ceremonyclient/pebble/internal/arenaskl/node.go

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2024-01-03 07:31:42 +00:00
/*
* Copyright 2017 Dgraph Labs, Inc. and Contributors
* Modifications copyright (C) 2017 Andy Kimball and Contributors
*
* 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 arenaskl
import (
"math"
"sync/atomic"
"github.com/cockroachdb/pebble/internal/base"
)
// MaxNodeSize returns the maximum space needed for a node with the specified
// key and value sizes. This could overflow a uint32, which is why a uint64
// is used here. If a key/value overflows a uint32, it should not be added to
// the skiplist.
func MaxNodeSize(keySize, valueSize uint32) uint64 {
const maxPadding = nodeAlignment - 1
return uint64(maxNodeSize) + uint64(keySize) + uint64(valueSize) + maxPadding
}
type links struct {
nextOffset atomic.Uint32
prevOffset atomic.Uint32
}
func (l *links) init(prevOffset, nextOffset uint32) {
l.nextOffset.Store(nextOffset)
l.prevOffset.Store(prevOffset)
}
type node struct {
// Immutable fields, so no need to lock to access key.
keyOffset uint32
keySize uint32
keyTrailer uint64
valueSize uint32
allocSize uint32
// Most nodes do not need to use the full height of the tower, since the
// probability of each successive level decreases exponentially. Because
// these elements are never accessed, they do not need to be allocated.
// Therefore, when a node is allocated in the arena, its memory footprint
// is deliberately truncated to not include unneeded tower elements.
//
// All accesses to elements should use CAS operations, with no need to lock.
tower [maxHeight]links
}
func newNode(
arena *Arena, height uint32, key base.InternalKey, value []byte,
) (nd *node, err error) {
if height < 1 || height > maxHeight {
panic("height cannot be less than one or greater than the max height")
}
keySize := len(key.UserKey)
if int64(keySize) > math.MaxUint32 {
panic("key is too large")
}
valueSize := len(value)
if int64(len(value)) > math.MaxUint32 {
panic("value is too large")
}
if int64(len(value))+int64(keySize)+int64(maxNodeSize) > math.MaxUint32 {
panic("combined key and value size is too large")
}
nd, err = newRawNode(arena, height, uint32(keySize), uint32(valueSize))
if err != nil {
return
}
nd.keyTrailer = key.Trailer
copy(nd.getKeyBytes(arena), key.UserKey)
copy(nd.getValue(arena), value)
return
}
func newRawNode(arena *Arena, height uint32, keySize, valueSize uint32) (nd *node, err error) {
// Compute the amount of the tower that will never be used, since the height
// is less than maxHeight.
unusedSize := uint32((maxHeight - int(height)) * linksSize)
nodeSize := uint32(maxNodeSize) - unusedSize
nodeOffset, allocSize, err := arena.alloc(nodeSize+keySize+valueSize, nodeAlignment, unusedSize)
if err != nil {
return
}
nd = (*node)(arena.getPointer(nodeOffset))
nd.keyOffset = nodeOffset + nodeSize
nd.keySize = keySize
nd.valueSize = valueSize
nd.allocSize = allocSize
return
}
func (n *node) getKeyBytes(arena *Arena) []byte {
return arena.getBytes(n.keyOffset, n.keySize)
}
func (n *node) getValue(arena *Arena) []byte {
return arena.getBytes(n.keyOffset+n.keySize, uint32(n.valueSize))
}
func (n *node) nextOffset(h int) uint32 {
return n.tower[h].nextOffset.Load()
}
func (n *node) prevOffset(h int) uint32 {
return n.tower[h].prevOffset.Load()
}
func (n *node) casNextOffset(h int, old, val uint32) bool {
return n.tower[h].nextOffset.CompareAndSwap(old, val)
}
func (n *node) casPrevOffset(h int, old, val uint32) bool {
return n.tower[h].prevOffset.CompareAndSwap(old, val)
}