英文:
What does UDPConn Close really do?
问题
如果UDP是一种无连接的协议，那么为什么UDPConn有一个Close方法？文档中说“Close关闭连接”，但UDP是无连接的。在UDPConn对象上调用Close方法是否是良好的实践？有什么好处吗？
http://golang.org/pkg/net/#UDPConn.Close
英文:
If UDP is a connectionless protocol, then why does UDPConn have a Close method? The documentation says "Close closes the connection", but UDP is connectionless. Is it good practice to call Close on a UDPConn object? Is there any benefit?
答案1
得分: 4
好的，以下是udpconn.Close方法的代码：
func (c *conn) Close() error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.Close()
}
Close方法关闭了c.fd，那么c.fd是什么呢？
type conn struct {
fd *netFD
}
ok是一个netFD网络文件描述符。让我们看一下Close方法。
func (fd *netFD) Close() error {
fd.pd.Lock() // needed for both fd.incref(true) and pollDesc.Evict
if !fd.fdmu.IncrefAndClose() {
fd.pd.Unlock()
return errClosing
}
// Unblock any I/O. Once it all unblocks and returns,
// so that it cannot be referring to fd.sysfd anymore,
// the final decref will close fd.sysfd. This should happen
// fairly quickly, since all the I/O is non-blocking, and any
// attempts to block in the pollDesc will return errClosing.
doWakeup := fd.pd.Evict()
fd.pd.Unlock()
fd.decref()
if doWakeup {
fd.pd.Wakeup()
}
return nil
}
注意到了所有的decref吗？
所以回答你的问题，是的，这是一个好的做法，否则网络文件描述符会在内存中悬空。
英文:
Good Question, let's see the code of udpconn.Close
http://golang.org/src/pkg/net/net.go?s=3725:3753#L124
func (c *conn) Close() error {
if !c.ok() {
return syscall.EINVAL
}
return c.fd.Close()
}
Closes c.fd but what is c.fd ?
type conn struct {
fd *netFD
}
ok is a netFD net File Descriptor. Let's look at the Close method.
func (fd *netFD) Close() error {
fd.pd.Lock() // needed for both fd.incref(true) and pollDesc.Evict
if !fd.fdmu.IncrefAndClose() {
fd.pd.Unlock()
return errClosing
}
// Unblock any I/O. Once it all unblocks and returns,
// so that it cannot be referring to fd.sysfd anymore,
// the final decref will close fd.sysfd. This should happen
// fairly quickly, since all the I/O is non-blocking, and any
// attempts to block in the pollDesc will return errClosing.
doWakeup := fd.pd.Evict()
fd.pd.Unlock()
fd.decref()
if doWakeup {
fd.pd.Wakeup()
}
return nil
}
Notice all the decref
So to answer your question. Yes. Is good practice or you will leave hanging around in memory network file descriptors.
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