onBackpressureBufferToFile review please

The ability to buffer streams to disk has been something that I've wondered about for a while.

Can I get peoples comments/review of this new operator please?

Transformers.onBackpressureBufferToFile

I'd love to get review of this new operator in terms of

• what use cases have you got? (volume, serialized size, rate, platform, constraints)
• overall approach
• API
• correctness of code (a big one because of the numerous sections of code subject to concurrency)
• testing on different OS (currently just tested on linux)
• performance (I've favoured correctness initially)
• anything else you think of

The code is in the master branch and runtime jar is on Maven Central as described in rxjava-extras README.

A quick way of contributing is to run a long running test (~30 mins) on your machine:

git clone https://github.com/davidmoten/rxjava-extras.git
cd rxjava-extras
./test-long.sh 

On non-nix platform just run this command instead of test-long.sh:

mvn clean install -Dmax.small=100000000 -Dmax.medium=300000 -Dmax.seconds=600 -Dloops=10000