[SNMP4J] BindException: Address already in use, even with reuseAddress=true (with proposed fix)

[Frank Fock]

Hello Thomas,
I will try find a solution. However, other users reported the deadlock occurring on some operating systems when the join was made. The problem is, that you cannot be sure that the worker thread is already at the io wait. 
But you are right, the socket close should anyway terminate the thread...

Best regards 
Frank

> Am 27.05.2015 um 07:31 schrieb Thomas L <zlika_ese at hotmail.com>:
> 
> Hello Frank,
> 
> Thank you for your answer.
> Setting a socket timeout is not something I would like to do, because you have the choice between using a small value and wasting CPU time, or setting a large value and waiting a long time for the close method to complete. I do not want either.
> My solution seems completly safe: just do a join at the end of DefaultUdpTransportMapping.close(), after the socket has been closed. The worker thread is then already terminating, I just want the close method to wait a few ms just to be sure that when we exit the close method it is safe to immediatly try to rebind on the same port. I do not see any possible deadlock here.
> 
> Regards,
> Thomas
> 
>> Le 27 mai 2015 à 00:07, Frank Fock <fock at agentpp.com> a écrit :
>> 
>> Hi Thomas,
>> 
>> If you set the socket timeout to a value >0 (which is recommended), then
>> the worker thread is joined on the close().
>> If the timeout is 0, no join is performed because otherwise a deadlock would occur
>> if the interrupt call is triggered by the close() method while the worker thread
>> is not in the select method (i.e., waiting on IO).
>> 
>> Thus, I would not change the existing code.
>> 
>> Best regards,
>> Frank
>> 
>>> Am 26.05.2015 um 22:13 schrieb Thomas L:
>>> Hello,
>>> 
>>> I think I have found a bug in SNMP4J (2.3.3) where we can have a "BindException: Address already in use" exception when creating a DefaultUdpTransportMapping, whereas reuseAddress=true, if we have previously created and closed a similar DefaultUdpTransportMapping.
>>> In DefaultUdpTransportMapping.close(), the listener thread (WorkerTask) is not "joined", so it can still use the UDP port for some time, and creating a new DefaultUdpTransportMapping on the same port, even if reuseAddress=true, is not possible.
>>> My current dirty workaround is to access the "WorkerTask" field by reflection just before closing the Snmp object, and then calling "join()" on the object, so I am sure the thread is correctly terminated before any new attempt to create a new DefaultUdpTransportMapping.
>>> 
>>> Can this problem be solved in the next version of SNM4J?
>>> 
>>> Regards,
>>> Thomas
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>> 
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