class DataStreamer

A class which helps callers write streaming data operations to the underlying device.

This class provides the following value over calling "Journal::WriteData" directly:

Client-side coalescing.

This class groups together contiguous operations, only transmitting them to the writeback

subsystem once necessary.

Avoids blocking for large operations.

For operations which are larger than the underlying writeback buffer, caution must be taken to

avoid blocking on "Journal::WriteData", which creates a reservation, but does not begin

execution of the underlying data. To mitigate, this class begins execution of these data writes

if they are larger than an internal threshold (which is smaller than the entire writeback

buffer).

Allows ordering control over "all data", but not between intermediate data writes.

Typically, when data operations are issued, the caller cares that they all occur before a

following action, but the order between those data operations themselves does not matter. This

class enables callers to |Flush()| all prior data requests, without imposing an ordering on the

data requests issued by |StreamData()|.

This class is thread-compatible.