final attempt

on par with 1K sized object, but no so good with large ones

the default http flow control is better than current implementation.

weed/operation/grpc_client.go

@@ -7,6 +7,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"time"
 
 	"google.golang.org/grpc"
 
@@ -17,7 +18,7 @@ import (
 )
 
 var (
-	connectionPool     = make(map[string]*sync.Pool)
+	connectionPool     = make(map[string]*util.ResourcePool)
 	connectionPoolLock sync.Mutex
 )
 
@@ -53,41 +54,49 @@ func WithVolumeServerTcpConnection(volumeServer string, fn func(conn net.Conn) e
 		return err
 	}
 
-	conn := getConnection(tcpAddress)
+	conn, err := getConnection(tcpAddress)
+	if err != nil {
+		return err
+	}
 	defer releaseConnection(conn, tcpAddress)
 
 	err = fn(conn)
 	return err
 }
 
-func getConnection(tcpAddress string) net.Conn {
+func getConnection(tcpAddress string) (net.Conn, error) {
 	connectionPoolLock.Lock()
 	defer connectionPoolLock.Unlock()
 
 	pool, found := connectionPool[tcpAddress]
 	if !found {
 		println("creating pool for", tcpAddress)
-		pool = &sync.Pool{New: func() interface{} {
+
 		raddr, err := net.ResolveTCPAddr("tcp", tcpAddress)
 		if err != nil {
 			glog.Fatal(err)
 		}
 
+		pool = util.NewResourcePool(16, func() (interface{}, error) {
+
 			conn, err := net.DialTCP("tcp", nil, raddr)
 			if err != nil {
-				glog.Errorf("failed to connect to %s: %v", tcpAddress, err)
-				return conn
+				return conn, err
 			}
 			conn.SetKeepAlive(true)
 			conn.SetNoDelay(true)
 			println("connected", tcpAddress, "=>", conn.LocalAddr().String())
-			return conn
-		}}
+			return conn, nil
+		})
 		connectionPool[tcpAddress] = pool
 	}
-	conn := pool.Get().(net.Conn)
+
+	connObj, err := pool.Get(time.Minute)
+	if err != nil {
+		return nil, err
+	}
 	// println("get connection", tcpAddress, "=>", conn.LocalAddr().String())
-	return conn
+	return connObj.(net.Conn), nil
 }
 
 func releaseConnection(conn net.Conn, tcpAddress string) {
@@ -99,7 +108,7 @@ func releaseConnection(conn net.Conn, tcpAddress string) {
 		println("can not return connection", tcpAddress, "=>", conn.LocalAddr().String())
 		return
 	}
-	pool.Put(conn)
+	pool.Release(conn)
 	// println("returned connection", tcpAddress, "=>", conn.LocalAddr().String())
 }
 

weed/util/pool.go

@@ -0,0 +1,98 @@
+package util
+
+import (
+	"errors"
+	"sync"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+var (
+	TimeoutErr = errors.New("timeout")
+)
+
+// A bufferedChan implemented by a buffered channel
+type ResourcePool struct {
+	sync.Mutex
+	bufferedChan  chan interface{}
+	poolSizeLimit int
+	inuse         int
+	newFn         func() (interface{}, error)
+}
+
+func NewResourcePool(poolSizeLimit int, newFn func() (interface{}, error)) *ResourcePool {
+	p := &ResourcePool{
+		poolSizeLimit: poolSizeLimit,
+		newFn:         newFn,
+		bufferedChan:  make(chan interface{}, poolSizeLimit),
+	}
+	return p
+}
+
+func (p *ResourcePool) Size() int {
+	p.Lock()
+	defer p.Unlock()
+	return len(p.bufferedChan) + p.inuse
+}
+
+func (p *ResourcePool) Free() int {
+	p.Lock()
+	defer p.Unlock()
+	return p.poolSizeLimit - p.inuse
+}
+
+func (p *ResourcePool) Get(timeout time.Duration) (interface{}, error) {
+	d, err := p.get(timeout)
+	if err != nil {
+		return nil, err
+	}
+	if d == nil && p.newFn != nil {
+		var err error
+		d, err = p.newFn()
+		if err != nil {
+			return nil, err
+		}
+	}
+	p.Lock()
+	defer p.Unlock()
+	p.inuse++
+	return d, nil
+}
+
+func (p *ResourcePool) Release(v interface{}) {
+
+	p.Lock()
+	defer p.Unlock()
+	if p.inuse == 0 {
+		glog.V(0).Infof("released too many times?")
+		return
+	}
+	p.bufferedChan <- v
+	p.inuse--
+}
+
+func (p *ResourcePool) get(timeout time.Duration) (interface{}, error) {
+
+	select {
+	case v := <-p.bufferedChan:
+		return v, nil
+	default:
+	}
+
+	if p.Free() > 0 {
+		d, err := p.newFn()
+		if err != nil {
+			return nil, err
+		}
+		return d, nil
+	}
+
+	// wait for an freed item
+	select {
+	case v := <-p.bufferedChan:
+		return v, nil
+	case <-time.After(timeout):
+	}
+	return nil, TimeoutErr
+}