This is a follow-up to commit 7ee4afac.
This commit cleans up the `Pad{Sink,Src}Handler` by
- Keeping arguments which are strictly necessary.
- Passing arguments by value for the trait functions which return
a `Future`. The arguments which were previously passed by reference
were `clone`d internally and then `clone`d again in most
implementations.
There are unfortunate differences in trait function signatures
between those which return a `Future` and the sync functions. This
is due to the requirement for the arguments to be moved to the
resulting `Future`, whereas sync functions can rely on references.
One particular notable difference is the use of the `imp` in sync
functions instead of the `elem` in functions returning a `Future`.
Because the `imp` is not guaranteed to implement `Clone`, we can't
move it to the resulting `Future`, so the `elem` is used.
The threadshare executor was based on a modified version of tokio
which implemented the throttling strategy in the BasicScheduler.
Upstream tokio codebase has significantly diverged from what it
was when the throttling strategy was implemented making it hard
to follow. This means that we can hardly get updates from the
upstream project and when we cherry pick fixes, we can't reflect
the state of the project on our fork's version. As a consequence,
tools such as cargo-deny can't check for RUSTSEC fixes in our fork.
The smol ecosystem makes it quite easy to implement and maintain
a custom async executor. This MR imports the smol parts that
need modifications to comply with the threadshare model and implements
a throttling executor in place of the tokio fork.
Networking tokio specific types are replaced with Async wrappers
in the spirit of [smol-rs/async-io]. Note however that the Async
wrappers needed modifications in order to use the per thread
Reactor model. This means that higher level upstream networking
crates such as [async-net] can not be used with our Async
implementation.
Based on the example benchmark with ts-udpsrc, performances seem on par
with what we achieved using the tokio fork.
Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/issues/118
Related to https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/604
