* Always pass user-specified MaxDirectMemorySize
We had been testing whether a user had passed a value for
MaxDirectMemorySize by parsing the output of "java -XX:PrintFlagsFinal
-version". If MaxDirectMemorySize equals zero, we set it to half of max
heap. The problem is that on Windows with JDK 8, a JDK bug incorrectly
truncates values over 4g and returns multiples of 4g as zero. In order
to always respect the user-defined settings, we need to check our input
to see if an "-XX:MaxDirectMemorySize" value has been passed.
* Always warn for Windows/jdk8 ergo issue
Even if a user has set MaxDirectMemorySize, they aren't future-proof for
this JDK bug. With this change, we issue a general warning for the
windows/JDK8 issue, and a specific warning if MaxDirectMemorySize is
unset.
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