<core-libs-dev> sun.management.Agent: the properties.putAll API may fail with ConcurrentModifcationException on multi-thread scenario

[Dmitry Samersoff]

Deven,

After close look and off-line discussion with David Holmes,
the changes looks good for me.

I'll take care of the rest.

We have one more place in Agent.java executing exactly the same code
so I'll change both of them on your behalf.

-Dmitry


On 2012-04-23 11:43, Deven You wrote:
> Thanks David,
>
> So is it ok for you to contribute this patch?
>
> On 04/23/2012 02:36 PM, David Holmes wrote:
>> Except of course that Properties is a Hashtable and synchronizes on
>> 'this' for all public methods. So locking the properties object in the
>> client code will guarantee exclusive access to it.
>>
>> Sorry about that.
>>
>> David
>> -----
>>
>> On 23/04/2012 4:30 PM, David Holmes wrote:
>>> Deven,
>>>
>>> On 23/04/2012 3:54 PM, Deven You wrote:
>>>> On 04/18/2012 02:20 PM, Deven You wrote:
>>>>> On 04/18/2012 01:34 PM, Mandy Chung wrote:
>>>>>>
>>>>>>
>>>>>> I think this could still run into CME. System Properties is not a
>>>>>> synchronized map and the setter methods (System.setProperty or
>>>>>> Properties.put method) doesn't synchronize on the Properties object.
>>>>>>
>>>>>>
>>>>>> The setter methods I'm referring to are System.setProperty and
>>>>>> System.getProperties().put().
>>>>>>
>>>>>
>>>>> I have gone through the Agent.java, I think other set/put methods
>>>>> related to properties are protected properly.
>>>>>
>>>>> public static void agentmain using parseString(args) which return a
>>>>> properties which is a local var and is not possible to cause
>>>>> concurrent problem when call config_props.putAll(arg_props).
>>>>>
>>>>> private static synchronized void startLocalManagementAgent() is
>>>>> synchronized already.
>>>>>
>>>>> private static synchronized void startRemoteManagementAgent(String
>>>>> args) is synchronized also.
>>>>>
>>>>> Could you point where the CME may ocurr?
>>>>
>>>> Is there any suggestion from the mailing list?
>>>
>>> The problem is that System.getProperties() returns a globally accessible
>>> set of properties. So even if you prevent the Agent code from modifying
>>> those properties concurrently with other use in the Agent, you have no
>>> such guard for any other piece of code in the system which might also
>>> modify the properties. So the race condition you were trying to fix
>>> still exists. I don't see any way to fix this. No matter what you do
>>> another thread can modify the system properties while you are iterating
>>> them. Instead you need to anticipate the CME and try to recover from it
>>> (also non-trivial).
>>>
>>> Cheers,
>>> David Holmes
>>
>
>


-- 
Dmitry Samersoff
Java Hotspot development team, SPB04
* There will come soft rains ...