[icedtea-web][rfc] Fix for PR580: http://www.horaoficial.cl/ loads improperly

[Jiri Vanek]

On 01/29/2013 10:42 PM, Adam Domurad wrote:
> Hi all -- so this was a fix that I was working on for the unsigned applet confirmation pop-up
> dialogue (similar to Oracle's security levels).
>
> Turns out this applet is a pretty a good stress test. Basically it causes 13 createApplet calls,
> which is a good way to reveal concurrency issues in getInstance.
>
> Prior to patch:
>   - Some or all of the 3 times that show up never finish loading, except after refresh
>   After patch:
> - All times show without needing to refresh, as expected
>
> So why did it work mysteriously after refreshing ? After refresh, the shared classloader is still
> around (although it -should- be cleared! thats another bug!), and on the second round of loading all
> applets latch on to the correct classloader.
>
> There was some basic synchronization on urlToLoader, but not enough. It needs to synchronize all
> instances of the unique key for the entire duration of the get/put.
>
> The first approach I took was to simply make JNLPClassLoader#getInstance 'synchronized' -- however
> parallel loading of different-unique-key applets would suffer. While same-unique-key applets must
> load sequentially for correct behaviour, a long-loading applet could make a short-loading applet
> wait a long time if getInstance was simply synchronized.
>
> JNLPClassLoader continues to get more complicated, unfortunately ... but this fix is needed.
> I have also removed a try ... catch that did nothing but re-threw the exception -- although I know
> this is unrelated, it allowed the diff to be cleaner :-) Feel free to force it back ...
>
> Fix changelog:
> 2013-XX-XX  Adam Domurad  <adomurad at redhat.com>
>
>      Fix PR580: http://www.horaoficial.cl/ loads improperly. Applets that
>      must share a class-loader now load sequentially.
>      * NEWS:
>      Mention the fix.
>      * netx/net/sourceforge/jnlp/runtime/JNLPClassLoader.java
>      (getUniqueKeyLock): New, atomically grabs or creates a lock for the
>      unique key.
>      (getInstance): Ensure classloader initialization is locked by unique
>      key.
>      (decrementLoaderUseCount): Ensure classloader deinitialization is
>      locked by unique key, get rid of no-longer used locks.


I think ok for head. I have created an reproducer for this, so I think you can push to head. imho 
worthy to 1.3 after some  tiime in head

J.