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Revert "encoding/json: reduce unmarshal mallocs for unmapped fields"

This reverts commit df68afd (https://golang.org/cl/33276)

Reason for revert: made other benchmarks worse

Fixes #20693 (details)
Updates #17914
Updates #10335

Change-Id: If451b620803ccb0536b89c76c4353d2185d57d7e
Reviewed-on: https://go-review.googlesource.com/47211
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>
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bradfitz committed Jun 29, 2017
1 parent 68e1b3e commit 912bb817b08669acf99d0c2a665acf69558d93a6
Showing with 34 additions and 28 deletions.
  1. +34 −28 src/encoding/json/decode.go
@@ -361,40 +361,47 @@ func (d *decodeState) scanWhile(op int) int {
return newOp
}
// discardObject and discardArray are dummy data targets
// used by the (*decodeState).value method, which
// accepts a zero reflect.Value to discard a value.
// The (*decodeState).object and (*decodeState).array methods,
// however, require a valid reflect.Value destination.
// These are the target values used when the caller of value
// wants to skip a field.
//
// Because these values refer to zero-sized objects
// and thus can't be mutated, they're safe for concurrent use
// by different goroutines unmarshalling skipped fields.
var (
discardObject = reflect.ValueOf(struct{}{})
discardArray = reflect.ValueOf([0]interface{}{})
)
// value decodes a JSON value from d.data[d.off:] into the value.
// It updates d.off to point past the decoded value. If v is
// invalid, the JSON value is discarded.
// it updates d.off to point past the decoded value.
func (d *decodeState) value(v reflect.Value) {
if !v.IsValid() {
_, rest, err := nextValue(d.data[d.off:], &d.nextscan)
if err != nil {
d.error(err)
}
d.off = len(d.data) - len(rest)
// d.scan thinks we're still at the beginning of the item.
// Feed in an empty string - the shortest, simplest value -
// so that it knows we got to the end of the value.
if d.scan.redo {
// rewind.
d.scan.redo = false
d.scan.step = stateBeginValue
}
d.scan.step(&d.scan, '"')
d.scan.step(&d.scan, '"')
n := len(d.scan.parseState)
if n > 0 && d.scan.parseState[n-1] == parseObjectKey {
// d.scan thinks we just read an object key; finish the object
d.scan.step(&d.scan, ':')
d.scan.step(&d.scan, '"')
d.scan.step(&d.scan, '"')
d.scan.step(&d.scan, '}')
}
return
}
switch op := d.scanWhile(scanSkipSpace); op {
default:
d.error(errPhase)
case scanBeginArray:
if !v.IsValid() {
v = discardArray
}
d.array(v)
case scanBeginObject:
if !v.IsValid() {
v = discardObject
}
d.object(v)
case scanBeginLiteral:
@@ -512,7 +519,8 @@ func (d *decodeState) array(v reflect.Value) {
d.off--
d.next()
return
case reflect.Array, reflect.Slice:
case reflect.Array:
case reflect.Slice:
break
}
@@ -791,9 +799,7 @@ func (d *decodeState) literal(v reflect.Value) {
d.off--
d.scan.undo(op)
if v.IsValid() {
d.literalStore(d.data[start:d.off], v, false)
}
d.literalStore(d.data[start:d.off], v, false)
}
// convertNumber converts the number literal s to a float64 or a Number

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