blob: 3b94cf0c6a8b1bb56666dfffff19620aa7cd2bf7 [file] [log] [blame]
sslobodrd046be82019-01-16 10:02:22 -05001// Copyright 2014 Google Inc. All rights reserved.
2// Use of this source code is governed by the Apache 2.0
3// license that can be found in the LICENSE file.
4
5package internal
6
7// This file implements a network dialer that limits the number of concurrent connections.
8// It is only used for API calls.
9
10import (
11 "log"
12 "net"
13 "runtime"
14 "sync"
15 "time"
16)
17
18var limitSem = make(chan int, 100) // TODO(dsymonds): Use environment variable.
19
20func limitRelease() {
21 // non-blocking
22 select {
23 case <-limitSem:
24 default:
25 // This should not normally happen.
26 log.Print("appengine: unbalanced limitSem release!")
27 }
28}
29
30func limitDial(network, addr string) (net.Conn, error) {
31 limitSem <- 1
32
33 // Dial with a timeout in case the API host is MIA.
34 // The connection should normally be very fast.
35 conn, err := net.DialTimeout(network, addr, 500*time.Millisecond)
36 if err != nil {
37 limitRelease()
38 return nil, err
39 }
40 lc := &limitConn{Conn: conn}
41 runtime.SetFinalizer(lc, (*limitConn).Close) // shouldn't usually be required
42 return lc, nil
43}
44
45type limitConn struct {
46 close sync.Once
47 net.Conn
48}
49
50func (lc *limitConn) Close() error {
51 defer lc.close.Do(func() {
52 limitRelease()
53 runtime.SetFinalizer(lc, nil)
54 })
55 return lc.Conn.Close()
56}