Task state machines used to execute in an executor from the Futures
crate. State transitions actions and iteration functions were then
spawned on the target threadshare Context.
This commit directly spawns the task state machine on the threadshare
Context. This simplifies code a bit and paves the way for the changes
described in [1].
Also introduces struct `StateMachineHandle`, which gather together
fields to communicate and synchronize with the StateMachine. Renamed
`StateMachine::run` as `spawn` and return `StateMachineHandle`.
[1]: https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/793#note_1464400
The way the runtime::Task is implemented, UdpSinkTask is available
as a mutable ref in all the TaskImpl functions, which offers the
opportunity to avoid using Mutexes.
Main higlights:
- Removed the back and forth calls between UdpSinkPadHandler
and UdpSinkTask.
- Udp sockets are now part of UdpSinkTask, which is also in
charge of preparing them instead of leaving this to UdpSink.
This removed the need for Context::enter since
TaskImpl::prepare already operates under the target Context.
- In order for the clients list to be visible from the UdpSink,
this list was maintained by UdpSinkPadHandler which was also
in charge of (un)configuring the Udp sockets. The sockets are
now part of UdpSinkTask, which is also in charge of the
(un)configuration. Add/remove/replace requests are passed as
commands to the UdpSinkTask via a channel.
- The clients list visible to the UdpSink is now part of the
Settings (it is also a read/write property). Since the actual
socket (un)configuration is asynchronously handled by the Task,
the clients list is updated by the add/remove/replace signals
and set_property("clients", ..). Should a problem occur during
the async (un)configuration, and only in this case, the
UdpSinkTask would update the clients lists in Settings
accordingly so that it stays consistent with the internal state.
- The function clear_clients was renamed as replace_with_clients.
- clients is now based on a BTreeSet instead of a Vec. All the
managing functions perform some sort of lookup prior to updating
the collection. It also ease implementation.
- Removed the UdpSinkPadHandler RwLock. Using flume channels, we
are able to clone the Receiver so it can be stored in UdpSink
and reused when preparing the UdpSinkTask.
The I/O handle was dropped prior to removing it from the reactor,
which caused `Poller::delete` to fail due to an invalid file
descriptor. This used to happen silently unless the same fd was
added again, e.g. by changing states in the pipeline as follow:
Null -> Playing -> Null -> Playing.
In which case `Poller::add` failed due to an already existing file.
This commit makes sure the fd is removed from the reactor prior to
dropping the handle. In order to achieve this, a new task is spawned
on the `Context` on which the I/O was originally registered, allowing
it to access the proper `Reactor`. The I/O can then safely be dropped.
Because the I/O handle is moved to the spawned future, this solution
requires adding the `Send + 'static` bounds to the I/O handle used
within the `Async` wrapper. This appears not too restrictive for
existing implementations though. Other attempts were considered,
but they would cause deadlocks.
This new approach also solves a potential race condition where a
fd could be re-registered in a `Reactor` before it was removed.
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
cargo-c will produce a pkg-config file making it easier to statically
link plugins.
Also add 'static' features for plugins depending on < 1.14 as this is the
minimal required version to use static linking because of ABI changes in
core.
There is no way to dynamically ask Cargo to build static or dynamic lib
so we have to build both and pick the one we care when doing the meson
processing.
Fix#88
StateMachines are spawned on a runtime::Context which uses a tokio
runtime. The StateMachine doesn't need all the features from tokio
such as the IO and timers drivers.
This commit makes use of a light-weight futures executor to spawn
the StateMachines.
