that it can be re-used. It should

  // not return false if the buffer is still full (otherwise we can

  // get into an infinite loop).

  virtual bool should_enqueue_buffer() { return true; }

  void handle_zero_index();

  void locking_enqueue_completed_buffer(void** buf);

  void enqueue_known_active(void* ptr);

  size_t size() {

    assert(_sz >= _index, "Invariant.");

    return _buf == NULL ? 0 : _sz - _index;

  }

  bool is_empty() {

    return _buf == NULL || _sz == _index;

  }

  // Set the "active" property of the queue to "b".  An enqueue to an

  // inactive thread is a no-op.  Setting a queue to inactive resets its

  // log to the empty state.

  void set_active(bool b) {

    _active = b;

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

      _index = _sz;

    } else if (b && _buf != NULL) {

      assert(_index == _sz, "invariant: queues are empty when activated.");

    }

  }

  bool is_active() { return _active; }

  static size_t byte_index_to_index(size_t ind) {

    assert((ind % sizeof(void*)) == 0, "Invariant.");

    return ind / sizeof(void*);

  }

  // To support compiler.

protected:

  template<typename Derived>

  static ByteSize byte_offset_of_index() {

    return byte_offset_of(Derived, _index);

  }

  static ByteSize byte_width_of_index() { return in_ByteSize(sizeof(size_t)); }

  template<typename Derived>

  static ByteSize byte_offset_of_buf() {

    return byte_offset_of(Derived, _buf);

  }

  static ByteSize byte_width_of_buf() { return in_ByteSize(sizeof(void*)); }

  template<typename Derived>

  static ByteSize byte_offset_of_active() {

    return byte_offset_of(Derived, _active);

  }

  static ByteSize byte_width_of_active() { return in_ByteSize(sizeof(bool)); }

};

class BufferNode {

  size_t _index;

  BufferNode* _next;

  void* _buffer[1];             // Pseudo flexible array member.

  BufferNode() : _index(0), _next(NULL) { }

  ~BufferNode() { }

  static size_t buffer_offset() {

    return offset_of(BufferNode, _buffer);

  }

public:

  BufferNode* next() const     { return _next;  }

  void set_next(BufferNode* n) { _next = n;     }

  size_t index() const         { return _index; }

  void set_index(size_t i)     { _index = i;    }

  // Allocate a new BufferNode with the "buffer" having size bytes.

  static BufferNode* allocate(size_t byte_size);

  // Free a BufferNode.

  static void deallocate(BufferNode* node);

  // Return the BufferNode containing the buffer.

  static BufferNode* make_node_from_buffer(void** buffer) {

    return reinterpret_cast<BufferNode*>(

      reinterpret_cast<char*>(buffer) - buffer_offset());

  }

  // Return the buffer for node.

  static void** make_buffer_from_node(BufferNode *node) {

    // &_buffer[0] might lead to index out of bounds warnings.

    return reinterpret_cast<void**>(

      reinterpret_cast<char*>(node) + buffer_offset());

  }

};

// A PtrQueueSet represents resources common to a set of pointer queues.

// In particular, the individual queues allocate buffers from this shared

// set, and return completed buffers to the set.

// All these variables are are protected by the TLOQ_CBL_mon. XXX ???

class PtrQueueSet VALUE_OBJ_CLASS_SPEC {

protected:

  Monitor* _cbl_mon;  // Protects the fields below.

  BufferNode* _completed_buffers_head;

  BufferNode* _completed_buffers_tail;

  int _process_completed_threshold;

  volatile bool _process_completed;

  // This (and the interpretation of the first element as a "next"

  // pointer) are protected by the TLOQ_FL_lock.

  Mutex* _fl_lock;

  BufferNode* _buf_free_list;

  size_t _buf_free_list_sz;

  // Queue set can share a freelist. The _fl_owner variable

  // specifies the owner. It is set to "this" by default.

  PtrQueueSet* _fl_owner;

  // The size of all buffers in the set.

  size_t _sz;

  bool _all_active;

  // If true, notify_all on _cbl_mon when the threshold is reached.

  bool _notify_when_complete;

  // Maximum number of elements allowed on completed queue: after that,

  // enqueuer does the work itself.  Zero indicates no maximum.

  int _max_completed_queue;

  void assert_completed_buffer_list_len_correct_locked();

  void assert_completed_buffer_list_len_correct();

protected:

  // A mutator thread does the the work of processing a buffer.

  // Returns "true" iff the work is complete (and the buffer may be

  // deallocated).

  virtual bool mut_process_buffer(void** buf) {

    ShouldNotReachHere();

    return false;

  }

  // Create an empty ptr queue set.

  PtrQueueSet(bool notify_when_complete = false);

  ~PtrQueueSet();

  // Because of init-order concerns, we can't pass these as constructor

  // arguments.

  void initialize(Monitor* cbl_mon,

                  Mutex* fl_lock,

                  int process_completed_threshold,

                  int max_completed_queue,

                  PtrQueueSet *fl_owner = NULL);

public:

  // Return an empty array of size _sz (required to be non-zero).

  void** allocate_buffer();

  // Return an empty buffer to the free list.  The "buf" argument is

  // required to be a pointer to the head of an array of length "_sz".

  void deallocate_buffer(void** buf);

  // Declares that "buf" is a complete buffer.

  void enqueue_complete_buffer(void** buf, size_t index = 0);

  // To be invoked by the mutator.

  bool process_or_enqueue_complete_buffer(void** buf);

  bool completed_buffers_exist_dirty() {

    return _n_completed_buffers > 0;

  }

  bool process_completed_buffers() { return _process_completed; }

  void set_process_completed(bool x) { _process_completed = x; }

  bool is_active() { return _all_active; }

  // Set the buffer size.  Should be called before any "enqueue" operation

  // can be called.  And should only be called once.

  void set_buffer_size(size_t sz);

  // Get the buffer size.

  size_t buffer_size() { return _sz; }

  // Get/Set the number of completed buffers that triggers log processing.

  void set_process_completed_threshold(int sz) { _process_completed_threshold = sz; }

  int process_completed_threshold() const { return _process_completed_threshold; }

  // Must only be called at a safe point.  Indicates that the buffer free

  // list size may be reduced, if that is deemed desirable.

  void reduce_free_list();

  void merge_bufferlists(PtrQueueSet* src);

  void set_max_completed_queue(int m) { _max_completed_queue = m; }

  int max_completed_queue() { return _max_completed_queue; }

  // Notify the consumer if the number of buffers crossed the threshold

  void notify_if_necessary();

};

#endif // SHARE_VM_GC_G1_PTRQUEUE_HPP