[Bugfix] Abort requests when the connection to /v1/completions is interrupted (#4363)

tests/async_engine/test_merge_async_iterators.py

+import asyncio
+from typing import AsyncIterator, Tuple
+
+import pytest
+
+from vllm.utils import merge_async_iterators
+
+
+@pytest.mark.asyncio
+async def test_merge_async_iterators():
+
+    async def mock_async_iterator(idx: int) -> AsyncIterator[str]:
+        try:
+            while True:
+                yield f"item from iterator {idx}"
+                await asyncio.sleep(0.1)
+        except asyncio.CancelledError:
+            pass
+
+    iterators = [mock_async_iterator(i) for i in range(3)]
+    merged_iterator: AsyncIterator[Tuple[int, str]] = merge_async_iterators(
+        *iterators)
+
+    async def stream_output(generator: AsyncIterator[Tuple[int, str]]):
+        async for idx, output in generator:
+            print(f"idx: {idx}, output: {output}")
+
+    task = asyncio.create_task(stream_output(merged_iterator))
+    await asyncio.sleep(0.5)
+    task.cancel()
+    with pytest.raises(asyncio.CancelledError):
+        await task
+
+    for iterator in iterators:
+        try:
+            await asyncio.wait_for(anext(iterator), 1)
+        except StopAsyncIteration:
+            # All iterators should be cancelled and print this message.
+            print("Iterator was cancelled normally")
+        except (Exception, asyncio.CancelledError) as e:
+            raise AssertionError() from e

vllm/utils.py

@@ -225,11 +225,18 @@ def merge_async_iterators(
     ]
 
     async def consumer():
-        while not all(finished) or not queue.empty():
-            item = await queue.get()
-            if isinstance(item, Exception):
-                raise item
-            yield item
+        try:
+            while not all(finished) or not queue.empty():
+                item = await queue.get()
+                if isinstance(item, Exception):
+                    raise item
+                yield item
+        except (Exception, asyncio.CancelledError) as e:
+            for task in _tasks:
+                # NOTE: Pass the error msg in cancel()
+                # when only Python 3.9+ is supported.
+                task.cancel()
+            raise e
         await asyncio.gather(*_tasks)
 
     return consumer()