github.com/graybobo/golang.org-package-offline-cache@v0.0.0-20200626051047-6608995c132f/x/net/netutil/listen.go (about)

     1  // Copyright 2013 The Go Authors.  All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  // Package netutil provides network utility functions, complementing the more
     6  // common ones in the net package.
     7  package netutil // import "golang.org/x/net/netutil"
     8  
     9  import (
    10  	"net"
    11  	"sync"
    12  )
    13  
    14  // LimitListener returns a Listener that accepts at most n simultaneous
    15  // connections from the provided Listener.
    16  func LimitListener(l net.Listener, n int) net.Listener {
    17  	return &limitListener{l, make(chan struct{}, n)}
    18  }
    19  
    20  type limitListener struct {
    21  	net.Listener
    22  	sem chan struct{}
    23  }
    24  
    25  func (l *limitListener) acquire() { l.sem <- struct{}{} }
    26  func (l *limitListener) release() { <-l.sem }
    27  
    28  func (l *limitListener) Accept() (net.Conn, error) {
    29  	l.acquire()
    30  	c, err := l.Listener.Accept()
    31  	if err != nil {
    32  		l.release()
    33  		return nil, err
    34  	}
    35  	return &limitListenerConn{Conn: c, release: l.release}, nil
    36  }
    37  
    38  type limitListenerConn struct {
    39  	net.Conn
    40  	releaseOnce sync.Once
    41  	release     func()
    42  }
    43  
    44  func (l *limitListenerConn) Close() error {
    45  	err := l.Conn.Close()
    46  	l.releaseOnce.Do(l.release)
    47  	return err
    48  }