blob: 3b94cf0c6a8b1bb56666dfffff19620aa7cd2bf7 [file] [log] [blame]
// Copyright 2014 Google Inc. All rights reserved.
// Use of this source code is governed by the Apache 2.0
// license that can be found in the LICENSE file.
package internal
// This file implements a network dialer that limits the number of concurrent connections.
// It is only used for API calls.
import (
var limitSem = make(chan int, 100) // TODO(dsymonds): Use environment variable.
func limitRelease() {
// non-blocking
select {
case <-limitSem:
// This should not normally happen.
log.Print("appengine: unbalanced limitSem release!")
func limitDial(network, addr string) (net.Conn, error) {
limitSem <- 1
// Dial with a timeout in case the API host is MIA.
// The connection should normally be very fast.
conn, err := net.DialTimeout(network, addr, 500*time.Millisecond)
if err != nil {
return nil, err
lc := &limitConn{Conn: conn}
runtime.SetFinalizer(lc, (*limitConn).Close) // shouldn't usually be required
return lc, nil
type limitConn struct {
close sync.Once
func (lc *limitConn) Close() error {
defer lc.close.Do(func() {
runtime.SetFinalizer(lc, nil)
return lc.Conn.Close()