RFR 8066708: JMXStartStopTest fails to connect to port 38112

[Dmitry Samersoff]

Jaroslav,

You can set SO_LINGER to zero, in this case socket will be closed
immediately without waiting in TIME_WAIT

But there are no reliable way to predict whether you can take this port
or not after you close it.

So the only valid solution is to try to connect to a random port and if
this attempt fails try another random port. Everything else will cause
more or less frequent intermittent failures.

-Dmitry


On 2014-12-11 17:06, Jaroslav Bachorik wrote:
> On 12/09/2014 01:25 PM, Jaroslav Bachorik wrote:
>> On 12/09/2014 01:39 AM, Stuart Marks wrote:
>>> On 12/8/14 12:35 PM, Jaroslav Bachorik wrote:
>>>> Please, review the following test change
>>>>
>>>> Issue : https://bugs.openjdk.java.net/browse/JDK-8066708
>>>> Webrev: http://cr.openjdk.java.net/~jbachorik/8066708/webrev.00
>>>>
>>>> The test fails very intermittently when RMI registry is trying to bind
>>>> to a port
>>>> previously used in the test (via ServerSocket).
>>>>
>>>> This seems to be caused by the sockets created via `new
>>>> ServerSocket(0)` and
>>>> being in reusable mode. The fix attempts to prevent this by explicitly
>>>> forbidding the reusable mode.
>>>
>>> Hi Jaroslav,
>>>
>>> I happened to see this fly by, and there are (I think) some similar
>>> issues going on in the RMI tests.
>>>
>>> But first I'll note that I don't think setReuseAddress() will have the
>>> effect that you want. Typically it's set to true before binding a
>>> socket, so that a subsequent bind operation will succeed even if the
>>> address/port is already in use. ServerSockets created with new
>>> ServerSocket(0) are already bound, and I'm not sure what calling
>>> setReuseAddress(false) will do on such sockets. The spec says behavior
>>> is undefined, but my bet is that it does nothing.
>>>
>>> I guess it doesn't hurt to try this out to see if it makes a difference,
>>> but I don't have much confidence it will help.
>>>
>>> The potential similarity to the RMI tests is exemplified by JDK-8049202
>>> (sorry, this bug report isn't open) but briefly this tests the RMI
>>> registry as follows:
>>>
>>> 1. Opens port 1099 using new ServerSocket(1099) [1099 is the default
>>>     RMI registry port] in order to ensure that 1099 isn't in use by
>>>     something else already;
>>>
>>> 2. If this succeeds, it immediately closes the ServerSocket.
>>>
>>> 3. Then it creates a new RMI registry on port 1099.
>>>
>>> In principle, this should succeed, yet it fails around 10% of the time
>>> on some systems. The error is "port already in use". My best theory is
>>> that even though the socket has just been closed by a user program, the
>>> kernel has to run the socket through some of the socket states such as
>>> FIN_WAIT_1, FIN_WAIT_2, or CLOSING before the socket is actually closed
>>> and is available for reuse. If a program -- even the same one --
>>> attempts to open a socket on the same port before the socket has reached
>>> its final state, it will get an "already in use error".
>>>
>>> If this is true I don't believe that setting SO_REUSEADDR will work if
>>> the socket is in one of these final states. (I remember reading this
>>> somewhere but I'm not sure where at the moment. I can try to dig it up
>>> if there is interest.)
>>>
>>> I admit this is just a theory and I'm open to alternatives, and I'm also
>>> open to hearing about ways to deal with this problem.
>>>
>>> Could something similar be going on with this JMX test?
>>
>> Hm, this is exactly what happened with this test :(
>>
>> The problem is that the port is reported as available while it is still
>> occupied and RMI registry attempts to start using that port.
>>
>> If setting SO_REUSEADDR does not work then the only solution would be to
>> retry the test case when this exception occurs.
> 
> Further investigation shows that the problem was rather the client
> connecting to a socket being shut down.
> 
> It sounds like setting SO_REUSEADDR to false should prevent this failure.
> 
> From the ServerSocket javadoc:
> "When a TCP connection is closed the connection may remain in a timeout
> state for a period of time after the connection is closed (typically
> known as the TIME_WAIT state or 2MSL wait state). For applications using
> a well known socket address or port it may not be possible to bind a
> socket to the required SocketAddress if there is a connection in the
> timeout state involving the socket address or port."
> 
> It also turns out that the test does not close the server sockets
> properly so there might be several sockets being opened or timed out
> dangling around.
> 
> I've updated the test so it is setting SO_REUSEADDR for all the new
> ServerSockets instances + introduced the mechanism to run the test code
> while properly cleaning up any allocated ports.
> 
> http://cr.openjdk.java.net/~jbachorik/8066708/webrev.01/
> 
> -JB-
> 
>>
>> -JB-
>>
>>>
>>> s'marks
>>
> 


-- 
Dmitry Samersoff
Oracle Java development team, Saint Petersburg, Russia
* I would love to change the world, but they won't give me the sources.