Skadic / sharded_map

A sharded hash map for C++20

Sharded Map

A sharded hash map implementation for parallel processing written for C++20.

The central type is ShardedMap<K, V, SeqHashMapType, UpdateFn>.

• K is the type of the keys.
• V is the type of the values.
• SeqHashMapType is the type of the hash map each thread will have locally. Any std::unordered_map compatible map should work.
• UpdateFn is an update function denoting what happens, if a new value is inserted or an existing value is updated. For examples, check the sharded_map::update_functions namespace or the examples/ folder in this repository.

Documentation is available here.

Usage

This is a header-only library, so you can just use the sharded_map.hpp header as is. If you use CMake, you can for example add this repo as a git submodule to your project, and add this to your CMakeLists.txt:

add_subdirectory(path/to/this/repo/sharded_map)

target_link_libraries(your_target PRIVATE sharded_map)

Tests

You can build and run tests using these commands:

cmake --preset=test
cmake --build --preset=test --config=Release
ctest --preset=default

Example

#include <sharded_map/sharded_map.hpp>
#include <atomic>
#include <omp.h>

using namespace sharded_map;

int main() {
  using Map = ShardedMap<size_t, size_t, std::unordered_map, update_functions::Overwrite<size_t, size_t>>;

  Map map(4, 128);
  // Iterate in parallel from 0 to 100'000 and insert the pair (i, 2*i) for each index
  map.batch_insert(0, 100'000, [&s](size_t i) { return std::pair(i, 2*i); });
}

For a more extensive and commented example, check the examples/ folder. You can build the examples using these commands:

cmake --preset=examples
cmake --build --preset=examples --config=Release

Then you can find the built binaries in ./build/examples/Release/.