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Remove futures dependency in lightning-background-processor
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As `futures` apparently makes no guarantees on MSRVs even in patch
releases we really can't rely on it at all, and while it currently
has an acceptable MSRV without the macros feature, its best to just
remove it wholesale.

Luckily, removing it is relatively trivial, even if it requires
the most trivial of unsafe tags.
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TheBlueMatt committed Mar 30, 2023
1 parent 0ea19f3 commit cf0e7dc
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Showing 2 changed files with 38 additions and 34 deletions.
3 changes: 1 addition & 2 deletions lightning-background-processor/Cargo.toml
Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,7 @@ all-features = true
rustdoc-args = ["--cfg", "docsrs"]

[features]
futures = [ "futures-util" ]
futures = [ ]
std = ["lightning/std", "lightning-rapid-gossip-sync/std"]

default = ["std"]
Expand All @@ -23,7 +23,6 @@ default = ["std"]
bitcoin = { version = "0.29.0", default-features = false }
lightning = { version = "0.0.114", path = "../lightning", default-features = false }
lightning-rapid-gossip-sync = { version = "0.0.114", path = "../lightning-rapid-gossip-sync", default-features = false }
futures-util = { version = "0.3", default-features = false, optional = true }

[dev-dependencies]
lightning = { version = "0.0.114", path = "../lightning", features = ["_test_utils"] }
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69 changes: 37 additions & 32 deletions lightning-background-processor/src/lib.rs
Original file line number Diff line number Diff line change
Expand Up @@ -7,7 +7,7 @@
#![deny(private_intra_doc_links)]

#![deny(missing_docs)]
#![deny(unsafe_code)]
#![cfg_attr(not(feature = "futures"), deny(unsafe_code))]

#![cfg_attr(docsrs, feature(doc_auto_cfg))]

Expand Down Expand Up @@ -52,8 +52,6 @@ use std::thread::{self, JoinHandle};
#[cfg(feature = "std")]
use std::time::Instant;

#[cfg(feature = "futures")]
use futures_util::task;
#[cfg(not(feature = "std"))]
use alloc::vec::Vec;

Expand Down Expand Up @@ -385,38 +383,45 @@ macro_rules! define_run_body {
}

#[cfg(feature = "futures")]
use core::future::Future;
#[cfg(feature = "futures")]
use core::task::Poll;
#[cfg(feature = "futures")]
use core::pin::Pin;
#[cfg(feature = "futures")]
use core::marker::Unpin;
#[cfg(feature = "futures")]
struct Selecter<A: Future<Output=()> + Unpin, B: Future<Output=bool> + Unpin> {
a: A,
b: B,
}
#[cfg(feature = "futures")]
enum SelecterOutput {
A, B(bool),
}
pub(crate) mod futures_util {
use core::future::Future;
use core::task::{Poll, Waker, RawWaker, RawWakerVTable};
use core::pin::Pin;
use core::marker::Unpin;
pub(crate) struct Selecter<A: Future<Output=()> + Unpin, B: Future<Output=bool> + Unpin> {
pub a: A,
pub b: B,
}
pub(crate) enum SelecterOutput {
A, B(bool),
}

#[cfg(feature = "futures")]
impl<A: Future<Output=()> + Unpin, B: Future<Output=bool> + Unpin> Future for Selecter<A, B> {
type Output = SelecterOutput;
fn poll(mut self: Pin<&mut Self>, ctx: &mut core::task::Context<'_>) -> Poll<SelecterOutput> {
match Pin::new(&mut self.a).poll(ctx) {
Poll::Ready(()) => { return Poll::Ready(SelecterOutput::A); },
Poll::Pending => {},
}
match Pin::new(&mut self.b).poll(ctx) {
Poll::Ready(res) => { return Poll::Ready(SelecterOutput::B(res)); },
Poll::Pending => {},
impl<A: Future<Output=()> + Unpin, B: Future<Output=bool> + Unpin> Future for Selecter<A, B> {
type Output = SelecterOutput;
fn poll(mut self: Pin<&mut Self>, ctx: &mut core::task::Context<'_>) -> Poll<SelecterOutput> {
match Pin::new(&mut self.a).poll(ctx) {
Poll::Ready(()) => { return Poll::Ready(SelecterOutput::A); },
Poll::Pending => {},
}
match Pin::new(&mut self.b).poll(ctx) {
Poll::Ready(res) => { return Poll::Ready(SelecterOutput::B(res)); },
Poll::Pending => {},
}
Poll::Pending
}
Poll::Pending
}

fn dummy_waker_clone(_: *const ()) -> RawWaker { RawWaker::new(core::ptr::null(), &DUMMY_WAKER_VTABLE) }
fn dummy_waker_action(_: *const ()) { }

const DUMMY_WAKER_VTABLE: RawWakerVTable = RawWakerVTable::new(
dummy_waker_clone, dummy_waker_action, dummy_waker_action, dummy_waker_action);
pub(crate) fn dummy_waker() -> Waker { unsafe { Waker::from_raw(RawWaker::new(core::ptr::null(), &DUMMY_WAKER_VTABLE)) } }
}
#[cfg(feature = "futures")]
use futures_util::{Selecter, SelecterOutput, dummy_waker};
#[cfg(feature = "futures")]
use core::task;

/// Processes background events in a future.
///
Expand Down Expand Up @@ -517,7 +522,7 @@ where
}
}, |t| sleeper(Duration::from_secs(t)),
|fut: &mut SleepFuture, _| {
let mut waker = task::noop_waker();
let mut waker = dummy_waker();
let mut ctx = task::Context::from_waker(&mut waker);
core::pin::Pin::new(fut).poll(&mut ctx).is_ready()
})
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