Contrary to the existing Task Sink, the Async and Sync Mutex Sinks
handle buffers in the `PadSinkHandler` directly. The Async Mutex
Sink uses an async Mutex for the `PadSinkHandlerInner` while the
Sync Mutex Sink uses... a sync Mutex.
All Sinks share the same settings and stats manager.
Use the `--sink` command line option to select the sink (default is
`sync-mutex` since it allows evaluating the framework with as little
overhead as possible.
Also apply various fixes:
- Only keep the segment start instead of the full `Segment`. This
helps with cache locality (`Segment` is a plain struct with many
fields) and avoids downcasting the generic `Segment` upon each
buffer handling.
- Box the `Stat`s. This should improve cache locality a bit.
- Fix EOS handling which took ages for no benefits in this
particular use case.
- Use a macro to raise log level in the main element.
- Move error handling during item processing in `handle_loop_error`.
This function was precisely designed for this and it should reduce
the `handle_item`'s Future size.
Implement a test that initializes pipelines with minimalistic
theadshare src and sink. This can help with the evaluation of
changes to the threadshare runtime or with element
implementation details. It makes it easy to run flamegraph or
callgrind and to focus on the threadshare runtime overhead.
