bytes.Buffer: export the Grow method
Allows a client to pre-allocate buffer space that is known to be necessary,
avoiding expensive reallocations.
R=gri, gri, adg
CC=golang-dev
https://golang.org/cl/6392061
diff --git a/src/pkg/bytes/buffer_test.go b/src/pkg/bytes/buffer_test.go
index d0af11f..c385be8 100644
--- a/src/pkg/bytes/buffer_test.go
+++ b/src/pkg/bytes/buffer_test.go
@@ -8,6 +8,7 @@
. "bytes"
"io"
"math/rand"
+ "runtime"
"testing"
"unicode/utf8"
)
@@ -374,6 +375,37 @@
}
}
+func TestGrow(t *testing.T) {
+ x := []byte{'x'}
+ y := []byte{'y'}
+ tmp := make([]byte, 72)
+ for _, startLen := range []int{0, 100, 1000, 10000, 100000} {
+ xBytes := Repeat(x, startLen)
+ for _, growLen := range []int{0, 100, 1000, 10000, 100000} {
+ buf := NewBuffer(xBytes)
+ // If we read, this affects buf.off, which is good to test.
+ readBytes, _ := buf.Read(tmp)
+ buf.Grow(growLen)
+ yBytes := Repeat(y, growLen)
+ // Check no allocation occurs in write, as long as we're single-threaded.
+ var m1, m2 runtime.MemStats
+ runtime.ReadMemStats(&m1)
+ buf.Write(yBytes)
+ runtime.ReadMemStats(&m2)
+ if runtime.GOMAXPROCS(-1) == 1 && m1.Mallocs != m2.Mallocs {
+ t.Errorf("allocation occurred during write")
+ }
+ // Check that buffer has correct data.
+ if !Equal(buf.Bytes()[0:startLen-readBytes], xBytes[readBytes:]) {
+ t.Errorf("bad initial data at %d %d", startLen, growLen)
+ }
+ if !Equal(buf.Bytes()[startLen-readBytes:startLen-readBytes+growLen], yBytes) {
+ t.Errorf("bad written data at %d %d", startLen, growLen)
+ }
+ }
+ }
+}
+
// Was a bug: used to give EOF reading empty slice at EOF.
func TestReadEmptyAtEOF(t *testing.T) {
b := new(Buffer)
