libcappuccino - C++17 Cache and Associative Data Structure Library

https://github.com/jbaldwin/libcappuccino

libcappuccino is licensed under the Apache 2.0 license.

Overview

Thread safe cache and associative datastructures.
- Can disable thread safety for singly threaded apps via thread_safe::no.
The following eviction policies are currently supported:
- Cache (Fixed size contiguous memory).
  - First in first out (FIFO).
  - Least frequently used (LFU).
  - Least frequently used with dynamic aging (LFUDA).
  - Least recently used (LRU).
  - Most recently used (MRU).
  - Random Replacement (RR).
  - Time aware least recently used (TLRU).
  - Uniform time aware least recently used (UTLRU).
- Associative (Dynamic size non-contiguous memory).
  - Uniform time aware set (UTSET).
  - Uniform time aware map (UTMAP).

Usage

Examples

See all of the examples under the examples/ directory. Below are some simple examples to get your started on using libcappuccino.

Indivudal item TTL Least Recently Used Example

This example provides a individual item TTL LRU cache. This means each item placed in the cache can have its own TTL value and the eviction policy is TTL expired first and then LRU second. This cache is useful when items should have various TTLs applied to them. Use the Uniform TTL LRU if every item has the same TTL as it is more efficient on CPU and memory usage. This type of cache could be compared to the likes of how Redis/Memcached work but in memory of the application rather than a separate process.

    #include <cappuccino/cappuccino.hpp>
    
    #include <chrono>
    #include <iostream>
    
    int main()
    {
        using namespace std::chrono_literals;
    
        // Create a cache with up to 3 items.
        cappuccino::tlru_cache<uint64_t, std::string> cache{3};
    
        // Insert "hello", "world" with different TTLs.
        cache.insert(1h, 1, "Hello");
        cache.insert(2h, 2, "World");
    
        // Insert a third value to fill the cache.
        cache.insert(3h, 3, "nope");
    
        {
            // Grab hello and world, this update their LRU positions.
            auto hello = cache.find(1);
            auto world = cache.find(2);
    
            std::cout << hello.value() << ", " << world.value() << "!" << std::endl;
        }
    
        // Insert "hola", this will replace "nope" since its the oldest lru item,
        // nothing has expired at this time.
        cache.insert(30min, 4, "Hola");
    
        {
            auto hola  = cache.find(4); // "hola" was just inserted, it will be found
            auto hello = cache.find(1); // "hello" will also have a value, it is at the end of the lru list
            auto world = cache.find(2); // "world" is in the middle of our 3 lru list.
            auto nope  = cache.find(3); // "nope" was lru'ed when "hola" was inserted
                                        // since "hello" and "world were fetched
    
            if (hola.has_value())
            {
                std::cout << hola.value() << "\n";
            }
    
            if (hello.has_value())
            {
                std::cout << hello.value() << "\n";
            }
    
            if (world.has_value())
            {
                std::cout << world.value() << "\n";
            }
    
            if (!nope.has_value())
            {
                std::cout << "Nope was LRU'ed out of the cache.\n";
            }
        }
    
        return 0;
    }

Insert, Update, Insert Or Update

Each insert() method on the various caches takes an optional parameter allow that tells the cache how the insert call should behave. By default this parameter is set to allow insert_or_update on the elements being inserted into the cache. This means if they do not exist in the cache they will be added and if they do exists the values will be udpated and any metadata like TTLs will be adjusted/reset. The caller can also specify this parameter as just insert to only allow the item to be added if it doesn't already exist or as update to only change the item in the cahce if it already exists.

    #include <cappuccino/cappuccino.hpp>
    
    int main()
    {
        using namespace std::chrono_literals;
        using namespace cappuccino;
        // Uniform TTL LRU cache with a 1 hour TTL and 200 element cache capacity.
        // The key is uint64_t and the value is std::string.
        utlru_cache<uint64_t, std::string> cache{1h, 200};
    
        cache.insert(1, "Hello", allow::insert); // OK
        cache.insert(1, "Hello", allow::insert); // ERROR! already exists
    
        // Note that allow::insert can succeed if the item is TTLed out
        // in certain types of caches that support TTLs.
    
        cache.insert(1, "Hola", allow::update);  // OK exists
        cache.insert(2, "World", allow::update); // ERROR! doesn't exist
    
        cache.insert(2, "World"); // OK, parameter defaults to allow::insert_or_update
        return 0;
    }

Requirements

C++17 compiler (g++/clang++)
CMake
make and/or ninja

Instructions

Building

# This will produce a shared and static library to link against your project.
mkdir Release && cd Release
cmake -DCMAKE_BUILD_TYPE=Release ..
cmake --build .

CMake Projects

add_subdirectory()

To use within your cmake project you can clone the project or use git submodules and then add_subdirectory in the parent project's CMakeList.txt, assuming the cappuccino code is in a libcappuccino/ subdirectory of the parent project:

    add_subdirectory(libcappuccino)

To link to the <project_name> then use the following:

add_executable(<project_name> main.cpp)
target_link_libraries(<project_name> PRIVATE cappuccino)

Include cappuccino in the project's code by simply including #include <cappuccino/Cappuccino.hpp> as needed.

FetchContent

CMake can also include the project directly via a FetchContent declaration. In your project's CMakeLists.txt include the following code to download the git repository and make it available to link to.

    cmake_minimum_required(VERSION 3.11)
    
    # ... cmake project stuff ...
    
    include(FetchContent)
    FetchContent_Declare(
        cappuccino
        GIT_REPOSITORY https://github.com/jbaldwin/libcappuccino.git
        GIT_TAG        <TAG_OR_GIT_HASH>
    )
    FetchContent_MakeAvailable(cappuccino)
    
    # ... cmake project more stuff ...
    
    target_link_libraries(${PROJECT_NAME} PRIVATE cappuccino)

Contributing and Testing

This project has a GitHub Actions CI implementation to compile and run unit tests.

Currently tested distros:

ubuntu:latest
fedora:latest
msvc:latest

Currently tested compilers:

g++
clang
msvc

Contributing a new feature should include relevant tests. Examples are welcome if understanding how the feature works is difficult or provides some additional value the tests otherwise cannot.

CMake is setup to understand how to run the tests. Building and then running ctest will execute the tests locally.

mkdir Release && cd Release
cmake -DCMAKE_BUILD_TYPE=Release ..
cmake --build .
ctest -VV

Support

File bug reports, feature requests and questions using GitHub Issues