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// Copyright The OpenTelemetry Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package label
import (
"encoding/json"
"reflect"
"sort"
"sync"
)
type (
// Set is the representation for a distinct label set. It
// manages an immutable set of labels, with an internal cache
// for storing label encodings.
//
// This type supports the `Equivalent` method of comparison
// using values of type `Distinct`.
//
// This type is used to implement:
// 1. Metric labels
// 2. Resource sets
// 3. Correlation map (TODO)
Set struct {
equivalent Distinct
lock sync.Mutex
encoders [maxConcurrentEncoders]EncoderID
encoded [maxConcurrentEncoders]string
}
// Distinct wraps a variable-size array of `KeyValue`,
// constructed with keys in sorted order. This can be used as
// a map key or for equality checking between Sets.
Distinct struct {
iface interface{}
}
// Filter supports removing certain labels from label sets.
// When the filter returns true, the label will be kept in
// the filtered label set. When the filter returns false, the
// label is excluded from the filtered label set, and the
// label instead appears in the `removed` list of excluded labels.
Filter func(KeyValue) bool
// Sortable implements `sort.Interface`, used for sorting
// `KeyValue`. This is an exported type to support a
// memory optimization. A pointer to one of these is needed
// for the call to `sort.Stable()`, which the caller may
// provide in order to avoid an allocation. See
// `NewSetWithSortable()`.
Sortable []KeyValue
)
var (
// keyValueType is used in `computeDistinctReflect`.
keyValueType = reflect.TypeOf(KeyValue{})
// emptySet is returned for empty label sets.
emptySet = &Set{
equivalent: Distinct{
iface: [0]KeyValue{},
},
}
)
const maxConcurrentEncoders = 3
func EmptySet() *Set {
return emptySet
}
// reflect abbreviates `reflect.ValueOf`.
func (d Distinct) reflect() reflect.Value {
return reflect.ValueOf(d.iface)
}
// Valid returns true if this value refers to a valid `*Set`.
func (d Distinct) Valid() bool {
return d.iface != nil
}
// Len returns the number of labels in this set.
func (l *Set) Len() int {
if l == nil || !l.equivalent.Valid() {
return 0
}
return l.equivalent.reflect().Len()
}
// Get returns the KeyValue at ordered position `idx` in this set.
func (l *Set) Get(idx int) (KeyValue, bool) {
if l == nil {
return KeyValue{}, false
}
value := l.equivalent.reflect()
if idx >= 0 && idx < value.Len() {
// Note: The Go compiler successfully avoids an allocation for
// the interface{} conversion here:
return value.Index(idx).Interface().(KeyValue), true
}
return KeyValue{}, false
}
// Value returns the value of a specified key in this set.
func (l *Set) Value(k Key) (Value, bool) {
if l == nil {
return Value{}, false
}
rValue := l.equivalent.reflect()
vlen := rValue.Len()
idx := sort.Search(vlen, func(idx int) bool {
return rValue.Index(idx).Interface().(KeyValue).Key >= k
})
if idx >= vlen {
return Value{}, false
}
keyValue := rValue.Index(idx).Interface().(KeyValue)
if k == keyValue.Key {
return keyValue.Value, true
}
return Value{}, false
}
// HasValue tests whether a key is defined in this set.
func (l *Set) HasValue(k Key) bool {
if l == nil {
return false
}
_, ok := l.Value(k)
return ok
}
// Iter returns an iterator for visiting the labels in this set.
func (l *Set) Iter() Iterator {
return Iterator{
storage: l,
idx: -1,
}
}
// ToSlice returns the set of labels belonging to this set, sorted,
// where keys appear no more than once.
func (l *Set) ToSlice() []KeyValue {
iter := l.Iter()
return iter.ToSlice()
}
// Equivalent returns a value that may be used as a map key. The
// Distinct type guarantees that the result will equal the equivalent
// Distinct value of any label set with the same elements as this,
// where sets are made unique by choosing the last value in the input
// for any given key.
func (l *Set) Equivalent() Distinct {
if l == nil || !l.equivalent.Valid() {
return emptySet.equivalent
}
return l.equivalent
}
// Equals returns true if the argument set is equivalent to this set.
func (l *Set) Equals(o *Set) bool {
return l.Equivalent() == o.Equivalent()
}
// Encoded returns the encoded form of this set, according to
// `encoder`. The result will be cached in this `*Set`.
func (l *Set) Encoded(encoder Encoder) string {
if l == nil || encoder == nil {
return ""
}
id := encoder.ID()
if !id.Valid() {
// Invalid IDs are not cached.
return encoder.Encode(l.Iter())
}
var lookup *string
l.lock.Lock()
for idx := 0; idx < maxConcurrentEncoders; idx++ {
if l.encoders[idx] == id {
lookup = &l.encoded[idx]
break
}
}
l.lock.Unlock()
if lookup != nil {
return *lookup
}
r := encoder.Encode(l.Iter())
l.lock.Lock()
defer l.lock.Unlock()
for idx := 0; idx < maxConcurrentEncoders; idx++ {
if l.encoders[idx] == id {
return l.encoded[idx]
}
if !l.encoders[idx].Valid() {
l.encoders[idx] = id
l.encoded[idx] = r
return r
}
}
// TODO: This is a performance cliff. Find a way for this to
// generate a warning.
return r
}
func empty() Set {
return Set{
equivalent: emptySet.equivalent,
}
}
// NewSet returns a new `Set`. See the documentation for
// `NewSetWithSortableFiltered` for more details.
//
// Except for empty sets, this method adds an additional allocation
// compared with calls that include a `*Sortable`.
func NewSet(kvs ...KeyValue) Set {
// Check for empty set.
if len(kvs) == 0 {
return empty()
}
s, _ := NewSetWithSortableFiltered(kvs, new(Sortable), nil)
return s //nolint
}
// NewSetWithSortable returns a new `Set`. See the documentation for
// `NewSetWithSortableFiltered` for more details.
//
// This call includes a `*Sortable` option as a memory optimization.
func NewSetWithSortable(kvs []KeyValue, tmp *Sortable) Set {
// Check for empty set.
if len(kvs) == 0 {
return empty()
}
s, _ := NewSetWithSortableFiltered(kvs, tmp, nil)
return s //nolint
}
// NewSetWithFiltered returns a new `Set`. See the documentation for
// `NewSetWithSortableFiltered` for more details.
//
// This call includes a `Filter` to include/exclude label keys from
// the return value. Excluded keys are returned as a slice of label
// values.
func NewSetWithFiltered(kvs []KeyValue, filter Filter) (Set, []KeyValue) {
// Check for empty set.
if len(kvs) == 0 {
return empty(), nil
}
return NewSetWithSortableFiltered(kvs, new(Sortable), filter)
}
// NewSetWithSortableFiltered returns a new `Set`.
//
// Duplicate keys are eliminated by taking the last value. This
// re-orders the input slice so that unique last-values are contiguous
// at the end of the slice.
//
// This ensures the following:
//
// - Last-value-wins semantics
// - Caller sees the reordering, but doesn't lose values
// - Repeated call preserve last-value wins.
//
// Note that methods are defined on `*Set`, although this returns `Set`.
// Callers can avoid memory allocations by:
//
// - allocating a `Sortable` for use as a temporary in this method
// - allocating a `Set` for storing the return value of this
// constructor.
//
// The result maintains a cache of encoded labels, by label.EncoderID.
// This value should not be copied after its first use.
//
// The second `[]KeyValue` return value is a list of labels that were
// excluded by the Filter (if non-nil).
func NewSetWithSortableFiltered(kvs []KeyValue, tmp *Sortable, filter Filter) (Set, []KeyValue) {
// Check for empty set.
if len(kvs) == 0 {
return empty(), nil
}
*tmp = kvs
// Stable sort so the following de-duplication can implement
// last-value-wins semantics.
sort.Stable(tmp)
*tmp = nil
position := len(kvs) - 1
offset := position - 1
// The requirements stated above require that the stable
// result be placed in the end of the input slice, while
// overwritten values are swapped to the beginning.
//
// De-duplicate with last-value-wins semantics. Preserve
// duplicate values at the beginning of the input slice.
for ; offset >= 0; offset-- {
if kvs[offset].Key == kvs[position].Key {
continue
}
position--
kvs[offset], kvs[position] = kvs[position], kvs[offset]
}
if filter != nil {
return filterSet(kvs[position:], filter)
}
return Set{
equivalent: computeDistinct(kvs[position:]),
}, nil
}
// filterSet reorders `kvs` so that included keys are contiguous at
// the end of the slice, while excluded keys precede the included keys.
func filterSet(kvs []KeyValue, filter Filter) (Set, []KeyValue) {
var excluded []KeyValue
// Move labels that do not match the filter so
// they're adjacent before calling computeDistinct().
distinctPosition := len(kvs)
// Swap indistinct keys forward and distinct keys toward the
// end of the slice.
offset := len(kvs) - 1
for ; offset >= 0; offset-- {
if filter(kvs[offset]) {
distinctPosition--
kvs[offset], kvs[distinctPosition] = kvs[distinctPosition], kvs[offset]
continue
}
}
excluded = kvs[:distinctPosition]
return Set{
equivalent: computeDistinct(kvs[distinctPosition:]),
}, excluded
}
// Filter returns a filtered copy of this `Set`. See the
// documentation for `NewSetWithSortableFiltered` for more details.
func (l *Set) Filter(re Filter) (Set, []KeyValue) {
if re == nil {
return Set{
equivalent: l.equivalent,
}, nil
}
// Note: This could be refactored to avoid the temporary slice
// allocation, if it proves to be expensive.
return filterSet(l.ToSlice(), re)
}
// computeDistinct returns a `Distinct` using either the fixed- or
// reflect-oriented code path, depending on the size of the input.
// The input slice is assumed to already be sorted and de-duplicated.
func computeDistinct(kvs []KeyValue) Distinct {
iface := computeDistinctFixed(kvs)
if iface == nil {
iface = computeDistinctReflect(kvs)
}
return Distinct{
iface: iface,
}
}
// computeDistinctFixed computes a `Distinct` for small slices. It
// returns nil if the input is too large for this code path.
func computeDistinctFixed(kvs []KeyValue) interface{} {
switch len(kvs) {
case 1:
ptr := new([1]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 2:
ptr := new([2]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 3:
ptr := new([3]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 4:
ptr := new([4]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 5:
ptr := new([5]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 6:
ptr := new([6]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 7:
ptr := new([7]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 8:
ptr := new([8]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 9:
ptr := new([9]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
case 10:
ptr := new([10]KeyValue)
copy((*ptr)[:], kvs)
return *ptr
default:
return nil
}
}
// computeDistinctReflect computes a `Distinct` using reflection,
// works for any size input.
func computeDistinctReflect(kvs []KeyValue) interface{} {
at := reflect.New(reflect.ArrayOf(len(kvs), keyValueType)).Elem()
for i, keyValue := range kvs {
*(at.Index(i).Addr().Interface().(*KeyValue)) = keyValue
}
return at.Interface()
}
// MarshalJSON returns the JSON encoding of the `*Set`.
func (l *Set) MarshalJSON() ([]byte, error) {
return json.Marshal(l.equivalent.iface)
}
// Len implements `sort.Interface`.
func (l *Sortable) Len() int {
return len(*l)
}
// Swap implements `sort.Interface`.
func (l *Sortable) Swap(i, j int) {
(*l)[i], (*l)[j] = (*l)[j], (*l)[i]
}
// Less implements `sort.Interface`.
func (l *Sortable) Less(i, j int) bool {
return (*l)[i].Key < (*l)[j].Key
}