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Re: Strange Socket problem

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On Fri, 02 Mar 2012 17:18:04 -0800, Knute Johnson wrote:

> On 3/2/2012 4:00 PM, Lew wrote:
>> Knute Johnson wrote:
>>> The volatiles exist because the methods that access them can be called
>>> from other threads. I could have synchronized the start() stop()
>>> methods but not easily the socket variable in the run() method. I
>>> thought it was cleaner to just use volatile.
>>
>> I see a problem right there.
>>
>>> public void disconnect() {
>>> if (isConnected())
>>> if (socket != null)
>>> try {
>>> socket.close();
>>> } catch (IOException ioe) {
>>> ioe.printStackTrace();
>>> }
>>> }
>>
>> Since these are controlled by separate synchronization (different
>> 'volatile' variables) there's a race condition trying to work with both
>> at once.
> 
> I don't think so.
> 
>> Also, 'socket' can become 'null' between the check for not 'null' and
>> the 'close()' call.
> 
> Only if I set it to null and I don't.  That is there so that if the
> Socket doesn't make the first connection when disconnect() is called
> that I won't get a NPE.
> 
>> You need to synchronize with 'synchronized' or other strong mechanism.
> 
> I don't think so and here's why; isConnected only gets modified by one
> thread and read by another, socket is only modified by one thread and
> read by another.  In the disconnect() method, as soon as isConnected()
> is called, isConnected the volatile variable is read and that would make
> socket current even if it weren't volatile which it is but I didn't want
> to rely on side effects in case I changed code somewhere.
> 
> Anyway, disconnect() isn't getting called in this situation so it's not
> causing my problem.
> 
> I really appreciate everybody looking at this.  I've got a couple of
> ideas of where to code some traps and I'll have to put those in one
> night and see what happens.

new Socket() can return null (it says, but not why) but I don't think 
that is happening or you'd have seen an NPE.
 

-- 
martin@   | Martin Gregorie
gregorie. | Essex, UK
org       |

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Thread

Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 11:49 -0800
  Re: Strange Socket problem Steven Simpson <ss@domain.invalid> - 2012-03-01 20:59 +0000
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 13:30 -0800
      Re: Strange Socket problem Steven Simpson <ss@domain.invalid> - 2012-03-01 22:54 +0000
        Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 16:32 -0800
          Re: Strange Socket problem Steven Simpson <ss@domain.invalid> - 2012-03-03 09:08 +0000
            Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 17:48 -0800
  Re: Strange Socket problem markspace <-@.> - 2012-03-01 14:08 -0800
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 16:48 -0800
      Re: Strange Socket problem markspace <-@.> - 2012-03-02 08:33 -0800
        Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-02 15:29 -0800
          Re: Strange Socket problem markspace <-@.> - 2012-03-03 09:33 -0800
            Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 17:55 -0800
              Re: Strange Socket problem markspace <-@.> - 2012-03-03 20:06 -0800
                Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 21:02 -0800
                Re: Strange Socket problem "John B. Matthews" <nospam@nospam.invalid> - 2012-03-05 00:00 -0500
                Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-05 09:44 -0800
  Re: Strange Socket problem Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-01 22:15 +0000
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 16:43 -0800
      Re: Strange Socket problem Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-03 02:01 +0000
  Reiteration: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-01 16:51 -0800
    Re: Reiteration: Strange Socket problem Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-03 02:02 +0000
  Re: Strange Socket problem x <x@x.x> - 2012-03-02 21:18 +0100
    Re: Strange Socket problem Lew <noone@lewscanon.com> - 2012-03-02 15:06 -0800
      Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-02 15:38 -0800
        Re: Strange Socket problem Lew <noone@lewscanon.com> - 2012-03-02 16:00 -0800
          Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-02 17:18 -0800
            Re: Strange Socket problem Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-03 02:13 +0000
              Re: Strange Socket problem Steven Simpson <ss@domain.invalid> - 2012-03-03 08:41 +0000
                Re: Strange Socket problem Martin Gregorie <martin@address-in-sig.invalid> - 2012-03-03 18:26 +0000
        Re: Strange Socket problem x <x@x.x> - 2012-03-03 11:32 +0100
          Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 17:59 -0800
          Re: Strange Socket problem Lew <noone@lewscanon.com> - 2012-03-03 23:21 -0800
      Re: Strange Socket problem x <x@x.x> - 2012-03-03 10:59 +0100
        Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 18:08 -0800
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-02 15:33 -0800
  Re: Strange Socket problem Paka Small <paka-en@tumia.org> - 2012-03-03 03:32 -0800
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 18:00 -0800
  Re: Strange Socket problem x <x@x.x> - 2012-03-03 12:45 +0100
    Re: Strange Socket problem Knute Johnson <nospam@knutejohnson.com> - 2012-03-03 18:02 -0800

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