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use std::pin::Pin;
use anyhow::Result;
use anyhow::anyhow;
use futures::stream::StreamExt;
use futures::task::Poll;
use crate::Node;
use crate::NodeId;
use crate::DagBackend;
/// An async DAG, generic over Node, Node identifier and Backend implementation
pub struct AsyncDag<Id, N, Backend>
where Id: NodeId + Send,
N: Node<Id = Id>,
Backend: DagBackend<Id, N>
{
head: Id,
backend: Backend,
_node: std::marker::PhantomData<N>,
}
impl<Id, N, Backend> AsyncDag<Id, N, Backend>
where Id: NodeId + Send,
N: Node<Id = Id>,
Backend: DagBackend<Id, N>
{
pub async fn new(backend: Backend, head: N) -> Result<Self> {
backend
.get(head.id().clone())
.await?
.map(|node| {
AsyncDag {
head: node.id().clone(),
backend: backend,
_node: std::marker::PhantomData,
}
})
.ok_or_else(|| anyhow!("Head not found in backend"))
}
pub async fn has_id(&self, id: &Id) -> Result<bool> {
self.stream()
.map(|r| -> Result<bool> {
r.map(|node| node.id() == id)
})
.collect::<Vec<Result<bool>>>()
.await
.into_iter()
.fold(Ok(false), |acc, e| {
match (acc, e) {
(Err(e), _) => Err(e),
(Ok(_), Err(e)) => Err(e),
(Ok(a), Ok(b)) => Ok(a || b),
}
})
}
pub async fn get_next(&self, id: Id) -> Result<Vec<N>> {
self.backend
.get(id)
.await?
.ok_or_else(|| anyhow!("ID Not found"))?
.parent_ids()
.into_iter()
.map(|id| async move {
self.backend
.get(id)
.await
.transpose()
})
.collect::<futures::stream::FuturesUnordered<_>>()
.collect::<Vec<_>>()
.await
.into_iter()
.filter_map(|o| o)
.collect()
}
pub fn stream(&self) -> Stream<Id, N, Backend> {
Stream {
dag: self,
backlog: {
let mut v = Vec::with_capacity(2);
v.push(self.backend.get(self.head.clone()));
v
}
}
}
}
pub struct Stream<'a, Id, N, Backend>
where Id: NodeId + Send,
N: Node<Id = Id>,
Backend: DagBackend<Id, N>
{
dag: &'a AsyncDag<Id, N, Backend>,
backlog: Vec<Pin<Box<(dyn futures::future::Future<Output = Result<Option<N>>> + std::marker::Send + 'a)>>>,
}
impl<'a, Id, N, Backend> futures::stream::Stream for Stream<'a, Id, N, Backend>
where Id: NodeId + Send,
N: Node<Id = Id>,
Backend: DagBackend<Id, N>
{
type Item = Result<N>;
/// Attempt to resolve the next item in the stream.
/// Returns `Poll::Pending` if not ready, `Poll::Ready(Some(x))` if a value
/// is ready, and `Poll::Ready(None)` if the stream has completed.
fn poll_next(mut self: std::pin::Pin<&mut Self>, cx: &mut futures::task::Context<'_>) -> futures::task::Poll<Option<Self::Item>> {
if let Some(mut fut) = self.as_mut().backlog.pop() {
match fut.as_mut().poll(cx) {
Poll::Ready(Err(e)) => Poll::Ready(Some(Err(e))),
Poll::Ready(Ok(Some(node))) => {
for parent in node.parent_ids().into_iter() {
let fut = self.dag.backend.get(parent);
self.as_mut().backlog.push(fut);
}
Poll::Ready(Some(Ok(node)))
},
Poll::Ready(Ok(None)) => {
// backend.get() returned Ok(None), so the referenced node seems not to exist
//
// TODO: Decide whether we should return an error here.
cx.waker().wake_by_ref();
Poll::Pending
},
Poll::Pending => {
cx.waker().wake_by_ref();
Poll::Pending
}
}
} else {
Poll::Ready(None)
}
}
}
#[cfg(test)]
mod tests {
use std::pin::Pin;
use anyhow::Result;
use anyhow::anyhow;
use async_trait::async_trait;
use tokio_test::block_on;
use crate::DagBackend;
use crate::AsyncDag;
use crate::test_impl as test;
#[test]
fn test_dag_two_nodes() {
let head = test::Node {
id: test::Id(1),
parents: vec![test::Id(0)],
data: 43,
};
let b = test::Backend(vec![
{
Some(test::Node {
id: test::Id(0),
parents: vec![],
data: 42,
})
},
{
Some(head.clone())
},
]);
{
let node = tokio_test::block_on(b.get(test::Id(1))).unwrap().unwrap();
assert_eq!(node.data, 43);
assert_eq!(node.id, test::Id(1));
assert!(!node.parents.is_empty()); // to check whether the parent is set
}
let dag = tokio_test::block_on(AsyncDag::new(b, head));
assert!(dag.is_ok());
let dag = dag.unwrap();
{
let has_id = tokio_test::block_on(dag.has_id(&test::Id(0)));
assert!(has_id.is_ok());
let has_id = has_id.unwrap();
assert!(has_id);
}
{
let has_id = tokio_test::block_on(dag.has_id(&test::Id(1)));
assert!(has_id.is_ok());
let has_id = has_id.unwrap();
assert!(has_id);
}
{
let next = tokio_test::block_on(dag.get_next(test::Id(1)));
assert!(next.is_ok());
let mut next = next.unwrap();
assert_eq!(next.len(), 1);
let node = next.pop();
assert!(node.is_some());
let node = node.unwrap();
assert_eq!(node.id, test::Id(0));
assert_eq!(node.data, 42);
assert!(node.parents.is_empty());
}
}
#[test]
fn test_dag_two_nodes_stream() {
use futures::StreamExt;
let head = test::Node {
id: test::Id(1),
parents: vec![test::Id(0)],
data: 43,
};
let b = test::Backend(vec![
{
Some(test::Node {
id: test::Id(0),
parents: vec![],
data: 42,
})
},
{
Some(head.clone())
},
]);
let dag = tokio_test::block_on(AsyncDag::new(b, head));
assert!(dag.is_ok());
let dag = dag.unwrap();
let v = tokio_test::block_on(dag.stream().collect::<Vec<_>>());
assert_eq!(v.len(), 2, "Expected two nodes: {:?}", v);
assert_eq!(v[0].as_ref().unwrap().id, test::Id(1));
assert_eq!(v[1].as_ref().unwrap().id, test::Id(0));
}
}
|
