Abseil: C++ Common Libraries

To take from javascript, this is a mix of underscore (utility) and, uhh, babel(?) for essentially polyfilling certain runtime features slated for future (hypothetical) approval.

vvanders4• 9 years ago

Can't speak to Abseil but I won't let boost within 10,000 feet of any codebase I control.

I value my compile times more than anything it provides.

_slyo• 9 years ago

Boost contains over 120 libraries and counting, with over 70 authors and maintainers. There are many parts of Boost that I will never use (e.g. most of the pre c++11 libs), but the pros of having it available when you need it far outweigh the cons.

If a particular library is costing you more in compile time than it's worth in convenience, just rm -rf it from your Boost install -- better yet, write a script to prepend `static_assert(false, "this header is banned by decree of vvanders");` to the top of the banned headers.

There's plenty in Boost to love -- don't let a few rotten apples spoil the bunch.

Full disclosure: I'm a Boost developer

Layuso• 9 years ago

I value my developing times more than anything. Boost is one library which is developed and tested on almost every c++ target platform, providing us with stable, tested, and performing common utilities to speed up your developments and run anywhere.

Reasons not to use boost: - My code is one monolithic spaghetti and I do not use unit tests. - I do not want to learn Boost. - I don't trust template hippies.

Not using Boost is an irrational decision and you know it.

7197ghr918hf3• 9 years ago

A couple of my favorite types and functions in absl:

- Span

For when you want to take an array or a vector.

- string_view

Avoids string copies. Makes your program faster. Its creation was a reaction to situations like https://news.ycombinator.com/item?id=8704318. (It predates that revelation, but internally the plague of string copies has been known for some time.)

- Mutex

A better mutex with deadlock detection.

- Substitute

A string formatting function between 5 and 1000s of times faster than snprintf. Profile your code some time. If it's anything like mine, you might be surprised at how much this matters.

- base::Time and base::Duration

Excellent wall time utilities, similar to Go's wall clock time libraries.

roel_v2• 9 years ago

"- Span For when you want to take an array or a vector."

How's this different from taking a pair of iterators?

"string_view"

After having read all those articles about c++17's string_view, I still don't really get the real differences. OK, when parsing (i.e. using many substrings) it makes sense (but then you'd usually work with char* anyway); and maybe some people interact with C libraries that only take char* a lot (and in cases where they have to 'cross the boundary' often). So maybe in text-heavy applications (like I imagine C++ application for the web would be) it makes some sense, but I fail to understand why it's causing this much excitement.

"Substitute"

There are so many fast formatting libraries already - what does this one offer over those? Because it's generally a trade off between completeness/type safety on the one hand, and speed on the other. I use boost::format which is quite slow in benchmarks, but again I don't do much string processing.

"base::Time and base::Duration"

In what way are these different from boost::date_time and std::chrono? Here again the documentation (for Abseil) seem to be missing.

I mean, I'm all for batteries-included libraries - but this just seems to be a few loosely-related classes slapped together and the only reason it's even on here is because it's from Google. There are dozens of similar libraries languishing on sourceforge and github. Compare it to e.g. POCO - this is not even in the same league.

duneroadrunner4• 9 years ago

- Mutex

From their "Devguide":

Clients of Mutex must obey these rules:

1. Each time a thread acquires a Mutex it must later release it.

2. A thread may not attempt to release a Mutex unless it holds it.

3. A thread may not attempt to acquire an exclusive lock on a Mutex it already holds.

For basic sharing of resources between threads, using "access requesters"[1] can be safer and more convenient as they automatically take care of these rules for you.

And if you need to use the mutex directly, the SaferCPlusPlus library provides a "recursive_shared_timed_mutex"[2] (the one missing from the standard library), which allows a thread to hold multiple ("read" and/or "write") locks at the same time (relieving the "self-deadlock" issue). The mutex isn't documented, but it functions just as its name suggests.

[1] shameless plug: https://github.com/duneroadrunner/SaferCPlusPlus#asynchronou...

[2] https://github.com/duneroadrunner/SaferCPlusPlus/blob/master...

yegle• 9 years ago

A hidden perk of this project is the open source of "C++ Tips of the Week" (TotW internally). The plan, according to the page, is to post the revised and vetted TotW docs to the public.

https://abseil.io/tips/

erik_seaberg• 9 years ago

Also: https://news.ycombinator.com/item?id=15339564

RcouF1uZ4gsC2• 9 years ago

I think one of the biggest issues for adoption will be the Bazel build system. The C++ world seems to be slowly standardizing on CMake. Having to use another build system to incorporate this library will give people second thoughts about incorporating this library.

0xbear5• 9 years ago

Bazel is not just a build system though. It’s also dependency management system, parallel test system, cross language build system, cross platform build system, and a bunch of other things, with build file syntax a 10 year old could learn in an hour. Some of those things you could plausibly do with CMake, but a lot more effort. Once you learn how to use it (which doesn’t take long) Bazel is pretty darn nice.

mikepurvis• 9 years ago

Nonetheless, Bazel is very much set up for Google's mentality of building giant static binaries from head and shipping them off to a server somewhere, where they'll be replaced in two weeks with the next release, and then never thought of again. There's some software out here in the world that works like that, but most of it doesn't.

In any case, CMake is _also_ a dependency management system, but works with libraries in the way that they are shipped on a typical Linux distribution. It lets you find common stuff easily, and has multiple extension points in terms of adding support for new libraries. CMake itself can ship your find module, the library you're linking against can ship it, or you can ship it yourself.

krona2• 9 years ago

Once you learn how to use it (which doesn’t take long) Bazel is pretty darn nice.

I've spent a few hundred hours integrating bits of CMake build scripts in to various Bazel builds.

If you're doing something which is explicitly catered for by Bazel itself then it works well, so long as you avoid the bugs.

Otherwise, you'll have to confront the hermetic build abstractions which prevent otherwise simple operations. Bazel toolchain files are just as bad as CMake, if not worse.

I'll give Bazel another try in a few years. For now, I still prefer CMake+Ninja, worts and all.

haberman3• 9 years ago

Hi there, I work at Google on the Protocol Buffers team. The Abseil team will soon be adding CMake support (and automake, I hope). We need this for Protocol Buffers, which currently supports CMake and automake.

shahms2• 9 years ago

Why would you wish maintenance of either of those things on your coworkers?

RcouF1uZ4gsC2• 9 years ago

Glad to hear. This will make using it with our existing code base much easier.

Camillo• 9 years ago

It would be nice if Bazel could generate CMake projects.

weberc22• 9 years ago

CMake is the biggest reason I left C++ for Rust (there are others, of course), which is a shame because I actually came to like modern C++ (after years of using it). I just don't have time to maintain a complex build program (in a crappy, slow language to boot) when Cargo just works out of the box.

pjmlp2• 9 years ago

Cargo still doesn't work out of the box for linking against binary libraries.

That, alongside the lack of incremental compiler and linking, means my C++ work projects (native libraries for Java and .NET) actually do compile much faster than Rust occasional weekend projects.

malkia• 9 years ago

I think the opposite - the descriptive language of bazel (buck, pants, build.gn and others too) is the key feature. I haven't seen anything that comes so close to defining in very precise, and clean manner your exact dependencies across multiple build platforms.

It is a foreign lang for folks used to MSBuild, .vcxproj/.sln, etc. - like the debug/release, or CRT options are not right away visible (just saw a commit 15-20 hrs ago in bazel to support dynamic CRT linking), but I'm sure this is coming.

vvanders4• 9 years ago

My experience has been anything but positive in those systems. I spent ~3 hours trying to get build.gn to work for a "non-googler" config to build Chromium, gave up on it. Ditto Buck, hit some random dependency issue and would fail to run.

Honestly CMake gets a lot of hell but it's the only one I've seen work wide-scale. Short of a greenfield implementation (like say Rust's package manager) I don't think you'll do much better in C++.

erichocean• 9 years ago

I freaking LOVE Bazel. Convert every library I use from CMake to Bazel on first use. Fork + BUILD and you're good to go.

ezoe• 9 years ago

It looks like most of the libraries are C++11 implementation of some of the C++14/17 standard libraries.

katzdm2• 9 years ago

I wouldn't say "most", though this is definitely a slice of what is offered.

Some of this is also laying the groundwork for the release of further APIs, as well as making it easier for Google to release/support higher-level libraries (eg. Protobuf, TF, etc).

geofft2• 9 years ago

For distro packagers, is the idea that this should have SONAME libabseil.so.0 and remain at libabseil.so.0 forever?

(I know Google's preferred option is that we all realize that concepts like "distros" and "shared libraries" and "SONAMEs" are so last century, and tbh they are, but we'll have them for a long time yet, and it's helpful for upstream libraries to declare what their preferred SONAME is so that you can use the same dynamically-linked compiled binary on multiple distros.)

jlebar• 9 years ago

Since abseil doesn't promise ABI compatibility over time, I think the notion is you don't ship libabseil.so.0 as part of a distro.

(I'm a Googler, but this is not my project.)

geofft2• 9 years ago

Ugh, I missed that they promise indefinite API compatibility but not ABI compatibility.

Distros aren't going to like "statically link it, and recompile all the reverse-dependencies when there's a CVE" at all, but I totally understand why that's a sensible approach for something that Google releases.

fish_fan2• 9 years ago

It’s hard to see the value here of dynamic linking vs static linking, especially when it seems like a lot of the value is compile-time selection of implementations and lightweight utility code—not exactly a huge attack vector you’d want to be able to upgrade independently.

And of course it introduces dependency hell, which seems like a poor fit for a library without a consistent ABI.

jonstewart2• 9 years ago

Whatever happened to the B-Tree library? Will it be included in Abseil's container lib some day?

trimbo• 9 years ago

It's still available in the Google Code archive: https://code.google.com/archive/p/cpp-btree/

ggchappell2• 9 years ago

Is there any documentation?

This looks like it might be good, but I don't know how to tell whether it is. The "Codemap" is just links to repo directories. The "Abseil Introduction" link leads to basically to another version of the README. It does have an "Abseil C++ Quickstart" link, which tells you how to get the package, but doesn't tell you what's in it.

I see things about design philosophy, compatibility, etc. But what about: what functions can I call, what do they do, and how do I call them?

Is there any way to find out what's in this thing, other than reading source files?

------------------

EDIT. Style guidelines, exceptions policy, leaking checking, platforms guide, linking your code, feature check macros, yadda yadda yadda ....

WHAT FUNCTIONS CAN I CALL, WHAT DO THEY DO, AND HOW DO I CALL THEM?

(Sorry. I'll go calm down now.)

katzdm2• 9 years ago

https://abseil.io/docs/cpp/guides/

This provides partial coverage, for some of the most useful bits. I believe additional docs are in the works.

ggchappell2• 9 years ago

Very partial, yes. But thanks.

Abseil: C++ Common Libraries

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