1 //! Using `select!` to send and receive on the same channel at the same time.
2 //!
3 //! This example is based on the following program in Go.
4 //!
5 //! Source:
6 //! - https://web.archive.org/web/20171209034309/https://www.nada.kth.se/~snilsson/concurrency
7 //! - http://www.nada.kth.se/~snilsson/concurrency/src/matching.go
8 //!
9 //! Copyright & License:
10 //! - Stefan Nilsson
11 //! - Creative Commons Attribution 3.0 Unported License
12 //! - https://creativecommons.org/licenses/by/3.0/
13 //!
14 //! ```go
15 //! func main() {
16 //! people := []string{"Anna", "Bob", "Cody", "Dave", "Eva"}
17 //! match := make(chan string, 1) // Make room for one unmatched send.
18 //! wg := new(sync.WaitGroup)
19 //! for _, name := range people {
20 //! wg.Add(1)
21 //! go Seek(name, match, wg)
22 //! }
23 //! wg.Wait()
24 //! select {
25 //! case name := <-match:
26 //! fmt.Printf("No one received %s’s message.\n", name)
27 //! default:
28 //! // There was no pending send operation.
29 //! }
30 //! }
31 //!
32 //! // Seek either sends or receives, whichever possible, a name on the match
33 //! // channel and notifies the wait group when done.
34 //! func Seek(name string, match chan string, wg *sync.WaitGroup) {
35 //! select {
36 //! case peer := <-match:
37 //! fmt.Printf("%s received a message from %s.\n", name, peer)
38 //! case match <- name:
39 //! // Wait for someone to receive my message.
40 //! }
41 //! wg.Done()
42 //! }
43 //! ```
44
45 #[macro_use]
46 extern crate crossbeam_channel;
47 extern crate crossbeam_utils;
48
49 use crossbeam_channel::bounded;
50 use crossbeam_utils::thread;
51
main()52 fn main() {
53 let people = vec!["Anna", "Bob", "Cody", "Dave", "Eva"];
54 let (s, r) = bounded(1); // Make room for one unmatched send.
55
56 // Either send my name into the channel or receive someone else's, whatever happens first.
57 let seek = |name, s, r| {
58 select! {
59 recv(r) -> peer => println!("{} received a message from {}.", name, peer.unwrap()),
60 send(s, name) -> _ => {}, // Wait for someone to receive my message.
61 }
62 };
63
64 thread::scope(|scope| {
65 for name in people {
66 let (s, r) = (s.clone(), r.clone());
67 scope.spawn(move |_| seek(name, s, r));
68 }
69 })
70 .unwrap();
71
72 // Check if there is a pending send operation.
73 if let Ok(name) = r.try_recv() {
74 println!("No one received {}’s message.", name);
75 }
76 }
77