Revert "reduce"

This reverts commit 39746b6.

src/aiohappyeyeballs/_staggered.py

@@ -2,6 +2,7 @@
 import contextlib
 from typing import (
     TYPE_CHECKING,
+    Any,
     Awaitable,
     Callable,
     Iterable,
@@ -22,6 +23,27 @@ def _set_result(wait_next: "asyncio.Future[None]") -> None:
         wait_next.set_result(None)
 
 
+async def _wait_one(
+    futures: "Iterable[asyncio.Future[Any]]",
+    loop: asyncio.AbstractEventLoop,
+) -> _T:
+    """Wait for the first future to complete."""
+    wait_next = loop.create_future()
+
+    def _on_completion(fut: "asyncio.Future[Any]") -> None:
+        if not wait_next.done():
+            wait_next.set_result(fut)
+
+    for f in futures:
+        f.add_done_callback(_on_completion)
+
+    try:
+        return await wait_next
+    finally:
+        for f in futures:
+            f.remove_done_callback(_on_completion)
+
+
 async def staggered_race(
     coro_fns: Iterable[Callable[[], Awaitable[_T]]],
     delay: Optional[float],
@@ -116,9 +138,6 @@ async def run_one_coro(
     start_next: Optional[asyncio.Future[None]]
     task: asyncio.Task[Optional[Tuple[_T, int]]]
     done: Union[asyncio.Future[None], asyncio.Task[Optional[Tuple[_T, int]]]]
-    waiters: Iterable[
-        Union[asyncio.Future[None], asyncio.Task[Optional[Tuple[_T, int]]]]
-    ]
     coro_iter = iter(coro_fns)
     this_index = -1
     try:
@@ -136,12 +155,9 @@ async def run_one_coro(
                 break
 
             while tasks:
-                waiters = [*tasks, start_next] if start_next else tasks
-                dones, _ = await asyncio.wait(
-                    waiters,
-                    return_when=asyncio.FIRST_COMPLETED,
+                done = await _wait_one(
+                    [*tasks, start_next] if start_next else tasks, loop
                 )
-                done = dones.pop()
                 if done is start_next:
                     # The current task has failed or the timer has expired
                     # so we need to start the next task.