quickfix-ffi 0.2.1

/* -*- C++ -*- */

/****************************************************************************
** Copyright (c) 2001-2014
**
** This file is part of the QuickFIX FIX Engine
**
** This file may be distributed under the terms of the quickfixengine.org
** license as defined by quickfixengine.org and appearing in the file
** LICENSE included in the packaging of this file.
**
** This file is provided AS IS with NO WARRANTY OF ANY KIND, INCLUDING THE
** WARRANTY OF DESIGN, MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
**
** See http://www.quickfixengine.org/LICENSE for licensing information.
**
** Contact ask@quickfixengine.org if any conditions of this licensing are
** not clear to you.
**
****************************************************************************/

#ifndef SHARED_ARRAY
#define SHARED_ARRAY

#include "config-all.h"

#include <atomic>
#include <cstdlib>
#include <cstring>
#include <new>

namespace FIX {
/// Shared array with atomic reference count
#ifndef NO_UNALIGNED_ACCESS
template <typename T> class shared_array {
  enum {
    data_offset = (sizeof(std::atomic<long>) / sizeof(T) + 1)
  };

public:
  shared_array()
      : m_size(0),
        m_buffer(0) {}

  shared_array(const shared_array &rhs)
      : m_size(rhs.m_size),
        m_buffer(rhs.m_buffer) {
    rhs.attach();
  }

  shared_array(shared_array &&rhs)
      : m_size(rhs.m_size),
        m_buffer(rhs.m_buffer) {
    rhs.m_size = 0;
    rhs.m_buffer = 0;
  }

  ~shared_array() { release(); }

  shared_array &operator=(shared_array &&rhs) noexcept {
    if (&rhs == this) {
      return *this;
    }

    release();

    m_size = rhs.m_size;
    m_buffer = rhs.m_buffer;

    rhs.m_size = 0;
    rhs.m_buffer = 0;

    return *this;
  }

  shared_array &operator=(const shared_array &rhs) {
    if (&rhs == this) {
      return *this;
    }

    rhs.attach();
    release();

    m_size = rhs.m_size;
    m_buffer = rhs.m_buffer;

    return *this;
  }

  std::size_t size() const { return m_size; }

  bool empty() const { return m_buffer == 0; }

  operator T *() const { return &m_buffer[data_offset]; }

  // optimized function to allocate storage for buffer and counter object at once
  static shared_array create(const std::size_t nSize) {
    if (nSize == 0) {
      return shared_array();
    }

    // verify the needed buffer size to allocate counter object and nSize elements
    const std::size_t sizeToAllocate = data_offset + nSize;

    // allocate and zero-fill the buffer
    T *storage = new T[sizeToAllocate];
    memset(reinterpret_cast<void *>(storage), 0, sizeToAllocate * sizeof(T));

    // create the counter object at the end of the storage
    // with initial reference count set to 1
    new (storage) std::atomic<long>(1);

    return shared_array(storage, nSize);
  }

private:
  shared_array(T *buff, std::size_t nSize)
      : m_size(nSize),
        m_buffer(buff) {}

  std::atomic<long> *get_counter() const { return reinterpret_cast<std::atomic<long> *>(m_buffer); }

  void increment_reference_count() const {
    std::atomic<long> *counter = get_counter();
    ++(*counter);
  }

  long decrement_reference_count() const {
    std::atomic<long> *counter = get_counter();
    return --(*counter);
  }

  void attach() const {
    if (!empty()) {
      increment_reference_count();
    }
  }

  void release() {
    if (empty()) {
      return;
    }

    // free object if reference count has decreased to zero
    if (decrement_reference_count() == 0) {
      T *tmpBuff = m_buffer;
      std::atomic<long> *tmpCounter = get_counter();

      m_buffer = 0;
      m_size = 0;

      // explicitly call destructor for the counter object
      tmpCounter->~atomic<long>();

      delete[] tmpBuff;
    }
  }

  std::size_t m_size;
  T *m_buffer;
};
#else
template <typename T> class shared_array {
public:
  shared_array()
      : m_size(0),
        m_buffer(0),
        m_pCtr(0) {}

  shared_array(const shared_array &rhs)
      : m_size(rhs.m_size),
        m_buffer(rhs.m_buffer),
        m_pCtr(rhs.m_pCtr) {
    rhs.attach();
  }

  ~shared_array() { release(); }

  shared_array &operator=(const shared_array &rhs) {
    if (&rhs == this) {
      return *this;
    }

    rhs.attach();
    release();

    m_size = rhs.m_size;
    m_buffer = rhs.m_buffer;
    m_pCtr = rhs.m_pCtr;

    return *this;
  }

  std::size_t size() const { return m_size; }

  bool empty() const { return m_buffer == 0; }

  operator T *() const { return m_buffer; }

  // optimized function to allocate storage for buffer and counter object at once
  static shared_array create(const std::size_t nSize) {
    if (nSize <= 0) {
      return shared_array();
    }

    // verify the needed buffer size to allocate counter object and nSize elements
    const std::size_t sizeToAllocate = (nSize * sizeof(T)) + sizeof(std::atomic<long>) + 15;

    // allocate and zero-fill the buffer
    void *buf = std::malloc(sizeToAllocate);
    memset(buf, 0, sizeToAllocate);

    // create the counter object at the end of the storage
    // with initial reference count set to 1
    /* round up to multiple of alignment : add (alignment - 1) and then round down by masking */
    void *ptr = (void *)(((uintptr_t)(buf) + nSize * sizeof(T) + 15) & ~(uintptr_t)0x0F);
    new (ptr) std::atomic<long>(1);

    T *storage = reinterpret_cast<T *>(buf);
    return shared_array(storage, nSize, ptr);
  }

private:
  shared_array(T *buff, std::size_t nSize, void *pCtr)
      : m_size(nSize),
        m_buffer(buff),
        m_pCtr(pCtr) {}

  std::atomic<long> *get_counter() const { return reinterpret_cast<std::atomic<long> *>(m_pCtr); }

  void increment_reference_count() const {
    std::atomic<long> *counter = get_counter();
    ++(*counter);
  }

  long decrement_reference_count() const {
    std::atomic<long> *counter = get_counter();
    return --(*counter);
  }

  void attach() const {
    if (!empty()) {
      increment_reference_count();
    }
  }

  void release() {
    if (empty()) {
      return;
    }

    // free object if reference count has decreased to zero
    if (decrement_reference_count() == 0) {
      T *tmpBuff = m_buffer;
      std::atomic<long> *tmpCounter = get_counter();

      m_buffer = 0;
      m_size = 0;

      // explicitly call destructor for the counter object
      tmpCounter->~atomic<long>();

      std::free(tmpBuff);
    }
  }

  std::size_t m_size;
  T *m_buffer;
  void *m_pCtr;
};
#endif
} // namespace FIX

#endif