1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161

extern crate crossbeam_epoch;

pub mod leaf;
pub mod node;

use crossbeam_epoch::{Atomic, Guard};
use leaf::Leaf;
use node::{Error, LeafNodeScanner, Node};
use std::sync::atomic::Ordering::{Acquire, Relaxed, Release};

/// A scalable concurrent tree map implementation.
///
/// scc::TreeIndex is a B+ tree variant that is optimized for read operations.
/// Read operations, such as scan, read, are neither blocked nor interrupted by all the other types of operations.
/// Write operations, such as insert, remove, do not block if they do not entail structural changes to the tree.
pub struct TreeIndex<K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> {
    root: Atomic<Node<K, V>>,
}

impl<K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> TreeIndex<K, V> {
    /// Creates an empty TreeIndex instance.
    ///
    /// # Examples
    /// ```
    /// use scc::TreeIndex;
    ///
    /// let treeindex: TreeIndex<u64, u32> = TreeIndex::new();
    ///
    /// let result = treeindex.read(&1, |key, value| *value);
    /// assert!(result.is_none());
    /// ```
    pub fn new() -> TreeIndex<K, V> {
        TreeIndex {
            root: Atomic::new(Node::new(0)),
        }
    }

    /// Inserts a a key-value pair.
    ///
    /// # Examples
    /// ```
    /// use scc::TreeIndex;
    ///
    /// let treeindex: TreeIndex<u64, u32> = TreeIndex::new();
    ///
    /// let result = treeindex.insert(1, 10);
    /// assert!(result.is_ok());
    ///
    /// let result = treeindex.insert(1, 11);
    /// assert_eq!(result.err().unwrap(), (1, 11));
    ///
    /// let result = treeindex.read(&1, |key, value| *value);
    /// assert_eq!(result.unwrap(), 10);
    /// ```
    pub fn insert(&self, mut key: K, mut value: V) -> Result<(), (K, V)> {
        loop {
            let guard = crossbeam_epoch::pin();
            let root_node = self.root.load(Acquire, &guard);
            if root_node.is_null() {
                return Err((key, value));
            }
            let root_node_ref = unsafe { root_node.deref() };
            match root_node_ref.insert(key, value, None, &guard) {
                Ok(_) => return Ok(()),
                Err(error) => match error {
                    Error::Duplicated(entry) => return Err(entry),
                    Error::Full(entry) => {
                        root_node_ref.split_root(entry, &self.root, &guard);
                        return Ok(());
                    }
                    Error::Retry(entry) => {
                        key = entry.0;
                        value = entry.1;
                    }
                },
            }
        }
    }

    /// Reads a key-value pair.
    ///
    /// # Examples
    /// ```
    /// use scc::TreeIndex;
    ///
    /// let treeindex: TreeIndex<u64, u32> = TreeIndex::new();
    ///
    /// let result = treeindex.read(&1, |key, value| *value);
    /// assert!(result.is_none());
    ///
    /// let result = treeindex.insert(1, 10);
    /// assert!(result.is_ok());
    ///
    /// let result = treeindex.read(&1, |key, value| *value);
    /// assert_eq!(result.unwrap(), 10);
    /// ```
    pub fn read<U, F: FnOnce(&K, &V) -> U>(&self, key: &K, f: F) -> Option<U> {
        let guard = crossbeam_epoch::pin();
        let root_node = self.root.load(Acquire, &guard);
        if root_node.is_null() {
            return None;
        }
        let leaf_node_scanner = unsafe { root_node.deref().search(key, &guard) };
        leaf_node_scanner.map_or_else(
            || None,
            |scanner| {
                let entry = scanner.get();
                entry.map(|(key, value)| f(key, value))
            },
        )
    }

    /// Returns a Scanner.
    ///
    /// # Examples
    /// ```
    /// use scc::TreeIndex;
    ///
    /// let treeindex: TreeIndex<u64, u32> = TreeIndex::new();
    ///
    /// let scanner = treeindex.iter();
    /// ```
    pub fn iter(&self) -> Scanner<K, V> {
        Scanner::new(self)
    }
}

impl<K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> Drop for TreeIndex<K, V> {
    fn drop(&mut self) {}
}

pub struct Scanner<'a, K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> {
    tree_index: &'a TreeIndex<K, V>,
    leaf_node_scanner: Option<LeafNodeScanner<'a, K, V>>,
    guard: Guard,
}

impl<'a, K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> Scanner<'a, K, V> {
    fn new(tree_index: &'a TreeIndex<K, V>) -> Scanner<'a, K, V> {
        Scanner::<'a, K, V> {
            tree_index,
            leaf_node_scanner: None,
            guard: crossbeam_epoch::pin(),
        }
    }

    /// Returns a reference to the entry that the scanner is currently pointing to
    pub fn get(&self) -> Option<(&'a K, &'a V)> {
        if let Some(leaf_node_scanner) = self.leaf_node_scanner.as_ref() {
            return leaf_node_scanner.get();
        }
        None
    }
}

impl<'a, K: Clone + Ord + Send + Sync, V: Clone + Send + Sync> Iterator for Scanner<'a, K, V> {
    type Item = (&'a K, &'a V);
    fn next(&mut self) -> Option<Self::Item> {
        None
    }
}