Wrap an Asynchronous Class
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import asyncio | |
import atexit | |
import functools | |
import inspect | |
import threading | |
from concurrent.futures import wait | |
from typing import Optional | |
class TaskRunner: | |
"""A singleton task runner that runs an asyncio event loop on a background thread.""" | |
__instance = None | |
@staticmethod | |
def getInstance(): | |
if TaskRunner.__instance is None: | |
TaskRunner() | |
assert TaskRunner.__instance is not None | |
return TaskRunner.__instance | |
def __init__(self): | |
if TaskRunner.__instance is not None: | |
raise Exception("This class is a singleton!") | |
else: | |
TaskRunner.__instance = self | |
self.__io_loop: Optional[asyncio.AbstractEventLoop] = None | |
self.__runner_thread: Optional[threading.Thread] = None | |
self.__lock = threading.Lock() | |
atexit.register(self._close) | |
def _close(self): | |
if self.__io_loop: | |
self.__io_loop.stop() | |
def _runner(self): | |
loop = self.__io_loop | |
assert loop is not None | |
try: | |
loop.run_forever() | |
finally: | |
loop.close() | |
def run(self, coro): | |
"""Synchronously run a coroutine on a background thread.""" | |
with self.__lock: | |
if self.__io_loop is None: | |
self.__io_loop = asyncio.new_event_loop() | |
self.__runner_thread = threading.Thread(target=self._runner, daemon=True) | |
self.__runner_thread.start() | |
fut = asyncio.run_coroutine_threadsafe(coro, self.__io_loop) | |
wait([fut]) | |
return fut.result() | |
def synchronize_method(async_method, doc=None): | |
"""Decorate `async_method` so it runs synchronously. | |
The method runs on an event loop. | |
:Parameters: | |
- `async_method`: Unbound method of pymongo Collection, Database, | |
MongoClient, etc. | |
- `doc`: Optionally override async_method's docstring | |
""" | |
@functools.wraps(async_method) | |
def method(self, *args, **kwargs): | |
runner = TaskRunner.getInstance() | |
coro = async_method(self, *args, **kwargs) | |
return runner.run(coro) | |
# This is for the benefit of generating documentation with Sphinx. | |
method.is_sync_method = True # type: ignore[attr-defined] | |
if doc is not None: | |
method.__doc__ = doc | |
return method | |
def synchronize_class(kls): | |
"""Create a synchronous class from an asynchronous one.""" | |
name = kls.__name__.replace("Async", "") | |
subclass = type(name, (kls,), {}) | |
subclass._async_marker = False | |
for name in dir(subclass): | |
if name.startswith('_'): | |
continue | |
obj = getattr(subclass, name) | |
if inspect.iscoroutinefunction(obj): | |
setattr(subclass, name, synchronize_method(obj)) | |
return subclass | |
class AsyncMongoClient: | |
_async_marker = True | |
async def find_one(self): | |
kls = AsyncCursor if self._async_marker else Cursor | |
return kls() | |
class AsyncCursor: | |
_async_marker = True | |
def __iter__(self): | |
return self | |
def __next__(self): | |
raise StopIteration | |
async def __aiter__(self): | |
return self | |
async def __anext__(self): | |
raise StopAsyncIteration | |
async def fetch_something(self): | |
return 'foo' | |
MongoClient = synchronize_class(AsyncMongoClient) | |
Cursor = synchronize_class(AsyncCursor) | |
client = MongoClient() | |
print(client) | |
cursor = client.find_one() | |
print(cursor.fetch_something()) | |
for item in cursor: | |
print(item) | |
print(cursor) | |
print(str(cursor)) |
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