[jdk8u-dev] RFR: 8293562: KeepAliveCache Blocks Threads while Closing Connections

[Dhamoder Nalla]

Issue: [JDK-8293562](https://bugs.openjdk.org/browse/JDK-8293562): KeepAliveCache Blocks Threads while Closing Connections
Backport of PR https://github.com/openjdk/jdk11u-dev/pull/1890 fromJDK11 to JDK8.

The JDK11 patch doesn't apply cleanly 3/11 hunks need to be ported manually in KeepAliveCache.java.

Test performed:

JTreg jdk_tier1
JTreg jdk_tier2
New test case added to this PR passed with the fix and failed without it.

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Depends on: https://git.openjdk.org/jdk8u-dev/pull/407

Commit messages:
 - Backport 770c1f65c588f3156f9b70097df752d8059c1038

Changes: https://git.openjdk.org/jdk8u-dev/pull/409/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk8u-dev&pr=409&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8293562
  Stats: 306 lines in 3 files changed: 275 ins; 7 del; 24 mod
  Patch: https://git.openjdk.org/jdk8u-dev/pull/409.diff
  Fetch: git fetch https://git.openjdk.org/jdk8u-dev.git pull/409/head:pull/409

PR: https://git.openjdk.org/jdk8u-dev/pull/409