Generic_Sequence_T.h

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#ifndef guard_generic_sequence_hpp
#define guard_generic_sequence_hpp
/**
 * @file
 *
 * @brief Implement the generic version of CORBA sequences.
 *
 * All CORBA sequences are based on this class template.  The behavior
 * of this class is controlled by two sets of traits.  First, the
 * ALLOCATION_TRAITS control how buffers are allocated and
 * initialized.  Since this is where most of the variation between
 * unbounded and bounded sequences is found, the ALLOCATION_TRAITS can
 * be thought as the bounded aspect of the sequence.
 *
 * Second, the element traits control how are elements copied,
 * initialized and released.  Value-like types, such as integers and
 * structures, have trivial initialization and release requirements
 * (their constructor/destructors do the job!)   But reference-like
 * types, such as strings and object references, have more complicated
 * requirements.  This is yet another aspect of the sequences, we can
 * call it the "element copy semantics" or something.
 *
 * Oh, and let us not forget the type that the sequences encapsulates.
 *
 * The intent is not for sequences to simply derive or instantiate this
 * type.  Instead, different each sequence type is written using
 * composition.  They instantiate a generic sequence with the correct
 * traits, and implement the adapt the generic sequence interface to
 * whatever requirements the spec may impose.  For example, replace()
 * has different number of arguments in bounded vs. unbounded
 * sequences, and operator[] returns different types depending on the
 * underlying type of the sequence.
 *
 * This class offers the strong exception-safety guarantee, as long as
 * destructors and release operations do not throw.
 *
 * This class is not thread-safe.  Thread-safe collections are mostly
 * useless anyways.
 *
 * In general the performance characteristics of the class depends on
 * the traits.  Obviously, they can only be expressed on the number of
 * element constructor and destructor calls.  If the constructor takes
 * O(K) time that is not the sequence fault!
 *
 * All accessors are O(1), single-element modifiers are O(1), multiple
 * element modifiers are O(n + m) where n is the number of elements
 * originally in the sequence, and m is the number of elements left in
 * the sequence afterwards.
 *
 * Beware:
 * - get_buffer(true) may modify multiple elements
 * - length(CORBA::ULong) may modify multiple elements!
 *
 * $Id: Generic_Sequence_T.h 79667 2007-09-20 07:13:20Z johnnyw $
 *
 * @author Carlos O'Ryan
 */

#include "tao/Range_Checking_T.h"
#include "ace/checked_iterator.h"

#include <algorithm>

TAO_BEGIN_VERSIONED_NAMESPACE_DECL

namespace TAO
{
namespace details
{

template<typename T,
         class ALLOCATION_TRAITS,
         class ELEMENT_TRAITS>
class generic_sequence
{
public:
  typedef T value_type;
  typedef ALLOCATION_TRAITS allocation_traits;
  typedef ELEMENT_TRAITS element_traits;
  typedef range_checking<value_type,true> range;

  /// Default constructor.
  generic_sequence()
    : maximum_(allocation_traits::default_maximum())
    , length_(0)
    , buffer_(allocation_traits::default_buffer_allocation())
    , release_(buffer_ != 0)
  {
  }

  /// Constructor with control of ownership.
  explicit generic_sequence(CORBA::ULong maximum)
    : maximum_(maximum)
    , length_(0)
    , buffer_(allocbuf(maximum_))
    , release_(true)
  {
  }

  generic_sequence(
      CORBA::ULong maximum,
      CORBA::ULong length,
      value_type * data,
      CORBA::Boolean release)
    : maximum_(maximum)
    , length_(length)
    , buffer_(data)
    , release_(release)
  {
  }

  /// Copy constructor
  generic_sequence(generic_sequence const & rhs)
    : maximum_(0)
    , length_(0)
    , buffer_(0)
    , release_(false)
  {
    if (rhs.maximum_ == 0) return;
    generic_sequence tmp(rhs.maximum_);
    tmp.length_ = rhs.length_;
    element_traits::copy_range(
        rhs.buffer_,
        rhs.buffer_ + rhs.length_,
        ACE_make_checked_array_iterator (tmp.buffer_, tmp.length_));
    swap(tmp);
  }

  /// Assignment operator
  generic_sequence & operator=(generic_sequence const & rhs)
  {
    generic_sequence tmp(rhs);
    swap(tmp);
    return * this;
  }

  /// Destructor.
  ~generic_sequence()
  {
    if (release_)
    {
      freebuf(buffer_);
    }
  }

  /// Return the maximum length of the sequence
  inline CORBA::ULong maximum() const
  {
    return maximum_;
  }

  /// Returns the state of the sequence release flag.
  inline CORBA::Boolean release() const
  {
    return release_;
  }

  /// Returns the length of the sequence
  inline CORBA::ULong length() const
  {
    return length_;
  }

  /// Set a new length for the sequence
  void length(CORBA::ULong length)
  {
    if (length <= maximum_ || length <= length_)
    {
      if (buffer_ == 0)
        {
          buffer_ = allocbuf(maximum_);
          release_ = true;
        }

      if (length_ < length)
      {
        // TODO This code does not provide the strong-exception
        //      guarantee, but it does provide the weak-exception
        //      guarantee.  The problem would appear when
        //      initialize_range() raises an exception after several
        //      elements have been modified.  One could argue that
        //      this problem is irrelevant, as the elements already
        //      modified are unreachable to conforming applications.
        element_traits::initialize_range(
            buffer_ + length_, buffer_ + length);
      }
      length_ = length;
      return;
    }

    generic_sequence tmp(length);
    tmp.length_ = length;
    element_traits::copy_range(
      buffer_,
      buffer_ + length_,
      ACE_make_checked_array_iterator (tmp.buffer_, tmp.length_));
    element_traits::initialize_range(
        tmp.buffer_ + length_, tmp.buffer_ + length);

    swap(tmp);
  }

  /// Get a const element from the sequence
  value_type const & operator[](CORBA::ULong i) const
  {
    range::check(i, length_, maximum_, "operator[]() const");
    return buffer_[i];
  }

  /// Get an element from the sequence
  value_type & operator[](CORBA::ULong i)
  {
    range::check(i, length_, maximum_, "operator[]() non-const");
    return buffer_[i];
  }

  /**
   * Allows the buffer underlying a sequence to be replaced.  The
   * parameters to replace() are identical in type, order, and purpose
   * to those for the <T *data> constructor for the sequence.
   */
  void replace(
      CORBA::ULong maximum,
      CORBA::ULong length,
      value_type * data,
      CORBA::Boolean release)
  {
    generic_sequence tmp(maximum, length, data, release);
    swap(tmp);
  }

  /**
   * This function allows read-only access to the sequence buffer.
   * The sequence returns its buffer, allocating one of one has not
   * yet been allocated.  No direct modification of the returned
   * buffer by the caller is permitted.
   */
  value_type const * get_buffer() const
  {
    if (buffer_ == 0)
    {
      buffer_ = allocbuf(maximum_);
      release_ = true;
    }
    return buffer_;
  }

  /// Allows read-write access to the underlying buffer.
  /**
   * If @a orphan is FALSE the sequence returns a pointer to its buffer,
   * allocating one if it has not yet done so.  The number of elements in the
   * buffer can be determined from the sequence length() accessor.
   *
   * If the @a orphan argument to get_buffer() is FALSE, the sequence
   * maintains ownership of the underlying buffer.  Elements in the
   * returned buffer may be directly replaced by the caller.  For
   * sequences of strings, wide strings, and object references, the
   * caller must use the sequence @c release accessor to determine
   * whether elements should be freed (using @c string_free,
   * @c wstring_free, or @c CORBA::release for strings, wide strings,
   * and object references, respective) before being directly assigned
   * to.
   *
   * If the @a orphan argument to @a get_buffer is TRUE, the sequence
   * yields ownership of the buffer to the caller.  If @a orphan is
   * TRUE and the sequence does not own its buffer (i.e., its
   * release_ flag is FALSE), the return value is a null pointer.  If
   * the buffer is taken from the sequence using this form of
   * get_buffer(), the sequence reverts to the same state it would
   * have if constructed using its default constructor.  The caller
   * becomes responsible for eventually freeing each element of the
   * returned buffer (for strings, wide string, and object
   * references), and then freeing the returned buffer itself using
   * freebuf().
   */
  value_type * get_buffer(CORBA::Boolean orphan)
  {
    if (orphan && !release_)
    {
      return 0;
    }
    if (buffer_ == 0)
    {
      buffer_ = allocbuf(maximum_);
      if (!orphan)
        {
          release_ = true;
        }
    }
    if (!orphan)
    {
      return buffer_;
    }

    generic_sequence tmp;
    swap(tmp);
    tmp.release_ = false;

    return tmp.buffer_;
  }

  void swap(generic_sequence & rhs) throw()
  {
    std::swap(maximum_, rhs.maximum_);
    std::swap(length_, rhs.length_);
    std::swap(buffer_, rhs.buffer_);
    std::swap(release_, rhs.release_);
  }

  static value_type * allocbuf(CORBA::ULong maximum)
  {
    return allocation_traits::allocbuf(maximum);
  }

  static void freebuf(value_type * buffer)
  {
    allocation_traits::freebuf(buffer);
  }

private:
  /// The maximum number of elements the buffer can contain.
  CORBA::ULong maximum_;
  /// The current number of elements in the buffer.
  CORBA::ULong length_;
  /// The buffer with all the elements
  mutable value_type * buffer_;
  /// If true then the sequence should release the buffer when it is
  /// destroyed.
  mutable CORBA::Boolean release_;
};

} // namespace details
} // namespace TAO

TAO_END_VERSIONED_NAMESPACE_DECL

#endif // guard_generic_sequence_hpp

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