comparison rust/hg-core/src/dirstate_tree/dirstate_map.rs @ 48950:11c0411bf4e2

dirstate-tree: optimize HashMap lookups with raw_entry_mut

This switches to using `HashMap` from the hashbrown crate,
in order to use its `raw_entry_mut` method.
The standard library’s `HashMap` is also based on this same crate,
but `raw_entry_mut` is not yet stable there:
https://github.com/rust-lang/rust/issues/56167

Using version 0.9 because 0.10 is yanked and 0.11 requires Rust 1.49

This replaces in `DirstateMap::get_or_insert_node` a call to
`HashMap<K, V>::entry` with `K = WithBasename<Cow<'on_disk, HgPath>>`.

`entry` takes and consumes an "owned" `key: K` parameter, in case a new entry
ends up inserted. This key is converted by `to_cow` from a value that borrows
the `'path` lifetime.

When this function is called by `Dirstate::new_v1`, `'path` is in fact
the same as `'on_disk` so `to_cow` can return an owned key that contains
`Cow::Borrowed`.

For other callers, `to_cow` needs to create a `Cow::Owned` and thus make
a costly heap memory allocation. This is wasteful if this key was already
present in the map. Even when inserting a new node this is typically the case
for its ancestor nodes (assuming most directories have numerous descendants).

Differential Revision: https://phab.mercurial-scm.org/D12317

48949:469b9ee336a6

use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::DirstateStatus;
use crate::EntryState;
use crate::FastHashMap;
use crate::PatternFileWarning;
use crate::StatusError;
use crate::StatusOptions;

/// Append to an existing data file if the amount of unreachable data (not used

            WithBasename::inclusive_ancestors_of(path);
        let mut ancestor_path = inclusive_ancestor_paths
            .next()
            .expect("expected at least one inclusive ancestor");
        loop {
            // TODO: can we avoid allocating an owned key in cases where the
            // map already contains that key, without introducing double
            // lookup?
            let child_node = child_nodes
                .make_mut(on_disk, unreachable_bytes)?
                .entry(to_cow(ancestor_path))
                .or_default();
            if let Some(next) = inclusive_ancestor_paths.next() {
                each_ancestor(child_node);
                ancestor_path = next;
                child_nodes = &mut child_node.children;
            } else {

48950:11c0411bf4e2

use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::DirstateStatus;
use crate::EntryState;
use crate::FastHashbrownMap as FastHashMap;
use crate::PatternFileWarning;
use crate::StatusError;
use crate::StatusOptions;

/// Append to an existing data file if the amount of unreachable data (not used

            WithBasename::inclusive_ancestors_of(path);
        let mut ancestor_path = inclusive_ancestor_paths
            .next()
            .expect("expected at least one inclusive ancestor");
        loop {
            let (_, child_node) = child_nodes
                .make_mut(on_disk, unreachable_bytes)?
                .raw_entry_mut()
                .from_key(ancestor_path.base_name())
                .or_insert_with(|| (to_cow(ancestor_path), Node::default()));
            if let Some(next) = inclusive_ancestor_paths.next() {
                each_ancestor(child_node);
                ancestor_path = next;
                child_nodes = &mut child_node.children;
            } else {