consul/vendor/github.com/hashicorp/go-immutable-radix/iradix.go

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package iradix
import (
"bytes"
"strings"
"github.com/hashicorp/golang-lru/simplelru"
)
const (
// defaultModifiedCache is the default size of the modified node
// cache used per transaction. This is used to cache the updates
// to the nodes near the root, while the leaves do not need to be
// cached. This is important for very large transactions to prevent
// the modified cache from growing to be enormous. This is also used
// to set the max size of the mutation notify maps since those should
// also be bounded in a similar way.
defaultModifiedCache = 8192
)
// Tree implements an immutable radix tree. This can be treated as a
// Dictionary abstract data type. The main advantage over a standard
// hash map is prefix-based lookups and ordered iteration. The immutability
// means that it is safe to concurrently read from a Tree without any
// coordination.
type Tree struct {
root *Node
size int
}
// New returns an empty Tree
func New() *Tree {
t := &Tree{
root: &Node{
mutateCh: make(chan struct{}),
},
}
return t
}
// Len is used to return the number of elements in the tree
func (t *Tree) Len() int {
return t.size
}
// Txn is a transaction on the tree. This transaction is applied
// atomically and returns a new tree when committed. A transaction
// is not thread safe, and should only be used by a single goroutine.
type Txn struct {
// root is the modified root for the transaction.
root *Node
// snap is a snapshot of the root node for use if we have to run the
// slow notify algorithm.
snap *Node
// size tracks the size of the tree as it is modified during the
// transaction.
size int
// writable is a cache of writable nodes that have been created during
// the course of the transaction. This allows us to re-use the same
// nodes for further writes and avoid unnecessary copies of nodes that
// have never been exposed outside the transaction. This will only hold
// up to defaultModifiedCache number of entries.
writable *simplelru.LRU
// trackChannels is used to hold channels that need to be notified to
// signal mutation of the tree. This will only hold up to
// defaultModifiedCache number of entries, after which we will set the
// trackOverflow flag, which will cause us to use a more expensive
// algorithm to perform the notifications. Mutation tracking is only
// performed if trackMutate is true.
trackChannels map[chan struct{}]struct{}
trackOverflow bool
trackMutate bool
}
// Txn starts a new transaction that can be used to mutate the tree
func (t *Tree) Txn() *Txn {
txn := &Txn{
root: t.root,
snap: t.root,
size: t.size,
}
return txn
}
// TrackMutate can be used to toggle if mutations are tracked. If this is enabled
// then notifications will be issued for affected internal nodes and leaves when
// the transaction is committed.
func (t *Txn) TrackMutate(track bool) {
t.trackMutate = track
}
// trackChannel safely attempts to track the given mutation channel, setting the
// overflow flag if we can no longer track any more. This limits the amount of
// state that will accumulate during a transaction and we have a slower algorithm
// to switch to if we overflow.
func (t *Txn) trackChannel(ch chan struct{}) {
// In overflow, make sure we don't store any more objects.
if t.trackOverflow {
return
}
// If this would overflow the state we reject it and set the flag (since
// we aren't tracking everything that's required any longer).
if len(t.trackChannels) >= defaultModifiedCache {
// Mark that we are in the overflow state
t.trackOverflow = true
// Clear the map so that the channels can be garbage collected. It is
// safe to do this since we have already overflowed and will be using
// the slow notify algorithm.
t.trackChannels = nil
return
}
// Create the map on the fly when we need it.
if t.trackChannels == nil {
t.trackChannels = make(map[chan struct{}]struct{})
}
// Otherwise we are good to track it.
t.trackChannels[ch] = struct{}{}
}
// writeNode returns a node to be modified, if the current node has already been
// modified during the course of the transaction, it is used in-place. Set
// forLeafUpdate to true if you are getting a write node to update the leaf,
// which will set leaf mutation tracking appropriately as well.
func (t *Txn) writeNode(n *Node, forLeafUpdate bool) *Node {
// Ensure the writable set exists.
if t.writable == nil {
lru, err := simplelru.NewLRU(defaultModifiedCache, nil)
if err != nil {
panic(err)
}
t.writable = lru
}
// If this node has already been modified, we can continue to use it
// during this transaction. We know that we don't need to track it for
// a node update since the node is writable, but if this is for a leaf
// update we track it, in case the initial write to this node didn't
// update the leaf.
if _, ok := t.writable.Get(n); ok {
if t.trackMutate && forLeafUpdate && n.leaf != nil {
t.trackChannel(n.leaf.mutateCh)
}
return n
}
// Mark this node as being mutated.
if t.trackMutate {
t.trackChannel(n.mutateCh)
}
// Mark its leaf as being mutated, if appropriate.
if t.trackMutate && forLeafUpdate && n.leaf != nil {
t.trackChannel(n.leaf.mutateCh)
}
// Copy the existing node. If you have set forLeafUpdate it will be
// safe to replace this leaf with another after you get your node for
// writing. You MUST replace it, because the channel associated with
// this leaf will be closed when this transaction is committed.
nc := &Node{
mutateCh: make(chan struct{}),
leaf: n.leaf,
}
if n.prefix != nil {
nc.prefix = make([]byte, len(n.prefix))
copy(nc.prefix, n.prefix)
}
if len(n.edges) != 0 {
nc.edges = make([]edge, len(n.edges))
copy(nc.edges, n.edges)
}
// Mark this node as writable.
t.writable.Add(nc, nil)
return nc
}
// mergeChild is called to collapse the given node with its child. This is only
// called when the given node is not a leaf and has a single edge.
func (t *Txn) mergeChild(n *Node) {
// Mark the child node as being mutated since we are about to abandon
// it. We don't need to mark the leaf since we are retaining it if it
// is there.
e := n.edges[0]
child := e.node
if t.trackMutate {
t.trackChannel(child.mutateCh)
}
// Merge the nodes.
n.prefix = concat(n.prefix, child.prefix)
n.leaf = child.leaf
if len(child.edges) != 0 {
n.edges = make([]edge, len(child.edges))
copy(n.edges, child.edges)
} else {
n.edges = nil
}
}
// insert does a recursive insertion
func (t *Txn) insert(n *Node, k, search []byte, v interface{}) (*Node, interface{}, bool) {
// Handle key exhaustion
if len(search) == 0 {
var oldVal interface{}
didUpdate := false
if n.isLeaf() {
oldVal = n.leaf.val
didUpdate = true
}
nc := t.writeNode(n, true)
nc.leaf = &leafNode{
mutateCh: make(chan struct{}),
key: k,
val: v,
}
return nc, oldVal, didUpdate
}
// Look for the edge
idx, child := n.getEdge(search[0])
// No edge, create one
if child == nil {
e := edge{
label: search[0],
node: &Node{
mutateCh: make(chan struct{}),
leaf: &leafNode{
mutateCh: make(chan struct{}),
key: k,
val: v,
},
prefix: search,
},
}
nc := t.writeNode(n, false)
nc.addEdge(e)
return nc, nil, false
}
// Determine longest prefix of the search key on match
commonPrefix := longestPrefix(search, child.prefix)
if commonPrefix == len(child.prefix) {
search = search[commonPrefix:]
newChild, oldVal, didUpdate := t.insert(child, k, search, v)
if newChild != nil {
nc := t.writeNode(n, false)
nc.edges[idx].node = newChild
return nc, oldVal, didUpdate
}
return nil, oldVal, didUpdate
}
// Split the node
nc := t.writeNode(n, false)
splitNode := &Node{
mutateCh: make(chan struct{}),
prefix: search[:commonPrefix],
}
nc.replaceEdge(edge{
label: search[0],
node: splitNode,
})
// Restore the existing child node
modChild := t.writeNode(child, false)
splitNode.addEdge(edge{
label: modChild.prefix[commonPrefix],
node: modChild,
})
modChild.prefix = modChild.prefix[commonPrefix:]
// Create a new leaf node
leaf := &leafNode{
mutateCh: make(chan struct{}),
key: k,
val: v,
}
// If the new key is a subset, add to to this node
search = search[commonPrefix:]
if len(search) == 0 {
splitNode.leaf = leaf
return nc, nil, false
}
// Create a new edge for the node
splitNode.addEdge(edge{
label: search[0],
node: &Node{
mutateCh: make(chan struct{}),
leaf: leaf,
prefix: search,
},
})
return nc, nil, false
}
// delete does a recursive deletion
func (t *Txn) delete(parent, n *Node, search []byte) (*Node, *leafNode) {
// Check for key exhaustion
if len(search) == 0 {
if !n.isLeaf() {
return nil, nil
}
// Remove the leaf node
nc := t.writeNode(n, true)
nc.leaf = nil
// Check if this node should be merged
if n != t.root && len(nc.edges) == 1 {
t.mergeChild(nc)
}
return nc, n.leaf
}
// Look for an edge
label := search[0]
idx, child := n.getEdge(label)
if child == nil || !bytes.HasPrefix(search, child.prefix) {
return nil, nil
}
// Consume the search prefix
search = search[len(child.prefix):]
newChild, leaf := t.delete(n, child, search)
if newChild == nil {
return nil, nil
}
// Copy this node. WATCH OUT - it's safe to pass "false" here because we
// will only ADD a leaf via nc.mergeChild() if there isn't one due to
// the !nc.isLeaf() check in the logic just below. This is pretty subtle,
// so be careful if you change any of the logic here.
nc := t.writeNode(n, false)
// Delete the edge if the node has no edges
if newChild.leaf == nil && len(newChild.edges) == 0 {
nc.delEdge(label)
if n != t.root && len(nc.edges) == 1 && !nc.isLeaf() {
t.mergeChild(nc)
}
} else {
nc.edges[idx].node = newChild
}
return nc, leaf
}
// Insert is used to add or update a given key. The return provides
// the previous value and a bool indicating if any was set.
func (t *Txn) Insert(k []byte, v interface{}) (interface{}, bool) {
newRoot, oldVal, didUpdate := t.insert(t.root, k, k, v)
if newRoot != nil {
t.root = newRoot
}
if !didUpdate {
t.size++
}
return oldVal, didUpdate
}
// Delete is used to delete a given key. Returns the old value if any,
// and a bool indicating if the key was set.
func (t *Txn) Delete(k []byte) (interface{}, bool) {
newRoot, leaf := t.delete(nil, t.root, k)
if newRoot != nil {
t.root = newRoot
}
if leaf != nil {
t.size--
return leaf.val, true
}
return nil, false
}
// Root returns the current root of the radix tree within this
// transaction. The root is not safe across insert and delete operations,
// but can be used to read the current state during a transaction.
func (t *Txn) Root() *Node {
return t.root
}
// Get is used to lookup a specific key, returning
// the value and if it was found
func (t *Txn) Get(k []byte) (interface{}, bool) {
return t.root.Get(k)
}
// GetWatch is used to lookup a specific key, returning
// the watch channel, value and if it was found
func (t *Txn) GetWatch(k []byte) (<-chan struct{}, interface{}, bool) {
return t.root.GetWatch(k)
}
// Commit is used to finalize the transaction and return a new tree. If mutation
// tracking is turned on then notifications will also be issued.
func (t *Txn) Commit() *Tree {
nt := t.CommitOnly()
if t.trackMutate {
t.Notify()
}
return nt
}
// CommitOnly is used to finalize the transaction and return a new tree, but
// does not issue any notifications until Notify is called.
func (t *Txn) CommitOnly() *Tree {
nt := &Tree{t.root, t.size}
t.writable = nil
return nt
}
// slowNotify does a complete comparison of the before and after trees in order
// to trigger notifications. This doesn't require any additional state but it
// is very expensive to compute.
func (t *Txn) slowNotify() {
snapIter := t.snap.rawIterator()
rootIter := t.root.rawIterator()
for snapIter.Front() != nil || rootIter.Front() != nil {
// If we've exhausted the nodes in the old snapshot, we know
// there's nothing remaining to notify.
if snapIter.Front() == nil {
return
}
snapElem := snapIter.Front()
// If we've exhausted the nodes in the new root, we know we need
// to invalidate everything that remains in the old snapshot. We
// know from the loop condition there's something in the old
// snapshot.
if rootIter.Front() == nil {
close(snapElem.mutateCh)
if snapElem.isLeaf() {
close(snapElem.leaf.mutateCh)
}
snapIter.Next()
continue
}
// Do one string compare so we can check the various conditions
// below without repeating the compare.
cmp := strings.Compare(snapIter.Path(), rootIter.Path())
// If the snapshot is behind the root, then we must have deleted
// this node during the transaction.
if cmp < 0 {
close(snapElem.mutateCh)
if snapElem.isLeaf() {
close(snapElem.leaf.mutateCh)
}
snapIter.Next()
continue
}
// If the snapshot is ahead of the root, then we must have added
// this node during the transaction.
if cmp > 0 {
rootIter.Next()
continue
}
// If we have the same path, then we need to see if we mutated a
// node and possibly the leaf.
rootElem := rootIter.Front()
if snapElem != rootElem {
close(snapElem.mutateCh)
if snapElem.leaf != nil && (snapElem.leaf != rootElem.leaf) {
close(snapElem.leaf.mutateCh)
}
}
snapIter.Next()
rootIter.Next()
}
}
// Notify is used along with TrackMutate to trigger notifications. This must
// only be done once a transaction is committed via CommitOnly, and it is called
// automatically by Commit.
func (t *Txn) Notify() {
if !t.trackMutate {
return
}
// If we've overflowed the tracking state we can't use it in any way and
// need to do a full tree compare.
if t.trackOverflow {
t.slowNotify()
} else {
for ch := range t.trackChannels {
close(ch)
}
}
// Clean up the tracking state so that a re-notify is safe (will trigger
// the else clause above which will be a no-op).
t.trackChannels = nil
t.trackOverflow = false
}
// Insert is used to add or update a given key. The return provides
// the new tree, previous value and a bool indicating if any was set.
func (t *Tree) Insert(k []byte, v interface{}) (*Tree, interface{}, bool) {
txn := t.Txn()
old, ok := txn.Insert(k, v)
return txn.Commit(), old, ok
}
// Delete is used to delete a given key. Returns the new tree,
// old value if any, and a bool indicating if the key was set.
func (t *Tree) Delete(k []byte) (*Tree, interface{}, bool) {
txn := t.Txn()
old, ok := txn.Delete(k)
return txn.Commit(), old, ok
}
// Root returns the root node of the tree which can be used for richer
// query operations.
func (t *Tree) Root() *Node {
return t.root
}
// Get is used to lookup a specific key, returning
// the value and if it was found
func (t *Tree) Get(k []byte) (interface{}, bool) {
return t.root.Get(k)
}
// longestPrefix finds the length of the shared prefix
// of two strings
func longestPrefix(k1, k2 []byte) int {
max := len(k1)
if l := len(k2); l < max {
max = l
}
var i int
for i = 0; i < max; i++ {
if k1[i] != k2[i] {
break
}
}
return i
}
// concat two byte slices, returning a third new copy
func concat(a, b []byte) []byte {
c := make([]byte, len(a)+len(b))
copy(c, a)
copy(c[len(a):], b)
return c
}