RFR: 8338452: (dc) DatagramChannelImpl.blockingReceive with timeout may block indefinitely if all datagrams blocked by SecurityManager

[Alan Bateman]

A small regression from JDK-8338142 that arises with DatagramSocket.receive with a timeout and a SecurityManager, or when using a really small timeout (like 1ms). In these cases, the remaining time may be computed as negative which causes the receive to block indefinitely waiting for a datagram. 

Timed receive requires timeout adjustment in two places (outer and inner loops). This complexity will go away when the SecurityManager implementation is removed. For now, I've kept the changes as small as possible so that the adjustment in the outer loop is only done when the datagram is denied by the security manager.

The test java/net/DatagramSocket/TimeoutWithSM.java exercises this code. It has failed at least once since JDK-8338142 was integrated.

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/20609/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20609&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338452
  Stats: 15 lines in 1 file changed: 11 ins; 4 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20609.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20609/head:pull/20609

PR: https://git.openjdk.org/jdk/pull/20609