1### `folly/` 2 3### Components 4 5Below is a list of (some) Folly components in alphabetical order, along with 6a brief description of each. 7 8#### `Arena.h`, `ThreadCachedArena.h` 9 10Simple arena for memory allocation: multiple allocations get freed all 11at once. With threaded version. 12 13#### [`AtomicHashMap.h`, `AtomicHashArray.h`](AtomicHashMap.md), `AtomicHashArray.h`, `AtomicLinkedList.h`, ... 14 15High-performance atomic data-structures. Many of these are built with very specific 16tradeoffs and constraints in mind that make them faster than their more general 17counterparts. Each header should contain information about what these tradeoffs are. 18 19#### `Baton.h` 20 21A Baton allows a thread to block once and be awoken: it captures a single handoff. It is 22essentially a (very small, very fast) semaphore that supports only a single call to `sem_call` 23and `sem_wait`. 24 25#### [`Benchmark.h`](Benchmark.md) 26 27A small framework for benchmarking code. Client code registers 28benchmarks, optionally with an argument that dictates the scale of the 29benchmark (iterations, working set size etc). The framework runs 30benchmarks (subject to a command-line flag) and produces formatted 31output with timing information. 32 33#### `Bits.h` 34 35Various bit manipulation utilities optimized for speed; includes functions 36that wrap the 37[ffsl(l)](http://linux.die.net/man/3/ffsll) primitives in a uniform 38interface. 39 40#### `ConcurrentSkipList.h` 41 42An implementation of the structure described in [A Provably Correct 43Scalable Concurrent Skip 44List](http://www.cs.tau.ac.il/~shanir/nir-pubs-web/Papers/OPODIS2006-BA.pdf) 45by Herlihy et al. 46 47#### [`Conv.h`](Conv.md) 48 49A variety of data conversion routines (notably to and from string), 50optimized for speed and safety. 51 52#### `Demangle.h` 53 54Pretty-printing C++ types. 55 56#### `DiscriminatedPtr.h` 57 58Similar to `boost::variant`, but restricted to pointers only. Uses the 59highest-order unused 16 bits in a pointer as discriminator. So 60`sizeof(DiscriminatedPtr<int, string, Widget>) == sizeof(void*)`. 61 62#### [`dynamic.h`](Dynamic.md) 63 64Dynamically-typed object, created with JSON objects in mind. `DynamicConverter.h` is 65a utility for efficiently converting from a `dynamic` to a more concrete structure when 66the scheme is known (e.g. json -> `map<int,int>`). 67 68#### `EvictingCacheMap.h` 69 70A simple LRU hash map. 71 72#### [`FBString.h`](FBString.md) 73 74A drop-in implementation of `std::string` with a variety of optimizations. 75 76#### [`FBVector.h`](FBVector.md) 77 78A mostly drop-in implementation of `std::vector` with a variety of 79optimizations. 80 81#### `File.h` 82 83A C++ abstraction around files. 84 85#### `Fingerprint.h` 86 87Rabin fingerprinting. 88 89### [`Function.h`](Function.md) 90 91A polymorphic wrapper for callables similar to `std::function` but not copyable and therefore able to wrap non-copyable callables, such as lambdas that capture move-only types like `std::unique_ptr` or `folly::Promise`. 92 93### [`futures/`](Futures.md) 94 95Futures is a framework for expressing asynchronous code in C++ using the Promise/Future pattern. 96 97#### [`Format.h`](Format.md) 98 99Python-style formatting utilities. 100 101#### `gen/` 102 103This library makes it possible to write declarative comprehensions for 104processing sequences of values efficiently in C++ akin to C#'s LINQ. 105 106#### [`GroupVarint.h`](GroupVarint.md) 107 108[Group Varint 109encoding](http://www.ir.uwaterloo.ca/book/addenda-06-index-compression.html) 110for 32-bit values. 111 112#### `IPAddress.h` 113 114A collection of utilities to deal with IPAddresses, including ipv4 and ipv6. 115 116#### `io/` 117 118A collection of useful of abstractions for high-performance io. This is heavily relied upon 119in Facebook's internally networking code. 120 121#### `Hash.h` 122 123Various popular hash function implementations. 124 125#### [`Histogram.h`](Histogram.md) 126 127A simple class for collecting histogram data. 128 129#### `IntrusiveList.h` 130 131Convenience type definitions for using `boost::intrusive_list`. 132 133#### `json.h` 134 135JSON serializer and deserializer. Uses `dynamic.h`. 136 137#### `Likely.h` 138 139Wrappers around [`__builtin_expect`](http://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html). 140 141#### `Malloc.h`, `Memory.h` 142 143Memory allocation helpers, particularly when using jemalloc. 144 145#### `MicroSpinLock.h` 146 147A really, *really* small spinlock for fine-grained locking of lots of teeny-tiny data. 148 149#### `MPMCQueue.h` 150 151MPMCQueue<typename> is a high-performance bounded concurrent queue that 152supports multiple producers, multiple consumers, and optional blocking. 153The queue has a fixed capacity, for which all memory will be allocated 154 up front. 155 156The additional utility `MPMCPipeline.h` is an extension that lets you 157chain several queues together with processing steps in between. 158 159#### [`PackedSyncPtr.h`](PackedSyncPtr.md) 160 161A highly specialized data structure consisting of a pointer, a 1-bit 162spin lock, and a 15-bit integral, all inside one 64-bit word. 163 164#### [`Poly.h`](Poly.md) 165 166A class template that makes it relatively easy to define a type-erasing 167polymorphic object wrapper. 168 169#### `Preprocessor.h` 170 171Necessarily evil stuff. 172 173#### [`ProducerConsumerQueue.h`](ProducerConsumerQueue.md) 174 175Lock free single-reader, single-writer queue. 176 177#### `Random.h` 178 179Defines only one function---`randomNumberSeed()`. 180 181#### `Range.h` 182 183Boost-style range facility and the `StringPiece` specialization. 184 185#### `RWSpinLock.h` 186 187Fast and compact reader-writer spin lock. 188 189#### `ScopeGuard.h` 190 191C++11 incarnation of the old [ScopeGuard](http://drdobbs.com/184403758) idiom. 192 193#### `Singleton.h` 194 195A singleton to rule the singletons. This is an attempt to insert a layer between 196C++ statics and the fiasco that ensues, so that things can be created, and destroyed, 197correctly upon program creation, program end and sometimes `dlopen` and `fork`. 198 199Singletons are bad for you, but this may help. 200 201#### [`SmallLocks.h`](SmallLocks.md) 202 203Very small spin locks (1 byte and 1 bit). 204 205#### `small_vector.h` 206 207Vector with the small buffer optimization and an optional embedded 208`PicoSpinLock`. 209 210#### `sorted_vector_types.h` 211 212Collections similar to `std::map` but implemented as sorted vectors. 213 214#### `stats/` 215 216A collection of efficient utilities for collecting statistics: 217* time series counters, gauges, histograms, and quantiles; 218* single-pass mean and variance. 219 220#### `StlAllocator.h` 221 222STL allocator wrapping a simple allocate/deallocate interface. 223 224#### `String.h` 225 226String utilities that connect `folly::fbstring` with `std::string`. 227 228#### `Subprocess.h` 229 230Subprocess library, modeled after Python's subprocess module. 231 232#### [`Synchronized.h`](Synchronized.md) 233 234High-level synchronization library. 235 236#### `System.h` 237 238Demangling and errno utilities. 239 240#### [`ThreadCachedInt.h`](ThreadCachedInt.md) 241 242High-performance atomic increment using thread caching. 243 244#### [`ThreadLocal.h`](ThreadLocal.md) 245 246Improved thread local storage for non-trivial types. 247 248#### `TimeoutQueue.h` 249 250Queue with per-item timeout. 251 252#### `Traits.h` 253 254Type traits that complement those defined in the standard C++11 header 255`<traits>`. 256 257#### `Unicode.h` 258 259Defines the `codePointToUtf8` function. 260 261#### `Uri.h` 262 263A collection of utilities to deal with URIs. 264