Make reason for try_send errors clearer (#864)

tokio-sync/src/mpsc/bounded.rs

@@ -239,6 +239,24 @@ impl<T> TrySendError<T> {
     pub fn into_inner(self) -> T {
         self.value
     }
+
+    /// Did the send fail because the channel has been closed?
+    pub fn is_closed(&self) -> bool {
+        if let ErrorKind::Closed = self.kind {
+            true
+        } else {
+            false
+        }
+    }
+
+    /// Did the send fail because the channel was at capacity?
+    pub fn is_full(&self) -> bool {
+        if let ErrorKind::NoCapacity = self.kind {
+            true
+        } else {
+            false
+        }
+    }
 }
 
 impl<T: fmt::Debug> fmt::Display for TrySendError<T> {

tokio-sync/src/mpsc/unbounded.rs

@@ -48,7 +48,7 @@ impl<T> fmt::Debug for UnboundedReceiver<T> {
 #[derive(Debug)]
 pub struct UnboundedSendError(());
 
-/// Error returned by `UnboundedSender::try_send`.
+/// Returned by `UnboundedSender::try_send` when the channel has been closed.
 #[derive(Debug)]
 pub struct UnboundedTrySendError<T>(T);