differential_dataflow/trace/cursor/
mod.rs

1//! Traits and types for navigating order sequences of update tuples.
2//!
3//! The `Cursor` trait contains several methods for efficiently navigating ordered collections
4//! of tuples of the form `(key, val, time, diff)`. The cursor is different from an iterator
5//! both because it allows navigation on multiple levels (key and val), but also because it
6//! supports efficient seeking (via the `seek_key` and `seek_val` methods).
7
8use timely::progress::Timestamp;
9
10use crate::difference::Semigroup;
11// `pub use` for legacy reasons.
12pub use crate::IntoOwned;
13use crate::lattice::Lattice;
14
15pub mod cursor_list;
16
17pub use self::cursor_list::CursorList;
18
19/// A cursor for navigating ordered `(key, val, time, diff)` updates.
20pub trait Cursor {
21
22    /// Key by which updates are indexed.
23    type Key<'a>: Copy + Clone + Ord;
24    /// Values associated with keys.
25    type Val<'a>: Copy + Clone + Ord;
26    /// Timestamps associated with updates
27    type Time: Timestamp + Lattice + Ord + Clone;
28    /// Borrowed form of timestamp.
29    type TimeGat<'a>: Copy + IntoOwned<'a, Owned = Self::Time>;
30    /// Owned form of update difference.
31    type Diff: Semigroup + 'static;
32    /// Borrowed form of update difference.
33    type DiffGat<'a> : Copy + IntoOwned<'a, Owned = Self::Diff>;
34
35    /// Storage required by the cursor.
36    type Storage;
37
38    /// Indicates if the current key is valid.
39    ///
40    /// A value of `false` indicates that the cursor has exhausted all keys.
41    fn key_valid(&self, storage: &Self::Storage) -> bool;
42    /// Indicates if the current value is valid.
43    ///
44    /// A value of `false` indicates that the cursor has exhausted all values for this key.
45    fn val_valid(&self, storage: &Self::Storage) -> bool;
46
47    /// A reference to the current key. Asserts if invalid.
48    fn key<'a>(&self, storage: &'a Self::Storage) -> Self::Key<'a>;
49    /// A reference to the current value. Asserts if invalid.
50    fn val<'a>(&self, storage: &'a Self::Storage) -> Self::Val<'a>;
51
52    /// Returns a reference to the current key, if valid.
53    fn get_key<'a>(&self, storage: &'a Self::Storage) -> Option<Self::Key<'a>>;
54    /// Returns a reference to the current value, if valid.
55    fn get_val<'a>(&self, storage: &'a Self::Storage) -> Option<Self::Val<'a>>;
56
57    /// Applies `logic` to each pair of time and difference. Intended for mutation of the
58    /// closure's scope.
59    fn map_times<L: FnMut(Self::TimeGat<'_>, Self::DiffGat<'_>)>(&mut self, storage: &Self::Storage, logic: L);
60
61    /// Advances the cursor to the next key.
62    fn step_key(&mut self, storage: &Self::Storage);
63    /// Advances the cursor to the specified key.
64    fn seek_key(&mut self, storage: &Self::Storage, key: Self::Key<'_>);
65
66    /// Advances the cursor to the next value.
67    fn step_val(&mut self, storage: &Self::Storage);
68    /// Advances the cursor to the specified value.
69    fn seek_val(&mut self, storage: &Self::Storage, val: Self::Val<'_>);
70
71    /// Rewinds the cursor to the first key.
72    fn rewind_keys(&mut self, storage: &Self::Storage);
73    /// Rewinds the cursor to the first value for current key.
74    fn rewind_vals(&mut self, storage: &Self::Storage);
75
76    /// Rewinds the cursor and outputs its contents to a Vec
77    fn to_vec<K, V>(&mut self, storage: &Self::Storage) -> Vec<((K, V), Vec<(Self::Time, Self::Diff)>)>
78    where 
79        for<'a> Self::Key<'a> : IntoOwned<'a, Owned = K>,
80        for<'a> Self::Val<'a> : IntoOwned<'a, Owned = V>,
81    {
82        let mut out = Vec::new();
83        self.rewind_keys(storage);
84        while let Some(key) = self.get_key(storage) {
85            self.rewind_vals(storage);
86            while let Some(val) = self.get_val(storage) {
87                let mut kv_out = Vec::new();
88                self.map_times(storage, |ts, r| {
89                    kv_out.push((ts.into_owned(), r.into_owned()));
90                });
91                out.push(((key.into_owned(), val.into_owned()), kv_out));
92                self.step_val(storage);
93            }
94            self.step_key(storage);
95        }
96        out
97    }
98}
differential_dataflow/trace/cursor/mod.rs

differential_dataflow/trace/cursor/
mod.rs
