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Replace Ordered with an iterator in export.Labels. (#567)

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* Do not expose a slice of labels in export.Record

This is really an inconvenient implementation detail leak - we may
want to store labels in a different way. Replace it with an iterator -
it does not force us to use slice of key values as a storage in the
long run.

* Add Len to LabelIterator

It may come in handy in several situations, where we don't have access
to export.Labels object, but only to the label iterator.

* Use reflect value label iterator for the fixed labels

* add reset operation to iterator

Makes my life easier when writing a benchmark. Might also be an
alternative to cloning the iterator.

* Add benchmarks for iterators

* Add import comment

* Add clone operation to label iterator

* Move iterator tests to a separate package

* Add tests for cloning iterators

* Pass label iterator to export labels

* Use non-addressable array reflect values

By not using the value created by `reflect.New()`, but rather by
`reflect.ValueOf()`, we get a non-addressable array in the value,
which does not infer an allocation cost when getting an element from
the array.

* Drop zero iterator

This can be substituted by a reflect value iterator that goes over a
value with a zero-sized array.

* Add a simple iterator that implements label iterator

In the long run this will completely replace the LabelIterator
interface.

* Replace reflect value iterator with simple iterator

* Pass label storage to new export labels, not label iterator

* Drop label iterator interface, rename storage iterator to label iterator

* Drop clone operation from iterator

It's a leftover from interface times and now it's pointless - the
iterator is a simple struct, so cloning it is a simple copy.

* Drop Reset from label iterator

The sole existence of Reset was actually for benchmarking convenience.
Now we can just copy the iterator cheaply, so a need for Reset is no
more.

* Drop noop iterator tests

* Move back iterator tests to export package

* Eagerly get the reflect value of ordered labels

So we won't get into problems when several goroutines want to iterate
the same labels at the same time. Not sure if this would be a big
deal, since every goroutine would compute the same reflect.Value, but
concurrent write to the same memory is bad anyway. And it doesn't cost
us any extra allocations anyway.

* Replace NewSliceLabelIterator() with a method of LabelSlice

* Add some documentation

* Documentation fixes
This commit is contained in:
Krzesimir Nowak
2020-03-19 23:01:34 +01:00
committed by GitHub
parent d8682c1999
commit a01f63bec4
18 changed files with 381 additions and 124 deletions
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121
sdk/metric/sdk.go
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@ -82,14 +82,18 @@ type (
// repeatedly.
labels struct {
meter *SDK
// slice is a slice of `ordered`.
slice sortedLabels
// ordered is the output of sorting and deduplicating
// the labels, copied into an array of the correct
// size for use as a map key.
ordered orderedLabels
// sortSlice has a single purpose - as a temporary
// place for sorting during labels creation to avoid
// allocation
sortSlice sortedLabels
// cachedValue contains a `reflect.Value` of the `ordered`
// member
cachedValue reflect.Value
}
// mapkey uniquely describes a metric instrument in terms of
@ -150,11 +154,12 @@ type (
)
var (
_ api.MeterImpl = &SDK{}
_ api.LabelSet = &labels{}
_ api.AsyncImpl = &asyncInstrument{}
_ api.SyncImpl = &syncInstrument{}
_ api.BoundSyncImpl = &record{}
_ api.MeterImpl = &SDK{}
_ api.LabelSet = &labels{}
_ api.AsyncImpl = &asyncInstrument{}
_ api.SyncImpl = &syncInstrument{}
_ api.BoundSyncImpl = &record{}
_ export.LabelStorage = &labels{}
kvType = reflect.TypeOf(core.KeyValue{})
)
@ -295,11 +300,15 @@ func (s *syncInstrument) RecordOne(ctx context.Context, number core.Number, ls a
// own periodic collection.
func New(batcher export.Batcher, labelEncoder export.LabelEncoder) *SDK {
m := &SDK{
empty: labels{
ordered: [0]core.KeyValue{},
},
batcher: batcher,
labelEncoder: labelEncoder,
errorHandler: DefaultErrorHandler,
}
m.empty.meter = m
m.empty.cachedValue = reflect.ValueOf(m.empty.ordered)
return m
}
@ -307,8 +316,10 @@ func DefaultErrorHandler(err error) {
fmt.Fprintln(os.Stderr, "Metrics SDK error:", err)
}
// Labels returns a LabelSet corresponding to the arguments. Passed
// labels are de-duplicated, with last-value-wins semantics.
// Labels returns a LabelSet corresponding to the arguments. Passed labels
// are sorted and de-duplicated, with last-value-wins semantics. Note that
// sorting and deduplicating happens in-place to avoid allocation, so the
// passed slice will be modified.
func (m *SDK) Labels(kvs ...core.KeyValue) api.LabelSet {
// Check for empty set.
if len(kvs) == 0 {
@ -316,33 +327,15 @@ func (m *SDK) Labels(kvs ...core.KeyValue) api.LabelSet {
}
ls := &labels{ // allocation
meter: m,
slice: kvs,
meter: m,
sortSlice: kvs,
}
// Sort and de-duplicate. Note: this use of `ls.slice` avoids
// an allocation by using the address-able field rather than
// `kvs`. Labels retains a copy of this slice, i.e., the
// initial allocation at the varargs call site.
//
// Note that `ls.slice` continues to refer to this memory,
// even though a new array is allocated for `ls.ordered`. It
// is possible for the `slice` to refer to the same memory,
// although in the reflection code path of `computeOrdered` it
// costs an allocation to yield a slice through
// `(reflect.Value).Interface()`.
//
// TODO: There is a possibility that the caller passes values
// without an allocation (e.g., `meter.Labels(kvs...)`), and
// that the user could later modify the slice, leading to
// incorrect results. This is indeed a risk, one that should
// be quickly addressed via the following TODO.
//
// TODO: It would be better overall if the export.Labels interface
// did not expose a slice via `Ordered()`, if instead it exposed
// getter methods like `Len()` and `Order(i int)`. Then we would
// just implement the interface using the `orderedLabels` array.
sort.Stable(&ls.slice)
// Sort and de-duplicate. Note: this use of `ls.sortSlice`
// avoids an allocation by using the address-able field rather
// than `kvs`.
sort.Stable(&ls.sortSlice)
ls.sortSlice = nil
oi := 1
for i := 1; i < len(kvs); i++ {
@ -355,64 +348,81 @@ func (m *SDK) Labels(kvs ...core.KeyValue) api.LabelSet {
oi++
}
kvs = kvs[0:oi]
ls.slice = kvs
ls.computeOrdered(kvs)
return ls
}
func (ls *labels) NumLabels() int {
return ls.cachedValue.Len()
}
func (ls *labels) GetLabel(idx int) core.KeyValue {
return ls.cachedValue.Index(idx).Interface().(core.KeyValue)
}
func (ls *labels) computeOrdered(kvs []core.KeyValue) {
ls.ordered = computeOrderedFixed(kvs)
if ls.ordered == nil {
ls.ordered = computeOrderedReflect(kvs)
}
ls.cachedValue = reflect.ValueOf(ls.ordered)
}
func computeOrderedFixed(kvs []core.KeyValue) orderedLabels {
switch len(kvs) {
case 1:
ptr := new([1]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 2:
ptr := new([2]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 3:
ptr := new([3]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 4:
ptr := new([4]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 5:
ptr := new([5]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 6:
ptr := new([6]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 7:
ptr := new([7]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 8:
ptr := new([8]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 9:
ptr := new([9]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
case 10:
ptr := new([10]core.KeyValue)
copy((*ptr)[:], kvs)
ls.ordered = *ptr
return *ptr
default:
at := reflect.New(reflect.ArrayOf(len(kvs), kvType)).Elem()
for i := 0; i < len(kvs); i++ {
*(at.Index(i).Addr().Interface().(*core.KeyValue)) = kvs[i]
}
ls.ordered = at.Interface()
return nil
}
}
func computeOrderedReflect(kvs []core.KeyValue) interface{} {
at := reflect.New(reflect.ArrayOf(len(kvs), kvType)).Elem()
for i, kv := range kvs {
*(at.Index(i).Addr().Interface().(*core.KeyValue)) = kv
}
return at.Interface()
}
// labsFor sanitizes the input LabelSet. The input will be rejected
// if it was created by another Meter instance, for example.
func (m *SDK) labsFor(ls api.LabelSet) *labels {
@ -539,7 +549,8 @@ func (m *SDK) checkpoint(ctx context.Context, descriptor *metric.Descriptor, rec
// instead of once per bound instrument lifetime. This can be
// addressed similarly to OTEP 78, see
// https://github.com/jmacd/opentelemetry-go/blob/8bed2e14df7f9f4688fbab141924bb786dc9a3a1/api/context/internal/set.go#L89
exportLabels := export.NewLabels(labels.slice, m.labelEncoder.Encode(labels.slice), m.labelEncoder)
iter := export.NewLabelIterator(labels)
exportLabels := export.NewLabels(labels, m.labelEncoder.Encode(iter), m.labelEncoder)
exportRecord := export.NewRecord(descriptor, exportLabels, recorder)
err := m.batcher.Process(ctx, exportRecord)
if err != nil {