aosp12/external/rust/crates/walkdir

walkdir

A cross platform Rust library for efficiently walking a directory recursively. Comes with support for following symbolic links, controlling the number of open file descriptors and efficient mechanisms for pruning the entries in the directory tree.

Dual-licensed under MIT or the UNLICENSE.

Documentation

docs.rs/walkdir

Usage

To use this crate, add walkdir as a dependency to your project's Cargo.toml:

[dependencies]
walkdir = "2"

Example

The following code recursively iterates over the directory given and prints the path for each entry:

use walkdir::WalkDir;

for entry in WalkDir::new("foo") {
    let entry = entry.unwrap();
    println!("{}", entry.path().display());
}

Or, if you'd like to iterate over all entries and ignore any errors that may arise, use filter_map. (e.g., This code below will silently skip directories that the owner of the running process does not have permission to access.)

use walkdir::WalkDir;

for entry in WalkDir::new("foo").into_iter().filter_map(|e| e.ok()) {
    println!("{}", entry.path().display());
}

Example: follow symbolic links

The same code as above, except follow_links is enabled:

use walkdir::WalkDir;

for entry in WalkDir::new("foo").follow_links(true) {
    let entry = entry.unwrap();
    println!("{}", entry.path().display());
}

Example: skip hidden files and directories efficiently on unix

This uses the filter_entry iterator adapter to avoid yielding hidden files and directories efficiently:

use walkdir::{DirEntry, WalkDir};

fn is_hidden(entry: &DirEntry) -> bool {
    entry.file_name()
         .to_str()
         .map(|s| s.starts_with("."))
         .unwrap_or(false)
}

let walker = WalkDir::new("foo").into_iter();
for entry in walker.filter_entry(|e| !is_hidden(e)) {
    let entry = entry.unwrap();
    println!("{}", entry.path().display());
}

Minimum Rust version policy

This crate's minimum supported rustc version is 1.34.0.

The current policy is that the minimum Rust version required to use this crate can be increased in minor version updates. For example, if crate 1.0 requires Rust 1.20.0, then crate 1.0.z for all values of z will also require Rust 1.20.0 or newer. However, crate 1.y for y > 0 may require a newer minimum version of Rust.

In general, this crate will be conservative with respect to the minimum supported version of Rust.

Performance

The short story is that performance is comparable with find and glibc's nftw on both a warm and cold file cache. In fact, I cannot observe any performance difference after running find /, walkdir / and nftw / on my local file system (SSD, ~3 million entries). More precisely, I am reasonably confident that this crate makes as few system calls and close to as few allocations as possible.

I haven't recorded any benchmarks, but here are some things you can try with a local checkout of walkdir:

# The directory you want to recursively walk:
DIR=$HOME

# If you want to observe perf on a cold file cache, run this before *each*
# command:
sudo sh -c 'echo 3 > /proc/sys/vm/drop_caches'

# To warm the caches
find $DIR

# Test speed of `find` on warm cache:
time find $DIR

# Compile and test speed of `walkdir` crate:
cargo build --release --example walkdir
time ./target/release/examples/walkdir $DIR

# Compile and test speed of glibc's `nftw`:
gcc -O3 -o nftw ./compare/nftw.c
time ./nftw $DIR

# For shits and giggles, test speed of Python's (2 or 3) os.walk:
time python ./compare/walk.py $DIR

On my system, the performance of walkdir, find and nftw is comparable.