Folly — Facebook's High-Performance C++ Foundation Library

Introduction

Folly (Facebook Open Source Library) is an open-source C++ library developed at Meta that provides core building blocks for high-performance systems programming. It supplements the C++ standard library with components that have been hardened through years of production use at one of the world's largest-scale infrastructures.

What Folly Does

• Provides high-performance concurrent data structures like ConcurrentHashMap, AtomicHashMap, and lock-free queues
• Implements a futures and promises framework (folly::Future) for composable asynchronous programming
• Offers optimized string utilities including fbstring (a drop-in std::string replacement) and fbvector
• Supplies memory allocation helpers, custom allocators, and arena-based allocation for latency-sensitive code
• Includes IO utilities such as IOBuf for zero-copy buffer management and AsyncSocket for event-driven networking

Architecture Overview

Folly is organized as a modular collection of largely independent components built on top of C++17. Each module addresses a specific systems-programming concern, from low-level bit manipulation and hardware intrinsics up through higher-level abstractions like EventBase for event loops and Executor for task scheduling. The library relies on a thin portability layer to support Linux, macOS, and Windows, and integrates with other Meta open-source projects like Fizz (TLS) and Wangle (networking framework).

Self-Hosting & Configuration

• Build requires CMake 3.0.2+, a C++17-capable compiler (GCC 7+ or Clang 6+), Boost, and several system libraries
• Install dependencies on Ubuntu: sudo apt install libboost-all-dev libevent-dev libdouble-conversion-dev libgoogle-glog-dev libgflags-dev
• Use -DBUILD_SHARED_LIBS=ON to produce shared libraries instead of static
• Individual components can be consumed via find_package(folly) after installation
• Vcpkg and Conan packages are available for cross-platform dependency management

Key Features

• Battle-tested at Meta scale across billions of requests per day
• Optimized fbstring implementation with small-string optimization and copy-on-write semantics
• folly::Future provides a composable async model with .then() chaining and executor awareness
• IOBuf enables zero-copy networking with reference-counted buffer chains
• Comprehensive benchmarking utilities (folly::Benchmark) for micro-benchmarking C++ code

Comparison with Similar Tools

• Abseil (Google) — focuses on standard-library extensions with ABI stability; Folly targets raw performance with less ABI concern
• Boost — broader scope and committee-track focus; Folly is more opinionated and Meta-specific
• POCO — provides higher-level application frameworks; Folly stays closer to systems-level primitives
• libcds — specializes in concurrent data structures; Folly offers concurrency plus general utilities
• Intel TBB — focuses on parallelism and task scheduling; Folly covers a wider utility surface

FAQ

Q: Does Folly require the entire library to be linked? A: No. Folly is modular, and you can link only the components you need via CMake targets such as Folly::folly or individual sub-libraries.

Q: Is Folly ABI-stable? A: Folly does not guarantee ABI stability across releases. It is designed to be built from source alongside your project.

Q: What platforms does Folly support? A: Folly officially supports Linux (primary), macOS, and Windows. Linux receives the most testing and optimization.

Q: How does folly::Future differ from std::future? A: folly::Future supports .then() continuation chaining, executor-based scheduling, and composability features like collectAll that std::future lacks.

Sources

• https://github.com/facebook/folly
• https://github.com/facebook/folly/tree/main/folly/docs