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342 lines
13 KiB
Python
342 lines
13 KiB
Python
5 years ago
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import asyncio
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import asyncio.coroutines
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import functools
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import os
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import sys
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import threading
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from concurrent.futures import Future, ThreadPoolExecutor
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from .current_thread_executor import CurrentThreadExecutor
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from .local import Local
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try:
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import contextvars # Python 3.7+ only.
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except ImportError:
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contextvars = None
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class AsyncToSync:
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"""
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Utility class which turns an awaitable that only works on the thread with
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the event loop into a synchronous callable that works in a subthread.
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If the call stack contains an async loop, the code runs there.
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Otherwise, the code runs in a new loop in a new thread.
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Either way, this thread then pauses and waits to run any thread_sensitive
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code called from further down the call stack using SyncToAsync, before
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finally exiting once the async task returns.
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"""
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# Maps launched Tasks to the threads that launched them (for locals impl)
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launch_map = {}
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# Keeps track of which CurrentThreadExecutor to use. This uses an asgiref
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# Local, not a threadlocal, so that tasks can work out what their parent used.
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executors = Local()
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def __init__(self, awaitable, force_new_loop=False):
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self.awaitable = awaitable
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try:
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self.__self__ = self.awaitable.__self__
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except AttributeError:
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pass
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if force_new_loop:
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# They have asked that we always run in a new sub-loop.
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self.main_event_loop = None
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else:
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try:
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self.main_event_loop = asyncio.get_event_loop()
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except RuntimeError:
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# There's no event loop in this thread. Look for the threadlocal if
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# we're inside SyncToAsync
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self.main_event_loop = getattr(
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SyncToAsync.threadlocal, "main_event_loop", None
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)
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def __call__(self, *args, **kwargs):
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# You can't call AsyncToSync from a thread with a running event loop
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try:
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event_loop = asyncio.get_event_loop()
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except RuntimeError:
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pass
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else:
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if event_loop.is_running():
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raise RuntimeError(
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"You cannot use AsyncToSync in the same thread as an async event loop - "
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"just await the async function directly."
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)
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# Make a future for the return information
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call_result = Future()
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# Get the source thread
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source_thread = threading.current_thread()
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# Make a CurrentThreadExecutor we'll use to idle in this thread - we
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# need one for every sync frame, even if there's one above us in the
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# same thread.
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if hasattr(self.executors, "current"):
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old_current_executor = self.executors.current
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else:
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old_current_executor = None
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current_executor = CurrentThreadExecutor()
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self.executors.current = current_executor
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# Use call_soon_threadsafe to schedule a synchronous callback on the
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# main event loop's thread if it's there, otherwise make a new loop
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# in this thread.
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try:
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if not (self.main_event_loop and self.main_event_loop.is_running()):
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# Make our own event loop - in a new thread - and run inside that.
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loop = asyncio.new_event_loop()
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loop_executor = ThreadPoolExecutor(max_workers=1)
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loop_future = loop_executor.submit(
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self._run_event_loop,
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loop,
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self.main_wrap(
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args, kwargs, call_result, source_thread, sys.exc_info()
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),
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)
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if current_executor:
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# Run the CurrentThreadExecutor until the future is done
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current_executor.run_until_future(loop_future)
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# Wait for future and/or allow for exception propagation
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loop_future.result()
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else:
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# Call it inside the existing loop
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self.main_event_loop.call_soon_threadsafe(
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self.main_event_loop.create_task,
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self.main_wrap(
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args, kwargs, call_result, source_thread, sys.exc_info()
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),
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)
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if current_executor:
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# Run the CurrentThreadExecutor until the future is done
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current_executor.run_until_future(call_result)
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finally:
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# Clean up any executor we were running
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if hasattr(self.executors, "current"):
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del self.executors.current
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if old_current_executor:
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self.executors.current = old_current_executor
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# Wait for results from the future.
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return call_result.result()
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def _run_event_loop(self, loop, coro):
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"""
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Runs the given event loop (designed to be called in a thread).
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"""
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asyncio.set_event_loop(loop)
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try:
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loop.run_until_complete(coro)
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finally:
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try:
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# mimic asyncio.run() behavior
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# cancel unexhausted async generators
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if sys.version_info >= (3, 7, 0):
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tasks = asyncio.all_tasks(loop)
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else:
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tasks = asyncio.Task.all_tasks(loop)
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for task in tasks:
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task.cancel()
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loop.run_until_complete(asyncio.gather(*tasks, return_exceptions=True))
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for task in tasks:
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if task.cancelled():
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continue
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if task.exception() is not None:
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loop.call_exception_handler(
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{
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"message": "unhandled exception during loop shutdown",
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"exception": task.exception(),
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"task": task,
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}
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)
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if hasattr(loop, "shutdown_asyncgens"):
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loop.run_until_complete(loop.shutdown_asyncgens())
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finally:
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loop.close()
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asyncio.set_event_loop(self.main_event_loop)
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def __get__(self, parent, objtype):
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"""
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Include self for methods
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"""
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func = functools.partial(self.__call__, parent)
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return functools.update_wrapper(func, self.awaitable)
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async def main_wrap(self, args, kwargs, call_result, source_thread, exc_info):
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"""
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Wraps the awaitable with something that puts the result into the
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result/exception future.
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"""
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current_task = SyncToAsync.get_current_task()
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self.launch_map[current_task] = source_thread
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try:
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# If we have an exception, run the function inside the except block
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# after raising it so exc_info is correctly populated.
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if exc_info[1]:
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try:
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raise exc_info[1]
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except:
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result = await self.awaitable(*args, **kwargs)
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else:
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result = await self.awaitable(*args, **kwargs)
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except Exception as e:
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call_result.set_exception(e)
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else:
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call_result.set_result(result)
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finally:
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del self.launch_map[current_task]
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class SyncToAsync:
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"""
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Utility class which turns a synchronous callable into an awaitable that
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runs in a threadpool. It also sets a threadlocal inside the thread so
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calls to AsyncToSync can escape it.
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If thread_sensitive is passed, the code will run in the same thread as any
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outer code. This is needed for underlying Python code that is not
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threadsafe (for example, code which handles SQLite database connections).
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If the outermost program is async (i.e. SyncToAsync is outermost), then
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this will be a dedicated single sub-thread that all sync code runs in,
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one after the other. If the outermost program is sync (i.e. AsyncToSync is
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outermost), this will just be the main thread. This is achieved by idling
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with a CurrentThreadExecutor while AsyncToSync is blocking its sync parent,
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rather than just blocking.
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"""
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# If they've set ASGI_THREADS, update the default asyncio executor for now
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if "ASGI_THREADS" in os.environ:
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loop = asyncio.get_event_loop()
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loop.set_default_executor(
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ThreadPoolExecutor(max_workers=int(os.environ["ASGI_THREADS"]))
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)
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# Maps launched threads to the coroutines that spawned them
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launch_map = {}
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# Storage for main event loop references
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threadlocal = threading.local()
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# Single-thread executor for thread-sensitive code
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single_thread_executor = ThreadPoolExecutor(max_workers=1)
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def __init__(self, func, thread_sensitive=False):
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self.func = func
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functools.update_wrapper(self, func)
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self._thread_sensitive = thread_sensitive
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self._is_coroutine = asyncio.coroutines._is_coroutine
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try:
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self.__self__ = func.__self__
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except AttributeError:
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pass
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async def __call__(self, *args, **kwargs):
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loop = asyncio.get_event_loop()
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# Work out what thread to run the code in
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if self._thread_sensitive:
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if hasattr(AsyncToSync.executors, "current"):
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# If we have a parent sync thread above somewhere, use that
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executor = AsyncToSync.executors.current
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else:
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# Otherwise, we run it in a fixed single thread
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executor = self.single_thread_executor
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else:
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executor = None # Use default
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if contextvars is not None:
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context = contextvars.copy_context()
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child = functools.partial(self.func, *args, **kwargs)
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func = context.run
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args = (child,)
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kwargs = {}
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else:
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func = self.func
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# Run the code in the right thread
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future = loop.run_in_executor(
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executor,
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functools.partial(
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self.thread_handler,
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loop,
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self.get_current_task(),
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sys.exc_info(),
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func,
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*args,
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**kwargs
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),
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)
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ret = await asyncio.wait_for(future, timeout=None)
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if contextvars is not None:
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# Check for changes in contextvars, and set them to the current
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# context for downstream consumers
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for cvar in context:
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try:
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if cvar.get() != context.get(cvar):
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cvar.set(context.get(cvar))
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except LookupError:
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cvar.set(context.get(cvar))
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return ret
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def __get__(self, parent, objtype):
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"""
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Include self for methods
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"""
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return functools.partial(self.__call__, parent)
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def thread_handler(self, loop, source_task, exc_info, func, *args, **kwargs):
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"""
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Wraps the sync application with exception handling.
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"""
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# Set the threadlocal for AsyncToSync
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self.threadlocal.main_event_loop = loop
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# Set the task mapping (used for the locals module)
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current_thread = threading.current_thread()
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if AsyncToSync.launch_map.get(source_task) == current_thread:
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# Our parent task was launched from this same thread, so don't make
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# a launch map entry - let it shortcut over us! (and stop infinite loops)
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parent_set = False
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else:
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self.launch_map[current_thread] = source_task
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parent_set = True
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# Run the function
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try:
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# If we have an exception, run the function inside the except block
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# after raising it so exc_info is correctly populated.
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if exc_info[1]:
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try:
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raise exc_info[1]
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except:
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return func(*args, **kwargs)
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else:
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return func(*args, **kwargs)
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finally:
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# Only delete the launch_map parent if we set it, otherwise it is
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# from someone else.
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if parent_set:
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del self.launch_map[current_thread]
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@staticmethod
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def get_current_task():
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"""
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Cross-version implementation of asyncio.current_task()
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Returns None if there is no task.
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"""
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try:
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if hasattr(asyncio, "current_task"):
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# Python 3.7 and up
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return asyncio.current_task()
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else:
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# Python 3.6
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return asyncio.Task.current_task()
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except RuntimeError:
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return None
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# Lowercase is more sensible for most things
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sync_to_async = SyncToAsync
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async_to_sync = AsyncToSync
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