text: // 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{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
  }
  