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threadshare/runtime: Add a dummy context when blocking the current thread

Browse source 
This allows downstreams to function as if a normal context thread is
operating upstream apart from not being able to spawn new tasks.

Fixes https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/issues/96
This commit is contained in:
Sebastian Dröge 2020-03-16 15:03:15 +02:00
parent 12dcca3f17
commit 56895f35bc
3 changed files with 157 additions and 41 deletions
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184
gst-plugin-threadshare/src/runtime/executor.rs
View file

@ -77,28 +77,86 @@ tokio::task_local! {
static CURRENT_TASK_ID: TaskId;
}
/// Blocks on `future` in one way or another if possible.
///
/// IO & time related `Future`s must be handled within their own [`Context`].
/// Wait for the result using a [`JoinHandle`] or a `channel`.
///
/// If there's currently an active `Context` with a task, then the future is only queued up as a
/// pending sub task for that task.
///
/// Otherwise the current thread is blocking and the passed in future is executed.
///
/// Note that you must not pass any futures here that wait for the currently active task in one way
/// or another as this would deadlock!
pub fn block_on_or_add_sub_task<Fut: Future + Send + 'static>(future: Fut) -> Option<Fut::Output> {
if let Some((cur_context, cur_task_id)) = Context::current_task() {
gst_debug!(
RUNTIME_CAT,
"Adding subtask to task {:?} on context {}",
cur_task_id,
cur_context.name()
);
let _ = Context::add_sub_task(async move {
future.await;
Ok(())
});
return None;
}
// Not running in a Context thread so we can block
Some(block_on(future))
}
/// Blocks on `future`.
///
/// IO & time related `Future`s must be handled within their own [`Context`].
/// Wait for the result using a [`JoinHandle`] or a `channel`.
///
/// This function must NOT be called within a [`Context`] thread.
/// The reason is this would prevent any task operating on the
/// [`Context`] from making progress.
/// The current thread is blocking and the passed in future is executed.
///
/// # Panics
///
/// This function panics if called within a [`Context`] thread.
///
/// [`Context`]: struct.Context.html
/// [`JoinHandle`]: enum.JoinHandle.html
pub fn block_on<Fut: Future>(future: Fut) -> Fut::Output {
if Context::is_context_thread() {
panic!("Attempt to `block_on` within a `Context` thread");
}
assert!(!Context::is_context_thread());
// Not running in a Context thread so we can block
futures::executor::block_on(future)
gst_debug!(RUNTIME_CAT, "Blocking on new dummy context");
let context = Context(Arc::new(ContextInner {
real: None,
task_queues: Mutex::new((0, HashMap::new())),
}));
CURRENT_THREAD_CONTEXT.with(move |cur_ctx| {
*cur_ctx.borrow_mut() = Some(context.downgrade());
let res = futures::executor::block_on(async move {
let res = CURRENT_TASK_ID
.scope(TaskId(0), async move {
let task_id = CURRENT_TASK_ID.try_with(|task_id| *task_id).ok();
assert_eq!(task_id, Some(TaskId(0)));
let res = future.await;
while Context::current_has_sub_tasks() {
if Context::drain_sub_tasks().await.is_err() {
break;
}
}
res
})
.await;
res
});
*cur_ctx.borrow_mut() = None;
res
})
}
struct ContextThread {
@ -114,7 +172,15 @@ impl ContextThread {
});
let context = context_receiver.recv().expect("Context thread init failed");
*context.0.shutdown.join.lock().unwrap() = Some(join);
*context
.0
.real
.as_ref()
.unwrap()
.shutdown
.join
.lock()
.unwrap() = Some(join);
context
}
@ -139,9 +205,11 @@ impl ContextThread {
};
let context = Context(Arc::new(ContextInner {
name: self.name.clone(),
handle: Mutex::new(runtime.handle().clone()),
shutdown,
real: Some(ContextRealInner {
name: self.name.clone(),
handle: Mutex::new(runtime.handle().clone()),
shutdown,
}),
task_queues: Mutex::new((0, HashMap::new())),
}));
@ -279,19 +347,27 @@ impl<T> fmt::Debug for JoinHandle<T> {
}
#[derive(Debug)]
struct ContextInner {
struct ContextRealInner {
name: String,
handle: Mutex<tokio::runtime::Handle>,
// Only used for dropping
shutdown: ContextShutdown,
}
#[derive(Debug)]
struct ContextInner {
// Otherwise a dummy context
real: Option<ContextRealInner>,
task_queues: Mutex<(u64, HashMap<u64, SubTaskQueue>)>,
}
impl Drop for ContextInner {
fn drop(&mut self) {
let mut contexts = CONTEXTS.lock().unwrap();
gst_debug!(RUNTIME_CAT, "Finalizing context '{}'", self.name);
contexts.remove(&self.name);
if let Some(ref real) = self.real {
let mut contexts = CONTEXTS.lock().unwrap();
gst_debug!(RUNTIME_CAT, "Finalizing context '{}'", real.name);
contexts.remove(&real.name);
}
}
}
@ -329,11 +405,17 @@ impl Eq for Context {}
impl Context {
pub fn acquire(context_name: &str, wait: u32) -> Result<Self, io::Error> {
assert_ne!(context_name, "DUMMY");
let mut contexts = CONTEXTS.lock().unwrap();
if let Some(inner_weak) = contexts.get(context_name) {
if let Some(inner_strong) = inner_weak.upgrade() {
gst_debug!(RUNTIME_CAT, "Joining Context '{}'", inner_strong.name);
gst_debug!(
RUNTIME_CAT,
"Joining Context '{}'",
inner_strong.real.as_ref().unwrap().name
);
return Ok(Context(inner_strong));
}
}
@ -341,7 +423,11 @@ impl Context {
let context = ContextThread::start(context_name, wait);
contexts.insert(context_name.into(), Arc::downgrade(&context.0));
gst_debug!(RUNTIME_CAT, "New Context '{}'", context.0.name);
gst_debug!(
RUNTIME_CAT,
"New Context '{}'",
context.0.real.as_ref().unwrap().name
);
Ok(context)
}
@ -350,7 +436,10 @@ impl Context {
}
pub fn name(&self) -> &str {
self.0.name.as_str()
match self.0.real {
Some(ref real) => real.name.as_str(),
None => "DUMMY",
}
}
/// Returns `true` if a `Context` is running on current thread.
@ -376,7 +465,7 @@ impl Context {
.as_ref()
.and_then(|ctx_weak| ctx_weak.upgrade())
.and_then(|ctx| {
let task_id = ctx.enter(|| CURRENT_TASK_ID.try_with(|task_id| *task_id).ok());
let task_id = CURRENT_TASK_ID.try_with(|task_id| *task_id).ok();
task_id.map(move |task_id| (ctx, task_id))
})
@ -387,7 +476,12 @@ impl Context {
where
F: FnOnce() -> R,
{
self.0.handle.lock().unwrap().enter(f)
let real = match self.0.real {
Some(ref real) => real,
None => panic!("Can't enter on dummy context"),
};
real.handle.lock().unwrap().enter(f)
}
pub fn spawn<Fut>(&self, future: Fut) -> JoinHandle<Fut::Output>
@ -395,6 +489,11 @@ impl Context {
Fut: Future + Send + 'static,
Fut::Output: Send + 'static,
{
let real = match self.0.real {
Some(ref real) => real,
None => panic!("Can't spawn new tasks on dummy context"),
};
let mut task_queues = self.0.task_queues.lock().unwrap();
let id = task_queues.0;
task_queues.0 += 1;
@ -405,16 +504,18 @@ impl Context {
RUNTIME_CAT,
"Spawning new task {:?} on context {}",
id,
self.0.name
real.name
);
let join_handle = self.0.handle.lock().unwrap().spawn(async move {
let join_handle = real.handle.lock().unwrap().spawn(async move {
let ctx = Context::current().unwrap();
let real = ctx.0.real.as_ref().unwrap();
gst_trace!(
RUNTIME_CAT,
"Running task {:?} on context {}",
id,
ctx.0.name
real.name
);
let res = CURRENT_TASK_ID.scope(id, future).await;
@ -428,14 +529,14 @@ impl Context {
RUNTIME_CAT,
"Task {:?} on context {} has {} pending sub tasks",
id,
ctx.0.name,
real.name,
l
);
}
}
}
gst_trace!(RUNTIME_CAT, "Task {:?} on context {} done", id, ctx.0.name);
gst_trace!(RUNTIME_CAT, "Task {:?} on context {} done", id, real.name);
res
});
@ -479,12 +580,20 @@ impl Context {
let mut task_queues = ctx.0.task_queues.lock().unwrap();
match task_queues.1.get_mut(&task_id.0) {
Some(task_queue) => {
gst_trace!(
RUNTIME_CAT,
"Adding subtask to {:?} on context {}",
task_id,
ctx.0.name
);
if let Some(ref real) = ctx.0.real {
gst_trace!(
RUNTIME_CAT,
"Adding subtask to {:?} on context {}",
task_id,
real.name
);
} else {
gst_trace!(
RUNTIME_CAT,
"Adding subtask to {:?} on dummy context",
task_id,
);
}
task_queue.0.push_back(sub_task.boxed());
Ok(())
}
@ -519,7 +628,12 @@ impl Context {
}
};
let name = self.0.name.clone();
let name = self
.0
.real
.as_ref()
.map(|r| r.name.clone())
.unwrap_or_else(|| String::from("DUMMY"));
async move {
if !task_queue.0.is_empty() {
gst_log!(

5
gst-plugin-threadshare/src/runtime/pad.rs
View file

@ -83,7 +83,7 @@ use std::marker::PhantomData;
use std::sync;
use std::sync::{Arc, Weak};
use super::executor::Context;
use super::executor::{block_on_or_add_sub_task, Context};
use super::task::Task;
use super::RUNTIME_CAT;
@ -986,7 +986,8 @@ impl<'a> PadSinkRef<'a> {
// Note: we don't use `crate::runtime::executor::block_on` here
// because `Context::is_context_thread()` is checked in the `if`
// statement above.
futures::executor::block_on(fut.map(|res| res.map(|_| gst::FlowSuccess::Ok)))
block_on_or_add_sub_task(fut.map(|res| res.map(|_| gst::FlowSuccess::Ok)))
.unwrap_or(Ok(gst::FlowSuccess::Ok))
} else {
Ok(gst::FlowSuccess::Ok)
}

9
gst-plugin-threadshare/src/runtime/task.rs
View file

@ -27,6 +27,7 @@ use gst::{gst_debug, gst_log, gst_trace, gst_warning};
use std::fmt;
use std::sync::{Arc, Mutex};
use super::executor::block_on;
use super::{Context, JoinHandle, RUNTIME_CAT};
#[derive(Clone, Debug, Eq, PartialEq)]
@ -209,7 +210,7 @@ impl Task {
cur_task_id,
cur_context.name()
);
let _ = futures::executor::block_on(prepare_handle);
let _ = block_on(prepare_handle);
}
} else {
gst_debug!(
@ -217,7 +218,7 @@ impl Task {
"Synchronously waiting for task {:?}",
prepare_handle
);
let _ = futures::executor::block_on(prepare_handle);
let _ = block_on(prepare_handle);
}
}
@ -422,7 +423,7 @@ impl Task {
cur_task_id,
cur_context.name()
);
let _ = futures::executor::block_on(loop_handle);
let _ = block_on(loop_handle);
}
} else {
gst_debug!(
@ -430,7 +431,7 @@ impl Task {
"Synchronously waiting for task {:?}",
loop_handle
);
let _ = futures::executor::block_on(loop_handle);
let _ = block_on(loop_handle);
}
}