Re: Need some clarification and/or help with java NIO sockets

From: HDSkiFreak (user_at_inter.net2)
Date: 05/11/04 

Date: Tue, 11 May 2004 13:48:13 GMT

Thanks for the reply. I was hoping that I didn't have to do that,
although is pretty trivial to emulate.

I ran some tests using this approach, and it seems to have solved the
problem.

Thanks again,

HDSkiFreak

On Mon, 10 May 2004 23:55:10 +0100, "Yu SONG" <tips@mi6.gov.uk> wrote:

>"HDSkiFreak" <user@inter.net2>
>> Greetings:
>>
>> I'm having a bit of a problem with java NIO sockets. I've tried
>> searching around for a similar problem, but I haven't found much.
>>
>> I' using the 1.4.2 JDK under Linux RH 9. I'm working on an application
>> that needs to establish a TCP connection asyncrhonously, so I cannot
>> block while the connection is being established. I also need to assign
>> a limit (connection timeout) to the operation, and retry if needed.
>>
>> All communication with the tcp mulde is async, so I thought of using
>> NIO non-blocking (NB) sockets and select().
>>
>> Here's basically the gist of it:
>>
>> I decide to do the following:
>>
>> long timeout = 1000;
>> InetAddress addr = new InetSocketAddress("127.0.0.1", 1026);
>> SocketChannel sc = SocketChannel.open();
>> sc.socket().connect(addr, timeout);
>>
>> Then use the channel as prescribed:
>>
>> ByteBuffer buf = ByteBuffer.allocate(1024);
>> sc.write(buf);
>>
>>
>> And close it as prescribed:
>>
>> sc.close();
>>
>>
>> With that in mind, If I encapsulate all those operation iside a worker
>> thread, I find that the socket handle is never released, I my app
>> leaks handles like crazy. Eventually, the VM runs out of handles, and
>> the whole thing comes crashing down fast.
>>
>> I tried calling close() on the socket (since I call connect on the
>> socket), like this:
>>
>> // Close operation
>> sc.socket().close();
>> sc.close();
>>
>> But this had no effect. The handles were still leaking.
>>
>>
>> Now, if I change the connect logic to use:
>>
>> sc.connect(addr)
>>
>> instead of:
>>
>> sc.socket().connect(addr, timeout);
>>
>> The application does not leak handles, and it works fine. Naturally, I
>> have now lost the (easy) ability if connecting with a timeout.
>>
>>
>> My question is: Is this a known problem? I understand that I can
>> simulate the "connect with a timeout" situation using a NB socket
>> channel coupled with a select() call, but I'm not sure that is the
>> best course of action.
>>
>> Your feedback is greatly appreciated.
>>
>> Best Regards,
>>
>> HDSkiFreak
>
>Yes, I experienced the same problem.
>
>I recommend you to use select() call or other customized timeout class for
>the timeout, and use methods in the channel class for NB connect and NB
>read&write.

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