src/hotspot/share/gc/shared/ptrQueue.hpp

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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#ifndef SHARE_GC_SHARED_PTRQUEUE_HPP
#define SHARE_GC_SHARED_PTRQUEUE_HPP

#include "gc/shared/freeListAllocator.hpp"
#include "memory/padded.hpp"
#include "utilities/align.hpp"
#include "utilities/debug.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/lockFreeStack.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 BufferNode;
class PtrQueueSet;
class PtrQueue {
  friend class VMStructs;

  NONCOPYABLE(PtrQueue);

  // 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;
  }

  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;

  // Initialize this queue to contain a null buffer, and be part of the
  // given PtrQueueSet.
  PtrQueue(PtrQueueSet* qset);

  // Requires queue flushed.
  ~PtrQueue();

public:

  void** buffer() const { return _buf; }
  void set_buffer(void** buffer) { _buf = buffer; }

  size_t index() const {
    return byte_index_to_index(_index);
  }

  void set_index(size_t new_index) {
    assert(new_index <= capacity(), "precondition");
    _index = index_to_byte_index(new_index);
  }

  size_t capacity() const {
    return byte_index_to_index(capacity_in_bytes());
  }

  // To support compiler.

protected:
  template<typename Derived>
  static ByteSize byte_offset_of_index() {
    return byte_offset_of(Derived, _index);
  }

  static constexpr 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); }
};

class BufferNode {
  size_t _index;
  BufferNode* volatile _next;
  void* _buffer[1];             // Pseudo flexible array member.

  BufferNode() : _index(0), _next(nullptr) { }
  ~BufferNode() { }

  NONCOPYABLE(BufferNode);

  static size_t buffer_offset() {
    return offset_of(BufferNode, _buffer);
  }

public:
  static BufferNode* volatile* next_ptr(BufferNode& bn) { return &bn._next; }
  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 AllocatorConfig;
  class Allocator;              // Free-list based allocator.
  class TestSupport;            // Unit test support.
};

// We use BufferNode::AllocatorConfig to set the allocation options for the
// FreeListAllocator.
class BufferNode::AllocatorConfig : public FreeListConfig {
  const size_t _buffer_size;
public:
  explicit AllocatorConfig(size_t size);

  ~AllocatorConfig() = default;

  void* allocate() override;

  void deallocate(void* node) override;

  size_t buffer_size() const { return _buffer_size; }
};

class BufferNode::Allocator {
  friend class TestSupport;

  AllocatorConfig _config;
  FreeListAllocator _free_list;

  NONCOPYABLE(Allocator);

public:
  Allocator(const char* name, size_t buffer_size);
  ~Allocator() = default;

  size_t buffer_size() const { return _config.buffer_size(); }
  size_t free_count() const;
  BufferNode* allocate();
  void release(BufferNode* node);
};

// 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;

  NONCOPYABLE(PtrQueueSet);

protected:
  // Create an empty ptr queue set.
  PtrQueueSet(BufferNode::Allocator* allocator);
  ~PtrQueueSet();

  // Discard any buffered enqueued data.
  void reset_queue(PtrQueue& queue);

  // If queue has any buffered enqueued data, transfer it to this qset.
  // Otherwise, deallocate queue's buffer.
  void flush_queue(PtrQueue& queue);

  // Add value to queue's buffer, returning true.  If buffer is full
  // or if queue doesn't have a buffer, does nothing and returns false.
  bool try_enqueue(PtrQueue& queue, void* value);

  // Add value to queue's buffer.  The queue must have a non-full buffer.
  // Used after an initial try_enqueue has failed and the situation resolved.
  void retry_enqueue(PtrQueue& queue, void* value);

  // Installs a new buffer into queue.
  // Returns the old buffer, or null if queue didn't have a buffer.
  BufferNode* exchange_buffer_with_new(PtrQueue& queue);

  // Installs a new buffer into queue.
  void install_new_buffer(PtrQueue& queue);

public:

  // Return the associated BufferNode allocator.
  BufferNode::Allocator* allocator() const { return _allocator; }

  // 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.
  virtual void enqueue_completed_buffer(BufferNode* node) = 0;

  size_t buffer_size() const {
    return _allocator->buffer_size();
  }
};

#endif // SHARE_GC_SHARED_PTRQUEUE_HPP