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-- bb92c768e2271ddbebc1b1eb7e16a7b7c86a6e1c by Abseil Team <absl-team@google.com>: Automated g4 rollback of changelist 244998488. *** Reason for rollback *** I'm seeing test failures, rolling this back. *** Original change description *** BEGIN_PUBLIC The default constructor for optional<T> is filling dummy_ with zeros (see https://godbolt.org/z/IVea7X for a reduced example), which has a performance impact for large Ts. This comes from the gcc6 bugfix that made dummy as big as T. Because constexpr constructors are required to initialize all members of a struct, we cannot prevent this in a standard-compliant way as soon as dummy has any members (note that clang will happily accept adding a `constexpr dummy_type() {}` constructor... *** PiperOrigin-RevId: 245004716 -- 6e3ee35af50ffbee604c22300f3260ebc5f6cf52 by Abseil Team <absl-team@google.com>: The default constructor for optional<T> is filling dummy_ with zeros (see https://godbolt.org/z/IVea7X for a reduced example), which has a performance impact for large Ts. This comes from the gcc6 bugfix that made dummy as big as T. Because constexpr constructors are required to initialize all members of a struct, we cannot prevent this in a standard-compliant way as soon as dummy has any members (note that clang will happily accept adding a `constexpr dummy_type() {}` constructor to dummy_type to prevent zero-initialization, but this is UB AFAICT). This all stems from the fact that we're constructing an object by using placement new on dummy_. The solution I'm using here is to do the placement new on the actual data_. This creates a new issue in when T is volatile, because we can no longer use `&data_` to do the placement new. The solution I'm using here is to make data_ a non-const and non-volatile T, and only provide fully possibly qualified access through `reference()` accessors. I think this correctly prevents UB. PiperOrigin-RevId: 244998488 -- 4f52e64c4cf6aef8df6360007bcc53d8b00db2b4 by Abseil Team <absl-team@google.com>: Increase SYMBOL_BUF_SIZE from 2KB to 3KB. PiperOrigin-RevId: 244954529 GitOrigin-RevId: bb92c768e2271ddbebc1b1eb7e16a7b7c86a6e1c Change-Id: Iaed9a027064a9ecd194c5c146169c683b77f12ef |
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WORKSPACE |
Abseil - C++ Common Libraries
The repository contains the Abseil C++ library code. Abseil is an open-source collection of C++ code (compliant to C++11) designed to augment the C++ standard library.
Table of Contents
About Abseil
Abseil is an open-source collection of C++ library code designed to augment the C++ standard library. The Abseil library code is collected from Google's own C++ code base, has been extensively tested and used in production, and is the same code we depend on in our daily coding lives.
In some cases, Abseil provides pieces missing from the C++ standard; in others, Abseil provides alternatives to the standard for special needs we've found through usage in the Google code base. We denote those cases clearly within the library code we provide you.
Abseil is not meant to be a competitor to the standard library; we've just found that many of these utilities serve a purpose within our code base, and we now want to provide those resources to the C++ community as a whole.
Quickstart
If you want to just get started, make sure you at least run through the Abseil Quickstart. The Quickstart contains information about setting up your development environment, downloading the Abseil code, running tests, and getting a simple binary working.
Building Abseil
Bazel is the official build system for Abseil, which is supported on most major platforms (Linux, Windows, MacOS, for example) and compilers. See the quickstart for more information on building Abseil using the Bazel build system.
If you require CMake support, please check the CMake build instructions.
Codemap
Abseil contains the following C++ library components:
base
Abseil Fundamentals
Thebase
library contains initialization code and other code which all other Abseil code depends on. Code withinbase
may not depend on any other code (other than the C++ standard library).algorithm
Thealgorithm
library contains additions to the C++<algorithm>
library and container-based versions of such algorithms.container
Thecontainer
library contains additional STL-style containers, including Abseil's unordered "Swiss table" containers.debugging
Thedebugging
library contains code useful for enabling leak checks, and stacktrace and symbolization utilities.hash
Thehash
library contains the hashing framework and default hash functor implementations for hashable types in Abseil.memory
Thememory
library contains C++11-compatible versions ofstd::make_unique()
and related memory management facilities.meta
Themeta
library contains C++11-compatible versions of type checks available within C++14 and C++17 versions of the C++<type_traits>
library.numeric
Thenumeric
library contains C++11-compatible 128-bit integers.strings
Thestrings
library contains a variety of strings routines and utilities, including a C++11-compatible version of the C++17std::string_view
type.synchronization
Thesynchronization
library contains concurrency primitives (Abseil'sabsl::Mutex
class, an alternative tostd::mutex
) and a variety of synchronization abstractions.time
Thetime
library contains abstractions for computing with absolute points in time, durations of time, and formatting and parsing time within time zones.types
Thetypes
library contains non-container utility types, like a C++11-compatible version of the C++17std::optional
type.utility
Theutility
library contains utility and helper code.
License
The Abseil C++ library is licensed under the terms of the Apache license. See LICENSE for more information.
Links
For more information about Abseil:
- Consult our Abseil Introduction
- Read Why Adopt Abseil to understand our design philosophy.
- Peruse our Abseil Compatibility Guarantees to understand both what we promise to you, and what we expect of you in return.