RFR: 8332535: Mark java/nio/channels/DatagramChannel/Loopback.java as intermittent

[Alan Bateman]

On Mon, 20 May 2024 15:39:52 GMT, SendaoYan <syan at openjdk.org> wrote:

> Hi all,
>   The test `test/jdk/java/nio/channels/DatagramChannel/Loopback.java` intermittent fail, the failure probability is about 2/1000. This PR mark this test intermittent, and print more message to investigate the intermittent failure. Only change the testcase, no risk.

No objection to add the keyword. From a quick look at the logs then it hints that it may be a kernel issue rather than a JDK issue, e.g. here one of the failures in the logs you attached:


UNSPEC socket
join ff02:0:0:0:0:0:0:a @ veth87b01b2
set outgoing multicast interface to veth87b01b2
IP_MULTICAST_LOOP enabled
send /[0:0:0:0:0:0:0:0]:50287 -> /[ff02:0:0:0:0:0:0:a]:50287
received java.nio.HeapByteBuffer[pos=5 lim=100 cap=100] from /[fe80:0:0:0:8cf3:1bff:fe85:f8e6%5]:50287
IP_MULTICAST_LOOP disabled
send /[0:0:0:0:0:0:0:0]:50287 -> /[ff02:0:0:0:0:0:0:a]:50287
selected 1
received java.nio.HeapByteBuffer[pos=5 lim=5 cap=100] from /[fe80:0:0:0:8cf3:1bff:fe85:f8e6%5]:50287
STDERR:
java.lang.RuntimeException: Unexpected message


I assume veth87b01b2 is a virtual interface. When IP_MULTICAST_LOOP is enabled the 5-byte multicast datagram is looped as expected. When IP_MULTICAST_LOOP is disabled then it appears to be looped again.  So this may require digging into the kernel to better understand this. It would be interesting to know if it's always IPv6 where the failures happen.

-------------

PR Comment: https://git.openjdk.org/jdk/pull/19314#issuecomment-2120830503