[C++] Add asynchronous RecordBatchStreamWriter

[asfimport]

We may want to provide an option to limit the queuing depth. The async writer can be initialized from a synchronous writer

Reporter: Wes McKinney / @wesm

_{Note: This issue was originally created as ARROW-1013. Please see the migration documentation for further details.}

[asfimport]

Antoine Pitrou / @pitrou:
Write() is generally asynchronous (e.g. the OS will queue writes in the background and not have you wait for the disk operation), so I'm not sure this would be very useful.

[asfimport]

Wes McKinney / @wesm:
I'm thinking about an asynchronous IPC writer, not making OutputStream::Write asynchronous. Writing into RecordBatchStreamWriter::WriteRecordBatch does have a non-trivial cost – I guess that we measure it in different scenarios. Ideal context would be Getting from one Flight client and Putting into another. Does that make sense?

[asfimport]

Antoine Pitrou / @pitrou:
Ah, right. I suppose so. This should be designed depending on the intended use cases.

[asfimport]

Antoine Pitrou / @pitrou:
@lidavidm What is your opinion on this issue?

[asfimport]

David Li / @lidavidm:
Another case where it might be useful is to hide the cost of compression but I agree with Antoine that we should find a concrete use case where we think this will speed things up first.

[asfimport]

Antoine Pitrou / @pitrou:
Closing for now. The benefits would probably be small, we can revisit later.