File: page.go

package info (click to toggle)
golang-github-coreos-bbolt 1.3.1-coreos.5-3
  • links: PTS, VCS
  • area: main
  • in suites: buster
  • size: 600 kB
  • sloc: makefile: 25
file content (197 lines) | stat: -rw-r--r-- 4,889 bytes parent folder | download | duplicates (6)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
package bolt

import (
	"fmt"
	"os"
	"sort"
	"unsafe"
)

const pageHeaderSize = int(unsafe.Offsetof(((*page)(nil)).ptr))

const minKeysPerPage = 2

const branchPageElementSize = int(unsafe.Sizeof(branchPageElement{}))
const leafPageElementSize = int(unsafe.Sizeof(leafPageElement{}))

const (
	branchPageFlag   = 0x01
	leafPageFlag     = 0x02
	metaPageFlag     = 0x04
	freelistPageFlag = 0x10
)

const (
	bucketLeafFlag = 0x01
)

type pgid uint64

type page struct {
	id       pgid
	flags    uint16
	count    uint16
	overflow uint32
	ptr      uintptr
}

// typ returns a human readable page type string used for debugging.
func (p *page) typ() string {
	if (p.flags & branchPageFlag) != 0 {
		return "branch"
	} else if (p.flags & leafPageFlag) != 0 {
		return "leaf"
	} else if (p.flags & metaPageFlag) != 0 {
		return "meta"
	} else if (p.flags & freelistPageFlag) != 0 {
		return "freelist"
	}
	return fmt.Sprintf("unknown<%02x>", p.flags)
}

// meta returns a pointer to the metadata section of the page.
func (p *page) meta() *meta {
	return (*meta)(unsafe.Pointer(&p.ptr))
}

// leafPageElement retrieves the leaf node by index
func (p *page) leafPageElement(index uint16) *leafPageElement {
	n := &((*[0x7FFFFFF]leafPageElement)(unsafe.Pointer(&p.ptr)))[index]
	return n
}

// leafPageElements retrieves a list of leaf nodes.
func (p *page) leafPageElements() []leafPageElement {
	if p.count == 0 {
		return nil
	}
	return ((*[0x7FFFFFF]leafPageElement)(unsafe.Pointer(&p.ptr)))[:]
}

// branchPageElement retrieves the branch node by index
func (p *page) branchPageElement(index uint16) *branchPageElement {
	return &((*[0x7FFFFFF]branchPageElement)(unsafe.Pointer(&p.ptr)))[index]
}

// branchPageElements retrieves a list of branch nodes.
func (p *page) branchPageElements() []branchPageElement {
	if p.count == 0 {
		return nil
	}
	return ((*[0x7FFFFFF]branchPageElement)(unsafe.Pointer(&p.ptr)))[:]
}

// dump writes n bytes of the page to STDERR as hex output.
func (p *page) hexdump(n int) {
	buf := (*[maxAllocSize]byte)(unsafe.Pointer(p))[:n]
	fmt.Fprintf(os.Stderr, "%x\n", buf)
}

type pages []*page

func (s pages) Len() int           { return len(s) }
func (s pages) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s pages) Less(i, j int) bool { return s[i].id < s[j].id }

// branchPageElement represents a node on a branch page.
type branchPageElement struct {
	pos   uint32
	ksize uint32
	pgid  pgid
}

// key returns a byte slice of the node key.
func (n *branchPageElement) key() []byte {
	buf := (*[maxAllocSize]byte)(unsafe.Pointer(n))
	return (*[maxAllocSize]byte)(unsafe.Pointer(&buf[n.pos]))[:n.ksize]
}

// leafPageElement represents a node on a leaf page.
type leafPageElement struct {
	flags uint32
	pos   uint32
	ksize uint32
	vsize uint32
}

// key returns a byte slice of the node key.
func (n *leafPageElement) key() []byte {
	buf := (*[maxAllocSize]byte)(unsafe.Pointer(n))
	return (*[maxAllocSize]byte)(unsafe.Pointer(&buf[n.pos]))[:n.ksize:n.ksize]
}

// value returns a byte slice of the node value.
func (n *leafPageElement) value() []byte {
	buf := (*[maxAllocSize]byte)(unsafe.Pointer(n))
	return (*[maxAllocSize]byte)(unsafe.Pointer(&buf[n.pos+n.ksize]))[:n.vsize:n.vsize]
}

// PageInfo represents human readable information about a page.
type PageInfo struct {
	ID            int
	Type          string
	Count         int
	OverflowCount int
}

type pgids []pgid

func (s pgids) Len() int           { return len(s) }
func (s pgids) Swap(i, j int)      { s[i], s[j] = s[j], s[i] }
func (s pgids) Less(i, j int) bool { return s[i] < s[j] }

// merge returns the sorted union of a and b.
func (a pgids) merge(b pgids) pgids {
	// Return the opposite slice if one is nil.
	if len(a) == 0 {
		return b
	}
	if len(b) == 0 {
		return a
	}
	merged := make(pgids, len(a)+len(b))
	mergepgids(merged, a, b)
	return merged
}

// mergepgids copies the sorted union of a and b into dst.
// If dst is too small, it panics.
func mergepgids(dst, a, b pgids) {
	if len(dst) < len(a)+len(b) {
		panic(fmt.Errorf("mergepgids bad len %d < %d + %d", len(dst), len(a), len(b)))
	}
	// Copy in the opposite slice if one is nil.
	if len(a) == 0 {
		copy(dst, b)
		return
	}
	if len(b) == 0 {
		copy(dst, a)
		return
	}

	// Merged will hold all elements from both lists.
	merged := dst[:0]

	// Assign lead to the slice with a lower starting value, follow to the higher value.
	lead, follow := a, b
	if b[0] < a[0] {
		lead, follow = b, a
	}

	// Continue while there are elements in the lead.
	for len(lead) > 0 {
		// Merge largest prefix of lead that is ahead of follow[0].
		n := sort.Search(len(lead), func(i int) bool { return lead[i] > follow[0] })
		merged = append(merged, lead[:n]...)
		if n >= len(lead) {
			break
		}

		// Swap lead and follow.
		lead, follow = follow, lead[n:]
	}

	// Append what's left in follow.
	_ = append(merged, follow...)
}