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annotate rust/hg-core/examples/nodemap/index.rs @ 46127:c58c8f1d63b1

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copies-rust: hide most of the comparison details inside a closure The function that compares values needs various supporting elements that are the same for each call. We are about to both make change to these element and change to call sites in our upcoming work. So abstracting most of the details will help to avoid conflict while these works happen in parallel. Differential Revision: https://phab.mercurial-scm.org/D9426
author Pierre-Yves David <pierre-yves.david@octobus.net>
date Sat, 21 Nov 2020 10:50:14 +0100
parents 8f7c6656ac79
children e834b79def74
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1 // Copyright 2019-2020 Georges Racinet <georges.racinet@octobus.net>
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2 //
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3 // This software may be used and distributed according to the terms of the
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4 // GNU General Public License version 2 or any later version.
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5
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6 //! Minimal `RevlogIndex`, readable from standard Mercurial file format
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7 use hg::*;
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8 use memmap::*;
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9 use std::fs::File;
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10 use std::ops::Deref;
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11 use std::path::Path;
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12 use std::slice;
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13
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14 pub struct Index {
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15 data: Box<dyn Deref<Target = [IndexEntry]> + Send>,
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16 }
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17
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18 /// A fixed sized index entry. All numbers are big endian
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19 #[repr(C)]
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20 pub struct IndexEntry {
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21 not_used_yet: [u8; 24],
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22 p1: Revision,
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23 p2: Revision,
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24 node: Node,
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25 unused_node: [u8; 12],
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26 }
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27
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28 pub const INDEX_ENTRY_SIZE: usize = 64;
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29
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30 impl IndexEntry {
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31 fn parents(&self) -> [Revision; 2] {
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32 [Revision::from_be(self.p1), Revision::from_be(self.p1)]
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33 }
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34 }
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35
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36 impl RevlogIndex for Index {
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37 fn len(&self) -> usize {
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38 self.data.len()
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39 }
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40
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41 fn node(&self, rev: Revision) -> Option<&Node> {
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42 if rev == NULL_REVISION {
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43 return None;
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44 }
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45 let i = rev as usize;
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46 if i >= self.len() {
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47 None
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48 } else {
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49 Some(&self.data[i].node)
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50 }
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51 }
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52 }
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53
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54 impl Graph for &Index {
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55 fn parents(&self, rev: Revision) -> Result<[Revision; 2], GraphError> {
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56 let [p1, p2] = (*self).data[rev as usize].parents();
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57 let len = (*self).len();
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58 if p1 < NULL_REVISION
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59 || p2 < NULL_REVISION
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60 || p1 as usize >= len
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61 || p2 as usize >= len
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62 {
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63 return Err(GraphError::ParentOutOfRange(rev));
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64 }
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65 Ok([p1, p2])
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66 }
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67 }
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68
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69 struct IndexMmap(Mmap);
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70
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71 impl Deref for IndexMmap {
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72 type Target = [IndexEntry];
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73
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74 fn deref(&self) -> &[IndexEntry] {
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75 let ptr = self.0.as_ptr() as *const IndexEntry;
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76 // Any misaligned data will be ignored.
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77 debug_assert_eq!(
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78 self.0.len() % std::mem::align_of::<IndexEntry>(),
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79 0,
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80 "Misaligned data in mmap"
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81 );
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82 unsafe { slice::from_raw_parts(ptr, self.0.len() / INDEX_ENTRY_SIZE) }
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83 }
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84 }
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85
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86 impl Index {
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87 pub fn load_mmap(path: impl AsRef<Path>) -> Self {
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88 let file = File::open(path).unwrap();
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89 let msg = "Index file is missing, or missing permission";
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90 let mmap = unsafe { MmapOptions::new().map(&file) }.expect(msg);
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91 Self {
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92 data: Box::new(IndexMmap(mmap)),
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93 }
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94 }
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95 }