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//! Git stores all of its data as _Objects_, which are data along with a hash over all data. Thus it's an
//! object store indexed by the signature of data itself with inherent deduplication: the same data will have the same hash,
//! and thus occupy the same space within the store.
//!
//! There is only one all-round object store, also known as the [`Store`], as it supports ~~everything~~ most of what git has to offer.
//!
//! * loose object reading and writing
//! * access to packed objects
//! * multiple loose objects and pack locations as gathered from `alternates` files.
//! ## Feature Flags
#![cfg_attr(
all(doc, feature = "document-features"),
doc = ::document_features::document_features!()
)]
#![cfg_attr(all(doc, feature = "document-features"), feature(doc_cfg, doc_auto_cfg))]
#![deny(missing_docs, rust_2018_idioms, unsafe_code)]
use std::{
cell::RefCell,
path::PathBuf,
sync::{atomic::AtomicUsize, Arc},
};
use arc_swap::ArcSwap;
use gix_features::{threading::OwnShared, zlib::stream::deflate};
pub use gix_pack as pack;
mod store_impls;
pub use store_impls::{dynamic as store, loose};
pub mod alternate;
/// A way to access objects along with pre-configured thread-local caches for packed base objects as well as objects themselves.
///
/// By default, no cache will be used.
pub struct Cache<S> {
/// The inner provider of trait implementations we use in conjunction with our caches.
///
/// For calling methods on `inner`, prefer to make use of auto-dereferencing, i.e. `cache.inner_method()` instead of `cache.inner.inner_method()`.
inner: S,
// TODO: have single-threaded code-paths also for pack-creation (entries from counts) so that we can use OwnShared here
// instead of Arc. However, it's probably not that important as these aren't called often.
new_pack_cache: Option<Arc<cache::NewPackCacheFn>>,
new_object_cache: Option<Arc<cache::NewObjectCacheFn>>,
pack_cache: Option<RefCell<Box<cache::PackCache>>>,
object_cache: Option<RefCell<Box<cache::ObjectCache>>>,
}
///
pub mod cache;
///
/// It can optionally compress the content, similarly to what would happen when using a [`loose::Store`].
///
#[derive(Clone)]
pub struct Sink {
compressor: Option<RefCell<deflate::Write<std::io::Sink>>>,
object_hash: gix_hash::Kind,
}
/// Create a new [`Sink`] with compression disabled.
pub fn sink(object_hash: gix_hash::Kind) -> Sink {
Sink {
compressor: None,
object_hash,
}
}
mod sink;
///
pub mod find;
/// An object database equivalent to `/dev/null`, dropping all objects stored into it.
mod traits;
pub use traits::{Header, HeaderExt, Write};
///
pub mod write {
/// The error type returned by the [`Write`](crate::Write) trait.
pub type Error = Box<dyn std::error::Error + Send + Sync + 'static>;
}
/// A thread-local handle to access any object.
pub type Handle = Cache<store::Handle<OwnShared<Store>>>;
/// A thread-local handle to access any object, but thread-safe and independent of the actual type of `OwnShared` or feature toggles in `gix-features`.
pub type HandleArc = Cache<store::Handle<Arc<Store>>>;
use store::types;
/// The object store for use in any applications with support for auto-updates in the light of changes to the object database.
///
/// ### Features
///
/// - entirely lazy, creating an instance does no disk IO at all if [`Slots::Given`][store::init::Slots::Given] is used.
/// - multi-threaded lazy-loading of indices and packs
/// - per-thread pack and object caching avoiding cache trashing.
/// - most-recently-used packs are always first for speedups if objects are stored in the same pack, typical for packs organized by
/// commit graph and object age.
/// - lock-free reading for perfect scaling across all cores, and changes to it don't affect readers as long as these don't want to
/// enter the same branch.
/// - sync with the state on disk if objects aren't found to catch up with changes if an object seems to be missing.
/// - turn off the behaviour above for all handles if objects are expected to be missing due to spare checkouts.
pub struct Store {
/// The central write lock without which the slotmap index can't be changed.
write: parking_lot::Mutex<()>,
/// The source directory from which all content is loaded, and the central write lock for use when a directory refresh is needed.
pub(crate) path: PathBuf,
/// The current working directory at the time this store was instantiated. It becomes relevant when resolving alternate paths
/// when re-reading the store configuration on updates when an object was missed.
/// Keeping it here helps to assure consistency even while a process changes its CWD.
pub(crate) current_dir: PathBuf,
/// A set of replacements that given a source OID return a destination OID. The vector is sorted.
pub(crate) replacements: Vec<(gix_hash::ObjectId, gix_hash::ObjectId)>,
/// A list of indices keeping track of which slots are filled with data. These are usually, but not always, consecutive.
pub(crate) index: ArcSwap<types::SlotMapIndex>,
/// The below state acts like a slot-map with each slot is mutable when the write lock is held, but readable independently of it.
/// This allows multiple file to be loaded concurrently if there is multiple handles requesting to load packs or additional indices.
/// The map is static and cannot typically change.
/// It's read often and changed rarely.
pub(crate) files: Vec<types::MutableIndexAndPack>,
/// The amount of handles that would prevent us from unloading packs or indices
pub(crate) num_handles_stable: AtomicUsize,
/// The amount of handles that don't affect our ability to compact our internal data structures or unload packs or indices.
pub(crate) num_handles_unstable: AtomicUsize,
/// The amount of times we re-read the disk state to consolidate our in-memory representation.
pub(crate) num_disk_state_consolidation: AtomicUsize,
/// If true, we are allowed to use multi-pack indices and they must have the `object_hash` or be ignored.
use_multi_pack_index: bool,
/// The hash kind to use for some operations
object_hash: gix_hash::Kind,
}
/// Create a new cached handle to the object store with support for additional options.
///
/// `replacements` is an iterator over pairs of old and new object ids for replacement support.
/// This means that when asking for object `X`, one will receive object `X-replaced` given an iterator like `Some((X, X-replaced))`.
pub fn at_opts(
objects_dir: impl Into<PathBuf>,
replacements: impl IntoIterator<Item = (gix_hash::ObjectId, gix_hash::ObjectId)>,
options: store::init::Options,
) -> std::io::Result<Handle> {
let handle = OwnShared::new(Store::at_opts(
objects_dir.into(),
&mut replacements.into_iter(),
options,
)?)
.to_handle();
Ok(Cache::from(handle))
}
/// Create a new cached handle to the object store.
pub fn at(objects_dir: impl Into<PathBuf>) -> std::io::Result<Handle> {
at_opts(objects_dir, Vec::new(), Default::default())
}
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