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bytes: don't compact Buffer so aggressively

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benchmark                           old ns/op    new ns/op    delta
BenchmarkBufferNotEmptyWriteRead       848416       819983   -3.35%

Update #5154

R=golang-dev, gri, robryk
CC=golang-dev
https://golang.org/cl/8173043
This commit is contained in:
Brad Fitzpatrick 2013-03-29 13:49:14 -07:00
parent 994f59666f
commit 43e38d5def
2 changed files with 9 additions and 5 deletions
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8
src/pkg/bytes/buffer.go
View File

@ -87,9 +87,11 @@ func (b *Buffer) grow(n int) int {
var buf []byte
if b.buf == nil && n <= len(b.bootstrap) {
buf = b.bootstrap[0:]
} else if m+n <= cap(b.buf) {
// We can slide things down instead of
// allocating a new slice.
} else if m+n <= cap(b.buf)/2 {
// We can slide things down instead of allocating a new
// slice. We only need m+n <= cap(b.buf) to slide, but
// we instead let capacity get twice as large so we
// don't spend all our time copying.
copy(b.buf[:], b.buf[b.off:])
buf = b.buf[:m]
} else {

6
src/pkg/bytes/buffer_test.go
View File

@ -490,8 +490,10 @@ func TestBufferGrowth(t *testing.T) {
}
}
cap1 := b.Cap()
if cap1 > cap0 {
t.Errorf("buffer cap = %d; too big", cap1)
// (*Buffer).grow allows for 2x capacity slop before sliding,
// so set our error threshold at 3x.
if cap1 > cap0*3 {
t.Errorf("buffer cap = %d; too big (grew from %d)", cap1, cap0)
}
}