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// Copyright 2013 The LevelDB-Go 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 leveldb
import (
"os"
"sync"
"github.com/golang/leveldb/db"
"github.com/golang/leveldb/table"
)
type tableCache struct {
dirname string
fs db.FileSystem
opts *db.Options
size int
mu sync.Mutex
nodes map[uint64]*tableCacheNode
dummy tableCacheNode
}
func (c *tableCache) init(dirname string, fs db.FileSystem, opts *db.Options, size int) {
c.dirname = dirname
c.fs = fs
c.opts = opts
c.size = size
c.nodes = make(map[uint64]*tableCacheNode)
c.dummy.next = &c.dummy
c.dummy.prev = &c.dummy
}
func (c *tableCache) find(fileNum uint64, ikey internalKey) (db.Iterator, error) {
// Calling findNode gives us the responsibility of decrementing n's
// refCount. If opening the underlying table resulted in error, then we
// decrement this straight away. Otherwise, we pass that responsibility
// to the tableCacheIter, which decrements when it is closed.
n := c.findNode(fileNum)
x := <-n.result
if x.err != nil {
c.mu.Lock()
n.refCount--
if n.refCount == 0 {
go n.release()
}
c.mu.Unlock()
// Try loading the table again; the error may be transient.
go n.load(c)
return nil, x.err
}
n.result <- x
return &tableCacheIter{
Iterator: x.reader.Find(ikey, nil),
cache: c,
node: n,
}, nil
}
// releaseNode releases a node from the tableCache.
//
// c.mu must be held when calling this.
func (c *tableCache) releaseNode(n *tableCacheNode) {
delete(c.nodes, n.fileNum)
n.next.prev = n.prev
n.prev.next = n.next
n.refCount--
if n.refCount == 0 {
go n.release()
}
}
// findNode returns the node for the table with the given file number, creating
// that node if it didn't already exist. The caller is responsible for
// decrementing the returned node's refCount.
func (c *tableCache) findNode(fileNum uint64) *tableCacheNode {
c.mu.Lock()
defer c.mu.Unlock()
n := c.nodes[fileNum]
if n == nil {
n = &tableCacheNode{
fileNum: fileNum,
refCount: 1,
result: make(chan tableReaderOrError, 1),
}
c.nodes[fileNum] = n
if len(c.nodes) > c.size {
// Release the tail node.
c.releaseNode(c.dummy.prev)
}
go n.load(c)
} else {
// Remove n from the doubly-linked list.
n.next.prev = n.prev
n.prev.next = n.next
}
// Insert n at the front of the doubly-linked list.
n.next = c.dummy.next
n.prev = &c.dummy
n.next.prev = n
n.prev.next = n
// The caller is responsible for decrementing the refCount.
n.refCount++
return n
}
func (c *tableCache) evict(fileNum uint64) {
c.mu.Lock()
defer c.mu.Unlock()
if n := c.nodes[fileNum]; n != nil {
c.releaseNode(n)
}
}
func (c *tableCache) Close() error {
c.mu.Lock()
defer c.mu.Unlock()
for n := c.dummy.next; n != &c.dummy; n = n.next {
n.refCount--
if n.refCount == 0 {
go n.release()
}
}
c.nodes = nil
c.dummy.next = nil
c.dummy.prev = nil
return nil
}
type tableReaderOrError struct {
reader *table.Reader
err error
}
type tableCacheNode struct {
fileNum uint64
result chan tableReaderOrError
// The remaining fields are protected by the tableCache mutex.
next, prev *tableCacheNode
refCount int
}
func (n *tableCacheNode) load(c *tableCache) {
// Try opening the fileTypeTable first. If that file doesn't exist,
// fall back onto the fileTypeOldFashionedTable.
f, err := c.fs.Open(dbFilename(c.dirname, fileTypeTable, n.fileNum))
if os.IsNotExist(err) {
f, err = c.fs.Open(dbFilename(c.dirname, fileTypeOldFashionedTable, n.fileNum))
}
if err != nil {
n.result <- tableReaderOrError{err: err}
return
}
n.result <- tableReaderOrError{reader: table.NewReader(f, c.opts)}
}
func (n *tableCacheNode) release() {
x := <-n.result
if x.err != nil {
return
}
x.reader.Close()
}
type tableCacheIter struct {
db.Iterator
cache *tableCache
node *tableCacheNode
closeErr error
closed bool
}
func (i *tableCacheIter) Close() error {
if i.closed {
return i.closeErr
}
i.closed = true
i.cache.mu.Lock()
i.node.refCount--
if i.node.refCount == 0 {
go i.node.release()
}
i.cache.mu.Unlock()
i.closeErr = i.Iterator.Close()
return i.closeErr
}
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