C++ Persistent Memoization : cppersist

TLDR

Cppersist is a small framework which allows users to apply persistent memoization to a member function. Cppersist allows member functions to be memoized via a filesystem, MongoDB, or in-memory.

Documentation

The documentation of cppersist is found here. Navigate to the 'modules' tab for documentation on the user-visible parts of cppersist.

Minimal Working Example

~$ git clone https://github.com/tallalnparis4ev/cppersist.git
~$ cd ./cppersist/demo
~/cppersist/demo$ ./build_demo
~/cppersist/demo$ ./demo

You should see the output "2" twice. You should also have a directory called "persist" that is populated with entries.

Example C++ File Using cppersist

Here is an example of how cppersist is used:

#include <cppersist/local.hpp> //if you need to memoize with your filesystem
#include <cppersist/mongo.hpp> //if you need to memoize with MongoDB
#include <cppersist/memory.hpp> //if you need to memoize in-memory
#include <iostream>

//The class containing the function you want to memoize
class FibonacciSolver: public cpst::Memoizable<int, int>{ //<--- these templates must correspond to 
//<return type of function to memoize, comma separated list of input types of function to memoize>
  public:
    int solve(int n) override { //the function you want to memoize - must be called "solve"!
      if(n<=1) return n;
      return solve(n-1) + solve(n-2);
    }
};

//Serialization function
std::string intostr(int x){
  return std::to_string(x);
}
//Deserialization function
int strtoi(std::string x){
  return std::stoi(x);
}
//Key function
std::string keymaker(int x){
  return std::to_string(x);
}

int main(int argc, char** argv) {
  cpst::PersistentMemoized memoizedFib = cpst::getLocalMemoizedObj<FibonacciSolver>(keymaker,intostr,strtoi); //disk cache
  std::cout << memoizedFib(2) << std::endl;
  memoizedFib = cpst::getMongoMemoizedObj<FibonacciSolver>(keymaker,intostr,strtoi,"localhost:5000"); //mongo cache
  std::cout << memoizedFib(2) << std::endl;
  cpst::Memoized memoizedInMemoryFib = cpst::getMemoizedObj<FibonacciSolver>(keymaker,intostr,strtoi); //in-memory cache
  std::cout << memoizedInMemoryFib(2) << std::endl;
}

Example CMake File Building the Above File

To build your project, utilising cppersist, via CMake (version 3.15.2+ required):

cmake_minimum_required(VERSION 3.15.2)
set(CMAKE_CXX_STANDARD 17)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

#========= Change these lines for your project
project(demo)
add_executable(${CMAKE_PROJECT_NAME} fib.cpp)
#=============================================

#Get cppersist 
include(FetchContent)
FetchContent_Declare(cppersist GIT_REPOSITORY https://github.com/tallalnparis4ev/cppersist GIT_TAG master)
FetchContent_MakeAvailable(cppersist)
set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} ${cppersist_SOURCE_DIR}/cppersist/cmake)

#Link threading and filesystem libraries
set(THREADS_PREFER_PTHREAD_FLAG ON)
find_package(Threads REQUIRED)
find_package(Filesystem REQUIRED)

include_directories(${cppersist_SOURCE_DIR})

#Get cpr if needed
if(MONGO)
  FetchContent_Declare(cpr GIT_REPOSITORY https://github.com/tallalnparis4ev/cpr.git GIT_TAG stable)
  FetchContent_MakeAvailable(cpr)
  set(CPR "cpr::cpr")
endif()
target_link_libraries(${CMAKE_PROJECT_NAME} PRIVATE Threads::Threads std::filesystem ${CPR})

Build - only for filesystem cache

cmake .
make

Build - for MongoDB cache

cmake -DMONGO=true .
make

Setting up the MongoDB server

~/cppersist/$ cd mongo_server
~/cppersist/mongo_server$ python3 setup.py install
~/cppersist/mongo_server$ python3 run.py [desried port number]

This will run the MongoDB server at localhost:[desired port number]. The default port number is 5000, which will be used if a port number isn't passed in. The MongoDB server is configured by the settings.py file.

By default the MongoDB server communicates to a single MongoDB instance which should run at localhost:27017. You are responsible for setting up this MongoDB instance in any way you would like.

Running Tests

~$ cd ./cppersist/test
~/cppersist/test$ ./build_tests
~/cppersist/test$ ./run_tests

Note: for the MongoDB tests to pass you must setup two MongoDB servers - one listening at port 5000 and the other at port 5001. The MongoDB instance they communicate with must not have any entries with the funcName "test" in the collection "persist" of the database "memoisation".