Add cancel trait

[Thomasdezeeuw]

It's now implemented for both the Futures and AyscIterators:

a10/src/op.rs

Lines 722 to 746 in 6ca2971

	/// Attempt to cancel this operation.
	///
	#[doc = concat!("Also see [`", stringify!($name), "::cancel`].")]
	pub fn try_cancel(&mut self) -> $crate::io::CancelResult {
	match self.state {
	$crate::op::OpState::NotStarted(_) => $crate::io::CancelResult::NotStarted,
	$crate::op::OpState::Running(op_index) => {
	match self.fd.sq.add_no_result(|submission| unsafe { submission.cancel_op(op_index) }) {
	std::result::Result::Ok(()) => $crate::io::CancelResult::Canceled,
	std::result::Result::Err($crate::QueueFull(())) => $crate::io::CancelResult::QueueFull,
	}
	},
	$crate::op::OpState::Done => $crate::io::CancelResult::Canceled,
	}
	}
	/// Cancel this operation.
	pub fn cancel(&mut self) -> $crate::io::CancelOp {
	let op_index = match self.state {
	$crate::op::OpState::NotStarted(_) => None,
	$crate::op::OpState::Running(op_index) => Some(op_index),
	$crate::op::OpState::Done => None,
	};
	$crate::io::CancelOp { sq: &self.fd.sq, op_index }
	}

a10/src/op.rs

Lines 1027 to 1051 in 6ca2971

	/// Attempt to cancel this operation.
	///
	#[doc = concat!("Also see [`", stringify!($name), "::cancel`].")]
	pub fn try_cancel(&mut self) -> $crate::io::CancelResult {
	match self.state {
	$crate::op::OpState::NotStarted(_) => $crate::io::CancelResult::NotStarted,
	$crate::op::OpState::Running(op_index) => {
	match self.fd.sq.add_no_result(|submission| unsafe { submission.cancel_op(op_index) }) {
	std::result::Result::Ok(()) => $crate::io::CancelResult::Canceled,
	std::result::Result::Err($crate::QueueFull(())) => $crate::io::CancelResult::QueueFull,
	}
	},
	$crate::op::OpState::Done => $crate::io::CancelResult::Canceled,
	}
	}
	/// Cancel this operation.
	pub fn cancel(&mut self) -> $crate::io::CancelOp {
	let op_index = match self.state {
	$crate::op::OpState::NotStarted(_) => None,
	$crate::op::OpState::Running(op_index) => Some(op_index),
	$crate::op::OpState::Done => None,
	};
	$crate::io::CancelOp { sq: &self.fd.sq, op_index }
	}