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116 lines
3.0 KiB
116 lines
3.0 KiB
package diskv
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import (
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"sync"
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"github.com/google/btree"
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)
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// Index is a generic interface for things that can
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// provide an ordered list of keys.
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type Index interface {
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Initialize(less LessFunction, keys <-chan string)
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Insert(key string)
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Delete(key string)
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Keys(from string, n int) []string
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}
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// LessFunction is used to initialize an Index of keys in a specific order.
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type LessFunction func(string, string) bool
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// btreeString is a custom data type that satisfies the BTree Less interface,
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// making the strings it wraps sortable by the BTree package.
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type btreeString struct {
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s string
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l LessFunction
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}
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// Less satisfies the BTree.Less interface using the btreeString's LessFunction.
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func (s btreeString) Less(i btree.Item) bool {
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return s.l(s.s, i.(btreeString).s)
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}
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// BTreeIndex is an implementation of the Index interface using google/btree.
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type BTreeIndex struct {
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sync.RWMutex
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LessFunction
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*btree.BTree
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}
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// Initialize populates the BTree tree with data from the keys channel,
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// according to the passed less function. It's destructive to the BTreeIndex.
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func (i *BTreeIndex) Initialize(less LessFunction, keys <-chan string) {
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i.Lock()
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defer i.Unlock()
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i.LessFunction = less
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i.BTree = rebuild(less, keys)
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}
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// Insert inserts the given key (only) into the BTree tree.
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func (i *BTreeIndex) Insert(key string) {
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i.Lock()
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defer i.Unlock()
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if i.BTree == nil || i.LessFunction == nil {
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panic("uninitialized index")
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}
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i.BTree.ReplaceOrInsert(btreeString{s: key, l: i.LessFunction})
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}
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// Delete removes the given key (only) from the BTree tree.
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func (i *BTreeIndex) Delete(key string) {
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i.Lock()
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defer i.Unlock()
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if i.BTree == nil || i.LessFunction == nil {
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panic("uninitialized index")
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}
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i.BTree.Delete(btreeString{s: key, l: i.LessFunction})
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}
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// Keys yields a maximum of n keys in order. If the passed 'from' key is empty,
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// Keys will return the first n keys. If the passed 'from' key is non-empty, the
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// first key in the returned slice will be the key that immediately follows the
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// passed key, in key order.
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func (i *BTreeIndex) Keys(from string, n int) []string {
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i.RLock()
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defer i.RUnlock()
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if i.BTree == nil || i.LessFunction == nil {
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panic("uninitialized index")
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}
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if i.BTree.Len() <= 0 {
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return []string{}
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}
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btreeFrom := btreeString{s: from, l: i.LessFunction}
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skipFirst := true
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if len(from) <= 0 || !i.BTree.Has(btreeFrom) {
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// no such key, so fabricate an always-smallest item
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btreeFrom = btreeString{s: "", l: func(string, string) bool { return true }}
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skipFirst = false
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}
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keys := []string{}
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iterator := func(i btree.Item) bool {
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keys = append(keys, i.(btreeString).s)
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return len(keys) < n
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}
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i.BTree.AscendGreaterOrEqual(btreeFrom, iterator)
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if skipFirst && len(keys) > 0 {
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keys = keys[1:]
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}
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return keys
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}
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// rebuildIndex does the work of regenerating the index
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// with the given keys.
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func rebuild(less LessFunction, keys <-chan string) *btree.BTree {
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tree := btree.New(2)
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for key := range keys {
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tree.ReplaceOrInsert(btreeString{s: key, l: less})
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}
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return tree
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}
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