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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
scan scanner
errorContext struct { // provides context for type errors
Struct string
Struct reflect.Type
Field string
}
savedError error
@ -289,7 +289,7 @@ func (d *decodeState) init(data []byte) *decodeState {
d.data = data
d.off = 0
d.savedError = nil
d.errorContext.Struct = ""
d.errorContext.Struct = nil
d.errorContext.Field = ""
return d
}
@ -304,10 +304,10 @@ func (d *decodeState) saveError(err error) {
// addErrorContext returns a new error enhanced with information from d.errorContext
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) {
case *UnmarshalTypeError:
err.Struct = d.errorContext.Struct
err.Struct = d.errorContext.Struct.Name()
err.Field = d.errorContext.Field
return err
}
@ -744,7 +744,7 @@ func (d *decodeState) object(v reflect.Value) error {
subv = subv.Field(i)
}
d.errorContext.Field = f.name
d.errorContext.Struct = v.Type().Name()
d.errorContext.Struct = v.Type()
} else if d.disallowUnknownFields {
d.saveError(fmt.Errorf("json: unknown field %q", key))
}
@ -832,7 +832,7 @@ func (d *decodeState) object(v reflect.Value) error {
return errPhase
}
d.errorContext.Struct = ""
d.errorContext.Struct = nil
d.errorContext.Field = ""
}
return nil