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package bolt
import (
"fmt"
"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.
// If the page is already free then a panic will occur.
func (f *freelist) free(txid txid, p *page) {
_assert(p.id > 1, "cannot free page 0 or 1: %d", p.id)
// Verify that page is not already free.
minid, maxid := p.id, p.id+pgid(p.overflow)
for _, id := range f.ids {
if id >= minid && id <= maxid {
panic(fmt.Sprintf("page %d already freed in tx", id))
}
}
for ptxid, m := range f.pending {
for _, id := range m {
if id >= minid && id <= maxid {
panic(fmt.Sprintf("tx %d: page %d already freed in tx %d", txid, id, ptxid))
}
}
}
// Free page and all its overflow pages.
var ids = f.pending[txid]
for i := 0; i < int(p.overflow+1); i++ {
ids = append(ids, p.id+pgid(i))
}
f.pending[txid] = ids
}
// 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)
}
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