JezK
Edit File: sync.py
import asyncio import asyncio.coroutines import contextvars import functools import inspect import os import sys import threading import warnings import weakref from concurrent.futures import Future, ThreadPoolExecutor from typing import Any, Callable, Dict, Optional, overload from .current_thread_executor import CurrentThreadExecutor from .local import Local def _restore_context(context): # Check for changes in contextvars, and set them to the current # context for downstream consumers for cvar in context: try: if cvar.get() != context.get(cvar): cvar.set(context.get(cvar)) except LookupError: cvar.set(context.get(cvar)) # Python 3.12 deprecates asyncio.iscoroutinefunction() as an alias for # inspect.iscoroutinefunction(), whilst also removing the _is_coroutine marker. # The latter is replaced with the inspect.markcoroutinefunction decorator. # Until 3.12 is the minimum supported Python version, provide a shim. # Django 4.0 only supports 3.8+, so don't concern with the _or_partial backport. # Type hint: should be generic: whatever T it takes it returns. (Same id) def markcoroutinefunction(func: Any) -> Any: if hasattr(inspect, "markcoroutinefunction"): return inspect.markcoroutinefunction(func) else: func._is_coroutine = asyncio.coroutines._is_coroutine # type: ignore return func def iscoroutinefunction(func: Any) -> bool: if hasattr(inspect, "markcoroutinefunction"): return inspect.iscoroutinefunction(func) else: return asyncio.iscoroutinefunction(func) def _iscoroutinefunction_or_partial(func: Any) -> bool: # Python < 3.8 does not correctly determine partially wrapped # coroutine functions are coroutine functions, hence the need for # this to exist. Code taken from CPython. if sys.version_info >= (3, 8): return iscoroutinefunction(func) else: while inspect.ismethod(func): func = func.__func__ while isinstance(func, functools.partial): func = func.func return iscoroutinefunction(func) class ThreadSensitiveContext: """Async context manager to manage context for thread sensitive mode This context manager controls which thread pool executor is used when in thread sensitive mode. By default, a single thread pool executor is shared within a process. In Python 3.7+, the ThreadSensitiveContext() context manager may be used to specify a thread pool per context. This context manager is re-entrant, so only the outer-most call to ThreadSensitiveContext will set the context. Usage: >>> import time >>> async with ThreadSensitiveContext(): ... await sync_to_async(time.sleep, 1)() """ def __init__(self): self.token = None async def __aenter__(self): try: SyncToAsync.thread_sensitive_context.get() except LookupError: self.token = SyncToAsync.thread_sensitive_context.set(self) return self async def __aexit__(self, exc, value, tb): if not self.token: return executor = SyncToAsync.context_to_thread_executor.pop(self, None) if executor: executor.shutdown() SyncToAsync.thread_sensitive_context.reset(self.token) class AsyncToSync: """ Utility class which turns an awaitable that only works on the thread with the event loop into a synchronous callable that works in a subthread. If the call stack contains an async loop, the code runs there. Otherwise, the code runs in a new loop in a new thread. Either way, this thread then pauses and waits to run any thread_sensitive code called from further down the call stack using SyncToAsync, before finally exiting once the async task returns. """ # Maps launched Tasks to the threads that launched them (for locals impl) launch_map: "Dict[asyncio.Task[object], threading.Thread]" = {} # Keeps track of which CurrentThreadExecutor to use. This uses an asgiref # Local, not a threadlocal, so that tasks can work out what their parent used. executors = Local() # When we can't find a CurrentThreadExecutor from the context, such as # inside create_task, we'll look it up here from the running event loop. loop_thread_executors: "Dict[asyncio.AbstractEventLoop, CurrentThreadExecutor]" = {} def __init__(self, awaitable, force_new_loop=False): if not callable(awaitable) or ( not _iscoroutinefunction_or_partial(awaitable) and not _iscoroutinefunction_or_partial( getattr(awaitable, "__call__", awaitable) ) ): # Python does not have very reliable detection of async functions # (lots of false negatives) so this is just a warning. warnings.warn( "async_to_sync was passed a non-async-marked callable", stacklevel=2 ) self.awaitable = awaitable try: self.__self__ = self.awaitable.__self__ except AttributeError: pass if force_new_loop: # They have asked that we always run in a new sub-loop. self.main_event_loop = None else: try: self.main_event_loop = asyncio.get_running_loop() except RuntimeError: # There's no event loop in this thread. Look for the threadlocal if # we're inside SyncToAsync main_event_loop_pid = getattr( SyncToAsync.threadlocal, "main_event_loop_pid", None ) # We make sure the parent loop is from the same process - if # they've forked, this is not going to be valid any more (#194) if main_event_loop_pid and main_event_loop_pid == os.getpid(): self.main_event_loop = getattr( SyncToAsync.threadlocal, "main_event_loop", None ) else: self.main_event_loop = None def __call__(self, *args, **kwargs): # You can't call AsyncToSync from a thread with a running event loop try: event_loop = asyncio.get_running_loop() except RuntimeError: pass else: if event_loop.is_running(): raise RuntimeError( "You cannot use AsyncToSync in the same thread as an async event loop - " "just await the async function directly." ) # Wrapping context in list so it can be reassigned from within # `main_wrap`. context = [contextvars.copy_context()] # Make a future for the return information call_result = Future() # Get the source thread source_thread = threading.current_thread() # Make a CurrentThreadExecutor we'll use to idle in this thread - we # need one for every sync frame, even if there's one above us in the # same thread. if hasattr(self.executors, "current"): old_current_executor = self.executors.current else: old_current_executor = None current_executor = CurrentThreadExecutor() self.executors.current = current_executor loop = None # Use call_soon_threadsafe to schedule a synchronous callback on the # main event loop's thread if it's there, otherwise make a new loop # in this thread. try: awaitable = self.main_wrap( args, kwargs, call_result, source_thread, sys.exc_info(), context ) if not (self.main_event_loop and self.main_event_loop.is_running()): # Make our own event loop - in a new thread - and run inside that. loop = asyncio.new_event_loop() self.loop_thread_executors[loop] = current_executor loop_executor = ThreadPoolExecutor(max_workers=1) loop_future = loop_executor.submit( self._run_event_loop, loop, awaitable ) if current_executor: # Run the CurrentThreadExecutor until the future is done current_executor.run_until_future(loop_future) # Wait for future and/or allow for exception propagation loop_future.result() else: # Call it inside the existing loop self.main_event_loop.call_soon_threadsafe( self.main_event_loop.create_task, awaitable ) if current_executor: # Run the CurrentThreadExecutor until the future is done current_executor.run_until_future(call_result) finally: # Clean up any executor we were running if loop is not None: del self.loop_thread_executors[loop] if hasattr(self.executors, "current"): del self.executors.current if old_current_executor: self.executors.current = old_current_executor _restore_context(context[0]) # Wait for results from the future. return call_result.result() def _run_event_loop(self, loop, coro): """ Runs the given event loop (designed to be called in a thread). """ asyncio.set_event_loop(loop) try: loop.run_until_complete(coro) finally: try: # mimic asyncio.run() behavior # cancel unexhausted async generators tasks = asyncio.all_tasks(loop) for task in tasks: task.cancel() async def gather(): await asyncio.gather(*tasks, return_exceptions=True) loop.run_until_complete(gather()) for task in tasks: if task.cancelled(): continue if task.exception() is not None: loop.call_exception_handler( { "message": "unhandled exception during loop shutdown", "exception": task.exception(), "task": task, } ) if hasattr(loop, "shutdown_asyncgens"): loop.run_until_complete(loop.shutdown_asyncgens()) finally: loop.close() asyncio.set_event_loop(self.main_event_loop) def __get__(self, parent, objtype): """ Include self for methods """ func = functools.partial(self.__call__, parent) return functools.update_wrapper(func, self.awaitable) async def main_wrap( self, args, kwargs, call_result, source_thread, exc_info, context ): """ Wraps the awaitable with something that puts the result into the result/exception future. """ if context is not None: _restore_context(context[0]) current_task = SyncToAsync.get_current_task() self.launch_map[current_task] = source_thread try: # If we have an exception, run the function inside the except block # after raising it so exc_info is correctly populated. if exc_info[1]: try: raise exc_info[1] except BaseException: result = await self.awaitable(*args, **kwargs) else: result = await self.awaitable(*args, **kwargs) except BaseException as e: call_result.set_exception(e) else: call_result.set_result(result) finally: del self.launch_map[current_task] context[0] = contextvars.copy_context() class SyncToAsync: """ Utility class which turns a synchronous callable into an awaitable that runs in a threadpool. It also sets a threadlocal inside the thread so calls to AsyncToSync can escape it. If thread_sensitive is passed, the code will run in the same thread as any outer code. This is needed for underlying Python code that is not threadsafe (for example, code which handles SQLite database connections). If the outermost program is async (i.e. SyncToAsync is outermost), then this will be a dedicated single sub-thread that all sync code runs in, one after the other. If the outermost program is sync (i.e. AsyncToSync is outermost), this will just be the main thread. This is achieved by idling with a CurrentThreadExecutor while AsyncToSync is blocking its sync parent, rather than just blocking. If executor is passed in, that will be used instead of the loop's default executor. In order to pass in an executor, thread_sensitive must be set to False, otherwise a TypeError will be raised. """ # Maps launched threads to the coroutines that spawned them launch_map: "Dict[threading.Thread, asyncio.Task[object]]" = {} # Storage for main event loop references threadlocal = threading.local() # Single-thread executor for thread-sensitive code single_thread_executor = ThreadPoolExecutor(max_workers=1) # Maintain a contextvar for the current execution context. Optionally used # for thread sensitive mode. thread_sensitive_context: "contextvars.ContextVar[str]" = contextvars.ContextVar( "thread_sensitive_context" ) # Contextvar that is used to detect if the single thread executor # would be awaited on while already being used in the same context deadlock_context: "contextvars.ContextVar[bool]" = contextvars.ContextVar( "deadlock_context" ) # Maintaining a weak reference to the context ensures that thread pools are # erased once the context goes out of scope. This terminates the thread pool. context_to_thread_executor: "weakref.WeakKeyDictionary[object, ThreadPoolExecutor]" = ( weakref.WeakKeyDictionary() ) def __init__( self, func: Callable[..., Any], thread_sensitive: bool = True, executor: Optional["ThreadPoolExecutor"] = None, ) -> None: if ( not callable(func) or _iscoroutinefunction_or_partial(func) or _iscoroutinefunction_or_partial(getattr(func, "__call__", func)) ): raise TypeError("sync_to_async can only be applied to sync functions.") self.func = func functools.update_wrapper(self, func) self._thread_sensitive = thread_sensitive markcoroutinefunction(self) if thread_sensitive and executor is not None: raise TypeError("executor must not be set when thread_sensitive is True") self._executor = executor try: self.__self__ = func.__self__ # type: ignore except AttributeError: pass async def __call__(self, *args, **kwargs): loop = asyncio.get_running_loop() # Work out what thread to run the code in if self._thread_sensitive: if hasattr(AsyncToSync.executors, "current"): # If we have a parent sync thread above somewhere, use that executor = AsyncToSync.executors.current elif self.thread_sensitive_context and self.thread_sensitive_context.get( None ): # If we have a way of retrieving the current context, attempt # to use a per-context thread pool executor thread_sensitive_context = self.thread_sensitive_context.get() if thread_sensitive_context in self.context_to_thread_executor: # Re-use thread executor in current context executor = self.context_to_thread_executor[thread_sensitive_context] else: # Create new thread executor in current context executor = ThreadPoolExecutor(max_workers=1) self.context_to_thread_executor[thread_sensitive_context] = executor elif loop in AsyncToSync.loop_thread_executors: # Re-use thread executor for running loop executor = AsyncToSync.loop_thread_executors[loop] elif self.deadlock_context and self.deadlock_context.get(False): raise RuntimeError( "Single thread executor already being used, would deadlock" ) else: # Otherwise, we run it in a fixed single thread executor = self.single_thread_executor if self.deadlock_context: self.deadlock_context.set(True) else: # Use the passed in executor, or the loop's default if it is None executor = self._executor context = contextvars.copy_context() child = functools.partial(self.func, *args, **kwargs) func = context.run args = (child,) kwargs = {} try: # Run the code in the right thread future = loop.run_in_executor( executor, functools.partial( self.thread_handler, loop, self.get_current_task(), sys.exc_info(), func, *args, **kwargs, ), ) ret = await asyncio.wait_for(future, timeout=None) finally: _restore_context(context) if self.deadlock_context: self.deadlock_context.set(False) return ret def __get__(self, parent, objtype): """ Include self for methods """ func = functools.partial(self.__call__, parent) return functools.update_wrapper(func, self.func) def thread_handler(self, loop, source_task, exc_info, func, *args, **kwargs): """ Wraps the sync application with exception handling. """ # Set the threadlocal for AsyncToSync self.threadlocal.main_event_loop = loop self.threadlocal.main_event_loop_pid = os.getpid() # Set the task mapping (used for the locals module) current_thread = threading.current_thread() if AsyncToSync.launch_map.get(source_task) == current_thread: # Our parent task was launched from this same thread, so don't make # a launch map entry - let it shortcut over us! (and stop infinite loops) parent_set = False else: self.launch_map[current_thread] = source_task parent_set = True # Run the function try: # If we have an exception, run the function inside the except block # after raising it so exc_info is correctly populated. if exc_info[1]: try: raise exc_info[1] except BaseException: return func(*args, **kwargs) else: return func(*args, **kwargs) finally: # Only delete the launch_map parent if we set it, otherwise it is # from someone else. if parent_set: del self.launch_map[current_thread] @staticmethod def get_current_task(): """ Implementation of asyncio.current_task() that returns None if there is no task. """ try: return asyncio.current_task() except RuntimeError: return None # Lowercase aliases (and decorator friendliness) async_to_sync = AsyncToSync @overload def sync_to_async( func: None = None, thread_sensitive: bool = True, executor: Optional["ThreadPoolExecutor"] = None, ) -> Callable[[Callable[..., Any]], SyncToAsync]: ... @overload def sync_to_async( func: Callable[..., Any], thread_sensitive: bool = True, executor: Optional["ThreadPoolExecutor"] = None, ) -> SyncToAsync: ... def sync_to_async( func=None, thread_sensitive=True, executor=None, ): if func is None: return lambda f: SyncToAsync( f, thread_sensitive=thread_sensitive, executor=executor, ) return SyncToAsync( func, thread_sensitive=thread_sensitive, executor=executor, )