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update.go
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update.go
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package radix
import (
"fmt"
"runtime"
"sync"
"sync/atomic"
)
const (
replaceEmptyRootWithLeaf uint32 = iota
replaceLeafRootWithNode
rootLeafUpdate
nodePrefixMiss
nodeLeafInsert
nodeLeafInsert256
nodeLeafUpdate
nodeLeafUpdate256
)
var debugOperationName = map[uint32]string{
replaceEmptyRootWithLeaf: "REPLACE_EMPTY_ROOT_WITH_LEAF",
replaceLeafRootWithNode: "REPLACE_LEAF_ROOT_WITH_NODE",
rootLeafUpdate: "ROOT_LEAF_UPDATE",
nodePrefixMiss: "NODE_PREFIX_MISS",
nodeLeafInsert: "NODE_LEAF_INSERT",
nodeLeafInsert256: "NODE_256_LEAF_INSERT",
nodeLeafUpdate: "NODE_LEAF_UPDATE",
nodeLeafUpdate256: "NODE_256_LEAF_UPDATE",
}
// UpdateOperation represents the action to insert a new value or update on existing value in a tree.
// An update operation is initiated through calling PrepareUpdate on a Tree or an Allocator.
type UpdateOperation struct {
// points to key data used in call to PrepareUpdate
Key []byte
// the value of the found item, if any
Value uint64
// the key data fetched by the caller after call to PrepareUpdate (and before FinalizeUpdate)
FetchedKey []byte
// set true by caller if FetchedKey equals Key
Match bool
// the radix tree for this operation
idx *Tree
// allocator for this operation
allocator *Allocator
// if the allocator should be released when operation is finalized or aborted
releaseAlloc bool
kind uint32
k byte
position int
nodeGen, parentGen int32
node, parent uint64
count int
depth int
// the extracted node prefix
prefix []byte
// the index into prefix where we got a mismatch against the current update key
prefixMismatch int
// points to where the node is inserted in the tree
nodePtr *uint64
// location of node data
data []uint64
prefixSlots int
// points to where the leaf is in the tree
leafPtr *uint64
// the current leaf value, to be used in CompareAndSwap
currentLeaf uint64
// current raw value of node
raw uint64
}
var updateOperationPool = sync.Pool{
New: func() interface{} {
return &UpdateOperation{}
},
}
// newUpdateOperation returns an UpdateOperation on *Tree idx using *Allocator alloc.
// If releaseAlloc is true, the allocator is released when the operation is completed or aborted.
func newUpdateOperation(idx *Tree, alloc *Allocator, releaseAlloc bool) (op *UpdateOperation) {
op = updateOperationPool.Get().(*UpdateOperation)
op.idx = idx
op.allocator = alloc
op.releaseAlloc = releaseAlloc
return
}
func (op *UpdateOperation) prepareUpdate(key []byte) (found bool) {
op.Key = key
op.Match = false
op.Value = 0
op.FetchedKey = op.FetchedKey[:0]
op.allocator.startOp()
S:
root := atomic.LoadUint64(&op.idx.root)
if root == 0 {
// index is empty, lock root
if !op.idx.lockLeafRoot(root) {
runtime.Gosched()
goto S
}
op.k = key[0]
op.kind = replaceEmptyRootWithLeaf
return false
}
if isLeaf(root) {
// root is a leaf, acquire a root lock
if !op.idx.lockLeafRoot(root) {
runtime.Gosched()
goto S
}
op.k = key[0]
op.currentLeaf = root
// check if key matches
if byte(root) == key[0] {
// key matches, this might be a hit, or we will have to insert a prefixed node here
op.kind = rootLeafUpdate
op.Value = getLeafValue(root)
return true
}
// we should replace root with a node-2 with two leafs (no prefix)
op.kind = replaceLeafRootWithNode
return false
}
op.depth = 0
op.nodePtr = &op.idx.root
op.raw = root
op.parent = 0
op.parentGen = 0
prefixLen := 0
searchLoop:
for {
_, op.node, op.count, prefixLen = explodeNode(op.raw)
// first fetch the current generation for node (it could actually be shared with multiple nodes)
op.nodeGen = op.idx.generation(op.node)
// now verify that the node has not been changed since we read it
if atomic.LoadUint64(op.nodePtr) != op.raw {
goto S
}
// in case the parent was changed while we where working through it the current node might now be disconnected
// so we check the current parent generation to safeguard against this.
if op.parent != 0 && op.parentGen != op.idx.generation(op.parent) {
goto S
}
block := int(op.node >> blockSlotsShift)
offset := int(op.node & blockSlotsOffsetMask)
op.data = op.idx.blocks[block].data[offset:]
data := op.data
if prefixLen > 0 {
op.prefix, op.prefixSlots = appendPrefix(op.prefix[:0], data, prefixLen)
// now check for prefix mismatch
for i, a := range op.prefix {
if key[op.depth+i] != a {
// part of or all of prefix did not match, we must insert a node here
// We are going to change data at nodePtrOffset, which is inside the data block of parent
// We will copy all children of node (node data block must also be protected)
if !op.lock() {
runtime.Gosched()
goto S
}
op.kind = nodePrefixMiss
op.k = key[op.depth]
op.prefixMismatch = i
return false
}
}
data = data[op.prefixSlots:]
op.depth += len(op.prefix)
} else {
op.prefix = op.prefix[:0]
op.prefixSlots = 0
}
op.k = key[op.depth]
// A. Check a node-256
if op.count >= fullAllocFrom {
p := &data[int(op.k)]
a := atomic.LoadUint64(p)
if a == 0 {
if !op.lock() {
runtime.Gosched()
goto S
}
op.kind = nodeLeafInsert256
op.leafPtr = p
return false
}
if isLeaf(a) {
if !op.lock() {
runtime.Gosched()
goto S
}
op.kind = nodeLeafUpdate256
op.leafPtr = p
op.currentLeaf = a
op.Value = getLeafValue(a)
return true
}
op.enterNode(p, a)
continue searchLoop
}
// B. Check a variable sized node
op.position = op.count
var (
p *uint64
a uint64
b byte
)
for i := range data[:op.count] {
p = &data[i]
a = atomic.LoadUint64(p)
b = byte(a)
if b >= op.k {
op.position = i
break
}
}
if b == op.k {
if isLeaf(a) {
if !op.lock() {
runtime.Gosched()
goto S
}
op.kind = nodeLeafUpdate
op.leafPtr = p
op.currentLeaf = a
op.Value = getLeafValue(a)
return true
}
op.enterNode(p, a)
continue searchLoop
}
if !op.lock() {
runtime.Gosched()
goto S
}
op.kind = nodeLeafInsert
return false
}
}
// Finalize performs the update or insert in the tree, storing the given value at the prepared location.
// In case the value is larger than 55 bits it will be truncated.
// It returns true if the update was successful. If false, there was a write conflict and the operation must be restarted.
// The *UpdateOperation may not be used again after the call.
func (op *UpdateOperation) Finalize(value uint64) (updated bool) {
switch op.kind {
case replaceEmptyRootWithLeaf:
updated = atomic.CompareAndSwapUint64(&op.idx.root, 0, buildLeaf(op.k, value))
op.idx.unlockRoot()
if updated {
op.allocator.itemCounter++
}
case replaceLeafRootWithNode:
newNode, data := op.idx.allocateNode(op.allocator, 2, 0)
addSortedChildren(data, op.currentLeaf, buildLeaf(op.k, value))
updated = atomic.CompareAndSwapUint64((*uint64)(&op.idx.root), op.currentLeaf, buildNode(0, newNode, 2, 0))
op.idx.unlockRoot()
if updated {
op.allocator.itemCounter++
}
case rootLeafUpdate:
if op.Match {
// root is a leaf, and it was match, simply update it
updated = atomic.CompareAndSwapUint64(&op.idx.root, op.currentLeaf, buildLeaf(op.k, value))
} else {
// check how many characters the keys have in common (we know it's >= 1)
prefixLen := 0
for op.Key[prefixLen] == op.FetchedKey[prefixLen] {
prefixLen++
// in case prefixLen == len(op.Key) or len(op.FetchedKey) we have a violoation of the rule that no key can be the prefix of another key!
if prefixLen == len(op.Key) || prefixLen == len(op.FetchedKey) {
panic("Prefix violation")
}
}
// allocate new NODE-2 and try to insert it
newNode, data := op.idx.allocateNodeWithPrefix(op.allocator, 2, op.Key[:prefixLen])
addSortedChildren(data,
buildLeaf(op.Key[prefixLen], value),
updateLeafKey(op.currentLeaf, op.FetchedKey[prefixLen]))
updated = atomic.CompareAndSwapUint64(&op.idx.root, op.currentLeaf, buildNode(0, newNode, 2, prefixLen))
if updated {
op.allocator.itemCounter++
}
}
op.idx.unlockRoot()
case nodePrefixMiss:
// None or only part of the prefix on a node matches, we must replace it with a shorter prefix node and insert the second part (with the node children untouched) as a child node
// The mismatch was at op.prefix[op.prefixMismatch]
a := op.Key[op.depth+op.prefixMismatch]
b := op.prefix[op.prefixMismatch]
// Clone the existing node but with an updated prefix
pl := len(op.prefix) - op.prefixMismatch - 1
updatedNode, dst := op.idx.allocateNodeWithPrefix(op.allocator, op.count, op.prefix[op.prefixMismatch+1:])
// copy children
src := op.data[op.prefixSlots:]
copy(dst, src[:op.count])
// create a new NODE-2 with the matched part of the prefix (if any) and insert it
newNode, data := op.idx.allocateNodeWithPrefix(op.allocator, 2, op.Key[op.depth:op.depth+op.prefixMismatch])
addSortedChildren(data,
buildLeaf(a, value),
buildNode(b, updatedNode, op.count, pl))
atomic.StoreUint64(op.nodePtr, buildNode(byte(op.raw), newNode, 2, op.prefixMismatch))
op.unlock()
op.allocator.recycle(op.node, op.count+op.prefixSlots)
op.allocator.itemCounter++
updated = true
case nodeLeafInsert256:
updated = atomic.CompareAndSwapUint64(op.leafPtr, 0, buildLeaf(op.k, value))
if updated {
op.allocator.itemCounter++
}
op.unlock()
case nodeLeafInsert:
// insert a leaf by making the node bigger using copy-on-write
if op.count < fullAllocAfter {
// GROW NODE SIZE BY 1
newNode, dst := op.idx.allocateNode(op.allocator, op.count+1, len(op.prefix))
src := op.data
split := op.prefixSlots + op.position
// copy full node up to insert position, including unmodified prefix
copy(dst, src[:split])
// append the new value as a leaf at op.position
dst[split] = buildLeaf(op.k, value)
// copy the rest
l := op.count - op.position
copy(dst[split+1:], src[split:split+l])
// insert the new node into the tree, no need to compare and swap since this is checked after locking
v := buildNode(byte(op.raw), newNode, op.count+1, len(op.prefix))
atomic.StoreUint64(op.nodePtr, v)
op.unlock()
op.allocator.recycle(op.node, op.count+op.prefixSlots)
op.allocator.itemCounter++
updated = true
} else {
// SWITCH TO A NODE-256
newNode, dst := op.idx.allocateNodeWithPrefix(op.allocator, 256, op.prefix)
// we need to zero it
for i := range dst[:256] {
dst[i] = 0
}
// put the existing nodes in their new places
src := op.data[op.prefixSlots : op.prefixSlots+op.count]
// set the new leaf
dst[int(op.k)] = buildLeaf(op.k, value)
// add the existing, while setting obsolete tag on to-be-removed nodes
for _, a := range src {
b := byte(a)
dst[int(b)] = a
}
// insert the new node
v := buildNode(byte(op.raw), newNode, 256, len(op.prefix))
atomic.StoreUint64(op.nodePtr, v)
op.unlock()
// recycle old node
op.allocator.recycle(op.node, op.count+op.prefixSlots)
op.allocator.itemCounter++
updated = true
}
case nodeLeafUpdate, nodeLeafUpdate256:
// These are pure leaf updates, so they never disconnected other nodes from the tree
if op.Match {
// compare and swap needed since leaf might have changed before we acquired the lock
updated = atomic.CompareAndSwapUint64(op.leafPtr, op.currentLeaf, buildLeaf(op.k, value))
} else {
// key did not match, replace leaf with a NODE-2
// check how many characters the keys have in common starting from depth+1 (we know they match at depth)
prefixLen := 0
i := op.depth + 1
for ; i < len(op.Key) && i < len(op.FetchedKey) && op.Key[i] == op.FetchedKey[i]; i++ {
prefixLen++
}
a := op.Key[i]
b := op.FetchedKey[i]
// creat a new NODE-2 and try to insert it
newNode, data := op.idx.allocateNodeWithPrefix(op.allocator, 2, op.Key[op.depth+1:op.depth+1+prefixLen])
addSortedChildren(data,
buildLeaf(a, value),
updateLeafKey(op.currentLeaf, b),
)
updated = atomic.CompareAndSwapUint64((*uint64)(op.leafPtr), op.currentLeaf, buildNode(op.k, newNode, 2, prefixLen))
if updated {
op.allocator.itemCounter++
}
}
op.unlock()
}
op.allocator.endOp()
if op.releaseAlloc {
op.idx.ReleaseAllocator(op.allocator)
}
updateOperationPool.Put(op)
return updated
}
// Abort aborts the update operation, unlocking any locks taken during the prepare call and recycles the *UpdateOperation.
// The *UpdateOperation may not be used again after the call.
func (op *UpdateOperation) Abort() {
switch op.kind {
case replaceEmptyRootWithLeaf, replaceLeafRootWithNode, rootLeafUpdate:
op.idx.unlockRoot()
default:
op.unlock()
}
op.allocator.endOp()
if op.releaseAlloc {
op.idx.allocatorQueue.put(op.allocator.id)
}
updateOperationPool.Put(op)
}
// String returns a description of the operation
func (op *UpdateOperation) String() (s string) {
s = fmt.Sprintf("Operation: %s\n Key: %s\n FetchedKey: %s\n Match=%v\n depth=%d\n Key at depth: %s\n node prefix: %s (%d bytes, %d slots)\nnode: %d\nparent: %d\n", debugOperationName[op.kind], op.Key, op.FetchedKey, op.Match, op.depth, op.Key[op.depth:], op.prefix, len(op.prefix), op.prefixSlots, op.node, op.parent)
switch op.kind {
case replaceLeafRootWithNode, rootLeafUpdate:
return s + fmt.Sprintf(" currentLeaf: %d\n", op.currentLeaf)
case nodePrefixMiss:
return s + fmt.Sprintf("\nat node=%d (parent=%d), current node count=%d, prefixMismatched=%d (%s), insert k=%x, insert depth=%d", op.node, op.parent, op.count, op.prefixMismatch, op.Key[op.depth:op.depth+op.prefixMismatch], op.k, op.depth)
}
return s
}
// lock is inlined by compiler
func (op *UpdateOperation) lock() bool {
return op.idx.lockNodes2(op.node, op.nodeGen, op.parent, op.parentGen)
}
// unlock is inlined by compiler
func (op *UpdateOperation) unlock() {
op.idx.unlockNodes2(op.node, op.parent)
}
// enterNode is inlined by compiler
func (op *UpdateOperation) enterNode(p *uint64, a uint64) {
op.parentGen = op.nodeGen
op.parent = op.node
op.nodePtr = p
op.raw = a
op.depth++
}
// addSortedChildren is inlined by compiler
func addSortedChildren(data []uint64, a, b uint64) {
if byte(a) < byte(b) {
data[0] = a
data[1] = b
return
}
data[0] = b
data[1] = a
}