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This CL includes follow-up changes from https://webrtc-review.googlesource.com/c/src/+/324280 Bug: none Change-Id: I6abad16e05cac7197c51ffa7b1d3fb991843df6e Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/325243 Reviewed-by: Danil Chapovalov <danilchap@webrtc.org> Commit-Queue: Tomas Gunnarsson <tommi@webrtc.org> Cr-Commit-Position: refs/heads/main@{#41030}
85 lines
2.9 KiB
Markdown
85 lines
2.9 KiB
Markdown
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<!--* freshness: {owner: 'danilchap' reviewed: '2021-05-12'} *-->
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# Using Abseil in WebRTC
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You may use a subset of the utilities provided by the [Abseil][abseil]
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library when writing WebRTC C++ code. Below, we list the explicitly
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*allowed* and the explicitly *disallowed* subsets of Abseil; if you
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find yourself in need of something that isn’t in either subset,
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please add it to the *allowed* subset in this doc in the same CL that
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adds the first use.
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[abseil]: https://abseil.io/about/
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## How to depend on Abseil
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For build targets of type `rtc_library`, `rtc_source_set` and
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`rtc_static_library`, dependencies on Abseil need to be listed in `absl_deps`
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instead of `deps`.
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This is needed in order to support the Abseil component build in Chromium. In
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that build mode, WebRTC will depend on a monolithic Abseil build target that
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will generate a shared library.
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## **Allowed**
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* `absl::AnyInvocable`
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* `absl::bind_front`
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* `absl::Cleanup`
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* `absl::InlinedVector`
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* `absl::Nonnull` and `absl::Nullable`
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* `absl::WrapUnique`
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* `absl::optional` and related stuff from `absl/types/optional.h`.
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* `absl::string_view`
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* The functions in `absl/strings/ascii.h`, `absl/strings/match.h`,
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and `absl/strings/str_replace.h`.
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* The functions in `absl/strings/escaping.h`.
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* `absl::is_trivially_copy_constructible`,
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`absl::is_trivially_copy_assignable`, and
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`absl::is_trivially_destructible` from `absl/meta/type_traits.h`.
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* `absl::variant` and related stuff from `absl/types/variant.h`.
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* The functions in `absl/algorithm/algorithm.h` and
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`absl/algorithm/container.h`.
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* `absl/base/const_init.h` for mutex initialization.
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* The macros in `absl/base/attributes.h`, `absl/base/config.h` and
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`absl/base/macros.h`.
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* `absl/numeric/bits.h`
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## **Disallowed**
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### `absl::make_unique`
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*Use `std::make_unique` instead.*
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### `absl::Mutex`
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*Use `webrtc::Mutex` instead.*
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Chromium has a ban on new static initializers, and `absl::Mutex` uses
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one. To make `absl::Mutex` available, we would need to nicely ask the
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Abseil team to remove that initializer (like they already did for a
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spinlock initializer). Additionally, `absl::Mutex` handles time in a
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way that may not be compatible with the rest of WebRTC.
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### `absl::Span`
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*Use `rtc::ArrayView` instead.*
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`absl::Span` differs from `rtc::ArrayView` on several points, and both
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of them differ from the `std::span` that was voted into
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C++20—and `std::span` is likely to undergo further changes
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before C++20 is finalized. We should just keep using `rtc::ArrayView`
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and avoid `absl::Span` until C++20 is finalized and the Abseil team
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has decided if they will change `absl::Span` to match.
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[Bug](https://bugs.webrtc.org/9214).
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### `absl::StrCat`, `absl::StrAppend`, `absl::StrJoin`, `absl::StrSplit`
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*Use `rtc::SimpleStringBuilder` to build strings.*
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These are optimized for speed, not binary size. Even `StrCat` calls
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with a modest number of arguments can easily add several hundred bytes
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to the binary.
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