jmx-dev Codereview: JDK-8065764 javax/management/monitor/CounterMonitorTest.java hangs

[shanliang]

Jaroslav Bachorik wrote:
> On 12/02/2014 06:56 PM, shanliang wrote:
>> Jaroslav Bachorik wrote:
>>> On 12/02/2014 05:22 PM, shanliang wrote:
>>>> Jaroslav Bachorik wrote:
>>>>> On 12/02/2014 04:22 PM, shanliang wrote:
>>>>>> Jaroslav Bachorik wrote:
>>>>>>> On 12/02/2014 02:40 PM, shanliang wrote:
>>>>>>>> Jaroslav Bachorik wrote:
>>>>>>>>> On 12/01/2014 02:50 PM, shanliang wrote:
>>>>>>>>>> Hi,
>>>>>>>>>> please review this test bug fix:
>>>>>>>>>>
>>>>>>>>>> webrev:
>>>>>>>>>> http://cr.openjdk.java.net/~sjiang/JDK-8065764/00/
>>>>>>>>>>
>>>>>>>>>> bug:
>>>>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8065764
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>> test/javax/management/monitor/CounterMonitorTest.java
>>>>>>>>> L61 - observedValue could be Integer
>>>>>>>> Could be, but not make difference, observedValue is only used
>>>>>>>> with the
>>>>>>>> operation "==", like
>>>>>>>>     while (value != observedValue)
>>>>>>>
>>>>>>> In that case having a correct type would make even more sense 
>>>>>>> for the
>>>>>>> readability.
>>>>>> Agree in general:) but the variable "count" is declared as 
>>>>>> "Object" in
>>>>>> StdObservedObject, and "observedValue" is used to save observed
>>>>>> "count"
>>>>>> value, so better to keep the same type for "more readability"? and
>>>>>> avoid
>>>>>> a casting when setting "observedValue"
>>>>>
>>>>> Any reason 'count' is declared as Object? The value is effectively an
>>>>> integer value - only integer values are ever assigned to it. All the
>>>>> operations silently suppose this would be an integer and yet the type
>>>>> information is thrown away and the data is stored as Object. Feels
>>>>> very strange ...
>>>> I think a possible reason is that the CounterMonitor supports only
>>>> Number type for comparing, and it accepts any type but detects whether
>>>> the observed variable could be "matched" to Number, pass an Object 
>>>> type
>>>> verifies this capability.
>>>
>>> Hm, could you direct me to the code doing this? 'setAttribute' method
>>> seems to be inherited from 'Monitor' class and does not do any
>>> additional checks. Then 'Monitor.monitor()' uses 'getAttribute'
>>> (again, not overridden) to get back to the attribute :(
>> ConterMonitor overrides Monitor.isComparableTypeValid(...)
>>
>> This method will be called by Monitor at the monitoring time and a
>> Notification with the type "jmx.monitor.error.type" will be sent out if
>> the observed attribute is not of type "Integer".
>>
>> Yes the monitor might have to do type check with the method:
>>     Monitor.setObservedAttribute("NbObjects");
>>
>> but the Javadoc declares only:
>>     Throws: IllegalArgumentException - The specified attribute is null.
>>
>> maybe it is not sure that a monitor could do type check at setting time,
>> for example if the MBeanInfo is null and getAttributeValue() returns 
>> null.
>
> I still don't see how using Object instead of Integer type could check 
> this functionality. But if you insist on keeping it this way I won't 
> block fixing this failing test any further. Reviewed.
You can simply pass an Object instead of an Integer to NbObjects, and 
see what happen. The monitor does type check only at monitoring time.

Thanks for review.
Shanliang
>
> -JB-
>
>>
>> Shanliang
>>>
>>> Thanks,
>>>
>>> -JB-
>>>
>>>>>
>>>>>>>
>>>>>>>>> L225-238 - you could replace this block with the usage of Phaser
>>>>>>>>> (if
>>>>>>>>> you'd do that you could completely remove 'observedValue')
>>>>>>>> Not sure that it is a good idea to remove "observedValue" by using
>>>>>>>> Phaser, yes using Phaser can tell when the monitor does an
>>>>>>>> observation,
>>>>>>>> but it is better to know which count value the monitor 
>>>>>>>> observed, in
>>>>>>>> case
>>>>>>>> the thread was waked up accidentally.
>>>>>>>
>>>>>>> I don't think phaser can be confused by spurious wake-ups.
>>>>>>>
>>>>>>> If you want to keep the current way of synchronizing then you 
>>>>>>> should
>>>>>>> make the 'count' variable volatile (L77) - it might be read and
>>>>>>> written to from different threads.
>>>>>> Phaser should not make a false wakeup, but use "observedValue" can
>>>>>> make
>>>>>> sure that the observation happens on the right "count" value.
>>>>>> Yes "count" should be declared as "volatile".
>>>>>>
>>>>>> Here is the new version:
>>>>>>     http://cr.openjdk.java.net/~sjiang/JDK-8065764/01/
>>>>>
>>>>> Still using 'derivedGange' instead of 'derivedGauge' :(
>>>> Oh I will change it before pushing, if no other modification.
>>>>
>>>> Thanks,
>>>> Shanliang
>>>>>
>>>>> -JB-
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Shanliang
>>>>>>
>>>>>>>
>>>>>>> -JB-
>>>>>>>
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Shanliang
>>>>>>>>>
>>>>>>>>> -JB-
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>> The test tested the mode "difference", according to the Javadoc:
>>>>>>>>>>       If the counter difference mode is used, the value of the
>>>>>>>>>> derived
>>>>>>>>>> gauge is calculated as the difference between the observed 
>>>>>>>>>> counter
>>>>>>>>>> values for two successive observations.
>>>>>>>>>>
>>>>>>>>>> The test set the first value and then waited 2 times of
>>>>>>>>>> granularityperiod at line 171, hoped that the monitor would get
>>>>>>>>>> the
>>>>>>>>>> first observation during this waiting time, but the test could
>>>>>>>>>> fail
>>>>>>>>>> because granularityperiod * 2 was not enough and the test did 
>>>>>>>>>> the
>>>>>>>>>> second
>>>>>>>>>> set before the monitor did the first observation.
>>>>>>>>>>
>>>>>>>>>> It is easy to make the test timeout by commenting out the line
>>>>>>>>>> 171.
>>>>>>>>>>
>>>>>>>>>> The proposed solution is to get informed when the monitor did
>>>>>>>>>> observation on calling:
>>>>>>>>>>     StdObservedObject.getNbObjects();
>>>>>>>>>>
>>>>>>>>>> Thanks,
>>>>>>>>>> Shanliang
>>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>