RFR: 8274736: Concurrent read/close of SSLSockets causes SSLSessions to be invalidated unnecessarily

[Jamil Nimeh]

This fix handles cases where two or more threads may be acting on a single SSLSocket instance.  In cases where one thread closes the socket while the other is in the middle of a read, a SocketException is appropriately thrown, but it results in SSLSession invalidation even though the session was legitimately negotiated at an earlier point in time and should remain in the cache.

JBS: https://bugs.openjdk.java.net/browse/JDK-8274736

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Commit messages:
 - Place server in background thread, minor cleanups
 - 8274736: Concurrent read/close of SSLSockets causes SSLSessions to be invalidated unnecessarily

Changes: https://git.openjdk.java.net/jdk/pull/6197/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6197&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274736
  Stats: 397 lines in 3 files changed: 393 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6197.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6197/head:pull/6197

PR: https://git.openjdk.java.net/jdk/pull/6197