RFR: 8308807: [AIX] MulticastSocket and jdp test fails due to joinGroup

[Deepa Kumari]

On Wed, 21 Jun 2023 15:45:41 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>>> IIUC what @deepa181 is saying, it looks like the "IPv4 socket being unable to join an IPv4 multicast group" problems surfaced when we moved away from PlainDatagramSocketImpl in JDK 17? Probably because the delegate created does not factor in the ProtocolFamily and though we started with attempting to have an "IPv4 multicast socket join an IPv4 group", we end up trying to have an "IPv4/IPv6 dual-stack socket (the delegate) join an IPv4 group" which AIX doesn't permit.
>> 
>> IIRC It has never been possible to create a non-dual `MulticastSocket` / `DatagramSocket` without setting the property `-Djava.net.preferIPv4Stack=true`. The possibility to select a protocol family independently of this property is only available with `DatagramChannel`.
>
>> IIRC It has never been possible to create a non-dual `MulticastSocket` / `DatagramSocket` without setting the property `-Djava.net.preferIPv4Stack=true`. The possibility to select a protocol family independently of this property is only available with `DatagramChannel`.
> 
> Right now, Net.canIPv6SocketJoinIPv4Group() returns false on AIX so it will never attempt to join an IPv4 multicast group when the socket is IPv6.  The old DatagamSocketImpl didn't have an eager check, which makes me wonder what AIX supports, it's not clear!

Hi @AlanBateman , 

 I ran the Jtreg tests on **jdk17** and observed  the following tests passed unexpectedly when I set the **VM_OPTIONS to `-Djdk.net.usePlainDatagramSocketImpl=true`**

1. java/net/MulticastSocket/B6427403.java
2. java/net/MulticastSocket/NoLoopbackPackets.java
3. java/net/MulticastSocket/SetLoopbackMode.java
4. java/net/MulticastSocket/Test.java

I am curious about how setting the `jdk.net.usePlainDatagramSocketImpl` property impacts their behavior. I would like to understand why they pass with this configuration and whether it has any implications.

Could you please share your insights on this matter? I appreciate your assistance in understanding this behavior and ensuring the correctness of the tests.

Thank you.

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PR Comment: https://git.openjdk.org/jdk/pull/14142#issuecomment-1663829993