will GC close unused connection ?

[casp...@gmail.com]

Will GC close unused connection ?

In a particular case, I found that if there's a connection won't be used for a while, it will be closed. If I disable GC, then the connection will not be closed.

In the test, I never call the close function manually. But this is a bit hard to reproduce. 

GC will close unused tcp connection, is my assumption right?

[Jan Mercl]

On Thu, Feb 16, 2017 at 8:20 AM <casp...@gmail.com> wrote:

> Will GC close unused connection ?

No. At least not directly. A finalizer can possibly do that and finalizers are possibly invoked by the GC.

--

-j

[casp...@gmail.com]

Thanks for you reply!

Means yes, GC will close unused connection, just indirectly?  Cause I found this:

#/opt/go/src/net/fd_unix.go
func (fd *netFD) setAddr(laddr, raddr Addr) {

        fd.laddr = laddr

        fd.raddr = raddr

        runtime.SetFinalizer(fd, (*netFD).Close)

}

And this function is called by netFD.dial in sock_posix.go:148


在 2017年2月16日星期四 UTC+8下午3:31:07，Jan Mercl写道：

[Axel Wagner]

Yes, in general, the GC will usually close connections when the corresponding files are collected. But a) you can't really rely on that and b) the number of file descriptors that a program can open is very limited and for many programs, the rate at which they are opened is high enough, that they will pass that threshold, because the GC doesn't collect them quickly enough.

Given how limited file descriptors are, you thus should still take care to actually close all files you open yourself.

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[Konstantin Khomoutov]

On Thu, 16 Feb 2017 00:29:04 -0800 (PST)

casp...@gmail.com wrote:

> > > Will GC close unused connection ?
> >
> > No. At least not directly. A finalizer can possibly do that and
> > finalizers are possibly invoked by the GC.

[...]

> Means yes, GC will close unused connection, just indirectly?
> Cause I found this:
> #/opt/go/src/net/fd_unix.go
> func (fd *netFD) setAddr(laddr, raddr Addr) {
> fd.laddr = laddr
> fd.raddr = raddr
> runtime.SetFinalizer(fd, (*netFD).Close)
> }
>
> And this function is called by netFD.dial in sock_posix.go:148

It means "the runtime _may_ eventually close the connection after the
Go's value wrapping it was garbage-collected, but this is not
guaranteed to happend, and quite likely it will not happen".

Please read this recent thread [1] dealing with finalizers.

1. https://groups.google.com/d/topic/golang-nuts/d8aF4rAob7U/discussion

[casp...@gmail.com]

Many thanks!

Yes, I know that it is wrong to keep connection without call Close func. just when I working on a bug, I found the connection was closed automatically somehow.


在 2017年2月16日星期四 UTC+8下午4:33:54，Axel Wagner写道：

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[casp...@gmail.com]

Thanks! I'm going to read it carefully.

在 2017年2月16日星期四 UTC+8下午4:40:54，Konstantin Khomoutov写道：