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archive/tar: reuse temporary buffer in writeHeader

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A temporary 512 bytes buffer is allocated for every call to
writeHeader. This buffer could be reused the lower the number
of memory allocations.

benchmark                   old ns/op     new ns/op     delta
BenchmarkWriteFiles100k     634622051     583810847     -8.01%

benchmark                   old allocs     new allocs     delta
BenchmarkWriteFiles100k     2701920        2602621        -3.68%

benchmark                   old bytes     new bytes     delta
BenchmarkWriteFiles100k     115383884     64349922      -44.23%

This change is very important if your code has to write a lot of
tarballs with a lot of files.

LGTM=dsymonds
R=golang-codereviews, dave, dsymonds
CC=golang-codereviews
https://golang.org/cl/107440043
This commit is contained in:
Cristian Staretu 2014-07-03 09:40:53 +10:00 committed by David Symonds
parent 372f399e00
commit fe5a358aae
1 changed files with 5 additions and 3 deletions
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8
src/pkg/archive/tar/writer.go
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@ -37,8 +37,9 @@ type Writer struct {
nb int64 // number of unwritten bytes for current file entry
pad int64 // amount of padding to write after current file entry
closed bool
usedBinary bool // whether the binary numeric field extension was used
preferPax bool // use pax header instead of binary numeric header
usedBinary bool // whether the binary numeric field extension was used
preferPax bool // use pax header instead of binary numeric header
hdrBuff [blockSize]byte // buffer to use in writeHeader
}
// NewWriter creates a new Writer writing to w.
@ -160,7 +161,8 @@ func (tw *Writer) writeHeader(hdr *Header, allowPax bool) error {
// subsecond time resolution, but for now let's just capture
// too long fields or non ascii characters
header := make([]byte, blockSize)
header := tw.hdrBuff[:]
copy(header, zeroBlock)
s := slicer(header)
// keep a reference to the filename to allow to overwrite it later if we detect that we can use ustar longnames instead of pax