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author | Josh Bleecher Snyder <josharian@gmail.com> | 2020-11-18 12:50:29 -0800 |
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committer | Josh Bleecher Snyder <josharian@gmail.com> | 2021-02-24 14:12:16 +0000 |
commit | 04edf418d285df410745118aae756f9e0a9a00f5 (patch) | |
tree | 6a03a63c804c33ca8184a64049ad977de8cc2bd9 /src/encoding | |
parent | e49612089196be102b4b7f86c417b8cfba2521aa (diff) | |
download | go-04edf418d285df410745118aae756f9e0a9a00f5.tar.gz go-04edf418d285df410745118aae756f9e0a9a00f5.zip |
encoding/json: reduce allocated space in Unmarshal
The decodeState type is a large part of the allocated space during Unmarshal.
The errorContext field is infrequently used, and only on error.
Extract it into a pointer and allocate it separate when necessary.
name old time/op new time/op delta
UnmarshalString-8 115ns ± 5% 114ns ± 3% ~ (p=0.170 n=15+15)
UnmarshalFloat64-8 113ns ± 2% 106ns ± 1% -6.42% (p=0.000 n=15+14)
UnmarshalInt64-8 93.3ns ± 1% 86.9ns ± 4% -6.89% (p=0.000 n=14+15)
name old alloc/op new alloc/op delta
UnmarshalString-8 192B ± 0% 160B ± 0% -16.67% (p=0.000 n=15+15)
UnmarshalFloat64-8 180B ± 0% 148B ± 0% -17.78% (p=0.000 n=15+15)
UnmarshalInt64-8 176B ± 0% 144B ± 0% -18.18% (p=0.000 n=15+15)
name old allocs/op new allocs/op delta
UnmarshalString-8 2.00 ± 0% 2.00 ± 0% ~ (all equal)
UnmarshalFloat64-8 2.00 ± 0% 2.00 ± 0% ~ (all equal)
UnmarshalInt64-8 1.00 ± 0% 1.00 ± 0% ~ (all equal)
Change-Id: I53f3f468e6c65f77a12e5138a2626455b197012d
Reviewed-on: https://go-review.googlesource.com/c/go/+/271338
Trust: Josh Bleecher Snyder <josharian@gmail.com>
Trust: Daniel Martí <mvdan@mvdan.cc>
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>
Diffstat (limited to 'src/encoding')
-rw-r--r-- | src/encoding/json/decode.go | 51 |
1 files changed, 31 insertions, 20 deletions
diff --git a/src/encoding/json/decode.go b/src/encoding/json/decode.go index 86d8a69db7..a9917e72c7 100644 --- a/src/encoding/json/decode.go +++ b/src/encoding/json/decode.go @@ -200,16 +200,19 @@ func (n Number) Int64() (int64, error) { return strconv.ParseInt(string(n), 10, 64) } +// An errorContext provides context for type errors during decoding. +type errorContext struct { + Struct reflect.Type + FieldStack []string +} + // decodeState represents the state while decoding a JSON value. type decodeState struct { - data []byte - off int // next read offset in data - opcode int // last read result - scan scanner - errorContext struct { // provides context for type errors - Struct reflect.Type - FieldStack []string - } + data []byte + off int // next read offset in data + opcode int // last read result + scan scanner + errorContext *errorContext savedError error useNumber bool disallowUnknownFields bool @@ -229,10 +232,11 @@ func (d *decodeState) init(data []byte) *decodeState { d.data = data d.off = 0 d.savedError = nil - d.errorContext.Struct = nil - - // Reuse the allocated space for the FieldStack slice. - d.errorContext.FieldStack = d.errorContext.FieldStack[:0] + if d.errorContext != nil { + d.errorContext.Struct = nil + // Reuse the allocated space for the FieldStack slice. + d.errorContext.FieldStack = d.errorContext.FieldStack[:0] + } return d } @@ -246,12 +250,11 @@ 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 != nil || len(d.errorContext.FieldStack) > 0 { + if d.errorContext != nil && (d.errorContext.Struct != nil || len(d.errorContext.FieldStack) > 0) { switch err := err.(type) { case *UnmarshalTypeError: err.Struct = d.errorContext.Struct.Name() err.Field = strings.Join(d.errorContext.FieldStack, ".") - return err } } return err @@ -657,7 +660,10 @@ func (d *decodeState) object(v reflect.Value) error { } var mapElem reflect.Value - origErrorContext := d.errorContext + var origErrorContext errorContext + if d.errorContext != nil { + origErrorContext = *d.errorContext + } for { // Read opening " of string key or closing }. @@ -732,6 +738,9 @@ func (d *decodeState) object(v reflect.Value) error { } subv = subv.Field(i) } + if d.errorContext == nil { + d.errorContext = new(errorContext) + } d.errorContext.FieldStack = append(d.errorContext.FieldStack, f.name) d.errorContext.Struct = t } else if d.disallowUnknownFields { @@ -812,11 +821,13 @@ func (d *decodeState) object(v reflect.Value) error { if d.opcode == scanSkipSpace { d.scanWhile(scanSkipSpace) } - // Reset errorContext to its original state. - // Keep the same underlying array for FieldStack, to reuse the - // space and avoid unnecessary allocs. - d.errorContext.FieldStack = d.errorContext.FieldStack[:len(origErrorContext.FieldStack)] - d.errorContext.Struct = origErrorContext.Struct + if d.errorContext != nil { + // Reset errorContext to its original state. + // Keep the same underlying array for FieldStack, to reuse the + // space and avoid unnecessary allocs. + d.errorContext.FieldStack = d.errorContext.FieldStack[:len(origErrorContext.FieldStack)] + d.errorContext.Struct = origErrorContext.Struct + } if d.opcode == scanEndObject { break } |