vendor/crossbeam-channel/examples/matching.rs

   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
  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 }