[AGENT++] Agent++ Thread Safety

[Frank Fock]

Hi Megan,

Both version are correct depending on the
usage scenario:

If an existing object (i.e., row,table,leaf) is
about to be deleted, you need:

  mib->lock_mib();
  table->start_synch();
  ..some code modifying table content..
  table->end_synch();
  mib->unlock();

If you will only modify an object's content or
add a row, for example, then

  mib->lock_mib();
  table->start_synch();
  mib->unlock();
  ..some code modifying table content..
  table->end_synch();

is sufficient.

Best regards,
Frank

Megan Smith wrote:
> Hi Frank,
> 
> Thank you for your quick response.
> 
> In the documentation for mib->lock_mib() the mib lock is only held until the
> mib object lock is acquired:
> 
> "While processing a (sub-)request the locking scheme is as follows: 1. This
> MIB lock is acquired. 2. The MIB object is identified, which is responsible
> for processing the sub-request. 3. The MIB objects lock (
> MibEntry::start_synch()<http://www.agentpp.com/doc3.x/classThreadManager.html#42bcd26c71747a3d01afd2a407b7f12e>)
> is acquired. 4. The MIB lock is released. 5. The sub-request is propagated
> to the MIB object. 6. When finished, the MIB objects lock is released."
> 
> But the procedure you just suggested:
> 
> mib->lock_mib();
> table->start_synch();
> ..some code modifying table content..
> table->end_synch();
> mib->unlock();
> 
> doesn't unlock the mib itself until the last step.  Which one is correct?
> Or are they for different situations?
> 
> 
> Thanks!
> Megan
> 
> 
> On 5/20/08, Frank Fock <fock at agentpp.com> wrote:
>> Hi Megan,
>>
>> You are probably on the wrong track here. The AVL
>> trees should not be modified in the AGENT++ code
>> concurrently anywhere.
>>
>> Such modifications have to be protected by
>>
>> mib->lock_mib();
>> ..some code modifying mib registration (AVL tree)..
>> mib->unlock_mib();
>>
>> or
>>
>> mib->lock_mib();
>> table->start_synch();
>> ..some code modifying table content..
>> table->end_synch();
>> mib->unlock();
>>
>> Best regards,
>> Frank
>>
>> Megan Smith wrote:
>>
>>> Hi,
>>>
>>> I posted this a few weeks ago and haven't heard any response yet.  We are
>>> using agent++ and have been experiencing segmentation faults from some
>>> corrupted memory in the mib tables during highly multi-threaded runs.
>>>  After
>>> running debugging utilities it appears that there are some static
>>> variables
>>> in the avl_map.cpp file that I can't find proper locks for anywhere.  Am I
>>> missing something?
>>>
>>> Thank you for your help,
>>> Megan
>>> _______________________________________________
>>> AGENTPP mailing list
>>> AGENTPP at agentpp.org
>>> http://lists.agentpp.org/mailman/listinfo/agentpp
>>>
>> --
>> AGENT++
>> http://www.agentpp.com
>> http://www.mibexplorer.com
>> http://www.mibdesigner.com
>>
> _______________________________________________
> AGENTPP mailing list
> AGENTPP at agentpp.org
> http://lists.agentpp.org/mailman/listinfo/agentpp

-- 
AGENT++
http://www.agentpp.com
http://www.mibexplorer.com
http://www.mibdesigner.com