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

[David Holmes]

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