RFR: 8027429: Add diagnostic command VM.info to get hs_err print-out

[Coleen Phillimore]

So I actually disagree.  I don't think there should be an additional 
separate mechanism to get the same information that we get with hs_err 
reporting.  I've wanted to have a feature like this for a long time.

I pre-reviewed this change and I thought it looked good in general. I 
didn't see the thread iteration problem that Fred refers to below, but I 
think the individual problems can be fixed.

The last thing I want is this code to be copied somewhere else.

Coleen

On 10/28/15 8:48 PM, David Holmes wrote:
> I agree with Fred, this kind of info reporting should not be 
> piggy-backed onto VMError handling for the reasons stated (and the 
> error handling logic is complicated enough as it is!). For things like 
> thread lists there are already safe management functions that 
> can/should be used.
>
> Thanks,
> David H.
>
> On 29/10/2015 3:29 AM, Frederic Parain wrote:
>> Hi David,
>>
>> I haven't review all the code yet, but I'm concerned with the
>> fact that the diagnostic command is calling VMError::report().
>> This method has been implemented to be executed in the particular
>> context of fatal errors, and its usage while the VM is running
>> normally seems dangerous.
>>
>> For instance, VMError::report() consciously avoids grabbing locks
>> because of the risk of deadlock during the error reporting.
>> The consequence is that some data structures are browsed in
>> an unsafe way. One example: VMError::report() calls
>> Threads::print_on_error() which iterates over the thread
>> list *without owning the Threads_lock*.
>>
>> The implementation of the diagnostic command seems also to
>> exclude a lot of reporting from the initial VMError::report()
>> method. Have you considered implementing a new MT-safe reporting
>> method rather than trying to modify the special VMError::report()
>> methods? (Note that some code factorization between VMError::report()
>> and this new method should be possible).
>>
>> Thanks,
>>
>> Fred
>>
>> On 28/10/2015 17:18, david buck wrote:
>>> Hi!
>>>
>>> Please review my change for this small enhancement.
>>>
>>> bug: https://bugs.openjdk.java.net/browse/JDK-8027429
>>> webrev: http://cr.openjdk.java.net/~dbuck/8027429_jdk9_01/
>>>
>>> Cheers,
>>> -Buck
>>