*: use limitedListener from golang

Godeps/Godeps.json

@@ -123,6 +123,10 @@
 			"ImportPath": "golang.org/x/net/context",
 			"Rev": "7dbad50ab5b31073856416cdcfeb2796d682f844"
 		},
+		{
+			"ImportPath": "golang.org/x/net/netutil",
+			"Rev": "7dbad50ab5b31073856416cdcfeb2796d682f844"
+		},
 		{
 			"ImportPath": "golang.org/x/oauth2",
 			"Rev": "3046bc76d6dfd7d3707f6640f85e42d9c4050f50"

Godeps/_workspace/src/golang.org/x/net/netutil/listen.go

@@ -0,0 +1,48 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package netutil provides network utility functions, complementing the more
+// common ones in the net package.
+package netutil
+
+import (
+	"net"
+	"sync"
+)
+
+// LimitListener returns a Listener that accepts at most n simultaneous
+// connections from the provided Listener.
+func LimitListener(l net.Listener, n int) net.Listener {
+	return &limitListener{l, make(chan struct{}, n)}
+}
+
+type limitListener struct {
+	net.Listener
+	sem chan struct{}
+}
+
+func (l *limitListener) acquire() { l.sem <- struct{}{} }
+func (l *limitListener) release() { <-l.sem }
+
+func (l *limitListener) Accept() (net.Conn, error) {
+	l.acquire()
+	c, err := l.Listener.Accept()
+	if err != nil {
+		l.release()
+		return nil, err
+	}
+	return &limitListenerConn{Conn: c, release: l.release}, nil
+}
+
+type limitListenerConn struct {
+	net.Conn
+	releaseOnce sync.Once
+	release     func()
+}
+
+func (l *limitListenerConn) Close() error {
+	err := l.Conn.Close()
+	l.releaseOnce.Do(l.release)
+	return err
+}

Godeps/_workspace/src/golang.org/x/net/netutil/listen_test.go

@@ -0,0 +1,103 @@
+// Copyright 2013 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build go1.3
+
+// (We only run this test on Go 1.3 because the HTTP client timeout behavior
+// was bad in previous releases, causing occasional deadlocks.)
+
+package netutil
+
+import (
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net"
+	"net/http"
+	"sync"
+	"sync/atomic"
+	"testing"
+	"time"
+)
+
+func TestLimitListener(t *testing.T) {
+	const (
+		max = 5
+		num = 200
+	)
+
+	l, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("Listen: %v", err)
+	}
+	defer l.Close()
+	l = LimitListener(l, max)
+
+	var open int32
+	go http.Serve(l, http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		if n := atomic.AddInt32(&open, 1); n > max {
+			t.Errorf("%d open connections, want <= %d", n, max)
+		}
+		defer atomic.AddInt32(&open, -1)
+		time.Sleep(10 * time.Millisecond)
+		fmt.Fprint(w, "some body")
+	}))
+
+	var wg sync.WaitGroup
+	var failed int32
+	for i := 0; i < num; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			c := http.Client{Timeout: 3 * time.Second}
+			r, err := c.Get("http://" + l.Addr().String())
+			if err != nil {
+				t.Logf("Get: %v", err)
+				atomic.AddInt32(&failed, 1)
+				return
+			}
+			defer r.Body.Close()
+			io.Copy(ioutil.Discard, r.Body)
+		}()
+	}
+	wg.Wait()
+
+	// We expect some Gets to fail as the kernel's accept queue is filled,
+	// but most should succeed.
+	if failed >= num/2 {
+		t.Errorf("too many Gets failed: %v", failed)
+	}
+}
+
+type errorListener struct {
+	net.Listener
+}
+
+func (errorListener) Accept() (net.Conn, error) {
+	return nil, errFake
+}
+
+var errFake = errors.New("fake error from errorListener")
+
+// This used to hang.
+func TestLimitListenerError(t *testing.T) {
+	donec := make(chan bool, 1)
+	go func() {
+		const n = 2
+		ll := LimitListener(errorListener{}, n)
+		for i := 0; i < n+1; i++ {
+			_, err := ll.Accept()
+			if err != errFake {
+				t.Fatalf("Accept error = %v; want errFake", err)
+			}
+		}
+		donec <- true
+	}()
+	select {
+	case <-donec:
+	case <-time.After(5 * time.Second):
+		t.Fatal("timeout. deadlock?")
+	}
+}

etcdmain/etcd.go

@@ -31,6 +31,7 @@ import (
 	systemdutil "github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/go-systemd/util"
 	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/coreos/pkg/capnslog"
 	"github.com/coreos/etcd/Godeps/_workspace/src/github.com/prometheus/client_golang/prometheus"
+	"github.com/coreos/etcd/Godeps/_workspace/src/golang.org/x/net/netutil"
 	"github.com/coreos/etcd/Godeps/_workspace/src/google.golang.org/grpc"
 	"github.com/coreos/etcd/discovery"
 	"github.com/coreos/etcd/etcdserver"
@@ -227,7 +228,7 @@ func startEtcd(cfg *config) (<-chan struct{}, error) {
 			if fdLimit <= reservedInternalFDNum {
 				plog.Fatalf("file descriptor limit[%d] of etcd process is too low, and should be set higher than %d to ensure internal usage", fdLimit, reservedInternalFDNum)
 			}
-			l = &transport.LimitedConnListener{Listener: l, RuntimeFDLimit: fdLimit - reservedInternalFDNum}
+			l = netutil.LimitListener(l, int(fdLimit-reservedInternalFDNum))
 		}
 
 		urlStr := u.String()