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

David Holmes david.holmes at oracle.com
Thu Jan 25 06:39:28 UTC 2018 

Hi Matthias,

On 25/01/2018 4:36 PM, Baesken, Matthias wrote:
>>
>> Bottom line: os::is_headless_jre() is dead code as far as I can see.
>>
> 
> Hi David,  so do you suggest I prepare a new webrev  where os::is_headless_jre()  is  completely removed ?
> 
> What about the code block in  hotspot/share/runtime/arguments.cpp  ,  do you think this can be completely removed as well ?

Yes - everything pertaining to os::is_headless_jre() can be removed.

Thanks,
David
-----

> 
> 3495  if (os::is_headless_jre()) {
> 3496    const char* headless = Arguments::get_property("java.awt.headless");
> 3497    if (headless == NULL) {
> 3498      const char *headless_env = ::getenv("JAVA_AWT_HEADLESS");
> 3499      if (headless_env == NULL) {
> 3500        if (!add_property("java.awt.headless=true")) {
> 3501          return JNI_ENOMEM;
> 3502        }
> 3503      } else {
> 3504        char buffer[256];
> 3505        jio_snprintf(buffer, sizeof(buffer), "java.awt.headless=%s", headless_env);
> 3506        if (!add_property(buffer)) {
> 3507          return JNI_ENOMEM;
> 3508        }
> 3509      }
> 3510    }
> 3511  }
> 
> Best regards, Matthias
> 
> 
> 
>> -----Original Message-----
>> From: David Holmes [mailto:david.holmes at oracle.com]
>> Sent: Donnerstag, 25. Januar 2018 02:16
>> To: Bob Vandette <bob.vandette at oracle.com>
>> Cc: Baesken, Matthias <matthias.baesken at sap.com>; 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
>>
>> On 24/01/2018 11:16 PM, Bob Vandette wrote:
>>>> On Jan 23, 2018, at 5:50 PM, David Holmes <david.holmes at oracle.com>
>> wrote:
>>>>
>>>> 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.
>>> The automatic setting of java.awt.headless has nothing to do with compact
>> profiles.  This support was available in JDK 7 before profiles even existed.
>> This
>>> automatic headless detection was added in order to allow Java to be
>> ported to platforms that do not have a native windowing toolkit available.
>> This was
>>> used in embedded to also reduce the size of the binary by removing this
>> big library.  A configuration that contains java.desktop can absolutely be
>> supported
>>> and the JCK can be passed without this native library.
>>>
>>> This Java property is only referenced by the desktop module.  This is why I
>> suggested that this functionality be moved out of the hotspot VM.
>>
>> Yes we forced the AWT into headless mode if there was no native graphics
>> library support available. For some of those platforms we even did this
>> at build time, not via a runtime check. For SE Embedded support we would
>> strip the library out at image build time, and so the runtime check
>> would force AWT into headless mode. For compact profiles there is no AWT
>> at all, and no native library in the built image so the runtime check
>> still (vacuously) sets the property for headless mode.
>>
>> If you have the java.desktop module, then you have everything - there is
>> no fragmentation of that module that I am aware of, that would allow you
>> strip out the library that triggers os::is_headless_jre() or some other
>> check that forces the AWT into headless mode. If you have java.desktop
>> and you want headless mode then you have to ask for it explicitly.
>>
>> Bottom line: os::is_headless_jre() is dead code as far as I can see.
>>
>> Separately I'll file a bug to remove the compact profile builds.
>>
>> David
>> -----
>>
>>> Bob.
>>>
>>>
>>>>
>>>> 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
>>>>>>>>
>>>

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