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
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
//! Multi-producer multi-consumer channels for message passing.
//!
//! This crate is an alternative to [`std::sync::mpsc`] with more features and better performance.
//!
//! # Hello, world!
//!
//! ```
//! use crossbeam_channel::unbounded;
//!
//! // Create a channel of unbounded capacity.
//! let (s, r) = unbounded();
//!
//! // Send a message into the channel.
//! s.send("Hello, world!").unwrap();
//!
//! // Receive the message from the channel.
//! assert_eq!(r.recv(), Ok("Hello, world!"));
//! ```
//!
//! # Channel types
//!
//! Channels can be created using two functions:
//!
//! * [`bounded`] creates a channel of bounded capacity, i.e. there is a limit to how many messages
//!   it can hold at a time.
//!
//! * [`unbounded`] creates a channel of unbounded capacity, i.e. it can hold any number of
//!   messages at a time.
//!
//! Both functions return a [`Sender`] and a [`Receiver`], which represent the two opposite sides
//! of a channel.
//!
//! Creating a bounded channel:
//!
//! ```
//! use crossbeam_channel::bounded;
//!
//! // Create a channel that can hold at most 5 messages at a time.
//! let (s, r) = bounded(5);
//!
//! // Can send only 5 messages without blocking.
//! for i in 0..5 {
//!     s.send(i).unwrap();
//! }
//!
//! // Another call to `send` would block because the channel is full.
//! // s.send(5).unwrap();
//! ```
//!
//! Creating an unbounded channel:
//!
//! ```
//! use crossbeam_channel::unbounded;
//!
//! // Create an unbounded channel.
//! let (s, r) = unbounded();
//!
//! // Can send any number of messages into the channel without blocking.
//! for i in 0..1000 {
//!     s.send(i).unwrap();
//! }
//! ```
//!
//! A special case is zero-capacity channel, which cannot hold any messages. Instead, send and
//! receive operations must appear at the same time in order to pair up and pass the message over:
//!
//! ```
//! use std::thread;
//! use crossbeam_channel::bounded;
//!
//! // Create a zero-capacity channel.
//! let (s, r) = bounded(0);
//!
//! // Sending blocks until a receive operation appears on the other side.
//! thread::spawn(move || s.send("Hi!").unwrap());
//!
//! // Receiving blocks until a send operation appears on the other side.
//! assert_eq!(r.recv(), Ok("Hi!"));
//! ```
//!
//! # Sharing channels
//!
//! Senders and receivers can be cloned and sent to other threads:
//!
//! ```
//! use std::thread;
//! use crossbeam_channel::bounded;
//!
//! let (s1, r1) = bounded(0);
//! let (s2, r2) = (s1.clone(), r1.clone());
//!
//! // Spawn a thread that receives a message and then sends one.
//! thread::spawn(move || {
//!     r2.recv().unwrap();
//!     s2.send(2).unwrap();
//! });
//!
//! // Send a message and then receive one.
//! s1.send(1).unwrap();
//! r1.recv().unwrap();
//! ```
//!
//! Note that cloning only creates a new handle to the same sending or receiving side. It does not
//! create a separate stream of messages in any way:
//!
//! ```
//! use crossbeam_channel::unbounded;
//!
//! let (s1, r1) = unbounded();
//! let (s2, r2) = (s1.clone(), r1.clone());
//! let (s3, r3) = (s2.clone(), r2.clone());
//!
//! s1.send(10).unwrap();
//! s2.send(20).unwrap();
//! s3.send(30).unwrap();
//!
//! assert_eq!(r3.recv(), Ok(10));
//! assert_eq!(r1.recv(), Ok(20));
//! assert_eq!(r2.recv(), Ok(30));
//! ```
//!
//! It's also possible to share senders and receivers by reference:
//!
//! ```
//! use crossbeam_channel::bounded;
//! use crossbeam_utils::thread::scope;
//!
//! let (s, r) = bounded(0);
//!
//! scope(|scope| {
//!     // Spawn a thread that receives a message and then sends one.
//!     scope.spawn(|_| {
//!         r.recv().unwrap();
//!         s.send(2).unwrap();
//!     });
//!
//!     // Send a message and then receive one.
//!     s.send(1).unwrap();
//!     r.recv().unwrap();
//! }).unwrap();
//! ```
//!
//! # Disconnection
//!
//! When all senders or all receivers associated with a channel get dropped, the channel becomes
//! disconnected. No more messages can be sent, but any remaining messages can still be received.
//! Send and receive operations on a disconnected channel never block.
//!
//! ```
//! use crossbeam_channel::{unbounded, RecvError};
//!
//! let (s, r) = unbounded();
//! s.send(1).unwrap();
//! s.send(2).unwrap();
//! s.send(3).unwrap();
//!
//! // The only sender is dropped, disconnecting the channel.
//! drop(s);
//!
//! // The remaining messages can be received.
//! assert_eq!(r.recv(), Ok(1));
//! assert_eq!(r.recv(), Ok(2));
//! assert_eq!(r.recv(), Ok(3));
//!
//! // There are no more messages in the channel.
//! assert!(r.is_empty());
//!
//! // Note that calling `r.recv()` does not block.
//! // Instead, `Err(RecvError)` is returned immediately.
//! assert_eq!(r.recv(), Err(RecvError));
//! ```
//!
//! # Blocking operations
//!
//! Send and receive operations come in three flavors:
//!
//! * Non-blocking (returns immediately with success or failure).
//! * Blocking (waits until the operation succeeds or the channel becomes disconnected).
//! * Blocking with a timeout (blocks only for a certain duration of time).
//!
//! A simple example showing the difference between non-blocking and blocking operations:
//!
//! ```
//! use crossbeam_channel::{bounded, RecvError, TryRecvError};
//!
//! let (s, r) = bounded(1);
//!
//! // Send a message into the channel.
//! s.send("foo").unwrap();
//!
//! // This call would block because the channel is full.
//! // s.send("bar").unwrap();
//!
//! // Receive the message.
//! assert_eq!(r.recv(), Ok("foo"));
//!
//! // This call would block because the channel is empty.
//! // r.recv();
//!
//! // Try receiving a message without blocking.
//! assert_eq!(r.try_recv(), Err(TryRecvError::Empty));
//!
//! // Disconnect the channel.
//! drop(s);
//!
//! // This call doesn't block because the channel is now disconnected.
//! assert_eq!(r.recv(), Err(RecvError));
//! ```
//!
//! # Iteration
//!
//! Receivers can be used as iterators. For example, method [`iter`] creates an iterator that
//! receives messages until the channel becomes empty and disconnected. Note that iteration may
//! block waiting for next message to arrive.
//!
//! ```
//! use std::thread;
//! use crossbeam_channel::unbounded;
//!
//! let (s, r) = unbounded();
//!
//! thread::spawn(move || {
//!     s.send(1).unwrap();
//!     s.send(2).unwrap();
//!     s.send(3).unwrap();
//!     drop(s); // Disconnect the channel.
//! });
//!
//! // Collect all messages from the channel.
//! // Note that the call to `collect` blocks until the sender is dropped.
//! let v: Vec<_> = r.iter().collect();
//!
//! assert_eq!(v, [1, 2, 3]);
//! ```
//!
//! A non-blocking iterator can be created using [`try_iter`], which receives all available
//! messages without blocking:
//!
//! ```
//! use crossbeam_channel::unbounded;
//!
//! let (s, r) = unbounded();
//! s.send(1).unwrap();
//! s.send(2).unwrap();
//! s.send(3).unwrap();
//! // No need to drop the sender.
//!
//! // Receive all messages currently in the channel.
//! let v: Vec<_> = r.try_iter().collect();
//!
//! assert_eq!(v, [1, 2, 3]);
//! ```
//!
//! # Selection
//!
//! The [`select!`] macro allows you to define a set of channel operations, wait until any one of
//! them becomes ready, and finally execute it. If multiple operations are ready at the same time,
//! a random one among them is selected.
//!
//! It is also possible to define a `default` case that gets executed if none of the operations are
//! ready, either right away or for a certain duration of time.
//!
//! An operation is considered to be ready if it doesn't have to block. Note that it is ready even
//! when it will simply return an error because the channel is disconnected.
//!
//! An example of receiving a message from two channels:
//!
//! ```
//! use std::thread;
//! use std::time::Duration;
//! use crossbeam_channel::{select, unbounded};
//!
//! let (s1, r1) = unbounded();
//! let (s2, r2) = unbounded();
//!
//! thread::spawn(move || s1.send(10).unwrap());
//! thread::spawn(move || s2.send(20).unwrap());
//!
//! // At most one of these two receive operations will be executed.
//! select! {
//!     recv(r1) -> msg => assert_eq!(msg, Ok(10)),
//!     recv(r2) -> msg => assert_eq!(msg, Ok(20)),
//!     default(Duration::from_secs(1)) => println!("timed out"),
//! }
//! ```
//!
//! If you need to select over a dynamically created list of channel operations, use [`Select`]
//! instead. The [`select!`] macro is just a convenience wrapper around [`Select`].
//!
//! # Extra channels
//!
//! Three functions can create special kinds of channels, all of which return just a [`Receiver`]
//! handle:
//!
//! * [`after`] creates a channel that delivers a single message after a certain duration of time.
//! * [`tick`] creates a channel that delivers messages periodically.
//! * [`never`](never()) creates a channel that never delivers messages.
//!
//! These channels are very efficient because messages get lazily generated on receive operations.
//!
//! An example that prints elapsed time every 50 milliseconds for the duration of 1 second:
//!
//! ```
//! use std::time::{Duration, Instant};
//! use crossbeam_channel::{after, select, tick};
//!
//! let start = Instant::now();
//! let ticker = tick(Duration::from_millis(50));
//! let timeout = after(Duration::from_secs(1));
//!
//! loop {
//!     select! {
//!         recv(ticker) -> _ => println!("elapsed: {:?}", start.elapsed()),
//!         recv(timeout) -> _ => break,
//!     }
//! }
//! ```
//!
//! [`send`]: Sender::send
//! [`recv`]: Receiver::recv
//! [`iter`]: Receiver::iter
//! [`try_iter`]: Receiver::try_iter

#![doc(test(
    no_crate_inject,
    attr(
        deny(warnings, rust_2018_idioms),
        allow(dead_code, unused_assignments, unused_variables)
    )
))]
#![warn(
    missing_docs,
    missing_debug_implementations,
    rust_2018_idioms,
    unreachable_pub
)]
#![cfg_attr(not(feature = "std"), no_std)]

use cfg_if::cfg_if;

cfg_if! {
    if #[cfg(feature = "std")] {
        mod channel;
        mod context;
        mod counter;
        mod err;
        mod flavors;
        mod select;
        mod select_macro;
        mod utils;
        mod waker;

        /// Crate internals used by the `select!` macro.
        #[doc(hidden)]
        pub mod internal {
            pub use crate::select::SelectHandle;
            pub use crate::select::{select, select_timeout, try_select};
        }

        pub use crate::channel::{after, at, never, tick};
        pub use crate::channel::{bounded, unbounded};
        pub use crate::channel::{IntoIter, Iter, TryIter};
        pub use crate::channel::{Receiver, Sender};

        pub use crate::select::{Select, SelectedOperation};

        pub use crate::err::{ReadyTimeoutError, SelectTimeoutError, TryReadyError, TrySelectError};
        pub use crate::err::{RecvError, RecvTimeoutError, TryRecvError};
        pub use crate::err::{SendError, SendTimeoutError, TrySendError};
    }
}