[RFC] PR 535: null pointer exceptions during applet initialization

[Deepak Bhole]

* Omair Majid <omajid at redhat.com> [2010-09-17 15:56]:
> Hi,
> 
> The attached patch fixes icedtea bug 535 [1]. Some calls to
> showAppletStatus are throwing null pointer exceptions. The problem
> appears to be that the AppletPanel is reparented during
> initialization (see PluginAppletViewer.reFrame()). There is a small
> window of time where the AppletPanel does not have a parent, which
> causes getParent() to return null and cause this
> NullPointerException.
> 
> The attached patch tries to avoid this problem by trying again if it
> detects the parent is null.
> 
> Any thoughts or comments?
> 
> Cheers,
> Omair
> 

Patch is fine. But as I commented on the bug, please hold off for now.
There are API changes I am working on that will add a common wait
function for this sort of stuff. There are many cases where threads need
to wait till the applet is ready, and one of the changes will add a
function that blocks till such a time.

Cheers,
Deepak

> [1] http://icedtea.classpath.org/bugzilla/show_bug.cgi?id=535

> diff -ruN openjdk.orig/jdk/src/share/classes/sun/applet/AppletViewerPanel.java openjdk/jdk/src/share/classes/sun/applet/AppletViewerPanel.java
> --- openjdk.orig/jdk/src/share/classes/sun/applet/AppletViewerPanel.java	2010-09-17 15:01:01.790221354 -0400
> +++ openjdk/jdk/src/share/classes/sun/applet/AppletViewerPanel.java	2010-09-17 15:17:21.758076505 -0400
> @@ -199,7 +199,22 @@
>       * also implemented by the AppletPanel class.
>       */
>      public AppletContext getAppletContext() {
> -        return (AppletContext)getParent();
> +        Object parent = getParent();
> +        int nullCount = 0;
> +        final int ERROR_THRESHOLD = 1000;
> +        // the AppletViewerPanel is reparented during initialization and 
> +        // there is a small window of time where it has no parent
> +        while (parent == null) {
> +            Thread.yield();
> +            nullCount++;
> +            // if we have waited too long and still dont have a parent, 
> +            // something is very wrong; dont try to mask it
> +            if (nullCount == ERROR_THRESHOLD) {
> +                return null;
> +            }
> +            parent = getParent();
> +        }
> +        return (AppletContext)parent;
>      }
>  
>      protected static void debug(String s) {