1// Copyright (c) 2013, Suryandaru Triandana <syndtr@gmail.com>
2// All rights reserved.
3//
4// Use of this source code is governed by a BSD-style license that can be
5// found in the LICENSE file.
6
7// Package util provides utilities used throughout leveldb.
8package util
9
10import (
11	"errors"
12)
13
14var (
15	ErrReleased    = errors.New("leveldb: resource already relesed")
16	ErrHasReleaser = errors.New("leveldb: releaser already defined")
17)
18
19// Releaser is the interface that wraps the basic Release method.
20type Releaser interface {
21	// Release releases associated resources. Release should always success
22	// and can be called multiple times without causing error.
23	Release()
24}
25
26// ReleaseSetter is the interface that wraps the basic SetReleaser method.
27type ReleaseSetter interface {
28	// SetReleaser associates the given releaser to the resources. The
29	// releaser will be called once coresponding resources released.
30	// Calling SetReleaser with nil will clear the releaser.
31	//
32	// This will panic if a releaser already present or coresponding
33	// resource is already released. Releaser should be cleared first
34	// before assigned a new one.
35	SetReleaser(releaser Releaser)
36}
37
38// BasicReleaser provides basic implementation of Releaser and ReleaseSetter.
39type BasicReleaser struct {
40	releaser Releaser
41	released bool
42}
43
44// Released returns whether Release method already called.
45func (r *BasicReleaser) Released() bool {
46	return r.released
47}
48
49// Release implements Releaser.Release.
50func (r *BasicReleaser) Release() {
51	if !r.released {
52		if r.releaser != nil {
53			r.releaser.Release()
54			r.releaser = nil
55		}
56		r.released = true
57	}
58}
59
60// SetReleaser implements ReleaseSetter.SetReleaser.
61func (r *BasicReleaser) SetReleaser(releaser Releaser) {
62	if r.released {
63		panic(ErrReleased)
64	}
65	if r.releaser != nil && releaser != nil {
66		panic(ErrHasReleaser)
67	}
68	r.releaser = releaser
69}
70
71type NoopReleaser struct{}
72
73func (NoopReleaser) Release() {}
74