// 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 "golang.org/x/net/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{ Listener: l, sem: make(chan struct{}, n), done: make(chan struct{}), } } type limitListener struct { net.Listener sem chan struct{} closeOnce sync.Once // ensures the done chan is only closed once done chan struct{} // no values sent; closed when Close is called } // acquire acquires the limiting semaphore. Returns true if successfully // accquired, false if the listener is closed and the semaphore is not // acquired. func (l *limitListener) acquire() bool { select { case <-l.done: return false case l.sem <- struct{}{}: return true } } func (l *limitListener) release() { <-l.sem } func (l *limitListener) Accept() (net.Conn, error) { acquired := l.acquire() // If the semaphore isn't acquired because the listener was closed, expect // that this call to accept won't block, but immediately return an error. c, err := l.Listener.Accept() if err != nil { if acquired { l.release() } return nil, err } return &limitListenerConn{Conn: c, release: l.release}, nil } func (l *limitListener) Close() error { err := l.Listener.Close() l.closeOnce.Do(func() { close(l.done) }) return err } 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 }