review request (S): 7199082 write warning messages to stderr

[Srinivas Ramakrishna]

While I haven't followed the discussion very closely, I believe that
separating warnings off into the error stream is in fact the right thing to
do,
because error streams are more likely to be looked at by users. As regards
silently ignoring the perm gen flag, ignoring is fine, but emitting a
warning while ignoring has, really, been how we've managed options changes
in the past, so there is precedent to this warning. It's really these
warnings that allow users to adjust their options/flags and become aware of
many of these kinds of changes.

So, personally, I think issuing a warning is the right thing to do, and the
change of sending warnings to the error stream also seems to me
to be a good thing, but then I may have missed some of the subtler
arguments against that move being discussed here (and perhaps I'll grok
them on a slower, more focused re-reading of them :-)

-- ramki

On Wed, Sep 19, 2012 at 7:47 AM, Coleen Phillimore <
coleen.phillimore at oracle.com> wrote:

> On 9/19/2012 3:11 AM, Staffan Larsen wrote:
>
>> Thanks for clarifying a bit on how tty and VM output works. I've re-read
>> the changes and the source code as well as discussed this with Stefan and
>> Bengt.
>>
>> There are two (or more) problems here:
>>
>> 1) VM output should default to stderr. But this should be discussed
>> separately and not as a quick fix to this specific problem. A good
>> timeframe for this could be JDK 8 since it's a major release. I agree with
>> David that we shouldn't special case some of the VM output, it should all
>> go to the same place (unless explicitly changed by the user).
>>
>
> Also, there are a lot of bugs and history about this, which always result
> in us backing away slowly.   If we want to make a change here, search the
> bug database for the discussions.   Some might be relevant now, some not.
> I think this is how we got the -XX:+DisplayOutputToStderr flag as a partial
> solution.
>
> Coleen
>
>
>
>> 2) The JDK build fails with the warnings issued for the deprecated
>> permgen flags. Perhaps this is better fixed in the JDK build by either
>> removing the usage of the permgen flags or adding
>> -XX:+DisplayVMOutputToStderr. How doable is that?
>>
>> It seems to me that we already have a precedent for writing warnings
>> about deprecated flags (the whole obsolete_jvm_flags list) and that the
>> permgen flags are a perfect fit for this list. I think it is reasonable
>> that we should issue warnings in jdk8 and error/abort in jdk9.
>>
>> Thanks,
>> /Staffan
>>
>>
>> On 19 sep 2012, at 07:51, David Holmes<David.Holmes at oracle.com**>  wrote:
>>
>>  On 19/09/2012 3:37 PM, Staffan Larsen wrote:
>>>
>>>> Looks good. All kinds of logging/warning/error messages from the JVM
>>>> should go to stderr.
>>>>
>>> In which case the correct fix would be to change tty from defaulting to
>>> stdout, to default to stderr.
>>>
>>> When you have a program that runs a program and they share stdout and
>>> stderr then you can't always win: no matter where the VM writes to it can
>>> interfere with what the app writes. So all hotspot output is nominally sent
>>> to 1 place - the tty - and you can then configure the tty to either connect
>>> to stdout (the default) or stderr. (And additionally some logging/tracing
>>> subsystems allow you to use files to get the VM output out of the picture
>>> completely.).
>>>
>>> Hence I really don't like that we are special casing warnings. :(
>>>
>>> I think this change will have repercussions, no matter what we try to do
>>> to fiddle the output streams, and the issue is whether those repercussions
>>> will become known before or after we ship JDK8.
>>>
>>> My opinion (as I've expressed elsewhere) is that we leave warnings/tty
>>> alone and instead we stop issuing the PermGen warnings for JDK8. We can
>>> then enable the warnings for JDK9 (and send them to wherever tty sends
>>> them) and in JDK10 simply abort if the options are given.
>>>
>>> David
>>>
>>>  /Staffan
>>>>
>>>> On 18 sep 2012, at 20:47, John Coomes<John.Coomes at oracle.com>   wrote:
>>>>
>>>>  Small change to warning() to write to error_stream() instead of tty.
>>>>>
>>>>> http://cr.openjdk.java.net/~**jcoomes/7199082-warn-stderr/<http://cr.openjdk.java.net/%7Ejcoomes/7199082-warn-stderr/>
>>>>>
>>>>> Bug link:
>>>>> http://bugs.sun.com/**bugdatabase/view_bug.do?bug_**id=7199082<http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7199082>
>>>>>
>>>>> -John
>>>>>
>>>>
>
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