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https://codeberg.org/forgejo/forgejo.git
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187 lines
4.9 KiB
Go
Vendored
187 lines
4.9 KiB
Go
Vendored
// Copyright (c) 2012, Suryandaru Triandana <syndtr@gmail.com>
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// All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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package leveldb
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import (
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"container/list"
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"fmt"
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"runtime"
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"sync"
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"sync/atomic"
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"github.com/syndtr/goleveldb/leveldb/iterator"
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"github.com/syndtr/goleveldb/leveldb/opt"
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"github.com/syndtr/goleveldb/leveldb/util"
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)
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type snapshotElement struct {
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seq uint64
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ref int
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e *list.Element
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}
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// Acquires a snapshot, based on latest sequence.
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func (db *DB) acquireSnapshot() *snapshotElement {
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db.snapsMu.Lock()
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defer db.snapsMu.Unlock()
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seq := db.getSeq()
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if e := db.snapsList.Back(); e != nil {
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se := e.Value.(*snapshotElement)
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if se.seq == seq {
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se.ref++
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return se
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} else if seq < se.seq {
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panic("leveldb: sequence number is not increasing")
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}
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}
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se := &snapshotElement{seq: seq, ref: 1}
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se.e = db.snapsList.PushBack(se)
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return se
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}
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// Releases given snapshot element.
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func (db *DB) releaseSnapshot(se *snapshotElement) {
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db.snapsMu.Lock()
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defer db.snapsMu.Unlock()
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se.ref--
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if se.ref == 0 {
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db.snapsList.Remove(se.e)
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se.e = nil
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} else if se.ref < 0 {
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panic("leveldb: Snapshot: negative element reference")
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}
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}
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// Gets minimum sequence that not being snapshotted.
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func (db *DB) minSeq() uint64 {
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db.snapsMu.Lock()
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defer db.snapsMu.Unlock()
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if e := db.snapsList.Front(); e != nil {
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return e.Value.(*snapshotElement).seq
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}
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return db.getSeq()
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}
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// Snapshot is a DB snapshot.
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type Snapshot struct {
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db *DB
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elem *snapshotElement
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mu sync.RWMutex
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released bool
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}
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// Creates new snapshot object.
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func (db *DB) newSnapshot() *Snapshot {
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snap := &Snapshot{
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db: db,
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elem: db.acquireSnapshot(),
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}
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atomic.AddInt32(&db.aliveSnaps, 1)
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runtime.SetFinalizer(snap, (*Snapshot).Release)
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return snap
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}
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func (snap *Snapshot) String() string {
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return fmt.Sprintf("leveldb.Snapshot{%d}", snap.elem.seq)
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}
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// Get gets the value for the given key. It returns ErrNotFound if
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// the DB does not contains the key.
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//
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// The caller should not modify the contents of the returned slice, but
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// it is safe to modify the contents of the argument after Get returns.
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func (snap *Snapshot) Get(key []byte, ro *opt.ReadOptions) (value []byte, err error) {
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err = snap.db.ok()
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if err != nil {
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return
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}
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snap.mu.RLock()
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defer snap.mu.RUnlock()
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if snap.released {
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err = ErrSnapshotReleased
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return
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}
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return snap.db.get(nil, nil, key, snap.elem.seq, ro)
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}
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// Has returns true if the DB does contains the given key.
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//
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// It is safe to modify the contents of the argument after Get returns.
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func (snap *Snapshot) Has(key []byte, ro *opt.ReadOptions) (ret bool, err error) {
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err = snap.db.ok()
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if err != nil {
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return
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}
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snap.mu.RLock()
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defer snap.mu.RUnlock()
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if snap.released {
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err = ErrSnapshotReleased
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return
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}
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return snap.db.has(nil, nil, key, snap.elem.seq, ro)
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}
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// NewIterator returns an iterator for the snapshot of the underlying DB.
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// The returned iterator is not safe for concurrent use, but it is safe to use
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// multiple iterators concurrently, with each in a dedicated goroutine.
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// It is also safe to use an iterator concurrently with modifying its
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// underlying DB. The resultant key/value pairs are guaranteed to be
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// consistent.
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//
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// Slice allows slicing the iterator to only contains keys in the given
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// range. A nil Range.Start is treated as a key before all keys in the
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// DB. And a nil Range.Limit is treated as a key after all keys in
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// the DB.
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//
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// WARNING: Any slice returned by interator (e.g. slice returned by calling
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// Iterator.Key() or Iterator.Value() methods), its content should not be
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// modified unless noted otherwise.
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//
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// The iterator must be released after use, by calling Release method.
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// Releasing the snapshot doesn't mean releasing the iterator too, the
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// iterator would be still valid until released.
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//
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// Also read Iterator documentation of the leveldb/iterator package.
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func (snap *Snapshot) NewIterator(slice *util.Range, ro *opt.ReadOptions) iterator.Iterator {
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if err := snap.db.ok(); err != nil {
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return iterator.NewEmptyIterator(err)
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}
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snap.mu.Lock()
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defer snap.mu.Unlock()
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if snap.released {
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return iterator.NewEmptyIterator(ErrSnapshotReleased)
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}
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// Since iterator already hold version ref, it doesn't need to
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// hold snapshot ref.
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return snap.db.newIterator(nil, nil, snap.elem.seq, slice, ro)
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}
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// Release releases the snapshot. This will not release any returned
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// iterators, the iterators would still be valid until released or the
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// underlying DB is closed.
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//
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// Other methods should not be called after the snapshot has been released.
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func (snap *Snapshot) Release() {
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snap.mu.Lock()
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defer snap.mu.Unlock()
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if !snap.released {
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// Clear the finalizer.
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runtime.SetFinalizer(snap, nil)
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snap.released = true
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snap.db.releaseSnapshot(snap.elem)
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atomic.AddInt32(&snap.db.aliveSnaps, -1)
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snap.db = nil
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snap.elem = nil
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}
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}
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