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facebook /folly

An open-source C++ library developed and used at Facebook.

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Folly: Facebook Open-source Library

Build Status

What is



Folly (acronymed loosely after Facebook Open Source Library) is a library of C++14 components designed with practicality and efficiency in mind. Folly contains a variety of core library components used extensively at Facebook. In particular, it's often a dependency of Facebook's other open source C++ efforts and place where those projects can share code.

It complements (as opposed to competing against) offerings such as Boost and of course


. In fact, we embark on defining our own component only when something we need is either not available, or does not meet the needed performance profile. We endeavor to remove things from folly if or when


or Boost obsoletes them.

Performance concerns permeate much of Folly, sometimes leading to designs that are more idiosyncratic than they would otherwise be (see e.g.




). Good performance at large scale is a unifying theme in all of Folly.

Logical Design

Folly is a collection of relatively independent components, some as simple as a few symbols. There is no restriction on internal dependencies, meaning that a given folly module may use any other folly components.

All symbols are defined in the top-level namespace


, except of course macros. Macro names are ALL_UPPERCASE and should be prefixed with `FOLLY_

. Namespace


defines other internal namespaces such as



detail`. User code should not depend on symbols in those namespaces.

Folly has an


directory as well. This designation connotes primarily that we feel the API may change heavily over time. This code, typically, is still in heavy use and is well tested.

Physical Design

At the top level Folly uses the classic "stuttering" scheme


used by Boost and others. The first directory serves as an installation root of the library (with possible versioning a la


), and the second is to distinguish the library when including files, e.g.

#include <folly></folly>


The directory structure is flat (mimicking the namespace structure), i.e. we don't have an elaborate directory hierarchy (it is possible this will change in future versions). The subdirectory


contains files that are used inside folly and possibly at Facebook but not considered stable enough for client use. Your code should not use files in


lest it may break when you update Folly.



subdirectory includes the unittests for all components, usually named


for each


. The


directory contains documentation.

What's in it?

Because of folly's fairly flat structure, the best way to see what's in it is to look at the headers in [top level


directory]( You can also check the [


folder]( for documentation, starting with theoverview.

Folly is published on GitHub at

Build Notes


folly supports gcc (5.1+), clang, or MSVC. It should run on Linux (x86-32, x86-64, and ARM), iOS, macOS, and Windows (x86-64). The CMake build is only tested on some of these platforms; at a minimum, we aim to support macOS and Linux (on the latest Ubuntu LTS release or newer.)

folly requires a version of boost compiled with C++14 support.

googletest is required to build and run folly's tests. You can download it from The following commands can be used to download and install it:

wget && \ tar zxf release-1.8.0.tar.gz && \ rm -f release-1.8.0.tar.gz && \ cd googletest-release-1.8.0 && \ cmake . && \ make && \ make install

Finding dependencies in non-default locations

If you have boost, gtest, or other dependencies installed in a non-default location, you can use the




variables to make CMAKE look also look for header files and libraries in non-standard locations. For example, to also search the directories




for header files and the directories




for libraries, you can invoke


as follows:

cmake \ -DCMAKE\_INCLUDE\_PATH=/alt/include/path1:/alt/include/path2 \ -DCMAKE\_LIBRARY\_PATH=/alt/lib/path1:/alt/lib/path2 ...

Building tests

By default, building the tests is disabled as part of the CMake


target. To build the tests, specify


to CMake at configure time.

Ubuntu 16.04 LTS

The following packages are required (feel free to cut and paste the apt-get command below):

sudo apt-get install \ g++ \ cmake \ libboost-all-dev \ libevent-dev \ libdouble-conversion-dev \ libgoogle-glog-dev \ libgflags-dev \ libiberty-dev \ liblz4-dev \ liblzma-dev \ libsnappy-dev \ make \ zlib1g-dev \ binutils-dev \ libjemalloc-dev \ libssl-dev \ pkg-config \ libunwind-dev

Folly relies on fmt which needs to be installed from source. The following commands will download, compile, and install fmt.

git clone && cd fmt mkdir \_build && cd \_build cmake .. make -j$(nproc) sudo make install

If advanced debugging functionality is required, use:

sudo apt-get install \ libunwind8-dev \ libelf-dev \ libdwarf-dev

In the folly directory (e.g. the checkout root or the archive unpack root), run:

mkdir \_build && cd \_build cmake .. make -j $(nproc) make install # with either sudo or DESTDIR as necessary

OS X (Homebrew)

folly is available as a Formula and releases may be built via

brew install folly


You may also use


to build against




This will create a build directory


in the top-level.

OS X (MacPorts)

Install the required packages from MacPorts:

sudo port install \ boost \ cmake \ gflags \ git \ google-glog \ libevent \ libtool \ lz4 \ lzma \ openssl \ snappy \ xz \ zlib

Download and install double-conversion:

git clone cd double-conversion cmake -DBUILD\_SHARED\_LIBS=ON . make sudo make install

Download and install folly with the parameters listed below:

git clone cd folly mkdir \_build cd \_build cmake .. make sudo make install

Windows (Vcpkg)

folly is available in Vcpkg and releases may be built via

vcpkg install folly:x64-windows


You may also use

vcpkg install folly:x64-windows --head

to build against



Other Linux distributions

Download and build double-conversion. You may need to tell cmake where to find it.


ln -s src double-conversion


mkdir build && cd build




  • additional platform specific dependencies:

Fedora >= 21 64-bit (last tested on Fedora 28 64-bit) - gcc - gcc-c++ - cmake - automake - boost-devel - libtool - lz4-devel - lzma-devel - snappy-devel - zlib-devel - glog-devel - gflags-devel - scons - double-conversion-devel - openssl-devel - libevent-devel

Optional - libdwarf-dev - libelf-dev - libunwind8-dev

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