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// read initializes the freelist from a freelist page.
func (f *freelist) read(p *page) {
// If the page.count is at the max uint16 value (64k) then it's considered
// an overflow and the size of the freelist is stored as the first element.
idx, count := 0, int(p.count)
if count == 0xFFFF {
idx = 1
count = int(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0])
}
// Copy the list of page ids from the freelist.
if count == 0 {
f.ids = nil
} else {
ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[idx:count]
f.ids = make([]pgid, len(ids))
copy(f.ids, ids)
// Make sure they're sorted.
sort.Sort(pgids(f.ids))
}
// Rebuild the page cache.
f.reindex()
}
// reindex rebuilds the free cache based on available and pending free lists.
// read initializes the freelist from a freelist page.
func (f *freelist) read(p *page) {
// If the page.count is at the max uint16 value (64k) then it's considered
// an overflow and the size of the freelist is stored as the first element.
idx, count := 0, int(p.count)
if count == 0xFFFF {
idx = 1
count = int(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0])
}
// Copy the list of page ids from the freelist.
if count == 0 {
f.ids = nil
} else {
ids := ((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[idx:count]
f.ids = make([]pgid, len(ids))
copy(f.ids, ids)
// Make sure they're sorted.
sort.Sort(pgids(f.ids))
}
// Rebuild the page cache.
f.reindex()
}
// 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) error {
// Combine the old free pgids and pgids waiting on an open transaction.
// Update the header flag.
p.flags |= freelistPageFlag
// The page.count can only hold up to 64k elements so if we overflow that
// number then we handle it by putting the size in the first element.
lenids := f.count()
if lenids == 0 {
p.count = uint16(lenids)
} else if lenids < 0xFFFF {
p.count = uint16(lenids)
f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[:])
} else {
p.count = 0xFFFF
((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[0] = pgid(lenids)
f.copyall(((*[maxAllocSize]pgid)(unsafe.Pointer(&p.ptr)))[1:])
}
return nil
}
// copyall copies into dst a list of all free ids and all pending ids in one sorted list.
// f.count returns the minimum length required for dst.
func (f *freelist) copyall(dst []pgid) {
m := make(pgids, 0, f.pending_count())
for _, list := range f.pending {
m = append(m, list...)
}
sort.Sort(m)
mergepgids(dst, f.ids, m)
}
// 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...)
}
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