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go/internal/gcimporter: don't waste CPU copying bytes in io.ReadAll

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`io.ReadAll` dynamically reallocates byte slice because it doesn't know
its size in advance. We don't need to read an entire file into memory
and therefore may use `bufio.Reader` to read its contents.

Fixes #46564

Change-Id: Id504b1512662b6dea4775d523455896fa4162ab3
Reviewed-on: https://go-review.googlesource.com/c/go/+/325429
Reviewed-by: Dominik Honnef <dominik@honnef.co>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Trust: Matthew Dempsky <mdempsky@google.com>
Trust: Dominik Honnef <dominik@honnef.co>
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
This commit is contained in:
Sergey Zagursky 2021-06-04 12:25:51 +03:00 committed by Matthew Dempsky
parent 9d669ed47a
commit e3cb381704
2 changed files with 15 additions and 17 deletions
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11
src/go/internal/gcimporter/gcimporter.go
View File

@ -145,17 +145,14 @@ func Import(fset *token.FileSet, packages map[string]*types.Package, path, srcDi
err = fmt.Errorf("import %q: old textual export format no longer supported (recompile library)", path)
case "$$B\n":
var data []byte
data, err = io.ReadAll(buf)
if err != nil {
break
}
var exportFormat byte
exportFormat, err = buf.ReadByte()
// The indexed export format starts with an 'i'; the older
// binary export format starts with a 'c', 'd', or 'v'
// (from "version"). Select appropriate importer.
if len(data) > 0 && data[0] == 'i' {
_, pkg, err = iImportData(fset, packages, data[1:], id)
if err == nil && exportFormat == 'i' {
pkg, err = iImportData(fset, packages, buf, id)
} else {
err = fmt.Errorf("import %q: old binary export format no longer supported (recompile library)", path)
}

21
src/go/internal/gcimporter/iimport.go
View File

@ -8,6 +8,7 @@
package gcimporter
import (
"bufio"
"bytes"
"encoding/binary"
"fmt"
@ -20,7 +21,7 @@ import (
)
type intReader struct {
*bytes.Reader
*bufio.Reader
path string
}
@ -61,7 +62,7 @@ const (
// and returns the number of bytes consumed and a reference to the package.
// If the export data version is not recognized or the format is otherwise
// compromised, an error is returned.
func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []byte, path string) (_ int, pkg *types.Package, err error) {
func iImportData(fset *token.FileSet, imports map[string]*types.Package, dataReader *bufio.Reader, path string) (pkg *types.Package, err error) {
const currentVersion = 1
version := int64(-1)
defer func() {
@ -74,7 +75,7 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
}
}()
r := &intReader{bytes.NewReader(data), path}
r := &intReader{dataReader, path}
version = int64(r.uint64())
switch version {
@ -86,10 +87,12 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
sLen := int64(r.uint64())
dLen := int64(r.uint64())
whence, _ := r.Seek(0, io.SeekCurrent)
stringData := data[whence : whence+sLen]
declData := data[whence+sLen : whence+sLen+dLen]
r.Seek(sLen+dLen, io.SeekCurrent)
data := make([]byte, sLen+dLen)
if _, err := io.ReadFull(r, data); err != nil {
errorf("cannot read %d bytes of stringData and declData: %s", len(data), err)
}
stringData := data[:sLen]
declData := data[sLen:]
p := iimporter{
ipath: path,
@ -165,9 +168,7 @@ func iImportData(fset *token.FileSet, imports map[string]*types.Package, data []
// package was imported completely and without errors
localpkg.MarkComplete()
consumed, _ := r.Seek(0, io.SeekCurrent)
return int(consumed), localpkg, nil
return localpkg, nil
}
type iimporter struct {