RFR : 8195857 : Posix platforms : move os::is_headless_jre check coding to os::Posix and remove test for libmawt

[David Holmes]

Hi Bob,

On 24/01/2018 1:25 AM, Bob Vandette wrote:
> If we are going to preserve this functionality and make alterations, I suggest that
> we try to move this into the desktop module and remove it from the hotspot sources.
> Other than finding an appropriate path at startup to initialize the property, there is
> no reason why this check can’t be written in Java.   This functionality has nothing to
> do with Hotspot or VMs.  (I should have probably done this when I first added this check).

Well we hacked it into the SE Embedded builds so we knew what lib was 
missing.

I don't think what you suggest really makes sense in a modular world 
because I don't think we expect to have java.desktop but not some of its 
native parts - so there would be no trigger to force into headless mode. 
More likely there is simply no java.desktop module at all.

That said I was reminded that this is also used by the Compact Profiles 
that were added in Java 8, but for which support was removed as from 
Java 9 (and modules). However the build logic is still present, and they 
still use this functionality. I think we can remove compact profiles 
completely in JDK 11, but that's a seperate tasks.

Meanwhile if we kill off the os::is_headless_jre() logic then the 
compact profiles would not default to headless mode even though they 
can't run headful (due to the missing native library as well as other 
Java APIs). But the only impact I can see there would be for running 
tests - and we're not testing compact profiles. So ... I still think 
this can be removed, but want to do a couple more checks.

Cheers,
David

> Bob.
> 
>> On Jan 23, 2018, at 5:57 AM, Baesken, Matthias <matthias.baesken at sap.com> wrote:
>>
>> Hi David, thanks for the comments.
>>
>>> I'd need to do some checking but I think this may all be effectively
>>> dead code.
>>
>> Please do the checking, maybe we can completely remove it.
>>
>> Best Regards, Matthias
>>
>>
>>> -----Original Message-----
>>> From: David Holmes [mailto:david.holmes at oracle.com]
>>> Sent: Dienstag, 23. Januar 2018 11:30
>>> To: Baesken, Matthias <matthias.baesken at sap.com>; 'hotspot-
>>> dev at openjdk.java.net' <hotspot-dev at openjdk.java.net>
>>> Subject: Re: RFR : 8195857 : Posix platforms : move os::is_headless_jre check
>>> coding to os::Posix and remove test for libmawt
>>>
>>> Hi Matthias,
>>>
>>> Some preliminary comments ...
>>>
>>> On 23/01/2018 6:24 PM, Baesken, Matthias wrote:
>>>> Hello,  I  noticed that  os::is_headless_jre()  still checks  on the Posix
>>> platforms  for libmawt  which is not present any longer.
>>>
>>> I wonder why that comment was put in but the code not changed ...
>>>
>>>> Additionally the  os::is_headless_jre()   function could be  put in a central
>>> place at os_posix  to avoid code duplication.
>>>
>>> I think you could simplify further and just define in os.cpp with three
>>> cases: windows, OS X, posix. I normally wouldn't suggest that but given
>>> Windows and OS X are always false, it's quite trivial.
>>>
>>> That said this may simplify even further because I don't know if the
>>> concept of a headless JRE is even meaningful anymore. This what put in
>>> place in 2010 to support Java SE Embedded. We had a special build
>>> process that would remove the library from the JRE image, then a runtime
>>> check os::is_headless_jre() run during argument processing, that if
>>> true, caused the java.awt.headless property to be set to true (unless
>>> already set). I don't think we can even build a "headless JRE" any more.
>>>
>>> I'd need to do some checking but I think this may all be effectively
>>> dead code.
>>>
>>> Thanks,
>>> David
>>> -------
>>>
>>>> Could you please review my change .
>>>>
>>>> Webrev :
>>>>
>>>> http://cr.openjdk.java.net/~mbaesken/webrevs/8195857/
>>>>
>>>> Bug :
>>>>
>>>> https://bugs.openjdk.java.net/browse/JDK-8195857
>>>>
>>>>
>>>>
>>>> Thanks, Matthias
>>>>
>