Codereview request: 8007710 runtime/7158988/FieldMonitor.java fails with com.sun.jdi.VMDisconnectedException: Connection closed

[shanliang]

serguei.spitsyn at oracle.com wrote:
> The fix looks good.
> But could you change "impossible" at line 45 to something more 
> adequate, i.e. "caught exception"? :
>
>   41         System.out.println("---TestPostFieldModification-run waiting to exit ...");
>   42         try {
>   43             System.in.read();
>   44         } catch (Exception e) {
>   45             System.out.println("---TestPostFieldModification-run impossible? "+e);
>   46             e.printStackTrace();
>   47         }
>
Done.
Thanks for reviewing.
Shanliang
>
> Thanks,
> Serguei
>
>
> On 2/11/14 9:30 AM, shanliang wrote:
>> Here is the new fix in which FieldMonitor will write to 
>> TestPostFieldModification, to inform the latter to quit, as suggested 
>> bu Jaroslav
>>    http://cr.openjdk.java.net/~sjiang/JDK-8007710/01/
>>
>> Thanks,
>> Shanliang
>>
>> shanliang wrote:
>>> shanliang wrote:
>>>> Jaroslav Bachorik wrote:
>>>>> On 11.2.2014 16:31, shanliang wrote:
>>>>>> Staffan Larsen wrote:
>>>>>>> Hi Shanliang,
>>>>>>>
>>>>>>> I can’t quite see how the test can fail in this way. When the
>>>>>>> ClassPrepareEvent happens, the debuggee will be suspended. So when
>>>>>>> addFieldWatch() is called, the debuggee should not have moved.
>>>>>> I am not expert of jdi so I may miss something here. I checked the
>>>>>> failure trace and saw the report exception happen when FieldMonitor
>>>>>> received ClassPrepareEvent and was doing addFieldWatch. 
>>>>>> FieldMonitor did
>>>>>> call "vm.resume()" before treating events.
>>>>>
>>>>> AFAICS, calling vm.resume() results in an almost immediate 
>>>>> debuggee death. The gc() invoking thread "d" is flagged as a 
>>>>> deamon and as such doesn't prevent the process from exiting. The 
>>>>> other thread is not a daemon but will finish in only few cycles.
>>>> I looked at the class com.sun.jdi.VirtualMachine, here is the 
>>>> Javadoc of the method "resume":
>>>>    /**
>>>>     * Continues the execution of the application running in this
>>>>     * virtual machine. All threads are resumed as documented in
>>>>     * {@link ThreadReference#resume}.
>>>>     *
>>>>     * @throws VMCannotBeModifiedException if the VirtualMachine is 
>>>> read-only - see {@link VirtualMachine#canBeModified()}.
>>>>     *
>>>>     * @see #suspend
>>>>     */
>>>>    void resume();
>>>> My understanding is that the debuggee resumes to work after this 
>>>> call, instead to die?
>>> In fact the problem is here, the vm (TestPostFieldModification) 
>>> should not die before FieldMonitor finishes addFieldWatch.
>>>
>>> Shanliang
>>>>>
>>>>>>
>>>>>> I reproduced the bug by add sleep(1000) after vm.resume() but before
>>>>>> calling eventQueue.remove();
>>>>>
>>>>> It looks like some kind of synchronization between the debugger 
>>>>> and the debuggee is necessary. But I wonder if you should better 
>>>>> use the process.getOuptuptStream() to write and flush a message 
>>>>> for the debugee indicating that it can exit. And in the debugee 
>>>>> you would just do System.in.read() as the last statement in the 
>>>>> main() method. Seems more robust than involving files.
>>>> It could work, but creating a file in the testing directory should 
>>>> have no issue, but yes maybe less performance.
>>>>
>>>> Thanks,
>>>> Shanliang
>>>>>
>>>>> Cheers,
>>>>>
>>>>> -JB-
>>>>>
>>>>>>
>>>>>> Thanks,
>>>>>> Shanliang
>>>>>>> One problem I do see with the test is that it does not wait for a
>>>>>>> VMStartEvent before setting up requests. I’m not sure if that could
>>>>>>> cause the failure in the bug report, though.
>>>>>>>
>>>>>>> /Staffan
>>>>>>>
>>>>>>> On 11 feb 2014, at 15:13, shanliang <shanliang.jiang at oracle.com> 
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Hi ,
>>>>>>>>
>>>>>>>> The problem could be that FieldMonitor did not have enough time to
>>>>>>>> "addFieldWatch" but the vm to monitor 
>>>>>>>> (TestPostFieldModification) was
>>>>>>>> already ended.
>>>>>>>>
>>>>>>>> So we should make sure that TestPostFieldModification exits after
>>>>>>>> FieldMonitor has done necessary. The solution proposed here is 
>>>>>>>> that
>>>>>>>> FieldMonitor creates a file after adding field watching, and
>>>>>>>> TestPostFieldModification quits only after finding the file.
>>>>>>>>
>>>>>>>> web:
>>>>>>>> http://icncweb.fr.oracle.com/~shjiang/webrev/8007710/00/
>>>>>>>>
>>>>>>>> bug:
>>>>>>>> https://bugs.openjdk.java.net/browse/JDK-8007710
>>>>>>>>
>>>>>>>> Thanks,
>>>>>>>> Shanliang
>>>>>>>
>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>

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