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go/types: fix race-y initialization of Struct.offsets

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Use sync.Once to ensure, that 'offsets' field is initialized
once only in a threadsafe way.

Fixes #12887

Change-Id: I90ef929c421ccd3094339c67a39b02d8f2e47211
Reviewed-on: https://go-review.googlesource.com/16013
Reviewed-by: Robert Griesemer <gri@golang.org>
This commit is contained in:
Aleksandr Demakin 2015-10-20 23:05:50 +03:00 committed by Robert Griesemer
parent 5ff309f48d
commit a4cd0a49c7
2 changed files with 37 additions and 26 deletions
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48
src/go/types/sizes.go
View File

@ -132,13 +132,8 @@ func (s *StdSizes) Sizeof(T Type) int64 {
if n == 0 {
return 0
}
offsets := t.offsets
if t.offsets == nil {
// compute offsets on demand
offsets = s.Offsetsof(t.fields)
t.offsets = offsets
}
return offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
setOffsets(t, s)
return t.offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
case *Interface:
return s.WordSize * 2
}
@ -159,24 +154,27 @@ func (conf *Config) alignof(T Type) int64 {
}
func (conf *Config) offsetsof(T *Struct) []int64 {
offsets := T.offsets
if offsets == nil && T.NumFields() > 0 {
var offsets []int64
if T.NumFields() > 0 {
// compute offsets on demand
if s := conf.Sizes; s != nil {
offsets = s.Offsetsof(T.fields)
// sanity checks
if len(offsets) != T.NumFields() {
panic("Config.Sizes.Offsetsof returned the wrong number of offsets")
}
for _, o := range offsets {
if o < 0 {
panic("Config.Sizes.Offsetsof returned an offset < 0")
calculated := setOffsets(T, s)
offsets = T.offsets
if calculated {
// sanity checks
if len(offsets) != T.NumFields() {
panic("Config.Sizes.Offsetsof returned the wrong number of offsets")
}
for _, o := range offsets {
if o < 0 {
panic("Config.Sizes.Offsetsof returned an offset < 0")
}
}
}
} else {
offsets = stdSizes.Offsetsof(T.fields)
setOffsets(T, &stdSizes)
offsets = T.offsets
}
T.offsets = offsets
}
return offsets
}
@ -209,3 +207,15 @@ func align(x, a int64) int64 {
y := x + a - 1
return y - y%a
}
// setOffsets sets the offsets of s for the given sizes if necessary.
// The result is true if the offsets were not set before; otherwise it
// is false.
func setOffsets(s *Struct, sizes Sizes) bool {
var calculated bool
s.offsetsOnce.Do(func() {
calculated = true
s.offsets = sizes.Offsetsof(s.fields)
})
return calculated
}

15
src/go/types/type.go
View File

@ -4,9 +4,10 @@
package types
import "sort"
// TODO(gri) Revisit factory functions - make sure they have all relevant parameters.
import (
"sort"
"sync"
)
// A Type represents a type of Go.
// All types implement the Type interface.
@ -120,10 +121,10 @@ func (s *Slice) Elem() Type { return s.elem }
// A Struct represents a struct type.
type Struct struct {
fields []*Var
tags []string // field tags; nil if there are no tags
// TODO(gri) access to offsets is not threadsafe - fix this
offsets []int64 // field offsets in bytes, lazily initialized
fields []*Var
tags []string // field tags; nil if there are no tags
offsets []int64 // field offsets in bytes, lazily initialized
offsetsOnce sync.Once // for threadsafe lazy initialization of offsets
}
// NewStruct returns a new struct with the given fields and corresponding field tags.