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Ettore Di Giacinto
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language: go

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Apache License
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# BTree implementation for Go
![Travis CI Build Status](https://api.travis-ci.org/google/btree.svg?branch=master)
This package provides an in-memory B-Tree implementation for Go, useful as
an ordered, mutable data structure.
The API is based off of the wonderful
http://godoc.org/github.com/petar/GoLLRB/llrb, and is meant to allow btree to
act as a drop-in replacement for gollrb trees.
See http://godoc.org/github.com/google/btree for documentation.

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// Copyright 2014 Google Inc.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package btree implements in-memory B-Trees of arbitrary degree.
//
// btree implements an in-memory B-Tree for use as an ordered data structure.
// It is not meant for persistent storage solutions.
//
// It has a flatter structure than an equivalent red-black or other binary tree,
// which in some cases yields better memory usage and/or performance.
// See some discussion on the matter here:
// http://google-opensource.blogspot.com/2013/01/c-containers-that-save-memory-and-time.html
// Note, though, that this project is in no way related to the C++ B-Tree
// implementation written about there.
//
// Within this tree, each node contains a slice of items and a (possibly nil)
// slice of children. For basic numeric values or raw structs, this can cause
// efficiency differences when compared to equivalent C++ template code that
// stores values in arrays within the node:
// * Due to the overhead of storing values as interfaces (each
// value needs to be stored as the value itself, then 2 words for the
// interface pointing to that value and its type), resulting in higher
// memory use.
// * Since interfaces can point to values anywhere in memory, values are
// most likely not stored in contiguous blocks, resulting in a higher
// number of cache misses.
// These issues don't tend to matter, though, when working with strings or other
// heap-allocated structures, since C++-equivalent structures also must store
// pointers and also distribute their values across the heap.
//
// This implementation is designed to be a drop-in replacement to gollrb.LLRB
// trees, (http://github.com/petar/gollrb), an excellent and probably the most
// widely used ordered tree implementation in the Go ecosystem currently.
// Its functions, therefore, exactly mirror those of
// llrb.LLRB where possible. Unlike gollrb, though, we currently don't
// support storing multiple equivalent values.
package btree
import (
"fmt"
"io"
"sort"
"strings"
"sync"
)
// Item represents a single object in the tree.
type Item interface {
// Less tests whether the current item is less than the given argument.
//
// This must provide a strict weak ordering.
// If !a.Less(b) && !b.Less(a), we treat this to mean a == b (i.e. we can only
// hold one of either a or b in the tree).
Less(than Item) bool
}
const (
DefaultFreeListSize = 32
)
var (
nilItems = make(items, 16)
nilChildren = make(children, 16)
)
// FreeList represents a free list of btree nodes. By default each
// BTree has its own FreeList, but multiple BTrees can share the same
// FreeList.
// Two Btrees using the same freelist are safe for concurrent write access.
type FreeList struct {
mu sync.Mutex
freelist []*node
}
// NewFreeList creates a new free list.
// size is the maximum size of the returned free list.
func NewFreeList(size int) *FreeList {
return &FreeList{freelist: make([]*node, 0, size)}
}
func (f *FreeList) newNode() (n *node) {
f.mu.Lock()
index := len(f.freelist) - 1
if index < 0 {
f.mu.Unlock()
return new(node)
}
n = f.freelist[index]
f.freelist[index] = nil
f.freelist = f.freelist[:index]
f.mu.Unlock()
return
}
// freeNode adds the given node to the list, returning true if it was added
// and false if it was discarded.
func (f *FreeList) freeNode(n *node) (out bool) {
f.mu.Lock()
if len(f.freelist) < cap(f.freelist) {
f.freelist = append(f.freelist, n)
out = true
}
f.mu.Unlock()
return
}
// ItemIterator allows callers of Ascend* to iterate in-order over portions of
// the tree. When this function returns false, iteration will stop and the
// associated Ascend* function will immediately return.
type ItemIterator func(i Item) bool
// New creates a new B-Tree with the given degree.
//
// New(2), for example, will create a 2-3-4 tree (each node contains 1-3 items
// and 2-4 children).
func New(degree int) *BTree {
return NewWithFreeList(degree, NewFreeList(DefaultFreeListSize))
}
// NewWithFreeList creates a new B-Tree that uses the given node free list.
func NewWithFreeList(degree int, f *FreeList) *BTree {
if degree <= 1 {
panic("bad degree")
}
return &BTree{
degree: degree,
cow: &copyOnWriteContext{freelist: f},
}
}
// items stores items in a node.
type items []Item
// insertAt inserts a value into the given index, pushing all subsequent values
// forward.
func (s *items) insertAt(index int, item Item) {
*s = append(*s, nil)
if index < len(*s) {
copy((*s)[index+1:], (*s)[index:])
}
(*s)[index] = item
}
// removeAt removes a value at a given index, pulling all subsequent values
// back.
func (s *items) removeAt(index int) Item {
item := (*s)[index]
copy((*s)[index:], (*s)[index+1:])
(*s)[len(*s)-1] = nil
*s = (*s)[:len(*s)-1]
return item
}
// pop removes and returns the last element in the list.
func (s *items) pop() (out Item) {
index := len(*s) - 1
out = (*s)[index]
(*s)[index] = nil
*s = (*s)[:index]
return
}
// truncate truncates this instance at index so that it contains only the
// first index items. index must be less than or equal to length.
func (s *items) truncate(index int) {
var toClear items
*s, toClear = (*s)[:index], (*s)[index:]
for len(toClear) > 0 {
toClear = toClear[copy(toClear, nilItems):]
}
}
// find returns the index where the given item should be inserted into this
// list. 'found' is true if the item already exists in the list at the given
// index.
func (s items) find(item Item) (index int, found bool) {
i := sort.Search(len(s), func(i int) bool {
return item.Less(s[i])
})
if i > 0 && !s[i-1].Less(item) {
return i - 1, true
}
return i, false
}
// children stores child nodes in a node.
type children []*node
// insertAt inserts a value into the given index, pushing all subsequent values
// forward.
func (s *children) insertAt(index int, n *node) {
*s = append(*s, nil)
if index < len(*s) {
copy((*s)[index+1:], (*s)[index:])
}
(*s)[index] = n
}
// removeAt removes a value at a given index, pulling all subsequent values
// back.
func (s *children) removeAt(index int) *node {
n := (*s)[index]
copy((*s)[index:], (*s)[index+1:])
(*s)[len(*s)-1] = nil
*s = (*s)[:len(*s)-1]
return n
}
// pop removes and returns the last element in the list.
func (s *children) pop() (out *node) {
index := len(*s) - 1
out = (*s)[index]
(*s)[index] = nil
*s = (*s)[:index]
return
}
// truncate truncates this instance at index so that it contains only the
// first index children. index must be less than or equal to length.
func (s *children) truncate(index int) {
var toClear children
*s, toClear = (*s)[:index], (*s)[index:]
for len(toClear) > 0 {
toClear = toClear[copy(toClear, nilChildren):]
}
}
// node is an internal node in a tree.
//
// It must at all times maintain the invariant that either
// * len(children) == 0, len(items) unconstrained
// * len(children) == len(items) + 1
type node struct {
items items
children children
cow *copyOnWriteContext
}
func (n *node) mutableFor(cow *copyOnWriteContext) *node {
if n.cow == cow {
return n
}
out := cow.newNode()
if cap(out.items) >= len(n.items) {
out.items = out.items[:len(n.items)]
} else {
out.items = make(items, len(n.items), cap(n.items))
}
copy(out.items, n.items)
// Copy children
if cap(out.children) >= len(n.children) {
out.children = out.children[:len(n.children)]
} else {
out.children = make(children, len(n.children), cap(n.children))
}
copy(out.children, n.children)
return out
}
func (n *node) mutableChild(i int) *node {
c := n.children[i].mutableFor(n.cow)
n.children[i] = c
return c
}
// split splits the given node at the given index. The current node shrinks,
// and this function returns the item that existed at that index and a new node
// containing all items/children after it.
func (n *node) split(i int) (Item, *node) {
item := n.items[i]
next := n.cow.newNode()
next.items = append(next.items, n.items[i+1:]...)
n.items.truncate(i)
if len(n.children) > 0 {
next.children = append(next.children, n.children[i+1:]...)
n.children.truncate(i + 1)
}
return item, next
}
// maybeSplitChild checks if a child should be split, and if so splits it.
// Returns whether or not a split occurred.
func (n *node) maybeSplitChild(i, maxItems int) bool {
if len(n.children[i].items) < maxItems {
return false
}
first := n.mutableChild(i)
item, second := first.split(maxItems / 2)
n.items.insertAt(i, item)
n.children.insertAt(i+1, second)
return true
}
// insert inserts an item into the subtree rooted at this node, making sure
// no nodes in the subtree exceed maxItems items. Should an equivalent item be
// be found/replaced by insert, it will be returned.
func (n *node) insert(item Item, maxItems int) Item {
i, found := n.items.find(item)
if found {
out := n.items[i]
n.items[i] = item
return out
}
if len(n.children) == 0 {
n.items.insertAt(i, item)
return nil
}
if n.maybeSplitChild(i, maxItems) {
inTree := n.items[i]
switch {
case item.Less(inTree):
// no change, we want first split node
case inTree.Less(item):
i++ // we want second split node
default:
out := n.items[i]
n.items[i] = item
return out
}
}
return n.mutableChild(i).insert(item, maxItems)
}
// get finds the given key in the subtree and returns it.
func (n *node) get(key Item) Item {
i, found := n.items.find(key)
if found {
return n.items[i]
} else if len(n.children) > 0 {
return n.children[i].get(key)
}
return nil
}
// min returns the first item in the subtree.
func min(n *node) Item {
if n == nil {
return nil
}
for len(n.children) > 0 {
n = n.children[0]
}
if len(n.items) == 0 {
return nil
}
return n.items[0]
}
// max returns the last item in the subtree.
func max(n *node) Item {
if n == nil {
return nil
}
for len(n.children) > 0 {
n = n.children[len(n.children)-1]
}
if len(n.items) == 0 {
return nil
}
return n.items[len(n.items)-1]
}
// toRemove details what item to remove in a node.remove call.
type toRemove int
const (
removeItem toRemove = iota // removes the given item
removeMin // removes smallest item in the subtree
removeMax // removes largest item in the subtree
)
// remove removes an item from the subtree rooted at this node.
func (n *node) remove(item Item, minItems int, typ toRemove) Item {
var i int
var found bool
switch typ {
case removeMax:
if len(n.children) == 0 {
return n.items.pop()
}
i = len(n.items)
case removeMin:
if len(n.children) == 0 {
return n.items.removeAt(0)
}
i = 0
case removeItem:
i, found = n.items.find(item)
if len(n.children) == 0 {
if found {
return n.items.removeAt(i)
}
return nil
}
default:
panic("invalid type")
}
// If we get to here, we have children.
if len(n.children[i].items) <= minItems {
return n.growChildAndRemove(i, item, minItems, typ)
}
child := n.mutableChild(i)
// Either we had enough items to begin with, or we've done some
// merging/stealing, because we've got enough now and we're ready to return
// stuff.
if found {
// The item exists at index 'i', and the child we've selected can give us a
// predecessor, since if we've gotten here it's got > minItems items in it.
out := n.items[i]
// We use our special-case 'remove' call with typ=maxItem to pull the
// predecessor of item i (the rightmost leaf of our immediate left child)
// and set it into where we pulled the item from.
n.items[i] = child.remove(nil, minItems, removeMax)
return out
}
// Final recursive call. Once we're here, we know that the item isn't in this
// node and that the child is big enough to remove from.
return child.remove(item, minItems, typ)
}
// growChildAndRemove grows child 'i' to make sure it's possible to remove an
// item from it while keeping it at minItems, then calls remove to actually
// remove it.
//
// Most documentation says we have to do two sets of special casing:
// 1) item is in this node
// 2) item is in child
// In both cases, we need to handle the two subcases:
// A) node has enough values that it can spare one
// B) node doesn't have enough values
// For the latter, we have to check:
// a) left sibling has node to spare
// b) right sibling has node to spare
// c) we must merge
// To simplify our code here, we handle cases #1 and #2 the same:
// If a node doesn't have enough items, we make sure it does (using a,b,c).
// We then simply redo our remove call, and the second time (regardless of
// whether we're in case 1 or 2), we'll have enough items and can guarantee
// that we hit case A.
func (n *node) growChildAndRemove(i int, item Item, minItems int, typ toRemove) Item {
if i > 0 && len(n.children[i-1].items) > minItems {
// Steal from left child
child := n.mutableChild(i)
stealFrom := n.mutableChild(i - 1)
stolenItem := stealFrom.items.pop()
child.items.insertAt(0, n.items[i-1])
n.items[i-1] = stolenItem
if len(stealFrom.children) > 0 {
child.children.insertAt(0, stealFrom.children.pop())
}
} else if i < len(n.items) && len(n.children[i+1].items) > minItems {
// steal from right child
child := n.mutableChild(i)
stealFrom := n.mutableChild(i + 1)
stolenItem := stealFrom.items.removeAt(0)
child.items = append(child.items, n.items[i])
n.items[i] = stolenItem
if len(stealFrom.children) > 0 {
child.children = append(child.children, stealFrom.children.removeAt(0))
}
} else {
if i >= len(n.items) {
i--
}
child := n.mutableChild(i)
// merge with right child
mergeItem := n.items.removeAt(i)
mergeChild := n.children.removeAt(i + 1)
child.items = append(child.items, mergeItem)
child.items = append(child.items, mergeChild.items...)
child.children = append(child.children, mergeChild.children...)
n.cow.freeNode(mergeChild)
}
return n.remove(item, minItems, typ)
}
type direction int
const (
descend = direction(-1)
ascend = direction(+1)
)
// iterate provides a simple method for iterating over elements in the tree.
//
// When ascending, the 'start' should be less than 'stop' and when descending,
// the 'start' should be greater than 'stop'. Setting 'includeStart' to true
// will force the iterator to include the first item when it equals 'start',
// thus creating a "greaterOrEqual" or "lessThanEqual" rather than just a
// "greaterThan" or "lessThan" queries.
func (n *node) iterate(dir direction, start, stop Item, includeStart bool, hit bool, iter ItemIterator) (bool, bool) {
var ok, found bool
var index int
switch dir {
case ascend:
if start != nil {
index, _ = n.items.find(start)
}
for i := index; i < len(n.items); i++ {
if len(n.children) > 0 {
if hit, ok = n.children[i].iterate(dir, start, stop, includeStart, hit, iter); !ok {
return hit, false
}
}
if !includeStart && !hit && start != nil && !start.Less(n.items[i]) {
hit = true
continue
}
hit = true
if stop != nil && !n.items[i].Less(stop) {
return hit, false
}
if !iter(n.items[i]) {
return hit, false
}
}
if len(n.children) > 0 {
if hit, ok = n.children[len(n.children)-1].iterate(dir, start, stop, includeStart, hit, iter); !ok {
return hit, false
}
}
case descend:
if start != nil {
index, found = n.items.find(start)
if !found {
index = index - 1
}
} else {
index = len(n.items) - 1
}
for i := index; i >= 0; i-- {
if start != nil && !n.items[i].Less(start) {
if !includeStart || hit || start.Less(n.items[i]) {
continue
}
}
if len(n.children) > 0 {
if hit, ok = n.children[i+1].iterate(dir, start, stop, includeStart, hit, iter); !ok {
return hit, false
}
}
if stop != nil && !stop.Less(n.items[i]) {
return hit, false // continue
}
hit = true
if !iter(n.items[i]) {
return hit, false
}
}
if len(n.children) > 0 {
if hit, ok = n.children[0].iterate(dir, start, stop, includeStart, hit, iter); !ok {
return hit, false
}
}
}
return hit, true
}
// Used for testing/debugging purposes.
func (n *node) print(w io.Writer, level int) {
fmt.Fprintf(w, "%sNODE:%v\n", strings.Repeat(" ", level), n.items)
for _, c := range n.children {
c.print(w, level+1)
}
}
// BTree is an implementation of a B-Tree.
//
// BTree stores Item instances in an ordered structure, allowing easy insertion,
// removal, and iteration.
//
// Write operations are not safe for concurrent mutation by multiple
// goroutines, but Read operations are.
type BTree struct {
degree int
length int
root *node
cow *copyOnWriteContext
}
// copyOnWriteContext pointers determine node ownership... a tree with a write
// context equivalent to a node's write context is allowed to modify that node.
// A tree whose write context does not match a node's is not allowed to modify
// it, and must create a new, writable copy (IE: it's a Clone).
//
// When doing any write operation, we maintain the invariant that the current
// node's context is equal to the context of the tree that requested the write.
// We do this by, before we descend into any node, creating a copy with the
// correct context if the contexts don't match.
//
// Since the node we're currently visiting on any write has the requesting
// tree's context, that node is modifiable in place. Children of that node may
// not share context, but before we descend into them, we'll make a mutable
// copy.
type copyOnWriteContext struct {
freelist *FreeList
}
// Clone clones the btree, lazily. Clone should not be called concurrently,
// but the original tree (t) and the new tree (t2) can be used concurrently
// once the Clone call completes.
//
// The internal tree structure of b is marked read-only and shared between t and
// t2. Writes to both t and t2 use copy-on-write logic, creating new nodes
// whenever one of b's original nodes would have been modified. Read operations
// should have no performance degredation. Write operations for both t and t2
// will initially experience minor slow-downs caused by additional allocs and
// copies due to the aforementioned copy-on-write logic, but should converge to
// the original performance characteristics of the original tree.
func (t *BTree) Clone() (t2 *BTree) {
// Create two entirely new copy-on-write contexts.
// This operation effectively creates three trees:
// the original, shared nodes (old b.cow)
// the new b.cow nodes
// the new out.cow nodes
cow1, cow2 := *t.cow, *t.cow
out := *t
t.cow = &cow1
out.cow = &cow2
return &out
}
// maxItems returns the max number of items to allow per node.
func (t *BTree) maxItems() int {
return t.degree*2 - 1
}
// minItems returns the min number of items to allow per node (ignored for the
// root node).
func (t *BTree) minItems() int {
return t.degree - 1
}
func (c *copyOnWriteContext) newNode() (n *node) {
n = c.freelist.newNode()
n.cow = c
return
}
type freeType int
const (
ftFreelistFull freeType = iota // node was freed (available for GC, not stored in freelist)
ftStored // node was stored in the freelist for later use
ftNotOwned // node was ignored by COW, since it's owned by another one
)
// freeNode frees a node within a given COW context, if it's owned by that
// context. It returns what happened to the node (see freeType const
// documentation).
func (c *copyOnWriteContext) freeNode(n *node) freeType {
if n.cow == c {
// clear to allow GC
n.items.truncate(0)
n.children.truncate(0)
n.cow = nil
if c.freelist.freeNode(n) {
return ftStored
} else {
return ftFreelistFull
}
} else {
return ftNotOwned
}
}
// ReplaceOrInsert adds the given item to the tree. If an item in the tree
// already equals the given one, it is removed from the tree and returned.
// Otherwise, nil is returned.
//
// nil cannot be added to the tree (will panic).
func (t *BTree) ReplaceOrInsert(item Item) Item {
if item == nil {
panic("nil item being added to BTree")
}
if t.root == nil {
t.root = t.cow.newNode()
t.root.items = append(t.root.items, item)
t.length++
return nil
} else {
t.root = t.root.mutableFor(t.cow)
if len(t.root.items) >= t.maxItems() {
item2, second := t.root.split(t.maxItems() / 2)
oldroot := t.root
t.root = t.cow.newNode()
t.root.items = append(t.root.items, item2)
t.root.children = append(t.root.children, oldroot, second)
}
}
out := t.root.insert(item, t.maxItems())
if out == nil {
t.length++
}
return out
}
// Delete removes an item equal to the passed in item from the tree, returning
// it. If no such item exists, returns nil.
func (t *BTree) Delete(item Item) Item {
return t.deleteItem(item, removeItem)
}
// DeleteMin removes the smallest item in the tree and returns it.
// If no such item exists, returns nil.
func (t *BTree) DeleteMin() Item {
return t.deleteItem(nil, removeMin)
}
// DeleteMax removes the largest item in the tree and returns it.
// If no such item exists, returns nil.
func (t *BTree) DeleteMax() Item {
return t.deleteItem(nil, removeMax)
}
func (t *BTree) deleteItem(item Item, typ toRemove) Item {
if t.root == nil || len(t.root.items) == 0 {
return nil
}
t.root = t.root.mutableFor(t.cow)
out := t.root.remove(item, t.minItems(), typ)
if len(t.root.items) == 0 && len(t.root.children) > 0 {
oldroot := t.root
t.root = t.root.children[0]
t.cow.freeNode(oldroot)
}
if out != nil {
t.length--
}
return out
}
// AscendRange calls the iterator for every value in the tree within the range
// [greaterOrEqual, lessThan), until iterator returns false.
func (t *BTree) AscendRange(greaterOrEqual, lessThan Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(ascend, greaterOrEqual, lessThan, true, false, iterator)
}
// AscendLessThan calls the iterator for every value in the tree within the range
// [first, pivot), until iterator returns false.
func (t *BTree) AscendLessThan(pivot Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(ascend, nil, pivot, false, false, iterator)
}
// AscendGreaterOrEqual calls the iterator for every value in the tree within
// the range [pivot, last], until iterator returns false.
func (t *BTree) AscendGreaterOrEqual(pivot Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(ascend, pivot, nil, true, false, iterator)
}
// Ascend calls the iterator for every value in the tree within the range
// [first, last], until iterator returns false.
func (t *BTree) Ascend(iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(ascend, nil, nil, false, false, iterator)
}
// DescendRange calls the iterator for every value in the tree within the range
// [lessOrEqual, greaterThan), until iterator returns false.
func (t *BTree) DescendRange(lessOrEqual, greaterThan Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(descend, lessOrEqual, greaterThan, true, false, iterator)
}
// DescendLessOrEqual calls the iterator for every value in the tree within the range
// [pivot, first], until iterator returns false.
func (t *BTree) DescendLessOrEqual(pivot Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(descend, pivot, nil, true, false, iterator)
}
// DescendGreaterThan calls the iterator for every value in the tree within
// the range (pivot, last], until iterator returns false.
func (t *BTree) DescendGreaterThan(pivot Item, iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(descend, nil, pivot, false, false, iterator)
}
// Descend calls the iterator for every value in the tree within the range
// [last, first], until iterator returns false.
func (t *BTree) Descend(iterator ItemIterator) {
if t.root == nil {
return
}
t.root.iterate(descend, nil, nil, false, false, iterator)
}
// Get looks for the key item in the tree, returning it. It returns nil if
// unable to find that item.
func (t *BTree) Get(key Item) Item {
if t.root == nil {
return nil
}
return t.root.get(key)
}
// Min returns the smallest item in the tree, or nil if the tree is empty.
func (t *BTree) Min() Item {
return min(t.root)
}
// Max returns the largest item in the tree, or nil if the tree is empty.
func (t *BTree) Max() Item {
return max(t.root)
}
// Has returns true if the given key is in the tree.
func (t *BTree) Has(key Item) bool {
return t.Get(key) != nil
}
// Len returns the number of items currently in the tree.
func (t *BTree) Len() int {
return t.length
}
// Clear removes all items from the btree. If addNodesToFreelist is true,
// t's nodes are added to its freelist as part of this call, until the freelist
// is full. Otherwise, the root node is simply dereferenced and the subtree
// left to Go's normal GC processes.
//
// This can be much faster
// than calling Delete on all elements, because that requires finding/removing
// each element in the tree and updating the tree accordingly. It also is
// somewhat faster than creating a new tree to replace the old one, because
// nodes from the old tree are reclaimed into the freelist for use by the new
// one, instead of being lost to the garbage collector.
//
// This call takes:
// O(1): when addNodesToFreelist is false, this is a single operation.
// O(1): when the freelist is already full, it breaks out immediately
// O(freelist size): when the freelist is empty and the nodes are all owned
// by this tree, nodes are added to the freelist until full.
// O(tree size): when all nodes are owned by another tree, all nodes are
// iterated over looking for nodes to add to the freelist, and due to
// ownership, none are.
func (t *BTree) Clear(addNodesToFreelist bool) {
if t.root != nil && addNodesToFreelist {
t.root.reset(t.cow)
}
t.root, t.length = nil, 0
}
// reset returns a subtree to the freelist. It breaks out immediately if the
// freelist is full, since the only benefit of iterating is to fill that
// freelist up. Returns true if parent reset call should continue.
func (n *node) reset(c *copyOnWriteContext) bool {
for _, child := range n.children {
if !child.reset(c) {
return false
}
}
return c.freeNode(n) != ftFreelistFull
}
// Int implements the Item interface for integers.
type Int int
// Less returns true if int(a) < int(b).
func (a Int) Less(b Item) bool {
return a < b.(Int)
}

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vendor/github.com/peterbourgon/diskv/LICENSE generated vendored Normal file
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Copyright (c) 2011-2012 Peter Bourgon
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.

141
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# What is diskv?
Diskv (disk-vee) is a simple, persistent key-value store written in the Go
language. It starts with an incredibly simple API for storing arbitrary data on
a filesystem by key, and builds several layers of performance-enhancing
abstraction on top. The end result is a conceptually simple, but highly
performant, disk-backed storage system.
[![Build Status][1]][2]
[1]: https://drone.io/github.com/peterbourgon/diskv/status.png
[2]: https://drone.io/github.com/peterbourgon/diskv/latest
# Installing
Install [Go 1][3], either [from source][4] or [with a prepackaged binary][5].
Then,
```bash
$ go get github.com/peterbourgon/diskv
```
[3]: http://golang.org
[4]: http://golang.org/doc/install/source
[5]: http://golang.org/doc/install
# Usage
```go
package main
import (
"fmt"
"github.com/peterbourgon/diskv"
)
func main() {
// Simplest transform function: put all the data files into the base dir.
flatTransform := func(s string) []string { return []string{} }
// Initialize a new diskv store, rooted at "my-data-dir", with a 1MB cache.
d := diskv.New(diskv.Options{
BasePath: "my-data-dir",
Transform: flatTransform,
CacheSizeMax: 1024 * 1024,
})
// Write three bytes to the key "alpha".
key := "alpha"
d.Write(key, []byte{'1', '2', '3'})
// Read the value back out of the store.
value, _ := d.Read(key)
fmt.Printf("%v\n", value)
// Erase the key+value from the store (and the disk).
d.Erase(key)
}
```
More complex examples can be found in the "examples" subdirectory.
# Theory
## Basic idea
At its core, diskv is a map of a key (`string`) to arbitrary data (`[]byte`).
The data is written to a single file on disk, with the same name as the key.
The key determines where that file will be stored, via a user-provided
`TransformFunc`, which takes a key and returns a slice (`[]string`)
corresponding to a path list where the key file will be stored. The simplest
TransformFunc,
```go
func SimpleTransform (key string) []string {
return []string{}
}
```
will place all keys in the same, base directory. The design is inspired by
[Redis diskstore][6]; a TransformFunc which emulates the default diskstore
behavior is available in the content-addressable-storage example.
[6]: http://groups.google.com/group/redis-db/browse_thread/thread/d444bc786689bde9?pli=1
**Note** that your TransformFunc should ensure that one valid key doesn't
transform to a subset of another valid key. That is, it shouldn't be possible
to construct valid keys that resolve to directory names. As a concrete example,
if your TransformFunc splits on every 3 characters, then
```go
d.Write("abcabc", val) // OK: written to <base>/abc/abc/abcabc
d.Write("abc", val) // Error: attempted write to <base>/abc/abc, but it's a directory
```
This will be addressed in an upcoming version of diskv.
Probably the most important design principle behind diskv is that your data is
always flatly available on the disk. diskv will never do anything that would
prevent you from accessing, copying, backing up, or otherwise interacting with
your data via common UNIX commandline tools.
## Adding a cache
An in-memory caching layer is provided by combining the BasicStore
functionality with a simple map structure, and keeping it up-to-date as
appropriate. Since the map structure in Go is not threadsafe, it's combined
with a RWMutex to provide safe concurrent access.
## Adding order
diskv is a key-value store and therefore inherently unordered. An ordering
system can be injected into the store by passing something which satisfies the
diskv.Index interface. (A default implementation, using Google's
[btree][7] package, is provided.) Basically, diskv keeps an ordered (by a
user-provided Less function) index of the keys, which can be queried.
[7]: https://github.com/google/btree
## Adding compression
Something which implements the diskv.Compression interface may be passed
during store creation, so that all Writes and Reads are filtered through
a compression/decompression pipeline. Several default implementations,
using stdlib compression algorithms, are provided. Note that data is cached
compressed; the cost of decompression is borne with each Read.
## Streaming
diskv also now provides ReadStream and WriteStream methods, to allow very large
data to be handled efficiently.
# Future plans
* Needs plenty of robust testing: huge datasets, etc...
* More thorough benchmarking
* Your suggestions for use-cases I haven't thought of

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package diskv
import (
"compress/flate"
"compress/gzip"
"compress/zlib"
"io"
)
// Compression is an interface that Diskv uses to implement compression of
// data. Writer takes a destination io.Writer and returns a WriteCloser that
// compresses all data written through it. Reader takes a source io.Reader and
// returns a ReadCloser that decompresses all data read through it. You may
// define these methods on your own type, or use one of the NewCompression
// helpers.
type Compression interface {
Writer(dst io.Writer) (io.WriteCloser, error)
Reader(src io.Reader) (io.ReadCloser, error)
}
// NewGzipCompression returns a Gzip-based Compression.
func NewGzipCompression() Compression {
return NewGzipCompressionLevel(flate.DefaultCompression)
}
// NewGzipCompressionLevel returns a Gzip-based Compression with the given level.
func NewGzipCompressionLevel(level int) Compression {
return &genericCompression{
wf: func(w io.Writer) (io.WriteCloser, error) { return gzip.NewWriterLevel(w, level) },
rf: func(r io.Reader) (io.ReadCloser, error) { return gzip.NewReader(r) },
}
}
// NewZlibCompression returns a Zlib-based Compression.
func NewZlibCompression() Compression {
return NewZlibCompressionLevel(flate.DefaultCompression)
}
// NewZlibCompressionLevel returns a Zlib-based Compression with the given level.
func NewZlibCompressionLevel(level int) Compression {
return NewZlibCompressionLevelDict(level, nil)
}
// NewZlibCompressionLevelDict returns a Zlib-based Compression with the given
// level, based on the given dictionary.
func NewZlibCompressionLevelDict(level int, dict []byte) Compression {
return &genericCompression{
func(w io.Writer) (io.WriteCloser, error) { return zlib.NewWriterLevelDict(w, level, dict) },
func(r io.Reader) (io.ReadCloser, error) { return zlib.NewReaderDict(r, dict) },
}
}
type genericCompression struct {
wf func(w io.Writer) (io.WriteCloser, error)
rf func(r io.Reader) (io.ReadCloser, error)
}
func (g *genericCompression) Writer(dst io.Writer) (io.WriteCloser, error) {
return g.wf(dst)
}
func (g *genericCompression) Reader(src io.Reader) (io.ReadCloser, error) {
return g.rf(src)
}

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vendor/github.com/peterbourgon/diskv/diskv.go generated vendored Normal file
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// Diskv (disk-vee) is a simple, persistent, key-value store.
// It stores all data flatly on the filesystem.
package diskv
import (
"bytes"
"errors"
"fmt"
"io"
"io/ioutil"
"os"
"path/filepath"
"strings"
"sync"
"syscall"
)
const (
defaultBasePath = "diskv"
defaultFilePerm os.FileMode = 0666
defaultPathPerm os.FileMode = 0777
)
var (
defaultTransform = func(s string) []string { return []string{} }
errCanceled = errors.New("canceled")
errEmptyKey = errors.New("empty key")
errBadKey = errors.New("bad key")
errImportDirectory = errors.New("can't import a directory")
)
// TransformFunction transforms a key into a slice of strings, with each
// element in the slice representing a directory in the file path where the
// key's entry will eventually be stored.
//
// For example, if TransformFunc transforms "abcdef" to ["ab", "cde", "f"],
// the final location of the data file will be <basedir>/ab/cde/f/abcdef
type TransformFunction func(s string) []string
// Options define a set of properties that dictate Diskv behavior.
// All values are optional.
type Options struct {
BasePath string
Transform TransformFunction
CacheSizeMax uint64 // bytes
PathPerm os.FileMode
FilePerm os.FileMode
// If TempDir is set, it will enable filesystem atomic writes by
// writing temporary files to that location before being moved
// to BasePath.
// Note that TempDir MUST be on the same device/partition as
// BasePath.
TempDir string
Index Index
IndexLess LessFunction
Compression Compression
}
// Diskv implements the Diskv interface. You shouldn't construct Diskv
// structures directly; instead, use the New constructor.
type Diskv struct {
Options
mu sync.RWMutex
cache map[string][]byte
cacheSize uint64
}
// New returns an initialized Diskv structure, ready to use.
// If the path identified by baseDir already contains data,
// it will be accessible, but not yet cached.
func New(o Options) *Diskv {
if o.BasePath == "" {
o.BasePath = defaultBasePath
}
if o.Transform == nil {
o.Transform = defaultTransform
}
if o.PathPerm == 0 {
o.PathPerm = defaultPathPerm
}
if o.FilePerm == 0 {
o.FilePerm = defaultFilePerm
}
d := &Diskv{
Options: o,
cache: map[string][]byte{},
cacheSize: 0,
}
if d.Index != nil && d.IndexLess != nil {
d.Index.Initialize(d.IndexLess, d.Keys(nil))
}
return d
}
// Write synchronously writes the key-value pair to disk, making it immediately
// available for reads. Write relies on the filesystem to perform an eventual
// sync to physical media. If you need stronger guarantees, see WriteStream.
func (d *Diskv) Write(key string, val []byte) error {
return d.WriteStream(key, bytes.NewBuffer(val), false)
}
// WriteStream writes the data represented by the io.Reader to the disk, under
// the provided key. If sync is true, WriteStream performs an explicit sync on
// the file as soon as it's written.
//
// bytes.Buffer provides io.Reader semantics for basic data types.
func (d *Diskv) WriteStream(key string, r io.Reader, sync bool) error {
if len(key) <= 0 {
return errEmptyKey
}
d.mu.Lock()
defer d.mu.Unlock()
return d.writeStreamWithLock(key, r, sync)
}
// createKeyFileWithLock either creates the key file directly, or
// creates a temporary file in TempDir if it is set.
func (d *Diskv) createKeyFileWithLock(key string) (*os.File, error) {
if d.TempDir != "" {
if err := os.MkdirAll(d.TempDir, d.PathPerm); err != nil {
return nil, fmt.Errorf("temp mkdir: %s", err)
}
f, err := ioutil.TempFile(d.TempDir, "")
if err != nil {
return nil, fmt.Errorf("temp file: %s", err)
}
if err := f.Chmod(d.FilePerm); err != nil {
f.Close() // error deliberately ignored
os.Remove(f.Name()) // error deliberately ignored
return nil, fmt.Errorf("chmod: %s", err)
}
return f, nil
}
mode := os.O_WRONLY | os.O_CREATE | os.O_TRUNC // overwrite if exists
f, err := os.OpenFile(d.completeFilename(key), mode, d.FilePerm)
if err != nil {
return nil, fmt.Errorf("open file: %s", err)
}
return f, nil
}
// writeStream does no input validation checking.
func (d *Diskv) writeStreamWithLock(key string, r io.Reader, sync bool) error {
if err := d.ensurePathWithLock(key); err != nil {
return fmt.Errorf("ensure path: %s", err)
}
f, err := d.createKeyFileWithLock(key)
if err != nil {
return fmt.Errorf("create key file: %s", err)
}
wc := io.WriteCloser(&nopWriteCloser{f})
if d.Compression != nil {
wc, err = d.Compression.Writer(f)
if err != nil {
f.Close() // error deliberately ignored
os.Remove(f.Name()) // error deliberately ignored
return fmt.Errorf("compression writer: %s", err)
}
}
if _, err := io.Copy(wc, r); err != nil {
f.Close() // error deliberately ignored
os.Remove(f.Name()) // error deliberately ignored
return fmt.Errorf("i/o copy: %s", err)
}
if err := wc.Close(); err != nil {
f.Close() // error deliberately ignored
os.Remove(f.Name()) // error deliberately ignored
return fmt.Errorf("compression close: %s", err)
}
if sync {
if err := f.Sync(); err != nil {
f.Close() // error deliberately ignored
os.Remove(f.Name()) // error deliberately ignored
return fmt.Errorf("file sync: %s", err)
}
}
if err := f.Close(); err != nil {
return fmt.Errorf("file close: %s", err)
}
if f.Name() != d.completeFilename(key) {
if err := os.Rename(f.Name(), d.completeFilename(key)); err != nil {
os.Remove(f.Name()) // error deliberately ignored
return fmt.Errorf("rename: %s", err)
}
}
if d.Index != nil {
d.Index.Insert(key)
}
d.bustCacheWithLock(key) // cache only on read
return nil
}
// Import imports the source file into diskv under the destination key. If the
// destination key already exists, it's overwritten. If move is true, the
// source file is removed after a successful import.
func (d *Diskv) Import(srcFilename, dstKey string, move bool) (err error) {
if dstKey == "" {
return errEmptyKey
}
if fi, err := os.Stat(srcFilename); err != nil {
return err
} else if fi.IsDir() {
return errImportDirectory
}
d.mu.Lock()
defer d.mu.Unlock()
if err := d.ensurePathWithLock(dstKey); err != nil {
return fmt.Errorf("ensure path: %s", err)
}
if move {
if err := syscall.Rename(srcFilename, d.completeFilename(dstKey)); err == nil {
d.bustCacheWithLock(dstKey)
return nil
} else if err != syscall.EXDEV {
// If it failed due to being on a different device, fall back to copying
return err
}
}
f, err := os.Open(srcFilename)
if err != nil {
return err
}
defer f.Close()
err = d.writeStreamWithLock(dstKey, f, false)
if err == nil && move {
err = os.Remove(srcFilename)
}
return err
}
// Read reads the key and returns the value.
// If the key is available in the cache, Read won't touch the disk.
// If the key is not in the cache, Read will have the side-effect of
// lazily caching the value.
func (d *Diskv) Read(key string) ([]byte, error) {
rc, err := d.ReadStream(key, false)
if err != nil {
return []byte{}, err
}
defer rc.Close()
return ioutil.ReadAll(rc)
}
// ReadStream reads the key and returns the value (data) as an io.ReadCloser.
// If the value is cached from a previous read, and direct is false,
// ReadStream will use the cached value. Otherwise, it will return a handle to
// the file on disk, and cache the data on read.
//
// If direct is true, ReadStream will lazily delete any cached value for the
// key, and return a direct handle to the file on disk.
//
// If compression is enabled, ReadStream taps into the io.Reader stream prior
// to decompression, and caches the compressed data.
func (d *Diskv) ReadStream(key string, direct bool) (io.ReadCloser, error) {
d.mu.RLock()
defer d.mu.RUnlock()
if val, ok := d.cache[key]; ok {
if !direct {
buf := bytes.NewBuffer(val)
if d.Compression != nil {
return d.Compression.Reader(buf)
}
return ioutil.NopCloser(buf), nil
}
go func() {
d.mu.Lock()
defer d.mu.Unlock()
d.uncacheWithLock(key, uint64(len(val)))
}()
}
return d.readWithRLock(key)
}
// read ignores the cache, and returns an io.ReadCloser representing the
// decompressed data for the given key, streamed from the disk. Clients should
// acquire a read lock on the Diskv and check the cache themselves before
// calling read.
func (d *Diskv) readWithRLock(key string) (io.ReadCloser, error) {
filename := d.completeFilename(key)
fi, err := os.Stat(filename)
if err != nil {
return nil, err
}
if fi.IsDir() {
return nil, os.ErrNotExist
}
f, err := os.Open(filename)
if err != nil {
return nil, err
}
var r io.Reader
if d.CacheSizeMax > 0 {
r = newSiphon(f, d, key)
} else {
r = &closingReader{f}
}
var rc = io.ReadCloser(ioutil.NopCloser(r))
if d.Compression != nil {
rc, err = d.Compression.Reader(r)
if err != nil {
return nil, err
}
}
return rc, nil
}
// closingReader provides a Reader that automatically closes the
// embedded ReadCloser when it reaches EOF
type closingReader struct {
rc io.ReadCloser
}
func (cr closingReader) Read(p []byte) (int, error) {
n, err := cr.rc.Read(p)
if err == io.EOF {
if closeErr := cr.rc.Close(); closeErr != nil {
return n, closeErr // close must succeed for Read to succeed
}
}
return n, err
}
// siphon is like a TeeReader: it copies all data read through it to an
// internal buffer, and moves that buffer to the cache at EOF.
type siphon struct {
f *os.File
d *Diskv
key string
buf *bytes.Buffer
}
// newSiphon constructs a siphoning reader that represents the passed file.
// When a successful series of reads ends in an EOF, the siphon will write
// the buffered data to Diskv's cache under the given key.
func newSiphon(f *os.File, d *Diskv, key string) io.Reader {
return &siphon{
f: f,
d: d,
key: key,
buf: &bytes.Buffer{},
}
}
// Read implements the io.Reader interface for siphon.
func (s *siphon) Read(p []byte) (int, error) {
n, err := s.f.Read(p)
if err == nil {
return s.buf.Write(p[0:n]) // Write must succeed for Read to succeed
}
if err == io.EOF {
s.d.cacheWithoutLock(s.key, s.buf.Bytes()) // cache may fail
if closeErr := s.f.Close(); closeErr != nil {
return n, closeErr // close must succeed for Read to succeed
}
return n, err
}
return n, err
}
// Erase synchronously erases the given key from the disk and the cache.
func (d *Diskv) Erase(key string) error {
d.mu.Lock()
defer d.mu.Unlock()
d.bustCacheWithLock(key)
// erase from index
if d.Index != nil {
d.Index.Delete(key)
}
// erase from disk
filename := d.completeFilename(key)
if s, err := os.Stat(filename); err == nil {
if s.IsDir() {
return errBadKey
}
if err = os.Remove(filename); err != nil {
return err
}
} else {
// Return err as-is so caller can do os.IsNotExist(err).
return err
}
// clean up and return
d.pruneDirsWithLock(key)
return nil
}
// EraseAll will delete all of the data from the store, both in the cache and on
// the disk. Note that EraseAll doesn't distinguish diskv-related data from non-
// diskv-related data. Care should be taken to always specify a diskv base
// directory that is exclusively for diskv data.
func (d *Diskv) EraseAll() error {
d.mu.Lock()
defer d.mu.Unlock()
d.cache = make(map[string][]byte)
d.cacheSize = 0
if d.TempDir != "" {
os.RemoveAll(d.TempDir) // errors ignored
}
return os.RemoveAll(d.BasePath)
}
// Has returns true if the given key exists.
func (d *Diskv) Has(key string) bool {
d.mu.Lock()
defer d.mu.Unlock()
if _, ok := d.cache[key]; ok {
return true
}
filename := d.completeFilename(key)
s, err := os.Stat(filename)
if err != nil {
return false
}
if s.IsDir() {
return false
}
return true
}
// Keys returns a channel that will yield every key accessible by the store,
// in undefined order. If a cancel channel is provided, closing it will
// terminate and close the keys channel.
func (d *Diskv) Keys(cancel <-chan struct{}) <-chan string {
return d.KeysPrefix("", cancel)
}
// KeysPrefix returns a channel that will yield every key accessible by the
// store with the given prefix, in undefined order. If a cancel channel is
// provided, closing it will terminate and close the keys channel. If the
// provided prefix is the empty string, all keys will be yielded.
func (d *Diskv) KeysPrefix(prefix string, cancel <-chan struct{}) <-chan string {
var prepath string
if prefix == "" {
prepath = d.BasePath
} else {
prepath = d.pathFor(prefix)
}
c := make(chan string)
go func() {
filepath.Walk(prepath, walker(c, prefix, cancel))
close(c)
}()
return c
}
// walker returns a function which satisfies the filepath.WalkFunc interface.
// It sends every non-directory file entry down the channel c.
func walker(c chan<- string, prefix string, cancel <-chan struct{}) filepath.WalkFunc {
return func(path string, info os.FileInfo, err error) error {
if err != nil {
return err
}
if info.IsDir() || !strings.HasPrefix(info.Name(), prefix) {
return nil // "pass"
}
select {
case c <- info.Name():
case <-cancel:
return errCanceled
}
return nil
}
}
// pathFor returns the absolute path for location on the filesystem where the
// data for the given key will be stored.
func (d *Diskv) pathFor(key string) string {
return filepath.Join(d.BasePath, filepath.Join(d.Transform(key)...))
}
// ensurePathWithLock is a helper function that generates all necessary
// directories on the filesystem for the given key.
func (d *Diskv) ensurePathWithLock(key string) error {
return os.MkdirAll(d.pathFor(key), d.PathPerm)
}
// completeFilename returns the absolute path to the file for the given key.
func (d *Diskv) completeFilename(key string) string {
return filepath.Join(d.pathFor(key), key)
}
// cacheWithLock attempts to cache the given key-value pair in the store's
// cache. It can fail if the value is larger than the cache's maximum size.
func (d *Diskv) cacheWithLock(key string, val []byte) error {
valueSize := uint64(len(val))
if err := d.ensureCacheSpaceWithLock(valueSize); err != nil {
return fmt.Errorf("%s; not caching", err)
}
// be very strict about memory guarantees
if (d.cacheSize + valueSize) > d.CacheSizeMax {
panic(fmt.Sprintf("failed to make room for value (%d/%d)", valueSize, d.CacheSizeMax))
}
d.cache[key] = val
d.cacheSize += valueSize
return nil
}
// cacheWithoutLock acquires the store's (write) mutex and calls cacheWithLock.
func (d *Diskv) cacheWithoutLock(key string, val []byte) error {
d.mu.Lock()
defer d.mu.Unlock()
return d.cacheWithLock(key, val)
}
func (d *Diskv) bustCacheWithLock(key string) {
if val, ok := d.cache[key]; ok {
d.uncacheWithLock(key, uint64(len(val)))
}
}
func (d *Diskv) uncacheWithLock(key string, sz uint64) {
d.cacheSize -= sz
delete(d.cache, key)
}
// pruneDirsWithLock deletes empty directories in the path walk leading to the
// key k. Typically this function is called after an Erase is made.
func (d *Diskv) pruneDirsWithLock(key string) error {
pathlist := d.Transform(key)
for i := range pathlist {
dir := filepath.Join(d.BasePath, filepath.Join(pathlist[:len(pathlist)-i]...))
// thanks to Steven Blenkinsop for this snippet
switch fi, err := os.Stat(dir); true {
case err != nil:
return err
case !fi.IsDir():
panic(fmt.Sprintf("corrupt dirstate at %s", dir))
}
nlinks, err := filepath.Glob(filepath.Join(dir, "*"))
if err != nil {
return err
} else if len(nlinks) > 0 {
return nil // has subdirs -- do not prune
}
if err = os.Remove(dir); err != nil {
return err
}
}
return nil
}
// ensureCacheSpaceWithLock deletes entries from the cache in arbitrary order
// until the cache has at least valueSize bytes available.
func (d *Diskv) ensureCacheSpaceWithLock(valueSize uint64) error {
if valueSize > d.CacheSizeMax {
return fmt.Errorf("value size (%d bytes) too large for cache (%d bytes)", valueSize, d.CacheSizeMax)
}
safe := func() bool { return (d.cacheSize + valueSize) <= d.CacheSizeMax }
for key, val := range d.cache {
if safe() {
break
}
d.uncacheWithLock(key, uint64(len(val)))
}
if !safe() {
panic(fmt.Sprintf("%d bytes still won't fit in the cache! (max %d bytes)", valueSize, d.CacheSizeMax))
}
return nil
}
// nopWriteCloser wraps an io.Writer and provides a no-op Close method to
// satisfy the io.WriteCloser interface.
type nopWriteCloser struct {
io.Writer
}
func (wc *nopWriteCloser) Write(p []byte) (int, error) { return wc.Writer.Write(p) }
func (wc *nopWriteCloser) Close() error { return nil }

115
vendor/github.com/peterbourgon/diskv/index.go generated vendored Normal file
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@@ -0,0 +1,115 @@
package diskv
import (
"sync"
"github.com/google/btree"
)
// Index is a generic interface for things that can
// provide an ordered list of keys.
type Index interface {
Initialize(less LessFunction, keys <-chan string)
Insert(key string)
Delete(key string)
Keys(from string, n int) []string
}
// LessFunction is used to initialize an Index of keys in a specific order.
type LessFunction func(string, string) bool
// btreeString is a custom data type that satisfies the BTree Less interface,
// making the strings it wraps sortable by the BTree package.
type btreeString struct {
s string
l LessFunction
}
// Less satisfies the BTree.Less interface using the btreeString's LessFunction.
func (s btreeString) Less(i btree.Item) bool {
return s.l(s.s, i.(btreeString).s)
}
// BTreeIndex is an implementation of the Index interface using google/btree.
type BTreeIndex struct {
sync.RWMutex
LessFunction
*btree.BTree
}
// Initialize populates the BTree tree with data from the keys channel,
// according to the passed less function. It's destructive to the BTreeIndex.
func (i *BTreeIndex) Initialize(less LessFunction, keys <-chan string) {
i.Lock()
defer i.Unlock()
i.LessFunction = less
i.BTree = rebuild(less, keys)
}
// Insert inserts the given key (only) into the BTree tree.
func (i *BTreeIndex) Insert(key string) {
i.Lock()
defer i.Unlock()
if i.BTree == nil || i.LessFunction == nil {
panic("uninitialized index")
}
i.BTree.ReplaceOrInsert(btreeString{s: key, l: i.LessFunction})
}
// Delete removes the given key (only) from the BTree tree.
func (i *BTreeIndex) Delete(key string) {
i.Lock()
defer i.Unlock()
if i.BTree == nil || i.LessFunction == nil {
panic("uninitialized index")
}
i.BTree.Delete(btreeString{s: key, l: i.LessFunction})
}
// Keys yields a maximum of n keys in order. If the passed 'from' key is empty,
// Keys will return the first n keys. If the passed 'from' key is non-empty, the
// first key in the returned slice will be the key that immediately follows the
// passed key, in key order.
func (i *BTreeIndex) Keys(from string, n int) []string {
i.RLock()
defer i.RUnlock()
if i.BTree == nil || i.LessFunction == nil {
panic("uninitialized index")
}
if i.BTree.Len() <= 0 {
return []string{}
}
btreeFrom := btreeString{s: from, l: i.LessFunction}
skipFirst := true
if len(from) <= 0 || !i.BTree.Has(btreeFrom) {
// no such key, so fabricate an always-smallest item
btreeFrom = btreeString{s: "", l: func(string, string) bool { return true }}
skipFirst = false
}
keys := []string{}
iterator := func(i btree.Item) bool {
keys = append(keys, i.(btreeString).s)
return len(keys) < n
}
i.BTree.AscendGreaterOrEqual(btreeFrom, iterator)
if skipFirst && len(keys) > 0 {
keys = keys[1:]
}
return keys
}
// rebuildIndex does the work of regenerating the index
// with the given keys.
func rebuild(less LessFunction, keys <-chan string) *btree.BTree {
tree := btree.New(2)
for key := range keys {
tree.ReplaceOrInsert(btreeString{s: key, l: less})
}
return tree
}