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Move call to attribute.NewSet outside lock when checking collisions #407

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Mar 1, 2023
Merged

Move call to attribute.NewSet outside lock when checking collisions #407

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Move call to attribute.NewSet outside lock when checking collisions
Mar 1, 2023
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Mar 1, 2023
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60 changes: 25 additions & 35 deletions lightstep/sdk/metric/internal/syncstate/sync.go
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Original file line number Diff line number Diff line change
Expand Up @@ -209,7 +209,7 @@ type record struct {
// this field is unused when Performance.IgnoreCollisions is true.
next *record

// once governs access to `accumulatorsUnsafe`. The caller
// once governs access to `accumulatorsUnsafe. The caller
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// that created the `record` must call once.Do(initialize) on
// its own code path, although another goroutine might
// actually perform the initialization. This is arranged with
Expand All @@ -225,22 +225,18 @@ type record struct {
// to ensure that once.Do(initialize) is called.
accumulatorUnsafe viewstate.Accumulator

// attrsListUnsafe is used as a temporary to calculate the
// attrsSet, which depends on whether collisions are checked.
//
// if IgnoreCollisions is true, this value is non-nil from the
// point of construction until once.Do(initialize) is called
// in the Update or Collect code path. After once.Do(initialize),
// this field is nil.
//
// if IgnoreCollisions is false, this value is set to a copy
// of the original input attribute list, for comparison,
// insife computeAttrsUnderLock.
attrsListUnsafe attribute.Sortable

// attrsSet is the attributeSet computed from the input attributes.
// when the accumulator has been computed, this is set to nil.
attrsSet attribute.Set
// attrsListInputUnsafe is a temporary copy of the caller's
// attribute list in its original order, possibly having duplicates.
// this is passed to attribute.NewSetWithSortable, which performs a
// stable-sort of the slice and resets the pointer to nil inside
// once.Do(initialize). This field is used consistently regardless
// of IgnoreCollisions.
attrsListInputUnsafe attribute.Sortable

// attrsListCopy is a copy of the original attribute list, only
// used when checking collisions (i.e., IgnoreCollisions is false).
// set in computeAttrsUnderLock.
attrsListCopy []attribute.KeyValue
}

// normalCollect equals conditionalCollect(false), is named
Expand Down Expand Up @@ -285,34 +281,28 @@ func (rec *record) readAccumulator() viewstate.Accumulator {

// initialize ensures that accumulatorUnsafe and attrsUnsafe are correctly initialized.
//
// readAttributes() and readAccumulator() call this inside a sync.Once.Do(). The
// behavior of this method depends on IgnoreCollisions, as documented in the
// corresponding "unsafe" fields.
// readAccumulator() calls this inside a sync.Once.Do().
func (rec *record) initialize() {
if rec.inst.performance.IgnoreCollisions {
rec.attrsSet = attribute.NewSetWithSortable(rec.attrsListUnsafe, &rec.attrsListUnsafe)
}
// Note that rec.attrsListInputUnsafe is set to nil in NewSetWithSortable().
aset := attribute.NewSetWithSortable(rec.attrsListInputUnsafe, &rec.attrsListInputUnsafe)

rec.accumulatorUnsafe = rec.inst.compiled.NewAccumulator(rec.attrsSet)
rec.attrsSet = attribute.Set{}
rec.accumulatorUnsafe = rec.inst.compiled.NewAccumulator(aset)
}

// computeAttrsUnderLock sets the attribute.Set that will be used to
// construct the accumulator.
func (rec *record) computeAttrsUnderLock(attrs []attribute.KeyValue) {
// The work of NewSetWithSortable and NewAccumulator is
// deferred until once.Do(initialize) outside of the lock.
rec.attrsListInputUnsafe = attrs

if rec.inst.performance.IgnoreCollisions {
// The work of NewSetWithSortable is deferred until
// once.Do(initialize) outside of the lock.
rec.attrsListUnsafe = attrs
return
}

acpy := make(attribute.Sortable, len(attrs))
acpy := make([]attribute.KeyValue, len(attrs))
copy(acpy, attrs)
rec.attrsSet = attribute.NewSetWithSortable(acpy, &rec.attrsListUnsafe)

// Note the next assignment has to follow NewSetWithSortable(), which clears the field.
rec.attrsListUnsafe = acpy
rec.attrsListCopy = acpy
}

func (inst *Observer) ObserveInt64(ctx context.Context, num int64, attrs ...attribute.KeyValue) {
Expand Down Expand Up @@ -448,7 +438,7 @@ func acquireRead(inst *Observer, fp uint64, attrs []attribute.KeyValue) *record

// Potentially test for hash collisions.
if !inst.performance.IgnoreCollisions {
for rec != nil && !attributesEqual(attrs, rec.attrsListUnsafe) {
for rec != nil && !attributesEqual(attrs, rec.attrsListCopy) {
rec = rec.next
}
}
Expand Down Expand Up @@ -507,7 +497,7 @@ func acquireWrite(inst *Observer, fp uint64, newRec *record) (*record, bool) {

for oldRec := inst.current[fp]; oldRec != nil; oldRec = oldRec.next {

if inst.performance.IgnoreCollisions || attributesEqual(oldRec.attrsListUnsafe, newRec.attrsListUnsafe) {
if inst.performance.IgnoreCollisions || attributesEqual(oldRec.attrsListCopy, newRec.attrsListCopy) {
if oldRec.refMapped.ref() {
return oldRec, true
}
Expand Down