rust/hg-core/src/dirstate_tree/dispatch.rs
author Simon Sapin <simon.sapin@octobus.net>
Mon, 27 Sep 2021 12:09:15 +0200
changeset 48083 bf8837e3d7ce
parent 48076 060cd909439f
permissions -rw-r--r--
dirstate: Remove the flat Rust DirstateMap implementation Before this changeset we had two Rust implementations of `DirstateMap`. This removes the "flat" DirstateMap so that the "tree" DirstateMap is always used when Rust enabled. This simplifies the code a lot, and will enable (in the next changeset) further removal of a trait abstraction. This is a performance regression when: * Rust is enabled, and * The repository uses the legacy dirstate-v1 file format, and * For `hg status`, unknown files are not listed (such as with `-mard`) The regression is about 100 milliseconds for `hg status -mard` on a semi-large repository (mozilla-central), from ~320ms to ~420ms. We deem this to be small enough to be worth it. The new dirstate-v2 is still experimental at this point, but we aim to stabilize it (though not yet enable it by default for new repositories) in Mercurial 6.0. Eventually, upgrating repositories to dirsate-v2 will eliminate this regression (and enable other performance improvements). # Background The flat DirstateMap was introduced with the first Rust implementation of the status algorithm. It works similarly to the previous Python + C one, with a single `HashMap` that associates file paths to a `DirstateEntry` (where Python has a dict). We later added the tree DirstateMap where the root of the tree contains nodes for files and directories that are directly at the root of the repository, and nodes for directories can contain child nodes representing the files and directly that *they* contain directly. The shape of this tree mirrors that of the working directory in the filesystem. This enables the status algorithm to traverse this tree in tandem with traversing the filesystem tree, which in turns enables a more efficient algorithm. Furthermore, the new dirstate-v2 file format is also based on a tree of the same shape. The tree DirstateMap can access a dirstate-v2 file without parsing it: binary data in a single large (possibly memory-mapped) bytes buffer is traversed on demand. This allows `DirstateMap` creation to take `O(1)` time. (Mutation works by creating new in-memory nodes with copy-on-write semantics, and serialization is append-mostly.) The tradeoff is that for "legacy" repositories that use the dirstate-v1 file format, parsing that file into a tree DirstateMap takes more time. Profiling shows that this time is dominated by `HashMap`. For a dirstate containing `F` files with an average `D` directory depth, the flat DirstateMap does parsing in `O(F)` number of HashMap operations but the tree DirstateMap in `O(F × D)` operations, since each node has its own HashMap containing its child nodes. This slower costs ~140ms on an old snapshot of mozilla-central, and ~80ms on an old snapshot of the Netbeans repository. The status algorithm is faster, but with `-mard` (when not listing unknown files) it is typically not faster *enough* to compensate the slower parsing. Both Rust implementations are always faster than the Python + C implementation # Benchmark results All benchmarks are run on changeset 98c0408324e6, with repositories that use the dirstate-v1 file format, on a server with 4 CPU cores and 4 CPU threads (no HyperThreading). `hg status` benchmarks show wall clock times of the entire command as the average and standard deviation of serveral runs, collected by https://github.com/sharkdp/hyperfine and reformated. Parsing benchmarks are wall clock time of the Rust function that converts a bytes buffer of the dirstate file into the `DirstateMap` data structure as used by the status algorithm. A single run each, collected by running `hg status` this environment variable: RUST_LOG=hg::dirstate::dirstate_map=trace,hg::dirstate_tree::dirstate_map=trace Benchmark 1: Rust flat DirstateMap → Rust tree DirstateMap hg status mozilla-clean 562.3 ms ± 2.0 ms → 462.5 ms ± 0.6 ms 1.22 ± 0.00 times faster mozilla-dirty 859.6 ms ± 2.2 ms → 719.5 ms ± 3.2 ms 1.19 ± 0.01 times faster mozilla-ignored 558.2 ms ± 3.0 ms → 457.9 ms ± 2.9 ms 1.22 ± 0.01 times faster mozilla-unknowns 859.4 ms ± 5.7 ms → 716.0 ms ± 4.7 ms 1.20 ± 0.01 times faster netbeans-clean 336.5 ms ± 0.9 ms → 339.5 ms ± 0.4 ms 0.99 ± 0.00 times faster netbeans-dirty 491.4 ms ± 1.6 ms → 475.1 ms ± 1.2 ms 1.03 ± 0.00 times faster netbeans-ignored 343.7 ms ± 1.0 ms → 347.8 ms ± 0.4 ms 0.99 ± 0.00 times faster netbeans-unknowns 484.3 ms ± 1.0 ms → 466.0 ms ± 1.2 ms 1.04 ± 0.00 times faster hg status -mard mozilla-clean 317.3 ms ± 0.6 ms → 422.5 ms ± 1.2 ms 0.75 ± 0.00 times faster mozilla-dirty 315.4 ms ± 0.6 ms → 417.7 ms ± 1.1 ms 0.76 ± 0.00 times faster mozilla-ignored 314.6 ms ± 0.6 ms → 417.4 ms ± 1.0 ms 0.75 ± 0.00 times faster mozilla-unknowns 312.9 ms ± 0.9 ms → 417.3 ms ± 1.6 ms 0.75 ± 0.00 times faster netbeans-clean 212.0 ms ± 0.6 ms → 283.6 ms ± 0.8 ms 0.75 ± 0.00 times faster netbeans-dirty 211.4 ms ± 1.0 ms → 283.4 ms ± 1.6 ms 0.75 ± 0.01 times faster netbeans-ignored 211.4 ms ± 0.9 ms → 283.9 ms ± 0.8 ms 0.74 ± 0.01 times faster netbeans-unknowns 211.1 ms ± 0.6 ms → 283.4 ms ± 1.0 ms 0.74 ± 0.00 times faster Parsing mozilla-clean 38.4ms → 177.6ms mozilla-dirty 38.8ms → 177.0ms mozilla-ignored 38.8ms → 178.0ms mozilla-unknowns 38.7ms → 176.9ms netbeans-clean 16.5ms → 97.3ms netbeans-dirty 16.5ms → 98.4ms netbeans-ignored 16.9ms → 97.4ms netbeans-unknowns 16.9ms → 96.3ms Benchmark 2: Python + C dirstatemap → Rust tree DirstateMap hg status mozilla-clean 1261.0 ms ± 3.6 ms → 461.1 ms ± 0.5 ms 2.73 ± 0.00 times faster mozilla-dirty 2293.4 ms ± 9.1 ms → 719.6 ms ± 3.6 ms 3.19 ± 0.01 times faster mozilla-ignored 1240.4 ms ± 2.3 ms → 457.7 ms ± 1.9 ms 2.71 ± 0.00 times faster mozilla-unknowns 2283.3 ms ± 9.0 ms → 719.7 ms ± 3.8 ms 3.17 ± 0.01 times faster netbeans-clean 879.7 ms ± 3.5 ms → 339.9 ms ± 0.5 ms 2.59 ± 0.00 times faster netbeans-dirty 1257.3 ms ± 4.7 ms → 474.6 ms ± 1.6 ms 2.65 ± 0.01 times faster netbeans-ignored 943.9 ms ± 1.9 ms → 347.3 ms ± 1.1 ms 2.72 ± 0.00 times faster netbeans-unknowns 1188.1 ms ± 5.0 ms → 465.2 ms ± 2.3 ms 2.55 ± 0.01 times faster hg status -mard mozilla-clean 903.2 ms ± 3.6 ms → 423.4 ms ± 2.2 ms 2.13 ± 0.01 times faster mozilla-dirty 884.6 ms ± 4.5 ms → 417.3 ms ± 1.4 ms 2.12 ± 0.01 times faster mozilla-ignored 881.9 ms ± 1.3 ms → 417.3 ms ± 0.8 ms 2.11 ± 0.00 times faster mozilla-unknowns 878.5 ms ± 1.9 ms → 416.4 ms ± 0.9 ms 2.11 ± 0.00 times faster netbeans-clean 434.9 ms ± 1.8 ms → 284.0 ms ± 0.8 ms 1.53 ± 0.01 times faster netbeans-dirty 434.1 ms ± 0.8 ms → 283.1 ms ± 0.8 ms 1.53 ± 0.00 times faster netbeans-ignored 431.7 ms ± 1.1 ms → 283.6 ms ± 1.8 ms 1.52 ± 0.01 times faster netbeans-unknowns 433.0 ms ± 1.3 ms → 283.5 ms ± 0.7 ms 1.53 ± 0.00 times faster Differential Revision: https://phab.mercurial-scm.org/D11516

use std::path::PathBuf;

use crate::dirstate::parsers::Timestamp;
use crate::dirstate::CopyMapIter;
use crate::dirstate::StateMapIter;
use crate::dirstate_tree::on_disk::DirstateV2ParseError;
use crate::matchers::Matcher;
use crate::utils::hg_path::{HgPath, HgPathBuf};
use crate::DirstateEntry;
use crate::DirstateError;
use crate::DirstateParents;
use crate::DirstateStatus;
use crate::PatternFileWarning;
use crate::StatusError;
use crate::StatusOptions;

/// `rust/hg-cpython/src/dirstate/dirstate_map.rs` implements in Rust a
/// `DirstateMap` Python class that wraps `Box<dyn DirstateMapMethods + Send>`,
/// a trait object of this trait. Except for constructors, this trait defines
/// all APIs that the class needs to interact with its inner dirstate map.
///
/// A trait object is used to support two different concrete types:
///
/// * `rust/hg-core/src/dirstate/dirstate_map.rs` defines the "flat dirstate
///   map" which is based on a few large `HgPath`-keyed `HashMap` and `HashSet`
///   fields.
/// * `rust/hg-core/src/dirstate_tree/dirstate_map.rs` defines the "tree
///   dirstate map" based on a tree data struture with nodes for directories
///   containing child nodes for their files and sub-directories. This tree
///   enables a more efficient algorithm for `hg status`, but its details are
///   abstracted in this trait.
///
/// The dirstate map associates paths of files in the working directory to
/// various information about the state of those files.
pub trait DirstateMapMethods {
    /// Remove information about all files in this map
    fn clear(&mut self);

    /// Add the given filename to the map if it is not already there, and
    /// associate the given entry with it.
    fn set_entry(
        &mut self,
        filename: &HgPath,
        entry: DirstateEntry,
    ) -> Result<(), DirstateV2ParseError>;

    /// Add or change the information associated to a given file.
    fn add_file(
        &mut self,
        filename: &HgPath,
        entry: DirstateEntry,
    ) -> Result<(), DirstateError>;

    /// Mark a file as "removed" (as in `hg rm`).
    fn remove_file(
        &mut self,
        filename: &HgPath,
        in_merge: bool,
    ) -> Result<(), DirstateError>;

    /// Drop information about this file from the map if any.
    ///
    /// `get` will now return `None` for this filename.
    fn drop_entry_and_copy_source(
        &mut self,
        filename: &HgPath,
    ) -> Result<(), DirstateError>;

    /// Returns whether the sub-tree rooted at the given directory contains any
    /// tracked file.
    ///
    /// A file is tracked if it has a `state` other than `EntryState::Removed`.
    fn has_tracked_dir(
        &mut self,
        directory: &HgPath,
    ) -> Result<bool, DirstateError>;

    /// Returns whether the sub-tree rooted at the given directory contains any
    /// file with a dirstate entry.
    fn has_dir(&mut self, directory: &HgPath) -> Result<bool, DirstateError>;

    /// Clear mtimes equal to `now` in entries with `state ==
    /// EntryState::Normal`, and serialize bytes to write the `.hg/dirstate`
    /// file to disk in dirstate-v1 format.
    fn pack_v1(
        &mut self,
        parents: DirstateParents,
        now: Timestamp,
    ) -> Result<Vec<u8>, DirstateError>;

    /// Clear mtimes equal to `now` in entries with `state ==
    /// EntryState::Normal`, and serialize  bytes to write a dirstate data file
    /// to disk in dirstate-v2 format.
    ///
    /// Returns new data and metadata together with whether that data should be
    /// appended to the existing data file whose content is at
    /// `self.on_disk` (true), instead of written to a new data file
    /// (false).
    ///
    /// Note: this is only supported by the tree dirstate map.
    fn pack_v2(
        &mut self,
        now: Timestamp,
        can_append: bool,
    ) -> Result<(Vec<u8>, Vec<u8>, bool), DirstateError>;

    /// Run the status algorithm.
    ///
    /// This is not sematically a method of the dirstate map, but a different
    /// algorithm is used for the flat v.s. tree dirstate map so having it in
    /// this trait enables the same dynamic dispatch as with other methods.
    fn status<'a>(
        &'a mut self,
        matcher: &'a (dyn Matcher + Sync),
        root_dir: PathBuf,
        ignore_files: Vec<PathBuf>,
        options: StatusOptions,
    ) -> Result<(DirstateStatus<'a>, Vec<PatternFileWarning>), StatusError>;

    /// Returns how many files in the dirstate map have a recorded copy source.
    fn copy_map_len(&self) -> usize;

    /// Returns an iterator of `(path, copy_source)` for all files that have a
    /// copy source.
    fn copy_map_iter(&self) -> CopyMapIter<'_>;

    /// Returns whether the givef file has a copy source.
    fn copy_map_contains_key(
        &self,
        key: &HgPath,
    ) -> Result<bool, DirstateV2ParseError>;

    /// Returns the copy source for the given file.
    fn copy_map_get(
        &self,
        key: &HgPath,
    ) -> Result<Option<&HgPath>, DirstateV2ParseError>;

    /// Removes the recorded copy source if any for the given file, and returns
    /// it.
    fn copy_map_remove(
        &mut self,
        key: &HgPath,
    ) -> Result<Option<HgPathBuf>, DirstateV2ParseError>;

    /// Set the given `value` copy source for the given `key` file.
    fn copy_map_insert(
        &mut self,
        key: HgPathBuf,
        value: HgPathBuf,
    ) -> Result<Option<HgPathBuf>, DirstateV2ParseError>;

    /// Returns the number of files that have an entry.
    fn len(&self) -> usize;

    /// Returns whether the given file has an entry.
    fn contains_key(&self, key: &HgPath)
        -> Result<bool, DirstateV2ParseError>;

    /// Returns the entry, if any, for the given file.
    fn get(
        &self,
        key: &HgPath,
    ) -> Result<Option<DirstateEntry>, DirstateV2ParseError>;

    /// Returns a `(path, entry)` iterator of files that have an entry.
    ///
    /// Because parse errors can happen during iteration, the iterated items
    /// are `Result`s.
    fn iter(&self) -> StateMapIter<'_>;

    /// Returns an iterator of tracked directories.
    ///
    /// This is the paths for which `has_tracked_dir` would return true.
    /// Or, in other words, the union of ancestor paths of all paths that have
    /// an associated entry in a "tracked" state in this dirstate map.
    ///
    /// Because parse errors can happen during iteration, the iterated items
    /// are `Result`s.
    fn iter_tracked_dirs(
        &mut self,
    ) -> Result<
        Box<
            dyn Iterator<Item = Result<&HgPath, DirstateV2ParseError>>
                + Send
                + '_,
        >,
        DirstateError,
    >;

    /// Return an iterator of `(path, (state, mode, size, mtime))` for every
    /// node stored in this dirstate map, for the purpose of the `hg
    /// debugdirstate` command.
    ///
    /// If `all` is true, include  nodes that don’t have an entry.
    /// For such nodes `state` is the ASCII space.
    /// An `mtime` may still be present. It is used to optimize `status`.
    ///
    /// Because parse errors can happen during iteration, the iterated items
    /// are `Result`s.
    fn debug_iter(
        &self,
        all: bool,
    ) -> Box<
        dyn Iterator<
                Item = Result<
                    (&HgPath, (u8, i32, i32, i32)),
                    DirstateV2ParseError,
                >,
            > + Send
            + '_,
    >;
}