RFR: 8280113: (dc) DatagramSocket.receive does not always throw when the channel is closed

[Alan Bateman]

This is an issue with the async close of a DatagramChannel when a thread is blocked in its adaptor's receive method and the underlying socket is non-blocking.  The async close causes poll to wakeup and the underlying receive to return 0 so it can't be distinguished from a receive of a zero-length datagram. The channel state needs to be checked to distinguish the two cases so that AsynchronousCloseException can be thrown if the channel has been closed. The bug goes back to JDK 14 when caching of sockaddr structured was introduced.

The test case creates the conditions to exercise the case for both the timed and untimed receive. The bug report is the timed case, which receives two datagrams before attempting a timed receive. The harder case to test is the untimed case so the test uses a virtual thread to force the underlying socket to be non-blocking.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/12674/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12674&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8280113
  Stats: 122 lines in 2 files changed: 115 ins; 0 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/12674.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12674/head:pull/12674

PR: https://git.openjdk.org/jdk/pull/12674