RFR 8072466: Deadlock when starting MulticastSocket and DatagramSocket

[Ivan Gerasimov]

Hello!

There has been a deadlock in jdk-net code noticed on Windows.

In the bug description there's a stack snippet showing that one of the 
deadlocked threads stuck in the native initialization code of 
DualStackPlainDatagramSocketImpl and the other -- in initializing of 
TwoStacksPlainDatagramSocketImpl.

I suspect that the reason might be due to unordered initialization:
AbstractPlainDatagramSocketImpl, the parent of both classes above, 
explicitly loads TwoStacksPlainDatagramSocketImpl from the native init().
Thus, when both classes are being initialized concurrently, it may end 
with a clash.


Another issue noticed by Mark Sheppard is that the Windows version of 
DefaultDatagramSocketImplFactory.createDatagramSocketImpl() isn't 
synchronized, but reads/modifies shared data.
Thus, I removed modification and declared all the accessed fields final.

Would you please help review the proposed fix?

BUGURL: https://bugs.openjdk.java.net/browse/JDK-8072466
WEBREV: http://cr.openjdk.java.net/~igerasim/8072466/0/webrev/

The build went fine on all the platforms, all the tests from 
(net|nio|io) passed Okay.

Sincerely yours,
Ivan