Merging upstream version 1.72.1+dfsg1.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 61 insertions, 14 deletions

diff --git a/vendor/tokio/src/macros/join.rs b/vendor/tokio/src/macros/join.rs
index 5f37af510..8a0198600 100644
--- a/vendor/tokio/src/macros/join.rs
+++ b/vendor/tokio/src/macros/join.rs
@@ -1,4 +1,4 @@
-/// Wait on multiple concurrent branches, returning when **all** branches
+/// Waits on multiple concurrent branches, returning when **all** branches
 /// complete.
 ///
 /// The `join!` macro must be used inside of async functions, closures, and
@@ -12,7 +12,7 @@
 /// for **all** branches complete regardless if any complete with `Err`. Use
 /// [`try_join!`] to return early when `Err` is encountered.
 ///
-/// [`try_join!`]: macro@try_join
+/// [`try_join!`]: crate::try_join
 ///
 /// # Notes
 ///
@@ -60,6 +60,9 @@ macro_rules! join {
         // normalization is complete.
         ( $($count:tt)* )
 
+        // The expression `0+1+1+ ... +1` equal to the number of branches.
+        ( $($total:tt)* )
+
         // Normalized join! branches
         $( ( $($skip:tt)* ) $e:expr, )*
 
@@ -69,24 +72,66 @@ macro_rules! join {
 
         // Safety: nothing must be moved out of `futures`. This is to satisfy
         // the requirement of `Pin::new_unchecked` called below.
+        //
+        // We can't use the `pin!` macro for this because `futures` is a tuple
+        // and the standard library provides no way to pin-project to the fields
+        // of a tuple.
         let mut futures = ( $( maybe_done($e), )* );
 
+        // This assignment makes sure that the `poll_fn` closure only has a
+        // reference to the futures, instead of taking ownership of them. This
+        // mitigates the issue described in
+        // <https://internals.rust-lang.org/t/surprising-soundness-trouble-around-pollfn/17484>
+        let mut futures = &mut futures;
+
+        // Each time the future created by poll_fn is polled, a different future will be polled first
+        // to ensure every future passed to join! gets a chance to make progress even if
+        // one of the futures consumes the whole budget.
+        //
+        // This is number of futures that will be skipped in the first loop
+        // iteration the next time.
+        let mut skip_next_time: u32 = 0;
+
         poll_fn(move |cx| {
+            const COUNT: u32 = $($total)*;
+
             let mut is_pending = false;
 
+            let mut to_run = COUNT;
+
+            // The number of futures that will be skipped in the first loop iteration.
+            let mut skip = skip_next_time;
+
+            skip_next_time = if skip + 1 == COUNT { 0 } else { skip + 1 };
+
+            // This loop runs twice and the first `skip` futures
+            // are not polled in the first iteration.
+            loop {
             $(
-                // Extract the future for this branch from the tuple.
-                let ( $($skip,)* fut, .. ) = &mut futures;
+                if skip == 0 {
+                    if to_run == 0 {
+                        // Every future has been polled
+                        break;
+                    }
+                    to_run -= 1;
 
-                // Safety: future is stored on the stack above
-                // and never moved.
-                let mut fut = unsafe { Pin::new_unchecked(fut) };
+                    // Extract the future for this branch from the tuple.
+                    let ( $($skip,)* fut, .. ) = &mut *futures;
 
-                // Try polling
-                if fut.poll(cx).is_pending() {
-                    is_pending = true;
+                    // Safety: future is stored on the stack above
+                    // and never moved.
+                    let mut fut = unsafe { Pin::new_unchecked(fut) };
+
+                    // Try polling
+                    if fut.poll(cx).is_pending() {
+                        is_pending = true;
+                    }
+                } else {
+                    // Future skipped, one less future to skip in the next iteration
+                    skip -= 1;
                 }
             )*
+            }
 
             if is_pending {
                 Pending
@@ -107,13 +152,15 @@ macro_rules! join {
 
     // ===== Normalize =====
 
-    (@ { ( $($s:tt)* ) $($t:tt)* } $e:expr, $($r:tt)* ) => {
-        $crate::join!(@{ ($($s)* _) $($t)* ($($s)*) $e, } $($r)*)
+    (@ { ( $($s:tt)* ) ( $($n:tt)* ) $($t:tt)* } $e:expr, $($r:tt)* ) => {
+        $crate::join!(@{ ($($s)* _) ($($n)* + 1) $($t)* ($($s)*) $e, } $($r)*)
     };
 
     // ===== Entry point =====
 
-    ( $($e:expr),* $(,)?) => {
-        $crate::join!(@{ () } $($e,)*)
+    ( $($e:expr),+ $(,)?) => {
+        $crate::join!(@{ () (0) } $($e,)*)
     };
+
+    () => { async {}.await }
 }