Java-Echo
diff --git a/‎.idea/.gitignore‎
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diff --git a/‎.idea/DistributedMiniSQL.iml‎
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diff --git a/‎.idea/modules.xml‎
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diff --git a/‎.idea/vcs.xml‎
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diff --git a/‎src/Buffermanager/LRU.go‎
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diff --git a/‎src/Buffermanager/block.go‎
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diff --git a/‎src/Buffermanager/buffermanager.go‎
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@@ -0,0 +1,108 @@
+package Buffermanager
+
+import "sync"
+
+const InitSize = 1024
+const DeleteSize = 256 // when the Cache is full
+
+type LRUList struct {
+	root block // using dummy header
+	len int
+}
+
+
+
+func NewLRUList() *LRUList{
+	list := new(LRUList)
+	// list is a loop
+	list.root.next = &list.root
+	list.root.prev = &list.root
+	return list
+}
+
+//return head
+
+func (l *LRUList) Front() *block{
+	if l.len == 0 {
+		return nil
+	}
+	return l.root.next
+}
+
+// insert a after b
+
+func (l *LRUList) insert(a, b *block) *block{
+	tmp := b.next
+	b.next = a
+	a.prev = b
+	a.next = tmp
+	tmp.prev = a
+	l.len += 1
+	return a
+}
+
+// remove a
+
+func (l *LRUList) remove(a *block) *block{
+	a.prev.next = a.next
+	a.next.prev = a.prev
+	l.len -= 1
+	return a // a is collected as garbage by GC (c++: ?
+}
+
+// move the recent accessed block to back
+func (l *LRUList) moveToBack(a *block){
+	if l.root.prev == a { // if it has only 1 block
+		return
+	}
+	l.insert(l.remove(a), l.root.prev)
+}
+
+// append a new block
+func (l *LRUList) append(a *block) {
+	l.insert(a,l.root.prev)
+}
+
+
+//using list and map to achieve LRU
+
+type LRUCache struct {
+	Capacity int
+	root *LRUList
+	blockMap map[int]*block
+	sync.Mutex
+}
+
+// new
+
+func NewLRUCache() *LRUCache{
+	cache := new(LRUCache)
+	cache.Capacity = InitSize
+	cache.root = NewLRUList()
+	cache.blockMap = make(map[int]*block, InitSize*2)
+	return cache
+}
+
+// put block int buffer
+func (cache *LRUCache)  insertBlock(val *block, index int) *block {
+	cache.Lock()
+	defer cache.Unlock()
+	return val
+}
+
+// map index to block
+func (cache *LRUCache) findBlock(index int) (bool, *block){
+	cache.Lock()
+	defer cache.Unlock()
+	if ret, err := cache.blockMap[index]; !err {
+		cache.root.moveToBack(ret)
+		return true,ret
+	}
+	return false,nil
+}
+
+
+
+
+
+
@@ -0,0 +1,96 @@
+package Buffermanager
+
+import (
+	"io"
+	"os"
+	"sync"
+)
+
+type block struct{
+	filename string
+	blockid uint64
+	isDirty bool
+	pin bool
+	Data []byte
+	next *block
+	prev *block // double linked list
+	sync.Mutex
+}
+
+// operations
+// set dirty page
+func (b *block) setDirty(){
+	b.isDirty = true
+}
+// set pin block
+func (b *block) setPin(){
+	b.pin = true
+}
+// unset pin block
+func (b *block) setUnPin(){
+	b.pin = false
+}
+// release the lock of reading block
+func (b *block) finishRead(){
+	b.Unlock()
+	return
+}
+
+//reset the block
+func (b *block) reset(){
+	b.isDirty = false
+	b.pin = false
+}
+
+// init the block
+func (b *block) init(filename string, bid uint64){
+	b.filename = filename
+	b.blockid = bid
+}
+
+// read the file
+func (b *block) read() error{
+	if b.isDirty {
+		return b.flush()
+	}
+	file,err := os.Open(b.filename)
+	if err != nil{
+		return nil
+	}
+	defer file.Close()
+	if err != nil {
+		return err
+	}
+	bid64 := int64(b.blockid)
+	_,err = file.Seek(bid64*blockSize,0)
+	if err != nil{
+		return err
+	}
+
+	_,err = io.ReadFull(file,b.Data)
+	if err != nil {
+		return err
+	}
+
+	return err
+}
+
+// read back and flush
+func (b *block)flush() error{
+	if !b.isDirty {
+		return nil
+	}
+	file,err := os.OpenFile(b.filename, os.O_WRONLY,0666) // read and write
+	defer file.Close()
+	if err != nil {
+		return err
+	}
+	bid64 := int64(b.blockid)
+	_, err = file.Seek(bid64*blockSize,0) // _ is a placeholder
+	if err != nil {
+		return err
+	}
+	_,err = file.Write(b.Data)
+	b.isDirty = false
+	return err
+}
@@ -0,0 +1,3 @@
+package Buffermanager
+
+const blockSize = 8192
Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+package Buffermanager`
	`2`	`+`
	`3`	`+const blockSize = 8192`