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.venv/lib/python3.9/site-packages/starlette/concurrency.py

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+import asyncio
+import functools
+import typing
+from typing import Any, AsyncGenerator, Iterator
+
+try:
+    import contextvars  # Python 3.7+ only.
+except ImportError:  # pragma: no cover
+    contextvars = None  # type: ignore
+
+T = typing.TypeVar("T")
+
+
+async def run_until_first_complete(*args: typing.Tuple[typing.Callable, dict]) -> None:
+    tasks = [handler(**kwargs) for handler, kwargs in args]
+    (done, pending) = await asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)
+    [task.cancel() for task in pending]
+    [task.result() for task in done]
+
+
+async def run_in_threadpool(
+    func: typing.Callable[..., T], *args: typing.Any, **kwargs: typing.Any
+) -> T:
+    loop = asyncio.get_event_loop()
+    if contextvars is not None:  # pragma: no cover
+        # Ensure we run in the same context
+        child = functools.partial(func, *args, **kwargs)
+        context = contextvars.copy_context()
+        func = context.run
+        args = (child,)
+    elif kwargs:  # pragma: no cover
+        # loop.run_in_executor doesn't accept 'kwargs', so bind them in here
+        func = functools.partial(func, **kwargs)
+    return await loop.run_in_executor(None, func, *args)
+
+
+class _StopIteration(Exception):
+    pass
+
+
+def _next(iterator: Iterator) -> Any:
+    # We can't raise `StopIteration` from within the threadpool iterator
+    # and catch it outside that context, so we coerce them into a different
+    # exception type.
+    try:
+        return next(iterator)
+    except StopIteration:
+        raise _StopIteration
+
+
+async def iterate_in_threadpool(iterator: Iterator) -> AsyncGenerator:
+    while True:
+        try:
+            yield await run_in_threadpool(_next, iterator)
+        except _StopIteration:
+            break