Libtorch on Raspberry can't load pt file but working on ubuntu

I'm trying to build a C++ program with libtorch on a Raspberry PI. The program is working on Ubuntu, but I've got the following error at build on Raspberry :

error: use of deleted function â€˜void torch::jit::script::Module::operator=(const torch::jit::script::Module&)â€™
In file included from /usr/include/torch/csrc/jit/ir.h:18,
                 from /usr/include/torch/csrc/jit/tracer.h:9,
                 from /usr/include/torch/csrc/autograd/generated/variable_factories.h:8,
                 from /usr/include/torch/csrc/api/include/torch/types.h:7,
                 from /usr/include/torch/script.h:3,
                 from /tmp/tmp.k6618dczxt/src/../include/suvoNet.h:26,
                 from /tmp/tmp.k6618dczxt/src/../include/classifier.h:17,
                 from /tmp/tmp.k6618dczxt/src/classifier.cpp:11:
/usr/include/torch/csrc/jit/script/module.h:319:3: note: declared here
   TH_DISALLOW_COPY_AND_ASSIGN(Module);

Here is the code that crashes :

MyClass::MyClass() {
    try {
        // Deserialize the ScriptModule from a file using torch::jit::load().
        network = torch::jit::load(MODEL_FILE);
    }
    catch (const c10::Error& e) {
        std::cerr << "Error loading the model\n";
        exit(-1);
    }
}

With network declared private torch::jit::script::Module network

I build libtorch for Raspberry (ARM) using pyTorch from github in version '1.0.0a0+8322165'

Solution

TLDR : Compile libtorch in 1.6.0 and that works fine.

How to compile Libtorch for Raspberry and use in my C++ Project ?

Prepare to build

Increase RBPi SWAP

First of all, if you have a Raspberry PI 3 or lower, you need to increase the SWAP, since the build is a RAM eater.

If you have a RBPi 4 or higher with more than 3GB of RAM, skip this step.

Modify the file /etc/dphys-swapfile :

CONF_SWAPFILE=2048M

Then call the following command to update changes.

sudo dphys-swapfile setup

Install base packages

Install the following packages:

sudo apt install build-essential make cmake git python3-pip libatlas-base-dev

Libtorch needs CMake>=3.15 to be built properly, check cmake version with cmake --version``

If it's lower than 3.15, follow the following commands to build a newer version and remove the previous one:

wget https://github.com/Kitware/CMake/releases/download/v3.18.0-rc1/cmake-3.18.0-rc1.tar.gz
tar -xzf cmake-3.18.0-rc1.tar.gz
cd cmake<version>
mkdir build
cd build
cmake ..
make
sudo make install

sudo apt remove cmake
sudo ln -s /usr/local/bin/cmake /usr/bin/cmake
sudo ldconfig

Building PyTorch from source to get libtorch backend for ARM

Don't forget to increase the SWAP to 2048M if you don't have 3GB or RAM.

Getting all needed libraries:

sudo apt-get update
sudo apt-get install build-essential tk-dev libncurses5-dev libncursesw5-dev libreadline6-dev libdb5.3-dev libgdbm-dev libsqlite3-dev libssl-dev libbz2-dev libexpat1-dev liblzma-dev zlib1g-dev

Getting PyTorch sources:

git clone --recursive https://github.com/pytorch/pytorch --branch=release/1.6
cd pytorch

Init all the submodules :

git submodule update --init --recursive
git submodule update --remote third_party/protobuf # To prevent a bug I had

Getting all needed libraries:

sudo apt-get update
sudo apt-get install build-essential tk-dev libncurses5-dev libncursesw5-dev libreadline6-dev libdb5.3-dev libgdbm-dev libsqlite3-dev libssl-dev libbz2-dev libexpat1-dev liblzma-dev zlib1g-dev

Getting PyTorch sources:

git clone --recursive https://github.com/pytorch/pytorch --branch=release/1.6
cd pytorch

Setting up environment variables for the build.

Add the following lines to the ~/.bashrc file.

export NO_CUDA=1
export NO_DISTRIBUTED=1
export NO_MKLDNN=1 
export NO_NNPACK=1
export NO_QNNPACK=1

sudo su
source /home/<user>/.bashrc

Install python dependencies

pip3 install setuptools pyyaml numpy

Build and install PyTorch, time to grab a :coffee:, it make take a while.

Don't forget the -E that forces the environment variables to be used.

sudo -E python3 setup.py install

Check the installation worked:

cd 
python3
import torch
torch.__version__

Building your program with Torch

In your CMakeLists.txt :

cmake_minimum_required(VERSION 2.6)
project(projectName)

set(CMAKE_PREFIX_PATH "/home/pi/pytorch/torch") # Adding the directory where torch as been installed
set(CMAKE_CXX_STANDARD 14) # C14 required to compile Torch
set(CMAKE_CXX_STANDARD_REQUIRED TRUE)
add_compile_definitions(_GLIBCXX_USE_CXX11_ABI=0) # Torch is compiled with CXX11_ABI, so your program needs to be also, or you may have conflicts in some libraries (such as GTest for example)

# Specifying we are using pthread for UNIX systems.
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${TORCH_CXX_FLAGS} -pthread -Wall")

find_package(Torch REQUIRED)

if(NOT Torch_FOUND)
    message(FATAL_ERROR "Pytorch Not Found!")
endif(NOT Torch_FOUND)

message(STATUS "Pytorch status :")
message(STATUS "    libraries: ${TORCH_LIBRARIES}")
message(STATUS "    Torch Flags: ${TORCH_CXX_FLAGS}")

# Program executable
add_executable(projectName <sources>)

target_link_libraries(projectName PRIVATE pthread dl util ${TORCH_LIBRARIES})