<AWT Dev> [9] Review request for 8151189: Possible getAppContext() NPE in java.awt.Desktop and java.awt.Taskbar

[Sergey Bylokhov]

On 16.11.16 0:16, Phil Race wrote:
> A "main" appcontext will be created if you are a standalone app, but
> not if running in webstart (although the means of determining that is
> somewhat hokey) :-
>    if (numAppContexts.get() == 0) {
>                             if (System.getProperty("javaplugin.version")
> == null &&
> System.getProperty("javawebstart.version") == null) {
>                                 initMainAppContext();
>
> So if that is not initialised it appears to rely solely on an appcontext
> being
> associated with the current threadgroup - or a parent threadgroup.
>
> If for some reason this does not return an appcontext you'll get the NPE.
> This doesn't have to mean it is the Toolkit thread.

Yes, that's true that main appcontext is not created in case of applets 
and webstart. And this is a feature. If we will get null appcontext here 
we are in incorrect state and should not try to workaround it, but 
should fail instead.
For example in the proposed fix we save Desktop to static var after 
security checks, so if the user will be able to call this methods after 
he will get Desktop object even if it is not have such permission.

> This example may be a little contrived but it illustrates the problem :-
> If the webstart system property is set you will never see "got desktop"
> printed
> because the finalizer thread gets an exception.
>
> ===
> import java.awt.Desktop;
>
> public class GD {
>
>  public void finalize() {
>     System.out.println("get desktop");
>     System.out.println(Desktop.getDesktop());
>     System.out.println("got desktop");
>  }
>
>  public static void main(String[] args) {
>     if (args.length == 0) {
>         System.out.println("Setting webstart version");
>         System.setProperty("javawebstart.version", "8");
>     }
>     while (true) {
>       new GD();
>       System.gc();
>     }
>  }
> }
> ====
>
> -phil.
>
> On 11/15/2016 10:48 AM, Phil Race wrote:
>> So are you saying we will never call this from the Toolkit thread, so
>> provably
>> there will never be an NPE ?
>>
>> Seems we have had a ton of NPE bugs from getAppContext() returning null
>> so I am not so confident about that.
>>
>> -phil.
>>
>> On 11/15/2016 10:44 AM, Sergey Bylokhov wrote:
>>> I guess this should be closed as not a defect. getAppContext() can
>>> return null if it will be called from the toolkit thread. If this
>>> method is called by the user then appcontext should not be null,
>>> additionally we should not cache this value in the static, so all
>>> other code will use this cached static value.
>>>
>>> On 15.11.16 20:38, Phil Race wrote:
>>>>
>>>> +1
>>>>
>>>> -phil.
>>>>
>>>> On 11/15/2016 08:24 AM, Alexander Zvegintsev wrote:
>>>>> Hello,
>>>>>
>>>>> please review the fix
>>>>>
>>>>> http://cr.openjdk.java.net/~azvegint/jdk/9/8151189/00/
>>>>>
>>>>> for the issue
>>>>>
>>>>> https://bugs.openjdk.java.net/browse/JDK-8151189
>>>>>
>>>>
>>>
>>>
>>
>


-- 
Best regards, Sergey.