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encoding/json: defer error context work until necessary

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Calling Name on a reflect.Type is somewhat expensive, as it involves a
number of nested calls and string handling.

This cost was showing up when decoding structs, as we were calling it to
set up an error context.

We can avoid the extra work unless we do encounter an error, which makes
decoding via struct types faster.

name           old time/op    new time/op    delta
CodeDecoder-4    31.0ms ± 1%    29.9ms ± 1%  -3.69%  (p=0.002 n=6+6)

name           old speed      new speed      delta
CodeDecoder-4  62.6MB/s ± 1%  65.0MB/s ± 1%  +3.83%  (p=0.002 n=6+6)

Updates #5683.

Change-Id: I48a3a85ef0ba96f524b7c3e9096cb2c4589e077a
Reviewed-on: https://go-review.googlesource.com/122467
Run-TryBot: Daniel Martí <mvdan@mvdan.cc>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
This commit is contained in:
Daniel Martí 2018-07-08 13:17:56 +01:00
parent 4a842f2559
commit 9a2a34e1c1
1 changed files with 6 additions and 6 deletions
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12
src/encoding/json/decode.go
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@ -267,7 +267,7 @@ type decodeState struct {
opcode int // last read result opcode int // last read result
scan scanner scan scanner
errorContext struct { // provides context for type errors errorContext struct { // provides context for type errors
Struct string Struct reflect.Type
Field string Field string
} }
savedError error savedError error
@ -289,7 +289,7 @@ func (d *decodeState) init(data []byte) *decodeState {
d.data = data d.data = data
d.off = 0 d.off = 0
d.savedError = nil d.savedError = nil
d.errorContext.Struct = "" d.errorContext.Struct = nil
d.errorContext.Field = "" d.errorContext.Field = ""
return d return d
} }
@ -304,10 +304,10 @@ func (d *decodeState) saveError(err error) {
// addErrorContext returns a new error enhanced with information from d.errorContext // addErrorContext returns a new error enhanced with information from d.errorContext
func (d *decodeState) addErrorContext(err error) error { func (d *decodeState) addErrorContext(err error) error {
if d.errorContext.Struct != "" || d.errorContext.Field != "" { if d.errorContext.Struct != nil || d.errorContext.Field != "" {
switch err := err.(type) { switch err := err.(type) {
case *UnmarshalTypeError: case *UnmarshalTypeError:
err.Struct = d.errorContext.Struct err.Struct = d.errorContext.Struct.Name()
err.Field = d.errorContext.Field err.Field = d.errorContext.Field
return err return err
} }
@ -744,7 +744,7 @@ func (d *decodeState) object(v reflect.Value) error {
subv = subv.Field(i) subv = subv.Field(i)
} }
d.errorContext.Field = f.name d.errorContext.Field = f.name
d.errorContext.Struct = v.Type().Name() d.errorContext.Struct = v.Type()
} else if d.disallowUnknownFields { } else if d.disallowUnknownFields {
d.saveError(fmt.Errorf("json: unknown field %q", key)) d.saveError(fmt.Errorf("json: unknown field %q", key))
} }
@ -832,7 +832,7 @@ func (d *decodeState) object(v reflect.Value) error {
return errPhase return errPhase
} }
d.errorContext.Struct = "" d.errorContext.Struct = nil
d.errorContext.Field = "" d.errorContext.Field = ""
} }
return nil return nil