A high-performance, concurrent hash table
C++ Other



libcuckoo provides a high-performance, compact hash table that allows multiple concurrent reader and writer threads.

The Doxygen-generated documentation is available at the project page.

Authors: Manu Goyal, Bin Fan, Xiaozhou Li, David G. Andersen, and Michael Kaminsky

For details about this algorithm and citations, please refer to our papers in NSDI 2013 and EuroSys 2014. Some of the details of the hashing algorithm have been improved since that work (e.g., the previous algorithm in 1 serializes all writer threads, while our current implementation supports multiple concurrent writers), however, and this source code is now the definitive reference.


This library has been tested on Mac OSX >= 10.8 and Ubuntu >= 12.04.

It compiles with clang++ >= 3.3 and g++ >= 4.7, however we strongly suggest using the latest versions of both compilers, as they have greatly improved support for atomic operations. Building the library requires CMake version >= 3.1.0. To install it on Ubuntu

$ sudo apt-get update && sudo apt-get install cmake


We suggest you build out of source, in a separate build directory:

$ mkdir build
$ cd build

There are numerous flags you can pass to CMake to set which parts of the repository it builds.

-DCMAKE_INSTALL_PREFIX : set the location where the libcuckoo header files are installed

-DCMAKE_BUILD_TYPE : enable different types of build flags for different purposes

-DBUILD_EXAMPLES=1 : tell CMake to build the examples directory

-DBUILD_TESTS=1 : build all tests in the tests directory

-DBUILD_STRESS_TESTS=1 : build all tests in the tests/stress-tests directory

-DBUILD_UNIT_TESTS=1 : build all tests in the tests/unit-tests directory

-DBUILD_UNIVERSAL_BENCHMARK=1 : build the universal benchmark in the tests/universal-benchmark directory. This benchmark allows you to test a variety of operations in arbitrary percentages, with specific keys and values. Consult the README in the benchmark directory for more details.

So, if, for example, we want to build all examples and all tests into a local installation directory, we'd run the following command from the build directory.

$ make all
$ make install


When compiling your own files with libcuckoo, always remember to enable C++11 features on your compiler. On g++, this would be -std=c++11, and on clang++, this would be -std=c++11 -stdlib=libc++.

Once you have installed the header files and the install location has been added to your search path, you can include <libcuckoo/cuckoohash_map.hh>, and any of the other headers you installed, into your source file.

If you want to use CityHash for strings, which we recommend, you should install it (either from your own repository or the included one, which uses autotools), and then include <libcuckoo/city_hasher.hh>, which is a wrapper for CityHash compatible with the std::hash type.

There is also a C wrapper around the table that can be leveraged to use libcuckoo in a C program. The interface consists of a template header and implementation file that can be used to generate instances of the hashtable for different key-value types.

See the examples directory for a demonstration of all of these features.


The tests directory contains a number of tests and benchmarks of the hash table, which also can serve as useful examples of how to use the table's various features. Make sure to enable the tests you want to build with the corresponding CMake flags. The test suite can be run with the make test command. The test executables can be run individually as well.

Issue Report

To let us know your questions or issues, we recommend you report an issue on github. You can also email us at libcuckoo-dev@googlegroups.com.


Copyright (C) 2013, Carnegie Mellon University and Intel Corporation

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at


Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

The third-party libraries have their own licenses, as detailed in their source files.