1 files changed, 72 insertions, 0 deletions
diff --git a/third_party/rust/crossbeam-channel/examples/matching.rs b/third_party/rust/crossbeam-channel/examples/matching.rs
new file mode 100644
index 0000000000..5421169b9d
--- /dev/null
+++ b/third_party/rust/crossbeam-channel/examples/matching.rs
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+//! Using `select!` to send and receive on the same channel at the same time.
+//!
+//! This example is based on the following program in Go.
+//!
+//! Source:
+//!   - https://web.archive.org/web/20171209034309/https://www.nada.kth.se/~snilsson/concurrency
+//!   - http://www.nada.kth.se/~snilsson/concurrency/src/matching.go
+//!
+//! Copyright & License:
+//!   - Stefan Nilsson
+//!   - Creative Commons Attribution 3.0 Unported License
+//!   - https://creativecommons.org/licenses/by/3.0/
+//!
+//! ```go
+//! func main() {
+//!     people := []string{"Anna", "Bob", "Cody", "Dave", "Eva"}
+//!     match := make(chan string, 1) // Make room for one unmatched send.
+//!     wg := new(sync.WaitGroup)
+//!     for _, name := range people {
+//!         wg.Add(1)
+//!         go Seek(name, match, wg)
+//!     }
+//!     wg.Wait()
+//!     select {
+//!     case name := <-match:
+//!         fmt.Printf("No one received %s’s message.\n", name)
+//!     default:
+//!         // There was no pending send operation.
+//!     }
+//! }
+//!
+//! // Seek either sends or receives, whichever possible, a name on the match
+//! // channel and notifies the wait group when done.
+//! func Seek(name string, match chan string, wg *sync.WaitGroup) {
+//!     select {
+//!     case peer := <-match:
+//!         fmt.Printf("%s received a message from %s.\n", name, peer)
+//!     case match <- name:
+//!         // Wait for someone to receive my message.
+//!     }
+//!     wg.Done()
+//! }
+//! ```
+
+use crossbeam_channel::{bounded, select};
+use crossbeam_utils::thread;
+
+fn main() {
+    let people = vec!["Anna", "Bob", "Cody", "Dave", "Eva"];
+    let (s, r) = bounded(1); // Make room for one unmatched send.
+
+    // Either send my name into the channel or receive someone else's, whatever happens first.
+    let seek = |name, s, r| {
+        select! {
+            recv(r) -> peer => println!("{} received a message from {}.", name, peer.unwrap()),
+            send(s, name) -> _ => {}, // Wait for someone to receive my message.
+        }
+    };
+
+    thread::scope(|scope| {
+        for name in people {
+            let (s, r) = (s.clone(), r.clone());
+            scope.spawn(move |_| seek(name, s, r));
+        }
+    })
+    .unwrap();
+
+    // Check if there is a pending send operation.
+    if let Ok(name) = r.try_recv() {
+        println!("No one received {}’s message.", name);
+    }
+}