ZeroCopySeq_T.h

Go to the documentation of this file.

/*
 *
 *
 * Distributed under the OpenDDS License.
 * See: http://www.opendds.org/license.html
 */

#ifndef ZEROCOPYSEQ_H
#define ZEROCOPYSEQ_H

#if !defined (ACE_LACKS_PRAGMA_ONCE)
# pragma once
#endif /* ACE_LACKS_PRAGMA_ONCE */

#include /**/ "ace/pre.h"

#include "dds/DCPS/ZeroCopySeqBase.h"
#include "dds/DCPS/ZeroCopyAllocator_T.h"
#include <ace/Vector_T.h>

namespace OpenDDS {
namespace DCPS {

class DataReaderImpl;
class ReceivedDataElement;

} // namespace DCPS
} // namespace OpenDDS

TAO_BEGIN_VERSIONED_NAMESPACE_DECL

//This must stay in namespace "TAO" until the tao_idl compiler is changed
namespace TAO {
namespace DCPS {

/**
* Provides [] operators returning sample references
*     but it is implemented as
*     an "array" of pointers to the samples so they can be
*     "loaned" to the application code.
*
* Design Goals:
*  - Provide enhanced performance known as "zero-copy" in the DDS spec
*  - Conform to the C++ CORBA mapping for sequences
*    - When necessary, certain uncommon sequence operations (resize,
*      get_buffer, replace) will cause copies.  Performance impacts are
*      noted in comments on the individual methods.
*/
template <class Sample_T, size_t DEF_MAX = DCPS_ZERO_COPY_SEQ_DEFAULT_SIZE>
class ZeroCopyDataSeq {
public:

  typedef Sample_T value_type;

  /**
  * Construct a sequence of sample data values that supports
  * zero-copy reads.
  *
  * @param maximum Maximum number of samples to insert into the sequence.
  *                If == 0 then use zero-copy reading.
  *                Defaults to zero hence supporting zero-copy reads/takes.
  *
  * @param init_size Initial size of the underlying array of pointers.
  *
  * @param alloc The allocator used to allocate the array of pointers
  *              to samples. If zero then use the default allocator.
  *
  * This constructor also serves as the "maximum" ctor and default ctor
  * in the CORBA spec.
  */
  explicit ZeroCopyDataSeq(CORBA::ULong maximum = 0,
                           CORBA::ULong init_size = DEF_MAX, ACE_Allocator* alloc = 0);

  ZeroCopyDataSeq(CORBA::ULong maximum, CORBA::ULong length,
                  Sample_T* buffer, CORBA::Boolean release = false);

  ZeroCopyDataSeq(const ZeroCopyDataSeq& frm);

  ZeroCopyDataSeq& operator=(const ZeroCopyDataSeq& frm);

  void swap(ZeroCopyDataSeq& frm);

  ~ZeroCopyDataSeq();

  CORBA::ULong maximum() const;

  /** Performance note: increasing the length of a zero-copy sequence past
   *  its current length may cause a copy (the sequence will no longer be
   *  zero-copy enabled).
   */
  void length(CORBA::ULong length);
  CORBA::ULong length() const;

  const Sample_T& operator[](CORBA::ULong i) const;
  Sample_T& operator[](CORBA::ULong i);

  CORBA::Boolean release() const;

  void replace(CORBA::ULong max, CORBA::ULong length, Sample_T* buffer,
               CORBA::Boolean release = false);

  Sample_T* get_buffer(CORBA::Boolean orphan = false);
  const Sample_T* get_buffer() const;

  static Sample_T* allocbuf(CORBA::ULong nelems);
  static void freebuf(Sample_T* buffer);

  void increment_references(void);

  ///Only used by the FooDataReaderImpl and tests
  class PrivateMemberAccess {
  public:
    explicit PrivateMemberAccess(ZeroCopyDataSeq& seq)
        : seq_(seq) {}

    CORBA::ULong max_slots() const {
      return seq_.max_slots();
    }

    void internal_set_length(CORBA::ULong len) {
      seq_.internal_set_length(len);
    }

    void set_loaner(OpenDDS::DCPS::DataReaderImpl* loaner) {
      seq_.set_loaner(loaner);
    }

    void assign_ptr(CORBA::ULong ii, OpenDDS::DCPS::ReceivedDataElement* item) {
      seq_.assign_ptr(ii, item);
    }

    OpenDDS::DCPS::ReceivedDataElement* get_ptr(CORBA::ULong ii) const {
      return seq_.get_ptr(ii);
    }

    void assign_sample(CORBA::ULong ii, const Sample_T& sample) {
      seq_.assign_sample(ii, sample);
    }

  private:
    ZeroCopyDataSeq& seq_;
  };
  friend class PrivateMemberAccess;

private:

  /** In some versions of ACE, ACE_Vector doesn't have a working swap()
    * function, so we have to provide our own.
    */
  class ZeroCopyVector
        : public ACE_Vector<OpenDDS::DCPS::ReceivedDataElement*, DEF_MAX> {
  public:
    ZeroCopyVector(const size_t init_size = DEF_MAX, ACE_Allocator* alloc = 0);

    void swap(ZeroCopyVector&);

    typedef ACE_Vector<OpenDDS::DCPS::ReceivedDataElement*, DEF_MAX> BASE;
    using BASE::allocator_;
    using BASE::array_;
  };

  /**
  * Current allocated number of sample slots.
  *
  * @note The DDS specification's use of maximum=0 to designate
  *       zero-copy read request requires some
  *       way of knowing the internally allocated slots
  *       for sample pointers that is not "maximum".
  */
  CORBA::ULong max_slots() const;

  void internal_set_length(CORBA::ULong len);

  void set_loaner(OpenDDS::DCPS::DataReaderImpl* loaner);

  void assign_ptr(CORBA::ULong ii, OpenDDS::DCPS::ReceivedDataElement* item);

  OpenDDS::DCPS::ReceivedDataElement* get_ptr(CORBA::ULong ii) const;

  void assign_sample(CORBA::ULong ii, const Sample_T& sample);

  bool is_zero_copy() const;

  void make_single_copy(CORBA::ULong maximum);

  /// The datareader that loaned its samples.
  OpenDDS::DCPS::DataReaderImpl* loaner_;

  /// the default allocator
  OpenDDS::DCPS::FirstTimeFastAllocator<OpenDDS::DCPS::ReceivedDataElement*, DEF_MAX>
  default_allocator_;

  typedef ZeroCopyVector Ptr_Seq_Type;

  /// array of pointers if the sequence is supporting zero-copy reads
  Ptr_Seq_Type ptrs_;
  static Sample_T default_;

  //single-copy (aka non-zero-copy) support
  CORBA::ULong sc_maximum_;
  CORBA::ULong sc_length_;
  mutable Sample_T* sc_buffer_;
  mutable CORBA::Boolean sc_release_;

}; // class ZeroCopyDataSeq

} // namespace DCPS
} // namespace TAO

TAO_END_VERSIONED_NAMESPACE_DECL

#if defined (__ACE_INLINE__)
#include "dds/DCPS/ZeroCopySeq_T.inl"
#endif /* __ACE_INLINE__ */

#if defined (ACE_TEMPLATES_REQUIRE_SOURCE)
#include "dds/DCPS/ZeroCopySeq_T.cpp"
#endif /* ACE_TEMPLATES_REQUIRE_SOURCE */

#if defined (ACE_TEMPLATES_REQUIRE_PRAGMA)
#pragma message ("ZeroCopySeq_T.cpp template inst")
#pragma implementation ("ZeroCopySeq_T.cpp")
#endif /* ACE_TEMPLATES_REQUIRE_PRAGMA */

#include /**/ "ace/post.h"

#endif /* ZEROCOPYSEQ_H  */

---