1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169

use async_std::channel::{bounded, Receiver, Sender};
use std::fmt;

/// A mechanism to wait for a single signal which can be checked at any time.
///
/// A Fuze can be checked synchronously, and will show up as burnt only once it’s been burnt. It
/// can be awaited while it’s unburnt, and it can be Cloned and used without `mut` at any time.
///
/// Useful for exit conditions and as a one-off no-payload channel.
///
/// # Example
///
/// Basic usage:
///
/// ```
/// use fuze::Fuze;
/// use async_std::task;
/// use std::time::Duration;
///
/// let f1 = Fuze::new();
/// assert_eq!(f1.burnt(), false);
///
/// let f2 = f1.clone();
/// task::block_on(async move {
///		assert_eq!(f2.burnt(), false);
///
///		let f3 = f2.clone();
///		task::spawn(async move {
///			assert_eq!(f3.burnt(), false);
///
///			task::sleep(Duration::from_secs(1)).await;
///
///			// this first burn unblocks anything that wait()s on the fuze:
///			f3.burn();
///
///			assert_eq!(f3.burnt(), true);
///
///			// this second burn does nothing:
///			f3.burn();
///
///			assert_eq!(f3.burnt(), true);
///		});
///
///		// this call will block until the f3.burn() call above:
///		println!("first");
///		f2.wait().await;
///		assert_eq!(f2.burnt(), true);
///
///		// now that the fuze is burnt, this call returns immediately:
///		println!("second");
///		f2.wait().await;
/// });
///
///	assert_eq!(f1.burnt(), true);
/// ```
///
/// With an existing channel:
///
/// ```
/// use fuze::Fuze;
/// use async_std::{channel, task};
/// use std::time::Duration;
///
/// let (s, r) = channel::unbounded::<bool>();
/// let f1 = Fuze::with_channel(s, r);
/// let f2 = f1.clone();
/// task::block_on(async move {
///		assert_eq!(f2.burnt(), false);
///
///		let f3 = f2.clone();
///		task::spawn(async move {
///			assert_eq!(f3.burnt(), false);
///			task::sleep(Duration::from_secs(1)).await;
///			f3.burn();
///			assert_eq!(f3.burnt(), true);
///		});
///
///		f2.wait().await;
///		assert_eq!(f2.burnt(), true);
/// });
///
///	assert_eq!(f1.burnt(), true);
/// ```
#[derive(Clone)]
pub struct Fuze<T> {
	s: Sender<T>,
	r: Receiver<T>,
}

impl<T> fmt::Debug for Fuze<T> {
	fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
		f.debug_struct("Fuze")
			.field("burnt", &self.burnt())
			.finish()
	}
}

impl<T> Default for Fuze<T> {
	/// Creates a new unburnt fuze.
	///
	/// # Examples
	///
	/// Basic usage:
	///
	/// ```
	/// # use fuze::Fuze;
	/// let fuze = Fuze::<bool>::default();
	///	assert_eq!(fuze.burnt(), false);
	/// fuze.burn();
	///	assert_eq!(fuze.burnt(), true);
	/// ```
	///
	/// For `Fuze<()>` you should probably use `Fuze::new()` instead.
	///
	/// ```
	/// # use fuze::Fuze;
	/// let fuze = Fuze::new();
	///	assert_eq!(fuze.burnt(), false);
	/// fuze.burn();
	///	assert_eq!(fuze.burnt(), true);
	/// ```
	fn default() -> Self {
		let (s, r) = bounded(1);
		Self {
			s,
			r,
		}
	}
}

impl Fuze<()> {
	/// Creates a new unburnt fuze.
	pub fn new() -> Self {
		let (s, r) = bounded(1);
		Self {
			s,
			r,
		}
	}
}

impl<T> Fuze<T> {
	/// Creates a fuze from an existing channel.
	///
	/// Note that the fuze can then be burnt if the channel is closed outside
	/// of the fuze’s purview.
	pub fn with_channel(s: Sender<T>, r: Receiver<T>) -> Self {
		Self { s, r }
	}

	/// Burns the fuze, unblocking everything that is waiting on it.
	pub fn burn(&self)  {
		if !self.s.is_closed() {
			self.s.close();
		}
	}

	/// Checks whether the fuze is burnt or not.
	pub fn burnt(&self) -> bool {
		self.s.is_closed()
	}

	/// Blocks (async-ly) until the fuze is burnt, then never blocks again.
	pub async fn wait(&self) {
		if !self.s.is_closed() {
			self.r.recv().await.ok();
		}
	}
}