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
|
package bolt
import (
"sort"
"unsafe"
)
// freelist represents a list of all pages that are available for allocation.
// It also tracks pages that have been freed but are still in use by open transactions.
type freelist struct {
ids []pgid
pending map[txid][]pgid
}
// size returns the size of the page after serialization.
func (f *freelist) size() int {
return pageHeaderSize + (int(unsafe.Sizeof(pgid(0))) * len(f.all()))
}
// all returns a list of all free ids and all pending ids in one sorted list.
func (f *freelist) all() []pgid {
ids := make([]pgid, len(f.ids))
copy(ids, f.ids)
for _, list := range f.pending {
ids = append(ids, list...)
}
sort.Sort(pgids(ids))
return ids
}
// allocate returns the starting page id of a contiguous list of pages of a given size.
// If a contiguous block cannot be found then 0 is returned.
func (f *freelist) allocate(n int) pgid {
if len(f.ids) == 0 {
return 0
}
var initial, previd pgid
for i, id := range f.ids {
_assert(id > 1, "invalid page allocation: %d", id)
// Reset initial page if this is not contiguous.
if previd == 0 || id-previd != 1 {
initial = id
}
// If we found a contiguous block then remove it and return it.
if (id-initial)+1 == pgid(n) {
// If we're allocating off the beginning then take the fast path
// and just adjust the existing slice. This will use extra memory
// temporarily but the append() in free() will realloc the slice
// as is necessary.
if (i + 1) == n {
f.ids = f.ids[i+1:]
} else {
copy(f.ids[i-n+1:], f.ids[i+1:])
f.ids = f.ids[:len(f.ids)-n]
}
return initial
}
previd = id
}
return 0
}
// free releases a page and its overflow for a given transaction id.
func (f *freelist) free(txid txid, p *page) {
var ids = f.pending[txid]
_assert(p.id > 1, "cannot free page 0 or 1: %d", p.id)
for i := 0; i < int(p.overflow+1); i++ {
ids = append(ids, p.id+pgid(i))
}
f.pending[txid] = ids
// DEBUG ONLY: f.check()
}
// release moves all page ids for a transaction id (or older) to the freelist.
func (f *freelist) release(txid txid) {
for tid, ids := range f.pending {
if tid <= txid {
f.ids = append(f.ids, ids...)
delete(f.pending, tid)
}
}
sort.Sort(pgids(f.ids))
}
// isFree returns whether a given page is in the free list.
func (f *freelist) isFree(pgid pgid) bool {
for _, id := range f.ids {
if id == pgid {
return true
}
}
for _, m := range f.pending {
for _, id := range m {
if id == pgid {
return true
}
}
}
return false
}
// read initializes the freelist from a freelist page.
func (f *freelist) read(p *page) {
ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0:p.count]
f.ids = make([]pgid, len(ids))
copy(f.ids, ids)
sort.Sort(pgids(f.ids))
}
// write writes the page ids onto a freelist page. All free and pending ids are
// saved to disk since in the event of a program crash, all pending ids will
// become free.
func (f *freelist) write(p *page) {
ids := f.all()
p.flags |= freelistPageFlag
p.count = uint16(len(ids))
copy(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:], ids)
}
// check verifies there are no double free pages.
// This is slow so it should only be used while debugging.
// If errors are found then a panic invoked.
/*
func (f *freelist) check() {
var lookup = make(map[pgid]txid)
for _, id := range f.ids {
if _, ok := lookup[id]; ok {
panic(fmt.Sprintf("page %d already freed", id))
}
lookup[id] = 0
}
for txid, m := range f.pending {
for _, id := range m {
if _, ok := lookup[id]; ok {
panic(fmt.Sprintf("tx %d: page %d already freed in tx %d", txid, id, lookup[id]))
}
lookup[id] = txid
}
}
}
*/
|
