RFR: 8316649: JMX connection timeout cannot be changed and uses the default of 0 (infinite)

[Kevin Walls]

RMI Connections (in general) should use a timeout on the Socket connect call by default.

JMX connections use RMI and some connection failures never terminate.  The hang described in 8316649 is hard to reproduce manually: the description says it can be caused by a firewall that never returns a response.

src/java.rmi/share/classes/sun/rmi/transport/tcp/TCPChannel.java
has other timeouts but nothing to control the initial Socket connect.

Defaulting to a 1 minute timeout on connect has no effect on existing tests for RMI and JMX, and should go unnoticed in applications unless there really is a significant connection delay.  Specifying zero for the new System Property sun.rmi.transport.tcp.initialConnectTimeout uses the old code path of a connect with no timeout.

I have a test, but it is not realistically usable: although specifying a 1 millisecond timeout will often fail (as expected/desired for the test), it will often pass as the connection happens immediately.

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Commit messages:
 - Ignore negative timeout values.
 - Make connect timeout static
 - 8316649: JMX connection timeout cannot be changed and uses the default of 0 (infinite)

Changes: https://git.openjdk.org/jdk/pull/16771/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16771&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316649
  Stats: 21 lines in 1 file changed: 19 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/16771.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16771/head:pull/16771

PR: https://git.openjdk.org/jdk/pull/16771