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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

 *

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 *

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 * 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).

 *

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 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

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#ifndef SHARE_GC_SHARED_PTRQUEUE_HPP

#define SHARE_GC_SHARED_PTRQUEUE_HPP

#include "memory/padded.hpp"

#include "utilities/align.hpp"

#include "utilities/debug.hpp"

#include "utilities/lockFreeStack.hpp"

#include "utilities/sizes.hpp"

class Mutex;

class Monitor;

// 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 BufferNode;

class PtrQueueSet;

class PtrQueue {

  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;

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

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

  // Value is always pointer-size aligned.

  size_t _index;

  // Size of the current buffer, in bytes.

  // Value is always pointer-size aligned.

  size_t _capacity_in_bytes;

  static const size_t _element_size = sizeof(void*);

  // Get the capacity, in bytes.  The capacity must have been set.

  size_t capacity_in_bytes() const {

    assert(_capacity_in_bytes > 0, "capacity not set");

    return _capacity_in_bytes;

  }

  void set_capacity(size_t entries) {

    size_t byte_capacity = index_to_byte_index(entries);

    assert(_capacity_in_bytes == 0 || _capacity_in_bytes == byte_capacity,

           "changing capacity " SIZE_FORMAT " -> " SIZE_FORMAT,

           _capacity_in_bytes, byte_capacity);

    _capacity_in_bytes = byte_capacity;

  }

  static size_t byte_index_to_index(size_t ind) {

    assert(is_aligned(ind, _element_size), "precondition");

    return ind / _element_size;

  }

  static size_t index_to_byte_index(size_t ind) {

    return ind * _element_size;

  }

protected:

  // The buffer.

  void** _buf;

  size_t index() const {

    return byte_index_to_index(_index);

  }

  void set_index(size_t new_index) {

    size_t byte_index = index_to_byte_index(new_index);

    assert(byte_index <= capacity_in_bytes(), "precondition");

    _index = byte_index;

  }

  size_t capacity() const {

    return byte_index_to_index(capacity_in_bytes());

  }

  // 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.

  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; }

  // Forcibly set empty.

  void reset() {

    if (_buf != NULL) {

      _index = capacity_in_bytes();

    }

  }

  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 enqueue_known_active(void* ptr);

  // Return the size of the in-use region.

  size_t size() const {

    size_t result = 0;

    if (_buf != NULL) {

      assert(_index <= capacity_in_bytes(), "Invariant");

      result = byte_index_to_index(capacity_in_bytes() - _index);

    }

    return result;

  }

  bool is_empty() const {

    return _buf == NULL || capacity_in_bytes() == _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) {

      reset();

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

      assert(index() == capacity(),

             "invariant: queues are empty when activated.");

    }

  }

  bool is_active() const { return _active; }

  // 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(_element_size); }

  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* volatile _next;

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

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

  ~BufferNode() { }

  static size_t buffer_offset() {

    return offset_of(BufferNode, _buffer);

  }

  static BufferNode* volatile* next_ptr(BufferNode& bn) { return &bn._next; }

AIX_ONLY(public:)               // xlC 12 on AIX doesn't implement C++ DR45.

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

  static BufferNode* allocate(size_t size);

  // Free a BufferNode.

  static void deallocate(BufferNode* node);

public:

  typedef LockFreeStack<BufferNode, &next_ptr> Stack;

  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; }

  // Return the BufferNode containing the buffer, after setting its index.

  static BufferNode* make_node_from_buffer(void** buffer, size_t index) {

    BufferNode* node =

      reinterpret_cast<BufferNode*>(

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

    node->set_index(index);

    return node;

  }

  // 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());

  }

  class Allocator;              // Free-list based allocator.

  class TestSupport;            // Unit test support.

};

// Allocation is based on a lock-free free list of nodes, linked through

// BufferNode::_next (see BufferNode::Stack).  To solve the ABA problem,

// popping a node from the free list is performed within a GlobalCounter

// critical section, and pushing nodes onto the free list is done after

// a GlobalCounter synchronization associated with the nodes to be pushed.

// This is documented behavior so that other parts of the node life-cycle

// can depend on and make use of it too.

class BufferNode::Allocator {

  friend class TestSupport;

  // Since we don't expect many instances, and measured >15% speedup

  // on stress gtest, padding seems like a good tradeoff here.

#define DECLARE_PADDED_MEMBER(Id, Type, Name) \

  Type Name; DEFINE_PAD_MINUS_SIZE(Id, DEFAULT_CACHE_LINE_SIZE, sizeof(Type))

  const size_t _buffer_size;

  char _name[DEFAULT_CACHE_LINE_SIZE - sizeof(size_t)]; // Use name as padding.

  DECLARE_PADDED_MEMBER(1, Stack, _pending_list);

  DECLARE_PADDED_MEMBER(2, Stack, _free_list);

  DECLARE_PADDED_MEMBER(3, volatile size_t, _pending_count);

  DECLARE_PADDED_MEMBER(4, volatile size_t, _free_count);

  DECLARE_PADDED_MEMBER(5, volatile bool, _transfer_lock);

#undef DECLARE_PADDED_MEMBER

  void delete_list(BufferNode* list);

  bool try_transfer_pending();

public:

  Allocator(const char* name, size_t buffer_size);

  ~Allocator();

  const char* name() const { return _name; }

  size_t buffer_size() const { return _buffer_size; }

  size_t free_count() const;

  BufferNode* allocate();

  void release(BufferNode* node);

  // Deallocate some of the available buffers.  remove_goal is the target

  // number to remove.  Returns the number actually deallocated, which may

  // be less than the goal if there were fewer available.

  size_t reduce_free_list(size_t remove_goal);

};

// 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.

class PtrQueueSet {

  BufferNode::Allocator* _allocator;

  Monitor* _cbl_mon;  // Protects the fields below.

  BufferNode* _completed_buffers_head;

  BufferNode* _completed_buffers_tail;

  size_t _n_completed_buffers;

  size_t _process_completed_buffers_threshold;

  volatile bool _process_completed_buffers;

  // 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.

  size_t _max_completed_buffers;

  size_t _completed_buffers_padding;

  void assert_completed_buffers_list_len_correct_locked() NOT_DEBUG_RETURN;

protected:

  bool _all_active;

  // 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(BufferNode* node) {

    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, BufferNode::Allocator* allocator);

  // For (unlocked!) iteration over the completed buffers.

  BufferNode* completed_buffers_head() const { return _completed_buffers_head; }

  // Deallocate all of the completed buffers.

  void abandon_completed_buffers();

public:

  // Return the buffer for a BufferNode of size buffer_size().

  void** allocate_buffer();

  // Return an empty buffer to the free list.  The node is required

  // to have been allocated with a size of buffer_size().

  void deallocate_buffer(BufferNode* node);

  // A completed buffer is a buffer the mutator is finished with, and

  // is ready to be processed by the collector.  It need not be full.

  // Adds node to the completed buffer list.

  void enqueue_completed_buffer(BufferNode* node);

  // If the number of completed buffers is > stop_at, then remove and

  // return a completed buffer from the list.  Otherwise, return NULL.

  BufferNode* get_completed_buffer(size_t stop_at = 0);

  // To be invoked by the mutator.

  bool process_or_enqueue_completed_buffer(BufferNode* node);

  bool process_completed_buffers() { return _process_completed_buffers; }

  void set_process_completed_buffers(bool x) { _process_completed_buffers = x; }

  bool is_active() { return _all_active; }

  size_t buffer_size() const {

    return _allocator->buffer_size();

  }

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

  // Log processing should be done when the number of buffers exceeds the

  // threshold.

  void set_process_completed_buffers_threshold(size_t sz) {

    _process_completed_buffers_threshold = sz;

  }

  size_t process_completed_buffers_threshold() const {

    return _process_completed_buffers_threshold;

  }

  static const size_t ProcessCompletedBuffersThresholdNever = ~size_t(0);

  size_t completed_buffers_num() const { return _n_completed_buffers; }

  void merge_bufferlists(PtrQueueSet* src);

  void set_max_completed_buffers(size_t m) {

    _max_completed_buffers = m;

  }

  size_t max_completed_buffers() const {

    return _max_completed_buffers;

  }

  static const size_t MaxCompletedBuffersUnlimited = ~size_t(0);

  void set_completed_buffers_padding(size_t padding) {

    _completed_buffers_padding = padding;

  }

  size_t completed_buffers_padding() const {

    return _completed_buffers_padding;

  }

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

  void notify_if_necessary();

};

#endif // SHARE_GC_SHARED_PTRQUEUE_HPP