RFR: JDK-8163102: Fix headless only configuration option

[David Holmes]

On 4/08/2016 6:24 PM, Erik Joelsson wrote:
> Hello,
>
> New webrev: http://cr.openjdk.java.net/~erikj/8163102/webrev.02
>
> The difference is in libraries.m4, where there was still a reference to
> SUPPORT_HEADFUL. I tried building a headless configuration without X11
> configured, but it unfortunately failed. libawt.so still requires X11
> headers to compile. I suppose we could differentiate between headers and
> libs being available, but I will leave that for another time.

Ok.

> On 2016-08-03 22:37, David Holmes wrote:
>> Hi Erik,
>>
>> The confusion around that variable due to its legacy always makes me
>> worried that something is misunderstood. It was originally to deal
>> with a build platform that had no headful support (no X11 libs and
>> headers etc) and so could not build headful no matter what. The flag
>> but not the functionality was carried into the new build system. What
>> you have now is a different beast entirely.
>>
> Right, but unfortunately it still requires X11 headers as said above,
> and tracing through history, this must always have been true for a long
> time.
>>> In this patch I'm replacing the configure option with
>>> --enable-headless-only. Default is disabled, where both headless and GUI
>>> support is built. When enabled, only headless support is built. These
>>> are the two variants we are ever interested in.
>>>
>>> On the makefile side, I redefined the variable as
>>> ENABLE_HEADLESS_ONLY=true/false.
>>
>> This all seems reasonable. Though of course you have to ensure that a
>> headless build can still execute all the necessary functionality. Even
>> for headless some of the AWT API's still have to be available
>> (printing support for one IIRC).
> As far as I can see, this should be fine, but perhaps someone from
> 2d/awt should comment. This is what --enable-headless-only removes:
>
> * policytool - a gui application which does not seem to have any
> functionality without a gui
> * appletviewer - seems pointless without a gui
> * libsplashscreen - seems pointless without a gui
> * libawt_xawt - the X11 specific parts of awt that links to libX11
> * A placeholder libjawt is built which just doesn't do anything
>
> These are also exactly the libraries and executables that link to X11.
> Regardless of if we can use this option at Oracle, I believe it's a good
> fix for OpenJDK.
>
>>
>>> I also needed to change jawt.c to get a headless only build to actually
>>> work. The requirement that -DJAVASE_EMBEDDED is set seems unnecessary
>>> and unrelated to me.
>>
>> The JAVASE_EMBEDDED stuff has now all been removed, but that change
>> hasn't reached dev yet.
>>
> Right, and that change conflicts with mine since it also removed the
> possibility of building a "headless" libjawt. This means I should hold
> on this change until hs gets into dev.

I'm not sure when my changes will hit jdk9/dev unfortunately. Otherwise 
if you push this Alejandro will have to resolve the conflict in jdk9/hs.

David

> /Erik