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 //----------------------------------*-C++-*----------------------------------//
 // Copyright 2020-2024 UT-Battelle, LLC, and other Celeritas developers.
 // See the top-level COPYRIGHT file for details.
 // SPDX-License-Identifier: (Apache-2.0 OR MIT)
 //---------------------------------------------------------------------------//
 //! \file corecel/sys/Device.hh
 //---------------------------------------------------------------------------//
 #pragma once
 
 #include <cstddef>
 #include <iosfwd>  // IWYU pragma: keep
 #include <map>
 #include <memory>
 #include <string>
 
 #include "corecel/Assert.hh"
 
 #include "ThreadId.hh"
 
 namespace celeritas
 {
 class MpiCommunicator;
 class Stream;
 namespace detail
 {
 class StreamStorage;
 }
 
 //---------------------------------------------------------------------------//
 /*!
  * Manage attributes of the GPU.
  *
  * CUDA/HIP translation table:
  *
  * CUDA/NVIDIA    | HIP/AMD        | Description
  * -------------- | -------------- | -----------------
  * thread         | work item      | individual local work element
  * warp           | wavefront      | "vectorized thread" operating in lockstep
  * block          | workgroup      | group of threads able to sync
  * multiprocessor | compute unit   | hardware executing one or more blocks
  * multiprocessor | execution unit | hardware executing one or more warps
  *
  * Each block/workgroup operates on the same hardware (compute unit) until
  * completion. Similarly, a warp/wavefront is tied to a single execution
  * unit. Each compute unit can execute one or more blocks: the higher the
  * number of blocks resident, the more latency can be hidden.
  *
  * \warning The current multithreading/multiprocess model is intended to have
  * one GPU serving multiple CPU threads simultaneously, and one MPI process per
  * GPU. The active CUDA device is a static thread-local property but  \c
  * global_device is global. CUDA needs to be activated using \c activate_device
  * or \c activate_device_local on every thread, using the same device ID.
  */
 class Device
 {
   public:
     //!@{
     //! \name Type aliases
     using MapStrInt = std::map<std::string, int>;
     //!@}
 
   public:
     // Number of devices available on the local compute node (0 if disabled)
     static int num_devices();
 
     // Whether verbose messages and error checking are enabled
     static bool debug();
 
     //// CONSTRUCTORS ////
 
     // Construct an inactive device (disable celeritas CUDA calls)
     Device() = default;
 
     // Construct from device ID
     explicit Device(int id);
 
     //// ACCESSORS ////
 
     // Get the device ID
     inline int device_id() const;
 
     //! True if device is initialized
     explicit operator bool() const { return id_ >= 0; }
 
     //! Device name
     std::string name() const { return name_; }
 
     //! Total memory capacity (bytes)
     std::size_t total_global_mem() const { return total_global_mem_; }
 
     //! Maximum number of threads per block (for launch limits)
     int max_threads_per_block() const { return max_threads_per_block_; }
 
     //! Maximum number of threads per block (for launch limits)
     int max_blocks_per_grid() const { return max_blocks_per_grid_; }
 
     //! Maximum number of concurrent threads per compute unit (for occupancy)
     int max_threads_per_cu() const { return max_threads_per_cu_; }
 
     //! Number of threads per warp
     unsigned int threads_per_warp() const { return threads_per_warp_; }
 
     //! Whether the device supports mapped pinned memory
     bool can_map_host_memory() const { return can_map_host_memory_; }
 
     //! Number of execution units per compute unit (1 for NVIDIA, 4 for AMD)
     unsigned int eu_per_cu() const { return eu_per_cu_; }
 
     //! Additional potentially interesting diagnostics
     MapStrInt const& extra() const { return extra_; }
 
     // Number of streams allocated
     StreamId::size_type num_streams() const;
 
     // Allocate the given number of streams
     void create_streams(unsigned int num_streams) const;
 
     // Access a stream
     Stream& stream(StreamId) const;
 
   private:
     struct StreamStorageDeleter
     {
         void operator()(detail::StreamStorage*) noexcept;
     };
 
     using UPStreamStorage
         = std::unique_ptr<detail::StreamStorage, StreamStorageDeleter>;
 
     //// DATA ////
 
     // Required values for default constructor
     int id_{-1};
     std::string name_{"<DISABLED>"};
 
     // Default values overridden in device-ID constructor
     std::size_t total_global_mem_{};
     int max_threads_per_block_{};
     int max_blocks_per_grid_{};
     int max_threads_per_cu_{};
     unsigned int threads_per_warp_{};
     bool can_map_host_memory_{};
     unsigned int eu_per_cu_{};
     MapStrInt extra_;
     UPStreamStorage streams_;
 };
 
 //---------------------------------------------------------------------------//
 // CELERITAS SHARED DEVICE
 //---------------------------------------------------------------------------//
 // Global active device (default is inactive/false)
 Device const& device();
 
 // Set and initialize the active GPU
 void activate_device(Device&& device);
 
 // Initialize the first device if available using celeritas::comm_world
 void activate_device();
 
 // Initialize a device in a round-robin fashion from a communicator.
 void activate_device(MpiCommunicator const&);
 
 // Call cudaSetDevice using the existing device, for thread-local safety
 void activate_device_local();
 
 //---------------------------------------------------------------------------//
 // FREE FUNCTIONS
 //---------------------------------------------------------------------------//
 // Print device info
 std::ostream& operator<<(std::ostream&, Device const&);
 
 // Increase CUDA stack size
 void set_cuda_stack_size(int limit);
 
 // Increase CUDA HEAP size
 void set_cuda_heap_size(int limit);
 
 //---------------------------------------------------------------------------//
 // INLINE DEFINITIONS
 //---------------------------------------------------------------------------//
 /*!
  * Get the CUDA device ID, if active.
  */
 int Device::device_id() const
 {
     CELER_EXPECT(*this);
     return id_;
 }
 
 //---------------------------------------------------------------------------//
 }  // namespace celeritas

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