GC closes my ServerSocket

[Neil Richards]

On Wed, 2012-06-13 at 17:23 +0800, Weijun Wang wrote:
> Please anyone take a review:
> 
>     http://cr.openjdk.java.net/~weijun/7176574/webrev.00/
> 
> By assigning to a local variable hopefully it stays alive on the stack 
> during the whole method.
> 
> Noreg-self.
> 
> *Chris*: I didn't indented the whole test by wrapping them into a 
> try-finally (or try-with-resources) block. The test runs in othervm and 
> I guess the sockets will be closed anyway.
> 
> Thanks
> Max
> 
> On 06/13/2012 05:08 PM, Chris Hegarty wrote:
> >
> >
> > On 13/06/2012 09:51, Alan Bateman wrote:
> >> On 13/06/2012 09:38, Weijun Wang wrote:
> >>> Hi All
> >>>
> >>> I have a test that basically looks like:
> >>>
> >>> int p = new ServerSocket(0).getLocalPort();
> >>> //....
> >>> new Socket("localhost", p);
> >>>
> >>> Recently it's failing on solaris-i586, and after some investigation, I
> >>> realize that the ServerSocket object is GC'ed and auto-closed.
> >>>
> >>> (But why only recently?)
> >>>
> >>> So I change the first line to
> >>>
> >>> ServerSocket ss = new ServerSocket(0);
> >>> int p = ss.getLocalPort();
> >>>
> >>> and it's running fine.
> >>>
> >>> I want to know if the ServerSocket object still has a chance to be
> >>> closed. If yes, I'll add a
> >>>
> >>> ss.close();
> >>>
> >>> at the end to be safer.
> >>>
> >>> Thanks
> >>> Max
> >> HotSpot changes I assume, perhaps changes to the reference processing or
> >> default heap settings.
> >
> > Right, I assume there was some VM change that started this test to fail
> > recently, but clearly this is a test issue. It was just passing all this
> > time by accident, and there is an inherent race between the test and the
> > GC/finalizer thread.
> >
> > You should fix the test as you suggested. Also close the serversocket in
> > a finally block ( or equivalent ). You should not rely on the finalizer
> > to close it out.
> >
> > -Chris.
> >
> >>
> >> -Alan

Would this be a good candidate to use Automatic Resource Management ?

i.e. instead of doing this:

        ServerSocket ss1 = null;
        ServerSocket ss2 = null;
        try {
                ss1 = new ServerSocket(0);
                ss2 = new ServerSocket(0);
                int p1 = ss1.getLocalPort();
                int p2 = ss1.getLocalPort();
                //...
        } finally {
                if (ss1 != null) ss1.close();
                if (ss2 != null) ss2.close();
        }

one would do this:

        try (ServerSocket ss1 = new ServerSocket(0);
                        ServerSocket ss2 = new ServerSocket(0)) {
                int p1 = ss1.getLocalPort();
                int p2 = ss1.getLocalPort();
                //...
        }

Regards,
Neil

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