mirror of https://github.com/hak5/bolt.git
112 lines
2.8 KiB
Go
112 lines
2.8 KiB
Go
package bolt
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import (
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"sort"
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"unsafe"
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)
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// freelist represents a list of all pages that are available for allocation.
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// It also tracks pages that have been freed but are still in use by open transactions.
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type freelist struct {
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ids []pgid
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pending map[txid][]pgid
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}
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// all returns a list of all free ids and all pending ids in one sorted list.
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func (f *freelist) all() []pgid {
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ids := make([]pgid, len(f.ids))
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copy(ids, f.ids)
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for _, list := range f.pending {
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ids = append(ids, list...)
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}
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sort.Sort(reverseSortedPgids(ids))
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return ids
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}
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// allocate returns the starting page id of a contiguous list of pages of a given size.
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// If a contiguous block cannot be found then 0 is returned.
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func (f *freelist) allocate(n int) pgid {
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var count int
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var previd pgid
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for i, id := range f.ids {
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// Reset count if this is not contiguous.
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if previd == 0 || previd-id != 1 {
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count = 1
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}
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// If we found a contiguous block then remove it and return it.
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if count == n {
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f.ids = append(f.ids[:i-(n-1)], f.ids[i+1:]...)
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_assert(id > 1, "cannot allocate page 0 or 1: %d", id)
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return id
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}
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previd = id
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count++
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}
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return 0
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}
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// free releases a page and its overflow for a given transaction id.
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func (f *freelist) free(txid txid, p *page) {
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var ids = f.pending[txid]
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_assert(p.id > 1, "cannot free page 0 or 1: %d", p.id)
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for i := 0; i < int(p.overflow+1); i++ {
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ids = append(ids, p.id+pgid(i))
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}
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f.pending[txid] = ids
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}
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// release moves all page ids for a transaction id (or older) to the freelist.
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func (f *freelist) release(txid txid) {
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for tid, ids := range f.pending {
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if tid <= txid {
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f.ids = append(f.ids, ids...)
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delete(f.pending, tid)
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}
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}
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sort.Sort(reverseSortedPgids(f.ids))
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}
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// isFree returns whether a given page is in the free list.
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func (f *freelist) isFree(pgid pgid) bool {
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for _, id := range f.ids {
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if id == pgid {
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return true
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}
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}
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for _, m := range f.pending {
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for _, id := range m {
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if id == pgid {
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return true
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}
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}
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}
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return false
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}
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// read initializes the freelist from a freelist page.
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func (f *freelist) read(p *page) {
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ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0:p.count]
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f.ids = make([]pgid, len(ids))
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copy(f.ids, ids)
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}
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// write writes the page ids onto a freelist page. All free and pending ids are
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// saved to disk since in the event of a program crash, all pending ids will
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// become free.
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func (f *freelist) write(p *page) {
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ids := f.all()
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p.flags |= freelistPageFlag
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p.count = uint16(len(ids))
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copy(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:], ids)
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}
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type reverseSortedPgids []pgid
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func (s reverseSortedPgids) Len() int { return len(s) }
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func (s reverseSortedPgids) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
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func (s reverseSortedPgids) Less(i, j int) bool { return s[i] > s[j] }
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