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lru.go
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lru.go
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// Copyright 2023 The Lit Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package main
import (
"bytes"
"runtime"
"github.com/pointlander/compress"
)
// Node is an entry in the LRU cache
type Node struct {
F, B *Node
Value []uint16
Key Symbols
}
// LRU is a least recently used cache
type LRU struct {
Size int
Head, Tail *Node
Nodes map[Symbols]*Node
Model map[Symbols][]uint8
}
// NewLRU creates a new LRU cache
func NewLRU(size int) LRU {
if size == 0 {
panic("size should not be 0")
}
return LRU{
Size: size,
Model: make(map[Symbols][]uint8),
}
}
// Flush flush the oldest entries in the cache
func (l *LRU) Flush() *Node {
size := l.Size
if len(l.Nodes) < size {
return nil
}
type N struct {
Key Symbols
Value []byte
}
done := make(chan N, runtime.NumCPU())
write := func(node *Node) {
index, data := 0, make([]byte, 2*Width)
for _, value := range node.Value {
data[index] = byte(value & 0xff)
index++
data[index] = byte((value >> 8) & 0xff)
index++
}
buffer := bytes.Buffer{}
compress.Mark1Compress1(data, &buffer)
done <- N{
Key: node.Key,
Value: buffer.Bytes(),
}
}
node := l.Tail
delete(l.Nodes, node.Key)
go write(node)
size >>= 1
n := <-done
l.Model[n.Key] = n.Value
i, j := 1, 0
for i < size && j < runtime.NumCPU() {
node = node.F
delete(l.Nodes, node.Key)
go write(node)
i++
j++
}
for i < size {
n := <-done
l.Model[n.Key] = n.Value
j--
node = node.F
delete(l.Nodes, node.Key)
go write(node)
i++
j++
}
for k := 0; k < j; k++ {
n := <-done
l.Model[n.Key] = n.Value
}
node.F.B, l.Tail, node.F = nil, node.F, nil
return node
}
// Flush flush the oldest entries in the cache
func (l *LRU) Close() {
node := l.Tail
write := func() {
delete(l.Nodes, node.Key)
index, data := 0, make([]byte, 2*Width)
for _, value := range node.Value {
data[index] = byte(value & 0xff)
index++
data[index] = byte((value >> 8) & 0xff)
index++
}
buffer := bytes.Buffer{}
compress.Mark1Compress1(data, &buffer)
l.Model[node.Key] = buffer.Bytes()
}
for node != nil {
write()
node = node.F
}
}
// Get gets an entry and sets it as the most recent
func (l *LRU) Get(key Symbols) (*Node, bool) {
length := len(l.Nodes)
if length > 0 {
if node := l.Nodes[key]; node != nil {
if node.F != nil {
if node.B != nil {
node.B.F, node.F.B = node.F, node.B
} else {
node.F.B, l.Tail = nil, node.F
}
node.F, node.B, l.Head, l.Head.F = nil, l.Head, node, node
}
return node, true
}
}
node, compressed := &Node{Key: key}, l.Model[key]
if compressed != nil {
decoded, index, buffer, output := make([]uint16, Width), 0, bytes.NewBuffer(compressed), make([]byte, 2*Width)
compress.Mark1Decompress1(buffer, output)
for key := range decoded {
decoded[key] = uint16(output[index])
index++
decoded[key] |= uint16(output[index]) << 8
index++
}
node.Value = decoded
} else {
node.Value = make([]uint16, Width)
}
node.B, l.Head = l.Head, node
if length == 0 {
l.Tail = node
l.Nodes = make(map[Symbols]*Node, l.Size)
} else {
node.B.F = node
}
l.Nodes[key] = node
return node, false
}