fmt: use sync.Pool

Update #4720

R=golang-dev, iant
CC=golang-dev
https://golang.org/cl/43990043

src/pkg/fmt/print.go

@@ -124,45 +124,13 @@ type pp struct {
 	fmt        fmt
 }
 
-// A cache holds a set of reusable objects.
-// The slice is a stack (LIFO).
-// If more are needed, the cache creates them by calling new.
-type cache struct {
-	mu    sync.Mutex
-	saved []interface{}
-	new   func() interface{}
+var ppFree = sync.Pool{
+	New: func() interface{} { return new(pp) },
 }
 
-func (c *cache) put(x interface{}) {
-	c.mu.Lock()
-	if len(c.saved) < cap(c.saved) {
-		c.saved = append(c.saved, x)
-	}
-	c.mu.Unlock()
-}
-
-func (c *cache) get() interface{} {
-	c.mu.Lock()
-	n := len(c.saved)
-	if n == 0 {
-		c.mu.Unlock()
-		return c.new()
-	}
-	x := c.saved[n-1]
-	c.saved = c.saved[0 : n-1]
-	c.mu.Unlock()
-	return x
-}
-
-func newCache(f func() interface{}) *cache {
-	return &cache{saved: make([]interface{}, 0, 100), new: f}
-}
-
-var ppFree = newCache(func() interface{} { return new(pp) })
-
 // newPrinter allocates a new pp struct or grab a cached one.
 func newPrinter() *pp {
-	p := ppFree.get().(*pp)
+	p := ppFree.Get().(*pp)
 	p.panicking = false
 	p.erroring = false
 	p.fmt.init(&p.buf)
@@ -178,7 +146,7 @@ func (p *pp) free() {
 	p.buf = p.buf[:0]
 	p.arg = nil
 	p.value = reflect.Value{}
-	ppFree.put(p)
+	ppFree.Put(p)
 }
 
 func (p *pp) Width() (wid int, ok bool) { return p.fmt.wid, p.fmt.widPresent }

src/pkg/fmt/scan.go

@@ -11,6 +11,7 @@ import (
 	"os"
 	"reflect"
 	"strconv"
+	"sync"
 	"unicode/utf8"
 )
 
@@ -380,7 +381,9 @@ func (r *readRune) ReadRune() (rr rune, size int, err error) {
 	return
 }
 
-var ssFree = newCache(func() interface{} { return new(ss) })
+var ssFree = sync.Pool{
+	New: func() interface{} { return new(ss) },
+}
 
 // newScanState allocates a new ss struct or grab a cached one.
 func newScanState(r io.Reader, nlIsSpace, nlIsEnd bool) (s *ss, old ssave) {
@@ -395,7 +398,7 @@ func newScanState(r io.Reader, nlIsSpace, nlIsEnd bool) (s *ss, old ssave) {
 		return
 	}
 
-	s = ssFree.get().(*ss)
+	s = ssFree.Get().(*ss)
 	if rr, ok := r.(io.RuneReader); ok {
 		s.rr = rr
 	} else {
@@ -427,7 +430,7 @@ func (s *ss) free(old ssave) {
 	}
 	s.buf = s.buf[:0]
 	s.rr = nil
-	ssFree.put(s)
+	ssFree.Put(s)
 }
 
 // skipSpace skips spaces and maybe newlines.