1 files changed, 115 insertions, 0 deletions
diff --git a/tokio/src/future/try_join.rs b/tokio/src/future/try_join.rs
new file mode 100644
index 00000000..478c69dc
--- /dev/null
+++ b/tokio/src/future/try_join.rs
@@ -0,0 +1,115 @@
+use crate::future::{maybe_done, MaybeDone};
+
+use std::future::Future;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pub(crate) fn try_join3<T1, F1, T2, F2, T3, F3, E>(
+    future1: F1,
+    future2: F2,
+    future3: F3,
+) -> TryJoin3<F1, F2, F3>
+where
+    F1: Future<Output = Result<T1, E>>,
+    F2: Future<Output = Result<T2, E>>,
+    F3: Future<Output = Result<T3, E>>,
+{
+    TryJoin3 {
+        future1: maybe_done(future1),
+        future2: maybe_done(future2),
+        future3: maybe_done(future3),
+    }
+}
+
+pub(crate) struct TryJoin3<F1, F2, F3>
+where
+    F1: Future,
+    F2: Future,
+    F3: Future,
+{
+    future1: MaybeDone<F1>,
+    future2: MaybeDone<F2>,
+    future3: MaybeDone<F3>,
+}
+
+impl<T1, F1, T2, F2, T3, F3, E> Future for TryJoin3<F1, F2, F3>
+where
+    F1: Future<Output = Result<T1, E>>,
+    F2: Future<Output = Result<T2, E>>,
+    F3: Future<Output = Result<T3, E>>,
+{
+    type Output = Result<(T1, T2, T3), E>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut all_done = true;
+
+        // Safety: the fn takes `Pin`, we don't move any data out of `self`.
+        unsafe {
+            let me = self.get_unchecked_mut();
+
+            if Pin::new_unchecked(&mut me.future1).poll(cx).is_pending() {
+                all_done = false;
+            } else if Pin::new_unchecked(&mut me.future1)
+                .output_mut()
+                .unwrap()
+                .is_err()
+            {
+                return Poll::Ready(Err(Pin::new_unchecked(&mut me.future1)
+                    .take_output()
+                    .unwrap()
+                    .err()
+                    .unwrap()));
+            }
+
+            if Pin::new_unchecked(&mut me.future2).poll(cx).is_pending() {
+                all_done = false;
+            } else if Pin::new_unchecked(&mut me.future2)
+                .output_mut()
+                .unwrap()
+                .is_err()
+            {
+                return Poll::Ready(Err(Pin::new_unchecked(&mut me.future2)
+                    .take_output()
+                    .unwrap()
+                    .err()
+                    .unwrap()));
+            }
+
+            if Pin::new_unchecked(&mut me.future3).poll(cx).is_pending() {
+                all_done = false;
+            } else if Pin::new_unchecked(&mut me.future3)
+                .output_mut()
+                .unwrap()
+                .is_err()
+            {
+                return Poll::Ready(Err(Pin::new_unchecked(&mut me.future3)
+                    .take_output()
+                    .unwrap()
+                    .err()
+                    .unwrap()));
+            }
+
+            if all_done {
+                Poll::Ready(Ok((
+                    Pin::new_unchecked(&mut me.future1)
+                        .take_output()
+                        .unwrap()
+                        .ok()
+                        .unwrap(),
+                    Pin::new_unchecked(&mut me.future2)
+                        .take_output()
+                        .unwrap()
+                        .ok()
+                        .unwrap(),
+                    Pin::new_unchecked(&mut me.future3)
+                        .take_output()
+                        .unwrap()
+                        .ok()
+                        .unwrap(),
+                )))
+            } else {
+                Poll::Pending
+            }
+        }
+    }
+}