Paramaterize max idle connections

Replaces maxIdleConnsPerAddr with DefaultMaxIdleConns, and adds a
paramter to Client, MaxIdleConns.

memcache/memcache.go

@@ -64,14 +64,17 @@ var (
 	ErrNoServers = errors.New("memcache: no servers configured or available")
 )
 
-// DefaultTimeout is the default socket read/write timeout.
-const DefaultTimeout = 100 * time.Millisecond
-
 const (
-	buffered            = 8 // arbitrary buffered channel size, for readability
-	maxIdleConnsPerAddr = 2 // TODO(bradfitz): make this configurable?
+	// DefaultTimeout is the default socket read/write timeout.
+	DefaultTimeout = 100 * time.Millisecond
+
+	// DefaultMaxIdleConns is the default maximum number of idle connections
+	// kept for any single address.
+	DefaultMaxIdleConns = 2
 )
 
+const buffered = 8 // arbitrary buffered channel size, for readability
+
 // resumableError returns true if err is only a protocol-level cache error.
 // This is used to determine whether or not a server connection should
 // be re-used or not. If an error occurs, by default we don't reuse the
@@ -133,6 +136,14 @@ type Client struct {
 	// If zero, DefaultTimeout is used.
 	Timeout time.Duration
 
+	// MaxIdleConns specifies the maximum number of idle connections that will
+	// be maintained per address. If less than one, DefaultMaxIdleConns will be
+	// used.
+	//
+	// Consider your expected traffic rates and latency carefully. This should
+	// be set to a number higher than your peak parallel requests.
+	MaxIdleConns int
+
 	selector ServerSelector
 
 	lk       sync.Mutex
@@ -199,7 +210,7 @@ func (c *Client) putFreeConn(addr net.Addr, cn *conn) {
 		c.freeconn = make(map[string][]*conn)
 	}
 	freelist := c.freeconn[addr.String()]
-	if len(freelist) >= maxIdleConnsPerAddr {
+	if len(freelist) >= c.maxIdleConns() {
 		cn.nc.Close()
 		return
 	}
@@ -228,6 +239,13 @@ func (c *Client) netTimeout() time.Duration {
 	return DefaultTimeout
 }
 
+func (c *Client) maxIdleConns() int {
+	if c.MaxIdleConns > 0 {
+		return c.MaxIdleConns
+	}
+	return DefaultMaxIdleConns
+}
+
 // ConnectTimeoutError is the error type used when it takes
 // too long to connect to the desired host. This level of
 // detail can generally be ignored.