Enrico Olivelli ac23f2485e Expose the global direct memory counter. (#8945)
Motivation:
This counter is very useful in order to monitor Netty without having every ByteBufAllocator in the JVM

Modification:
Expose the value of DIRECT_MEMORY_COUNTER as we are already doing for DIRECT_MEMORY_LIMIT.
We are returning -1 in case that DIRECT_MEMORY_COUNTER is not available.

Result:

Be able to get the amount of direct memory used.
2019-03-19 08:35:18 +01:00
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