RFE: NetworkChecker modifications

[jamoore]

See:

• ​https://github.com/openmicroscopy/openmicroscopy/issues/821 (J-M)
• ​https://github.com/openmicroscopy/openmicroscopy/pull/1070 (Zeb) (and ​https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=4509)
• ​https://github.com/openmicroscopy/openmicroscopy/pull/1075 (J-M)
• ​https://github.com/openmicroscopy/openmicroscopy/pull/1128 (Josh)

Now that isNetworkUp() is called on every remote invocation reducing blockages will become paramount.

Suggested improvements from a discussion with Chris Allan:

• Move from testing openmicroscopy.org.uk to testing the server/port that Ice is configured to use. This may require housing the NetworkChecker inside of the SecurityContext, though on shutdown it's unclear which one should be used.
• Set timeouts on all sockets. If using URL, set via ​URLConnection#setReadTimeout

Further improvements which could also be considered (perhaps as a second ticket):

• Check uses of getHostAddress for hanging (see ​https://github.com/openmicroscopy/openmicroscopy/pull/1075/files#L3R2384)
• Consider a reflection-based method which would use the improved Java 6 APIs if available. (Done in PR 1128)
• Refactor NetworkChecker? to include logging.

[jamoore]

See: ​https://www.openmicroscopy.org/qa2/qa/feedback/6622

[jburel]

Unfortunately it has to be made on every method call at the moment
Any Java 6 feature cannot be considered on 4.4.x since the minimum required is 1.5

[jburel]

Move from testing openmicroscopy.org.uk to testing the server/port that Ice is configured to use. This may require housing the NetworkChecker inside of the SecurityContext, though on shutdown it's unclear which one should be used.

That was the initial idea, but I did not have a chance to refactor the code. Note that the check only happens on linux due to again a limitation of Java 1.5

• First thing to do will be to re-activate the Java 1.6 or higher code on develop to see.