    // Copyright (C) 2015  Davis E. King (davis@dlib.net)
    // License: Boost Software License   See LICENSE.txt for the full license.
    #undef DLIB_GPU_DaTA_ABSTRACT_H_
    #ifdef DLIB_GPU_DaTA_ABSTRACT_H_

    #include "cuda_errors.h"
    #include "../serialize.h"

    namespace dlib
    {

    // ----------------------------------------------------------------------------------------

        class gpu_data
        {
            /*!
                WHAT THIS OBJECT REPRESENTS
                    This object is a block of size() floats, all stored contiguously in memory.
                    Importantly, it keeps two copies of the floats, one on the host CPU side
                    and another on the GPU device side. It automatically performs the necessary
                    host/device transfers to keep these two copies of the data in sync.

                    All transfers to the device happen asynchronously with respect to the
                    default CUDA stream so that CUDA kernel computations can overlap with data
                    transfers.  However, any transfers from the device to the host happen
                    synchronously in the default CUDA stream.  Therefore, you should perform
                    all your CUDA kernel launches on the default stream so that transfers back
                    to the host do not happen before the relevant computations have completed.

                    If DLIB_USE_CUDA is not #defined then this object will not use CUDA at all.
                    Instead, it will simply store one host side memory block of floats.

                THREAD SAFETY
                    Instances of this object are not thread-safe.  So don't touch one from
                    multiple threads at the same time.
            !*/
        public:

            gpu_data(
            );
            /*!
                ensures
                    - #size() == 0
                    - #host() == nullptr
                    - #device() == nullptr
                    - #host_ready() == true
                    - #device_ready() == true
                    - #device_id() == 0
            !*/

            // This object is not copyable, however, it is movable.
            gpu_data(const gpu_data&) = delete;
            gpu_data& operator=(const gpu_data&) = delete;
            gpu_data(gpu_data&& item);
            gpu_data& operator=(gpu_data&& item);

            int device_id(
            ) const;
            /*!
                ensures
                    - returns the ID of the CUDA device that allocated this memory. I.e. the
                      number returned by cudaGetDevice() when the memory was allocated.
                    - If CUDA is not being used then this function always returns 0.
            !*/

            void async_copy_to_device(
            );
            /*!
                ensures
                    - if (!device_ready()) then
                        - Begins asynchronously copying host data to the device once it is safe
                          to do so.  I.e. This function will wait until any previously
                          scheduled CUDA kernels, which are using the device() memory block,
                          have completed before transferring the new data to the device.
                        - A call to device() that happens before the transfer completes will
                          block until the transfer is complete.  That is, it is safe to call
                          async_copy_to_device() and then immediately call device().
            !*/

            void set_size(
                size_t new_size
            );
            /*!
                ensures
                    - #size() == new_size
            !*/

            bool host_ready (
            ) const;
            /*!
                ensures
                    - returns true if and only if the host's copy of the data is current.  The
                      host's data is current if there aren't any modifications to the data
                      which were made on the device side that have yet to be copied to the
                      host.
            !*/

            bool device_ready (
            ) const;
            /*!
                ensures
                    - returns true if and only if the device's copy of the data is current.
                      The device's data is current if there aren't any modifications to the
                      data which were made on the host side that have yet to be copied to the
                      device.
            !*/

            const float* host(
            ) const;
            /*!
                ensures
                    - returns a pointer to the host memory block of size() contiguous float
                      values or nullptr if size()==0.
                    - if (!host_ready()) then
                        - copies the data from the device to the host, while this is happening
                          the call to host() blocks.
                    - #host_ready() == true
            !*/

            float* host(
            );
            /*!
                ensures
                    - returns a pointer to the host memory block of size() contiguous float
                      values or nullptr if size()==0.
                    - if (!host_ready()) then
                        - copies the data from the device to the host, while this is happening
                          the call to host() blocks.
                    - #host_ready() == true
                    - #device_ready() == false
                      I.e. Marks the device side data as out of date so that the next call to
                      device() will perform a host to device transfer.  If you want to begin
                      the transfer immediately then you can call async_copy_to_device() after
                      calling host().
            !*/

            float* host_write_only(
            );
            /*!
                ensures
                    - This function returns the same pointer as host(), except that it never
                      performs a device to host memory copy.  Instead, it immediately marks the
                      device side data as out of date, effectively discarding it.  Therefore,
                      the values in the data pointed to by host_write_only() are undefined and
                      you should only call host_write_only() if you are going to assign to
                      every memory location in the returned memory block.
                    - #host_ready() == true
                    - #device_ready() == false
            !*/

            const float* device(
            ) const;
            /*!
                requires
                    - DLIB_USE_CUDA is #defined
                ensures
                    - returns a pointer to the device memory block of size() contiguous float
                      values or nullptr if size()==0.
                    - if (!device_ready()) then
                        - copies the data from the host to the device, while this is happening
                          the call to device() blocks.
                    - #device_ready() == true
            !*/

            float* device(
            );
            /*!
                requires
                    - DLIB_USE_CUDA is #defined
                ensures
                    - returns a pointer to the device memory block of size() contiguous float
                      values or nullptr if size()==0.
                    - if (!device_ready()) then
                        - copies the data from the host to the device, while this is happening
                          the call to device() blocks.
                    - #host_ready() == false
                    - #device_ready() == true
            !*/

            float* device_write_only(
            );
            /*!
                requires
                    - DLIB_USE_CUDA is #defined
                ensures
                    - This function returns the same pointer as device(), except that it never
                      performs a host to device memory copy.  Instead, it immediately marks the
                      host side data as out of date, effectively discarding it.  Therefore, the
                      values in the data pointed to by device_write_only() are undefined and
                      you should only call device_write_only() if you are going to assign to
                      every memory location in the returned memory block.
                    - #host_ready() == false
                    - #device_ready() == true
            !*/

            size_t size(
            ) const;
            /*!
                ensures
                    - returns the number of floats contained in this object.
            !*/

            void swap (
                gpu_data& item
            );
            /*!
                ensures
                    - swaps the state of *this and item
            !*/

        };

        void serialize(const gpu_data& item, std::ostream& out);
        void deserialize(gpu_data& item, std::istream& in);
        /*!
            provides serialization support
        !*/

        void memcpy (
            gpu_data& dest,
            const gpu_data& src
        );
        /*!
            requires
                - dest.size() == src.size()
            ensures
                - Copies the data in src to dest.  If the device data is current (i.e.
                  device_ready()==true) on both src and dest then the copy will happen entirely
                  on the device side.
                - It doesn't matter what GPU device is selected by cudaSetDevice().  You can
                  always copy gpu_data objects to and from each other regardless.
                - This function blocks until the copy has completed.
        !*/

        void memcpy (
            gpu_data& dest,
            size_t dest_offset,
            const gpu_data& src,
            size_t src_offset,
            size_t num
        );
        /*!
            requires
                - dest_offset + num <= dest.size()
                - src_offset  + num <= src.size()
            ensures
                - Copies the data in src to dest, but only copies data in the range
                  [src.host()+src_offset, src.host()+src_offset+num) to
                  [dest.host()+dest_offset, dest.host()+dest_offset+num).  Therefore, it is
                  just like the above memcpy() except that you can specify some subset of data
                  in a gpu_data object to be copied.
                - Like the above version of memcpy(), the copy will happen in the most
                  efficient way, automatically using the appropriate type of host/device
                  transfers based on where data is currently resident.
                - It doesn't matter what GPU device is selected by cudaSetDevice().  You can
                  always copy gpu_data objects to and from each other regardless.
                - This function blocks until the copy has completed.
        !*/

    // ----------------------------------------------------------------------------------------

    }

    #endif // DLIB_GPU_DaTA_ABSTRACT_H_