time: Use AppendFormat in Marshal[Text|JSON]

The current implementations of MarshalJSON and MarshalText use
time.Format which returns a string (converted from a byte slice),
only to convert it back to a byte slice.

Avoid the conversion (and thus an allocation) by directly appending
the formatted time to a preallocated byte slice, using the new
AppendFormat function, introduced in golang.org/cl/1760.

This reduces the allocations done in Marshal[Text|JSON] by 50%.

benchmark                old ns/op     new ns/op     delta
BenchmarkMarshalJSON     626           507           -19.01%
BenchmarkMarshalText     598           511           -14.55%

benchmark                old allocs     new allocs     delta
BenchmarkMarshalJSON     2              1              -50.00%
BenchmarkMarshalText     2              1              -50.00%

benchmark                old bytes     new bytes     delta
BenchmarkMarshalJSON     96            48            -50.00%
BenchmarkMarshalText     96            48            -50.00%

Fixes #11025

Change-Id: I468f78d075a6ecc1cdc839df7fb407fbc6ff2e70
Reviewed-on: https://go-review.googlesource.com/10555
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/time/time.go b/src/time/time.go
index 294cc77f417e62986f4c004efc4327cb8f98b4be..c78c80c43b81682c8deacfc3b040d2ee8b4354b4 100644 (file)
--- a/src/time/time.go
+++ b/src/time/time.go
@@ -935,7 +935,12 @@ func (t Time) MarshalJSON() ([]byte, error) {
                // See golang.org/issue/4556#c15 for more discussion.
                return nil, errors.New("Time.MarshalJSON: year outside of range [0,9999]")
        }
-       return []byte(t.Format(`"` + RFC3339Nano + `"`)), nil
+
+       b := make([]byte, 0, len(RFC3339Nano)+2)
+       b = append(b, '"')
+       b = t.AppendFormat(b, RFC3339Nano)
+       b = append(b, '"')
+       return b, nil
 }
 
 // UnmarshalJSON implements the json.Unmarshaler interface.
@@ -952,7 +957,9 @@ func (t Time) MarshalText() ([]byte, error) {
        if y := t.Year(); y < 0 || y >= 10000 {
                return nil, errors.New("Time.MarshalText: year outside of range [0,9999]")
        }
-       return []byte(t.Format(RFC3339Nano)), nil
+
+       b := make([]byte, 0, len(RFC3339Nano))
+       return t.AppendFormat(b, RFC3339Nano), nil
 }
 
 // UnmarshalText implements the encoding.TextUnmarshaler interface.

diff --git a/src/time/time_test.go b/src/time/time_test.go
index 2d16ea59ae3a9230a60b13d68b71d833c539ecd1..a925e98a838e2981e40d7ec3a8affc3b437c3c73 100644 (file)
--- a/src/time/time_test.go
+++ b/src/time/time_test.go
@@ -1060,6 +1060,20 @@ func BenchmarkFormatNow(b *testing.B) {
        }
 }
 
+func BenchmarkMarshalJSON(b *testing.B) {
+       t := Now()
+       for i := 0; i < b.N; i++ {
+               t.MarshalJSON()
+       }
+}
+
+func BenchmarkMarshalText(b *testing.B) {
+       t := Now()
+       for i := 0; i < b.N; i++ {
+               t.MarshalText()
+       }
+}
+
 func BenchmarkParse(b *testing.B) {
        for i := 0; i < b.N; i++ {
                Parse(ANSIC, "Mon Jan  2 15:04:05 2006")