<AWT Dev> [9] Review Request: 6815345 java.awt.Component.createImage(int width, int height) should remove behavioral optionality

Semyon Sadetsky semyon.sadetsky at oracle.com
Fri Sep 25 12:44:41 UTC 2015

On 9/25/2015 2:46 PM, Sergey Bylokhov wrote:
> On 25.09.15 10:13, Semyon Sadetsky wrote:
>> Native container based components are disabled. But other native
>> resources can be used if available.
> no hw components -> no backbuffers for them.
In my understanding it depends on the component. If component capable to 
work in the headless mode it can continue to use its peer, can't it?
>> All **Peer interfaces are public and external. Peer is not a hidden or
>> implementation specific term. It isn't allowed to application developers
>> for implementation, but it is used for porting client libs to other
>> platforms. Java specification has wider vision than one particular
>> implementation. And for porting the headless mode is very sensitive
>> topic because specific platforms are headless often.
> The java.awt.peer package is private and should be used by the awt 
> developers only. If the new port will be implemented then it should 
> follow the same specification as our implementation.
That's correct. And our specification should be reasonable in its turn. 
It must not be simply back-filled from our code otherwise it would 
unlikely have more than one implementation.
JCK team likes direct specs in "if-then" style. But I see that the 
initial doc was soft enough because it just clarify that exceptions from 
the general rule are possible depending on the specific implementation 
concept to leave more possibilities for porting. The article I send you 
also contains a lot of soft phrases.
>>> Maybe
>>>> Component#getImage() implementation should simply check for 
>>>> isHeadless()
>>>> and return null?
>> But what will happen if Unix DISPLAY variable is not set so
>> isHeadlessInstance()=true?  Will peer be allowed? Should component
>> buffering work smoothly?
> The peers are not allowed in the headless mode. The DISPLAY var is not 
> specified in the javadoc, this means that some implementation can work 
> when DISPLAY is empty/unset, but in this case they must return false 
> from the isHeadlessXX();
isHeadlessInstance() just tests DISPLAY on Linux.
>> Note this is a common network server scenario which runs Java app from
>> the text console. I cannot get from the spec is it completely different
>> headless mode or it is the same as the global headless?
>>>> And more global question: Why should we disable the creating of
>>>> component image buffer for the headless mode?It could be used for the
>>>> same performance reason as in non-headless.
>>> in the headless mode we cannot create most of the hw components,
>>> actually non of top level window can be created. And for lw components
>>> like in swing the one global buffer is used in the RepaintManager.
>> One global buffer means one global repaint
> No this is not true. If one component is changed then only one 
> component is repainted.
> off all components for any
>> single component change. Why can't we be isomorphic here?
>>>>>>> The headless case is covered, heavyweight components cannot be
>>>>>>> created
>>>>>>> in such mode, so only lightweight buttons are checked.
>>>>>>> On 24.09.15 15:58, Semyon Sadetsky wrote:
>>>>>>>> On 9/24/2015 3:25 PM, Sergey Bylokhov wrote:
>>>>>>>>> On 24.09.15 11:36, Semyon Sadetsky wrote:
>>>>>>>>>> Hi Sergey,
>>>>>>>>>>   isHeadless()=true must return null. If so please add the
>>>>>>>>>> corresponding
>>>>>>>>>> test case. It is not not obvious from the code.
>>>>>>>>> isHeadless()=true is headless mode where the frames are always 
>>>>>>>>> not
>>>>>>>>> displayable, so everything is similar to the current test except
>>>>>>>>> that
>>>>>>>>> in headless the pack() will be throw an exception and second
>>>>>>>>> part of
>>>>>>>>> the test in this mode is unnecessary.
>>>>>>>> Then maybe simply do not call pack() for the headless test?
>>>>>>>> Okay, let me rephrase what I meant. Since isHeadless()=true 
>>>>>>>> case is
>>>>>>>> mentioned in those 3 specs so explicitly it must be guarantied 
>>>>>>>> that
>>>>>>>> the
>>>>>>>> specified behavior works for the case as described. I cannot trace
>>>>>>>> the
>>>>>>>> result by reading the code of the createImage(), isHeadless()
>>>>>>>> method is
>>>>>>>> not even called there.  So the test case should be added. Or you
>>>>>>>> could
>>>>>>>> remove isHeadless() references from the specs. Or write something
>>>>>>>> like
>>>>>>>> "the result is non-deterministic if isHeadless() is not false..."
>>>>>>>>>> --Semyon
>>>>>>>>>> On 9/23/2015 9:14 PM, Sergey Bylokhov wrote:
>>>>>>>>>>> Hello.
>>>>>>>>>>> Please review the fix for jdk9.
>>>>>>>>>>> The specification is updated as suggested in JDK-6186530 and
>>>>>>>>>>> JDK-6815345. The test is added to prove that we always return
>>>>>>>>>>> null
>>>>>>>>>>> when the component is not displayable.
>>>>>>>>>>> ccc request will be created after the technical review. One
>>>>>>>>>>> additional
>>>>>>>>>>> bug filed https://bugs.openjdk.java.net/browse/JDK-8137047
>>>>>>>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-6815345
>>>>>>>>>>> Webrev can be found at:
>>>>>>>>>>> http://cr.openjdk.java.net/~serb/6815345/webrev.04

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