[base] Skip redundant FeatureList::CheckFeatureIdentity on cache hits In DCHECK builds, FeatureList::GetOverrideStateImpl() previously ran DCHECK(IsValidFeatureOrFieldTrialName(feature.name)) and DCHECK(CheckFeatureIdentity(feature)) before checking the per-Feature atomic cache (feature.cached_value). Because CheckFeatureIdentity() acquires feature_identity_tracker_lock_ and performs a string lookup in a std::map on every FeatureList::IsEnabled() call, it accounted for ~1.3% of total browser_tests CPU time on linux-chromeos-rel. Because cached_value is stored directly inside the base::Feature struct instance at &feature and is only populated after GetOverrideStateImpl() completes a cache miss for that specific instance, a cache hit (caching_context == caching_context_) proves that this exact &feature instance was already validated and registered in feature_identity_tracker_. Any duplicate base::Feature definition at a different address has its own unpopulated cached_value, so it will miss the cache on its first query and still trigger CheckFeatureIdentity(). Move the two DCHECKs immediately after the cache-hit fast path so cached FeatureList::IsEnabled() lookups remain lock-free in DCHECK builds while preserving duplicate-Feature detection. Estimated impact: ~1.0% to 1.5% of total browser_tests CPU time (~55-85 ms per test) on linux-chromeos-rel. Bug: 573256256 Agent-Generated: true Change-Id: I7de4746259121f76b8c215afef8f725333748397 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/8583661 Commit-Queue: Erik Chen <erikchen@chromium.org> Reviewed-by: Daniel Cheng <dcheng@chromium.org> Cr-Commit-Position: refs/heads/main@{#1720136} NOKEYCHECK=True GitOrigin-RevId: 521faa0655c271c9cebf2c225fd8f8ab32088bc5
Contains a written down set of principles and other information on //base. Please add to it!
Chromium is a very mature project. Most things that are generally useful are already here and things not here aren't generally useful.
The bar for adding stuff to base is that it must have demonstrated wide applicability. Prefer to add things closer to where they're used (i.e. “not base”), and pull into base only when needed. In a project our size, sometimes even duplication is OK and inevitable.
Adding a new logging macro DPVELOG_NE is not more clear than just writing the stuff you want to log in a regular logging statement, even if it makes your calling code longer. Just add it to your own code.
If the code in question does not need to be used inside base, but will have multiple consumers across the codebase, consider placing it in a new directory under components/ instead.
base is written for the Chromium project and is not intended to be used outside it. Using base outside of src.git is explicitly not supported, and base makes no guarantees about API (or even ABI) stability (like all other code in Chromium). New code that depends on base/ must be in src.git. Code that's not in src.git but pulled in through DEPS (for example, v8) cannot use base.
Owners are added when a contributor has shown the above qualifications and when they express interest. There isn't an upper bound on the number of OWNERS.
Since the primitives provided by //base are used very widely, it is important to ensure they scale to the necessary workloads and perform well under all supported platforms. The base_perftests target is a suite of synthetic microbenchmarks that measure performance in various scenarios:
thread_local, the implementation in //base, the POSIX/WinAPI directly)Regressions in these benchmarks can generally by caused by 1) operating system changes, 2) compiler version or flag changes or 3) changes in //base code itself.
Rust code in base should be organized into very small crates, split up by function. Merging crates is sometimes unavoidable (due to dependency cycles or the orphaning rule).
Rust files should live near the equivalent C++ files (if any), and use the same naming scheme (for example, run_loop.rs, not run_loop_rust.rs).
When adding FFI shims, prefer separate _shim.h files rather than adding code to existing C++ files. This helps avoid circular dependencies with the //base target. It also avoids adding code to commonly-used headers, which can increase compile size by a lot.
Crates which you expect to be widely used should be added to the public_deps of the //base:base_rust target, so that developers can simply depend on //base:base_rust the same way they do with //base.