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package wazevoapi
const poolPageSize = 128
// Pool is a pool of T that can be allocated and reset.
// This is useful to avoid unnecessary allocations.
type Pool[T any] struct {
pages []*[poolPageSize]T
resetFn func(*T)
allocated, index int
}
// NewPool returns a new Pool.
// resetFn is called when a new T is allocated in Pool.Allocate.
func NewPool[T any](resetFn func(*T)) Pool[T] {
var ret Pool[T]
ret.resetFn = resetFn
ret.Reset()
return ret
}
// Allocated returns the number of allocated T currently in the pool.
func (p *Pool[T]) Allocated() int {
return p.allocated
}
// Allocate allocates a new T from the pool.
func (p *Pool[T]) Allocate() *T {
if p.index == poolPageSize {
if len(p.pages) == cap(p.pages) {
p.pages = append(p.pages, new([poolPageSize]T))
} else {
i := len(p.pages)
p.pages = p.pages[:i+1]
if p.pages[i] == nil {
p.pages[i] = new([poolPageSize]T)
}
}
p.index = 0
}
ret := &p.pages[len(p.pages)-1][p.index]
if p.resetFn != nil {
p.resetFn(ret)
}
p.index++
p.allocated++
return ret
}
// View returns the pointer to i-th item from the pool.
func (p *Pool[T]) View(i int) *T {
page, index := i/poolPageSize, i%poolPageSize
return &p.pages[page][index]
}
// Reset resets the pool.
func (p *Pool[T]) Reset() {
p.pages = p.pages[:0]
p.index = poolPageSize
p.allocated = 0
}
// IDedPool is a pool of T that can be allocated and reset, with a way to get T by an ID.
type IDedPool[T any] struct {
pool Pool[T]
idToItems []*T
maxIDEncountered int
}
// NewIDedPool returns a new IDedPool.
func NewIDedPool[T any](resetFn func(*T)) IDedPool[T] {
return IDedPool[T]{pool: NewPool[T](resetFn), maxIDEncountered: -1}
}
// GetOrAllocate returns the T with the given id.
func (p *IDedPool[T]) GetOrAllocate(id int) *T {
if p.maxIDEncountered < id {
p.maxIDEncountered = id
}
if id >= len(p.idToItems) {
p.idToItems = append(p.idToItems, make([]*T, id-len(p.idToItems)+1)...)
}
if p.idToItems[id] == nil {
p.idToItems[id] = p.pool.Allocate()
}
return p.idToItems[id]
}
// Get returns the T with the given id, or nil if it's not allocated.
func (p *IDedPool[T]) Get(id int) *T {
if id >= len(p.idToItems) {
return nil
}
return p.idToItems[id]
}
// Reset resets the pool.
func (p *IDedPool[T]) Reset() {
p.pool.Reset()
for i := 0; i <= p.maxIDEncountered; i++ {
p.idToItems[i] = nil
}
p.maxIDEncountered = -1
}
// MaxIDEncountered returns the maximum id encountered so far.
func (p *IDedPool[T]) MaxIDEncountered() int {
return p.maxIDEncountered
}
// arraySize is the size of the array used in VarLengthPool's arrayPool.
// This is chosen to be 8, which is empirically a good number among 8, 12, 16 and 20.
const arraySize = 8
// VarLengthPool is a pool of VarLength[T] that can be allocated and reset.
type (
VarLengthPool[T any] struct {
arrayPool Pool[varLengthPoolArray[T]]
slicePool Pool[[]T]
}
// varLengthPoolArray wraps an array and keeps track of the next index to be used to avoid the heap allocation.
varLengthPoolArray[T any] struct {
arr [arraySize]T
next int
}
)
// VarLength is a variable length array that can be reused via a pool.
type VarLength[T any] struct {
arr *varLengthPoolArray[T]
slc *[]T
}
// NewVarLengthPool returns a new VarLengthPool.
func NewVarLengthPool[T any]() VarLengthPool[T] {
return VarLengthPool[T]{
arrayPool: NewPool[varLengthPoolArray[T]](func(v *varLengthPoolArray[T]) {
v.next = 0
}),
slicePool: NewPool[[]T](func(i *[]T) {
*i = (*i)[:0]
}),
}
}
// NewNilVarLength returns a new VarLength[T] with a nil backing.
func NewNilVarLength[T any]() VarLength[T] {
return VarLength[T]{}
}
// Allocate allocates a new VarLength[T] from the pool.
func (p *VarLengthPool[T]) Allocate(knownMin int) VarLength[T] {
if knownMin <= arraySize {
arr := p.arrayPool.Allocate()
return VarLength[T]{arr: arr}
}
slc := p.slicePool.Allocate()
return VarLength[T]{slc: slc}
}
// Reset resets the pool.
func (p *VarLengthPool[T]) Reset() {
p.arrayPool.Reset()
p.slicePool.Reset()
}
// Append appends items to the backing slice just like the `append` builtin function in Go.
func (i VarLength[T]) Append(p *VarLengthPool[T], items ...T) VarLength[T] {
if i.slc != nil {
*i.slc = append(*i.slc, items...)
return i
}
if i.arr == nil {
i.arr = p.arrayPool.Allocate()
}
arr := i.arr
if arr.next+len(items) <= arraySize {
for _, item := range items {
arr.arr[arr.next] = item
arr.next++
}
} else {
slc := p.slicePool.Allocate()
// Copy the array to the slice.
for ptr := 0; ptr < arr.next; ptr++ {
*slc = append(*slc, arr.arr[ptr])
}
i.slc = slc
*i.slc = append(*i.slc, items...)
}
return i
}
// View returns the backing slice.
func (i VarLength[T]) View() []T {
if i.slc != nil {
return *i.slc
} else if i.arr != nil {
arr := i.arr
return arr.arr[:arr.next]
}
return nil
}
// Cut cuts the backing slice to the given length.
// Precondition: n <= len(i.backing).
func (i VarLength[T]) Cut(n int) {
if i.slc != nil {
*i.slc = (*i.slc)[:n]
} else if i.arr != nil {
i.arr.next = n
}
}
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