Abseil Blog

The Danger of Atomic Operations

18 Jan 2022

By Ashley Hedberg, Software Engineer

The C++ Standard provides a library for performing fine-grained atomic operations (e.g. std::atomic). Engineers sometimes reach for these atomic operations in the hope to introduce some lock-free mechanism, or to introduce clever tricks to improve performance. At Google, we’ve found – more often than not – that such attempts lead to code that is difficult to get right, hard to understand, and can often introduce subtle and sometimes dangerous bugs.

We’ve now published a guide on the danger of these atomic operations, and are publishing it to Abseil as a general programming guide. Atomic operations should be used only in a handful of low-level data structures which are written by a few experts and then reviewed and tested thoroughly. Most programmers make mistakes when they attempt direct use of atomic operations. Even when they don’t, the resulting code is hard for others to maintain.

For more information, check out The Danger of Atomic Operations.

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SWE Book Freely Available

22 Apr 2021

Software Engineering at Google Book Availability

By Titus Winters, Tom Manshreck, and Hyrum Wright

We’re very pleased to announce that the “Software Engineering at Google” book (the Flamingo Book) is now freely available electronically under a Creative Commons license. You can get a PDF at SWE Book.

From the very beginning of this project, about three years ago, our intent has been to describe how Google thinks about Software Engineering, and to get people thinking about the same kinds of big interesting problems. We think that the best way to do that is to make sure that the content is available for everyone, so we’re providing it now, free of charge. We’re very grateful for our partners at O’Reilly for helping to make this possible (and of course we encourage you to support them and buy a physical copy if you can, etc).

Some of you may be aiming to land a job at Google in the future: we’ve heard from dozens of Nooglers that this is the handbook they needed to understand the unique and complex machine that is Google. We hope this book is useful for you.

Some of you may be running your own software companies. You’ll have different scales and problems, but hopefully you can learn from how we think about problems arising from Time and Scale, and how we evaluate the relevant Tradeoffs (these are the main themes threaded through every chapter of the book). You may want to lean on our thinking, or blaze your own trails. We hope the insights we’ve earned the hard way can make your path easier.

Some of you may know more than us. There are several topics in the book where we are still trying to find a good answer. We’re making our thinking public - why not show us where we’re wrong?

Over the past year we’ve heard from hundreds of you, all over the world, with stories about how this material has affected your practice and thinking. We’re also seeing this picked up by colleges and universities looking to modernize their discussion of software engineering topics. We’re thrilled at this reception, and very excited that we can take this next step in sharing this material.

As Nicole Forsgren told us once, “Accountants still have meetings to discuss their practices, and accountancy goes back thousands of years. Software Engineering is barely 50 years old. Give us a minute.” As an industry, and as a discipline, we’re still figuring things out. We hope that this book, in some small way, can help with that.

-Titus, Tom, and Hyrum

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Abseil Platform Support Update

01 Oct 2020

Abseil Platform Support Update

By Derek Mauro, Abseil Engineer

In September 2017, Abseil made the following support promise:

We will support our code for at least 5 years. We will support language versions, compilers, platforms, and workarounds as needed for 5 years after their replacement is available, when possible. If it is technically infeasible (such as support for MSVC before 2015, which has limited C++11 functionality), those will be noted specifically. After 5 years we will stop support and may remove workarounds. ABSL_HAVE_THREAD_LOCAL is a good example: the base language feature works on everything except Xcode prior to Xcode 8 ; once Xcode 8 is out for 5 years, we will drop that workaround support.

Read more

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Abseil Status

10 Sep 2020

By Xiaoyi Zhang, Google Engineer, Emeritus

The Abseil status library is now available on abseil.io. This library is used within Google for error handling and contains the following two abstractions:

• absl::Status
• absl::StatusOr<T>

Within Google, absl::Status is the primary mechanism to gracefully handle errors across API boundaries (and in particular across RPC boundaries). Some of these errors may be recoverable, but others may not. Most functions that can produce a recoverable error should be designed to return either an absl::Status (or the similar absl::StatusOr<T>, which holds either an object of type T or an error).

Read more

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Announcing TCMalloc

12 Feb 2020

By Chris Kennelly, Google Software Engineer

We are happy to announce the arrival of TCMalloc, a fast memory allocator with useful profiling and introspection features.

The source code can be found on Github. This is a distinct repository, allowing Abseil to be used independently of TCMalloc. The library includes:

• A lockfree, per-CPU cache implementation based on restartable sequences, available on modern Linux kernels, and a per-thread based fallback implementation.
• A hugepage-aware backend that reduces TLB stalls by more densely populating hugepage subregions while reducing memory waste.
• Optimizations leveraging modern C++ language features, including sized delete from C++14 and overaligned allocation from C++17.
• Always-on, sampling-based heap profiling, allowing an application to obtain a heap profile without additional configuration. We also provide a “peak heap” profile, a snapshot of the application’s memory usage near its high watermark of usage.

Read more

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