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//! Customized HashMap and Hasher implementation optimized for using `ObjectId`s as keys.
//!
//! The crate mirrors `std::collections` in layout for familiarity.
#![deny(missing_docs, rust_2018_idioms)]
#![forbid(unsafe_code)]
use gix_hash::ObjectId;
pub use hashbrown::{hash_map, hash_set, raw, Equivalent};
/// thread-safe types
pub mod sync {
/// A map for associating data with object ids in a thread-safe fashion. It should scale well up to 256 threads.
pub struct ObjectIdMap<V> {
/// Sharing is done by the first byte of the incoming object id.
shards: [parking_lot::Mutex<super::HashMap<gix_hash::ObjectId, V>>; 256],
}
impl<V> Default for ObjectIdMap<V> {
fn default() -> Self {
Self {
shards: std::array::from_fn(|_| parking_lot::Mutex::new(super::HashMap::default())),
}
}
}
/// access and modifications - we only implement what's used within the `gix-*` ecosystem.
impl<V> ObjectIdMap<V> {
/// Insert `value` at `key` and return `None` if it's the first value at that location, or `Some(previous-value)`
/// if `key` was already set.
pub fn insert(&self, key: gix_hash::ObjectId, value: V) -> Option<V> {
self.shards[key.as_slice()[0] as usize].lock().insert(key, value)
}
}
}
///
pub mod hash {
/// A Hasher for usage with HashMap keys that are already robust hashes (like an `ObjectId`).
/// The first `8` bytes of the hash are used as the `HashMap` hash
#[derive(Default, Clone, Copy)]
pub struct Hasher(u64);
impl std::hash::Hasher for Hasher {
fn finish(&self) -> u64 {
self.0
}
#[inline(always)]
fn write(&mut self, bytes: &[u8]) {
self.0 = u64::from_ne_bytes(bytes[..8].try_into().unwrap());
}
}
/// A Hasher for usage with HashMap keys that are already robust hashes (like an `ObjectId`).
/// The first `8` bytes of the hash are used as the `HashMap` hash
#[derive(Default, Clone, Copy)]
pub struct Builder;
impl std::hash::BuildHasher for Builder {
type Hasher = Hasher;
fn build_hasher(&self) -> Self::Hasher {
Hasher::default()
}
}
}
/// A HashMap for usage with keys that are already robust hashes (like an `ObjectId`).
/// The first `8` bytes of the hash are used as the `HashMap` hash
pub type HashMap<K, V> = hashbrown::HashMap<K, V, hash::Builder>;
/// A HashSet for usage with keys that are already robust hashes (like an `ObjectId`).
/// The first `8` bytes of the hash are used as the `HashMap` hash
pub type HashSet<T = ObjectId> = hashbrown::HashSet<T, hash::Builder>;
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