auto merge of #8908 : tikue/rust/master, r=anasazi

SyncChan blocks after sending a message until the SyncPort acknowledges receipt of the message.

src/libextra/comm.rs

@@ -1,4 +1,4 @@
-// Copyright 2012 The Rust Project Developers. See the COPYRIGHT
+// Copyright 2012-2013 The Rust Project Developers. See the COPYRIGHT
 // file at the top-level directory of this distribution and at
 // http://rust-lang.org/COPYRIGHT.
 //
@@ -90,9 +90,55 @@ pub fn DuplexStream<T:Send,U:Send>()
      })
 }
 
+/// An extension of `pipes::stream` that provides synchronous message sending.
+pub struct SyncChan<T> { priv duplex_stream: DuplexStream<T, ()> }
+/// An extension of `pipes::stream` that acknowledges each message received.
+pub struct SyncPort<T> { priv duplex_stream: DuplexStream<(), T> }
+
+impl<T: Send> GenericChan<T> for SyncChan<T> {
+    fn send(&self, val: T) {
+        assert!(self.try_send(val), "SyncChan.send: receiving port closed");
+    }
+}
+
+impl<T: Send> GenericSmartChan<T> for SyncChan<T> {
+    /// Sends a message, or report if the receiver has closed the connection before receiving.
+    fn try_send(&self, val: T) -> bool {
+        self.duplex_stream.try_send(val) && self.duplex_stream.try_recv().is_some()
+    }
+}
+
+impl<T: Send> GenericPort<T> for SyncPort<T> {
+    fn recv(&self) -> T {
+        self.try_recv().expect("SyncPort.recv: sending channel closed")
+    }
+
+    fn try_recv(&self) -> Option<T> {
+        do self.duplex_stream.try_recv().map_move |val| {
+            self.duplex_stream.try_send(());
+            val
+        }
+    }
+}
+
+impl<T: Send> Peekable<T> for SyncPort<T> {
+    fn peek(&self) -> bool {
+        self.duplex_stream.peek()
+    }
+}
+
+/// Creates a stream whose channel, upon sending a message, blocks until the message is received.
+pub fn rendezvous<T: Send>() -> (SyncPort<T>, SyncChan<T>) {
+    let (chan_stream, port_stream) = DuplexStream();
+    (SyncPort { duplex_stream: port_stream }, SyncChan { duplex_stream: chan_stream })
+}
+
 #[cfg(test)]
 mod test {
-    use comm::DuplexStream;
+    use comm::{DuplexStream, rendezvous};
+    use std::rt::test::run_in_newsched_task;
+    use std::task::spawn_unlinked;
+
 
     #[test]
     pub fn DuplexStream1() {
@@ -104,4 +150,58 @@ mod test {
         assert!(left.recv() == 123);
         assert!(right.recv() == ~"abc");
     }
+
+    #[test]
+    pub fn basic_rendezvous_test() {
+        let (port, chan) = rendezvous();
+
+        do spawn {
+            chan.send("abc");
+        }
+
+        assert!(port.recv() == "abc");
+    }
+
+    #[test]
+    fn recv_a_lot() {
+        // Rendezvous streams should be able to handle any number of messages being sent
+        do run_in_newsched_task {
+            let (port, chan) = rendezvous();
+            do spawn {
+                do 1000000.times { chan.send(()) }
+            }
+            do 1000000.times { port.recv() }
+        }
+    }
+
+    #[test]
+    fn send_and_fail_and_try_recv() {
+        let (port, chan) = rendezvous();
+        do spawn_unlinked {
+            chan.duplex_stream.send(()); // Can't access this field outside this module
+            fail!()
+        }
+        port.recv()
+    }
+
+    #[test]
+    fn try_send_and_recv_then_fail_before_ack() {
+        let (port, chan) = rendezvous();
+        do spawn_unlinked {
+            port.duplex_stream.recv();
+            fail!()
+        }
+        chan.try_send(());
+    }
+
+    #[test]
+    #[should_fail]
+    fn send_and_recv_then_fail_before_ack() {
+        let (port, chan) = rendezvous();
+        do spawn_unlinked {
+            port.duplex_stream.recv();
+            fail!()
+        }
+        chan.send(());
+    }
 }