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swarm/src/lib: Continue polling network when behaviour is blocked (#2304)

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With https://github.com/libp2p/rust-libp2p/pull/2248 a connection task
`await`s sending an event to the behaviour before polling for new events
from the behaviour [1].

When `Swarm::poll` is unable to deliver an event to a connection task it
returns `Poll::Pending` even though (a) polling `Swarm::network` might be
able to make progress (`network_not_ready` being `false`) and (b) it
does not register a waker to be woken up [2].

In combination this can lead to a deadlock where a connection task waits
to send an event to the behaviour and `Swarm::poll` returns
`Poll::Pending` failing to send an event to the connection task, not
registering a waiker in order to be polled again.

With this commit `Swarm::poll` will only return `Poll::Pending`, when
failing to deliver an event to a connection task, if the network is
unable to make progress (i.e. `network_not_ready` being `true`).

In the long-run `Swarm::poll` should likely be redesigned, prioritizing
the behaviour over the network, given the former is the control plane
and the latter potentially yields new work from the outside.

[1]: ca1b7cf043/core/src/connection/pool/task.rs (L224-L232)
[2]: ca1b7cf043/swarm/src/lib.rs (L756-L783)
This commit is contained in:
Max Inden
2021-10-26 22:23:55 +02:00
committed by GitHub
parent 97509519c5
commit 4ef57383a6
1 changed files with 20 additions and 4 deletions
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24
swarm/src/lib.rs
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@ -765,7 +765,11 @@ where
if let Some(mut conn) = peer.connection(conn_id) { if let Some(mut conn) = peer.connection(conn_id) {
if let Some(event) = notify_one(&mut conn, event, cx) { if let Some(event) = notify_one(&mut conn, event, cx) {
this.pending_event = Some((peer_id, handler, event)); this.pending_event = Some((peer_id, handler, event));
return Poll::Pending; if network_not_ready {
return Poll::Pending;
} else {
continue;
}
} }
} }
} }
@ -775,7 +779,11 @@ where
{ {
let handler = PendingNotifyHandler::Any(ids); let handler = PendingNotifyHandler::Any(ids);
this.pending_event = Some((peer_id, handler, event)); this.pending_event = Some((peer_id, handler, event));
return Poll::Pending; if network_not_ready {
return Poll::Pending;
} else {
continue;
}
} }
} }
} }
@ -843,7 +851,11 @@ where
if let Some(event) = notify_one(&mut conn, event, cx) { if let Some(event) = notify_one(&mut conn, event, cx) {
let handler = PendingNotifyHandler::One(connection); let handler = PendingNotifyHandler::One(connection);
this.pending_event = Some((peer_id, handler, event)); this.pending_event = Some((peer_id, handler, event));
return Poll::Pending; if network_not_ready {
return Poll::Pending;
} else {
continue;
}
} }
} }
} }
@ -854,7 +866,11 @@ where
{ {
let handler = PendingNotifyHandler::Any(ids); let handler = PendingNotifyHandler::Any(ids);
this.pending_event = Some((peer_id, handler, event)); this.pending_event = Some((peer_id, handler, event));
return Poll::Pending; if network_not_ready {
return Poll::Pending;
} else {
continue;
}
} }
} }
} }