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846 lines
30 KiB
846 lines
30 KiB
"""``tornado.gen`` implements generator-based coroutines.
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.. note::
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The "decorator and generator" approach in this module is a
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precursor to native coroutines (using ``async def`` and ``await``)
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which were introduced in Python 3.5. Applications that do not
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require compatibility with older versions of Python should use
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native coroutines instead. Some parts of this module are still
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useful with native coroutines, notably `multi`, `sleep`,
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`WaitIterator`, and `with_timeout`. Some of these functions have
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counterparts in the `asyncio` module which may be used as well,
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although the two may not necessarily be 100% compatible.
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Coroutines provide an easier way to work in an asynchronous
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environment than chaining callbacks. Code using coroutines is
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technically asynchronous, but it is written as a single generator
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instead of a collection of separate functions.
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For example, here's a coroutine-based handler:
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.. testcode::
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class GenAsyncHandler(RequestHandler):
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@gen.coroutine
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def get(self):
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http_client = AsyncHTTPClient()
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response = yield http_client.fetch("http://example.com")
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do_something_with_response(response)
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self.render("template.html")
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.. testoutput::
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:hide:
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Asynchronous functions in Tornado return an ``Awaitable`` or `.Future`;
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yielding this object returns its result.
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You can also yield a list or dict of other yieldable objects, which
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will be started at the same time and run in parallel; a list or dict
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of results will be returned when they are all finished:
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.. testcode::
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@gen.coroutine
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def get(self):
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http_client = AsyncHTTPClient()
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response1, response2 = yield [http_client.fetch(url1),
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http_client.fetch(url2)]
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response_dict = yield dict(response3=http_client.fetch(url3),
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response4=http_client.fetch(url4))
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response3 = response_dict['response3']
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response4 = response_dict['response4']
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.. testoutput::
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:hide:
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If ``tornado.platform.twisted`` is imported, it is also possible to
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yield Twisted's ``Deferred`` objects. See the `convert_yielded`
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function to extend this mechanism.
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.. versionchanged:: 3.2
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Dict support added.
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.. versionchanged:: 4.1
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Support added for yielding ``asyncio`` Futures and Twisted Deferreds
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via ``singledispatch``.
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"""
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import asyncio
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import builtins
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import collections
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from collections.abc import Generator
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import concurrent.futures
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import datetime
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import functools
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from functools import singledispatch
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from inspect import isawaitable
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import sys
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import types
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from tornado.concurrent import (
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Future,
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is_future,
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chain_future,
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future_set_exc_info,
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future_add_done_callback,
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future_set_result_unless_cancelled,
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)
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from tornado.ioloop import IOLoop
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from tornado.log import app_log
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from tornado.util import TimeoutError
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import typing
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from typing import Union, Any, Callable, List, Type, Tuple, Awaitable, Dict
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if typing.TYPE_CHECKING:
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from typing import Sequence, Deque, Optional, Set, Iterable # noqa: F401
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_T = typing.TypeVar("_T")
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_Yieldable = Union[
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None, Awaitable, List[Awaitable], Dict[Any, Awaitable], concurrent.futures.Future
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]
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class KeyReuseError(Exception):
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pass
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class UnknownKeyError(Exception):
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pass
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class LeakedCallbackError(Exception):
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pass
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class BadYieldError(Exception):
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pass
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class ReturnValueIgnoredError(Exception):
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pass
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def _value_from_stopiteration(e: Union[StopIteration, "Return"]) -> Any:
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try:
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# StopIteration has a value attribute beginning in py33.
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# So does our Return class.
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return e.value
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except AttributeError:
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pass
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try:
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# Cython backports coroutine functionality by putting the value in
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# e.args[0].
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return e.args[0]
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except (AttributeError, IndexError):
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return None
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def _create_future() -> Future:
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future = Future() # type: Future
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# Fixup asyncio debug info by removing extraneous stack entries
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source_traceback = getattr(future, "_source_traceback", ())
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while source_traceback:
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# Each traceback entry is equivalent to a
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# (filename, self.lineno, self.name, self.line) tuple
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filename = source_traceback[-1][0]
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if filename == __file__:
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del source_traceback[-1]
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else:
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break
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return future
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def coroutine(
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func: Callable[..., "Generator[Any, Any, _T]"]
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) -> Callable[..., "Future[_T]"]:
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"""Decorator for asynchronous generators.
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For compatibility with older versions of Python, coroutines may
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also "return" by raising the special exception `Return(value)
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<Return>`.
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Functions with this decorator return a `.Future`.
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.. warning::
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When exceptions occur inside a coroutine, the exception
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information will be stored in the `.Future` object. You must
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examine the result of the `.Future` object, or the exception
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may go unnoticed by your code. This means yielding the function
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if called from another coroutine, using something like
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`.IOLoop.run_sync` for top-level calls, or passing the `.Future`
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to `.IOLoop.add_future`.
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.. versionchanged:: 6.0
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The ``callback`` argument was removed. Use the returned
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awaitable object instead.
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"""
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@functools.wraps(func)
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def wrapper(*args, **kwargs):
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# type: (*Any, **Any) -> Future[_T]
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# This function is type-annotated with a comment to work around
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# https://bitbucket.org/pypy/pypy/issues/2868/segfault-with-args-type-annotation-in
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future = _create_future()
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try:
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result = func(*args, **kwargs)
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except (Return, StopIteration) as e:
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result = _value_from_stopiteration(e)
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except Exception:
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future_set_exc_info(future, sys.exc_info())
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try:
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return future
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finally:
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# Avoid circular references
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future = None # type: ignore
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else:
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if isinstance(result, Generator):
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# Inline the first iteration of Runner.run. This lets us
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# avoid the cost of creating a Runner when the coroutine
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# never actually yields, which in turn allows us to
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# use "optional" coroutines in critical path code without
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# performance penalty for the synchronous case.
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try:
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yielded = next(result)
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except (StopIteration, Return) as e:
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future_set_result_unless_cancelled(
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future, _value_from_stopiteration(e)
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)
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except Exception:
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future_set_exc_info(future, sys.exc_info())
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else:
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# Provide strong references to Runner objects as long
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# as their result future objects also have strong
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# references (typically from the parent coroutine's
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# Runner). This keeps the coroutine's Runner alive.
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# We do this by exploiting the public API
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# add_done_callback() instead of putting a private
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# attribute on the Future.
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# (Github issues #1769, #2229).
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runner = Runner(result, future, yielded)
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future.add_done_callback(lambda _: runner)
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yielded = None
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try:
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return future
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finally:
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# Subtle memory optimization: if next() raised an exception,
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# the future's exc_info contains a traceback which
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# includes this stack frame. This creates a cycle,
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# which will be collected at the next full GC but has
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# been shown to greatly increase memory usage of
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# benchmarks (relative to the refcount-based scheme
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# used in the absence of cycles). We can avoid the
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# cycle by clearing the local variable after we return it.
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future = None # type: ignore
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future_set_result_unless_cancelled(future, result)
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return future
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wrapper.__wrapped__ = func # type: ignore
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wrapper.__tornado_coroutine__ = True # type: ignore
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return wrapper
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def is_coroutine_function(func: Any) -> bool:
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"""Return whether *func* is a coroutine function, i.e. a function
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wrapped with `~.gen.coroutine`.
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.. versionadded:: 4.5
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"""
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return getattr(func, "__tornado_coroutine__", False)
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class Return(Exception):
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"""Special exception to return a value from a `coroutine`.
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If this exception is raised, its value argument is used as the
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result of the coroutine::
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@gen.coroutine
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def fetch_json(url):
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response = yield AsyncHTTPClient().fetch(url)
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raise gen.Return(json_decode(response.body))
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In Python 3.3, this exception is no longer necessary: the ``return``
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statement can be used directly to return a value (previously
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``yield`` and ``return`` with a value could not be combined in the
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same function).
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By analogy with the return statement, the value argument is optional,
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but it is never necessary to ``raise gen.Return()``. The ``return``
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statement can be used with no arguments instead.
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"""
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def __init__(self, value: Any = None) -> None:
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super(Return, self).__init__()
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self.value = value
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# Cython recognizes subclasses of StopIteration with a .args tuple.
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self.args = (value,)
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class WaitIterator(object):
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"""Provides an iterator to yield the results of awaitables as they finish.
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Yielding a set of awaitables like this:
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``results = yield [awaitable1, awaitable2]``
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pauses the coroutine until both ``awaitable1`` and ``awaitable2``
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return, and then restarts the coroutine with the results of both
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awaitables. If either awaitable raises an exception, the
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expression will raise that exception and all the results will be
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lost.
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If you need to get the result of each awaitable as soon as possible,
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or if you need the result of some awaitables even if others produce
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errors, you can use ``WaitIterator``::
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wait_iterator = gen.WaitIterator(awaitable1, awaitable2)
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while not wait_iterator.done():
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try:
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result = yield wait_iterator.next()
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except Exception as e:
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print("Error {} from {}".format(e, wait_iterator.current_future))
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else:
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print("Result {} received from {} at {}".format(
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result, wait_iterator.current_future,
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wait_iterator.current_index))
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Because results are returned as soon as they are available the
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output from the iterator *will not be in the same order as the
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input arguments*. If you need to know which future produced the
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current result, you can use the attributes
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``WaitIterator.current_future``, or ``WaitIterator.current_index``
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to get the index of the awaitable from the input list. (if keyword
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arguments were used in the construction of the `WaitIterator`,
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``current_index`` will use the corresponding keyword).
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On Python 3.5, `WaitIterator` implements the async iterator
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protocol, so it can be used with the ``async for`` statement (note
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that in this version the entire iteration is aborted if any value
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raises an exception, while the previous example can continue past
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individual errors)::
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async for result in gen.WaitIterator(future1, future2):
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print("Result {} received from {} at {}".format(
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result, wait_iterator.current_future,
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wait_iterator.current_index))
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.. versionadded:: 4.1
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.. versionchanged:: 4.3
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Added ``async for`` support in Python 3.5.
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"""
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_unfinished = {} # type: Dict[Future, Union[int, str]]
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def __init__(self, *args: Future, **kwargs: Future) -> None:
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if args and kwargs:
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raise ValueError("You must provide args or kwargs, not both")
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if kwargs:
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self._unfinished = dict((f, k) for (k, f) in kwargs.items())
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futures = list(kwargs.values()) # type: Sequence[Future]
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else:
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self._unfinished = dict((f, i) for (i, f) in enumerate(args))
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futures = args
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self._finished = collections.deque() # type: Deque[Future]
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self.current_index = None # type: Optional[Union[str, int]]
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self.current_future = None # type: Optional[Future]
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self._running_future = None # type: Optional[Future]
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for future in futures:
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future_add_done_callback(future, self._done_callback)
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def done(self) -> bool:
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"""Returns True if this iterator has no more results."""
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if self._finished or self._unfinished:
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return False
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# Clear the 'current' values when iteration is done.
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self.current_index = self.current_future = None
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return True
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def next(self) -> Future:
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"""Returns a `.Future` that will yield the next available result.
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Note that this `.Future` will not be the same object as any of
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the inputs.
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"""
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self._running_future = Future()
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if self._finished:
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self._return_result(self._finished.popleft())
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return self._running_future
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def _done_callback(self, done: Future) -> None:
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if self._running_future and not self._running_future.done():
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self._return_result(done)
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else:
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self._finished.append(done)
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def _return_result(self, done: Future) -> None:
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"""Called set the returned future's state that of the future
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we yielded, and set the current future for the iterator.
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"""
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if self._running_future is None:
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raise Exception("no future is running")
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chain_future(done, self._running_future)
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self.current_future = done
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self.current_index = self._unfinished.pop(done)
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def __aiter__(self) -> typing.AsyncIterator:
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return self
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def __anext__(self) -> Future:
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if self.done():
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# Lookup by name to silence pyflakes on older versions.
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raise getattr(builtins, "StopAsyncIteration")()
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return self.next()
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def multi(
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children: Union[List[_Yieldable], Dict[Any, _Yieldable]],
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quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
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) -> "Union[Future[List], Future[Dict]]":
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"""Runs multiple asynchronous operations in parallel.
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``children`` may either be a list or a dict whose values are
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yieldable objects. ``multi()`` returns a new yieldable
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object that resolves to a parallel structure containing their
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results. If ``children`` is a list, the result is a list of
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results in the same order; if it is a dict, the result is a dict
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with the same keys.
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That is, ``results = yield multi(list_of_futures)`` is equivalent
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to::
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results = []
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for future in list_of_futures:
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results.append(yield future)
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If any children raise exceptions, ``multi()`` will raise the first
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one. All others will be logged, unless they are of types
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contained in the ``quiet_exceptions`` argument.
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In a ``yield``-based coroutine, it is not normally necessary to
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call this function directly, since the coroutine runner will
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do it automatically when a list or dict is yielded. However,
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it is necessary in ``await``-based coroutines, or to pass
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the ``quiet_exceptions`` argument.
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This function is available under the names ``multi()`` and ``Multi()``
|
|
for historical reasons.
|
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Cancelling a `.Future` returned by ``multi()`` does not cancel its
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children. `asyncio.gather` is similar to ``multi()``, but it does
|
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cancel its children.
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|
|
.. versionchanged:: 4.2
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If multiple yieldables fail, any exceptions after the first
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(which is raised) will be logged. Added the ``quiet_exceptions``
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argument to suppress this logging for selected exception types.
|
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|
|
.. versionchanged:: 4.3
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|
Replaced the class ``Multi`` and the function ``multi_future``
|
|
with a unified function ``multi``. Added support for yieldables
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other than ``YieldPoint`` and `.Future`.
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"""
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return multi_future(children, quiet_exceptions=quiet_exceptions)
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Multi = multi
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|
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|
def multi_future(
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children: Union[List[_Yieldable], Dict[Any, _Yieldable]],
|
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quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
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) -> "Union[Future[List], Future[Dict]]":
|
|
"""Wait for multiple asynchronous futures in parallel.
|
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|
|
Since Tornado 6.0, this function is exactly the same as `multi`.
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|
|
.. versionadded:: 4.0
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|
|
.. versionchanged:: 4.2
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|
If multiple ``Futures`` fail, any exceptions after the first (which is
|
|
raised) will be logged. Added the ``quiet_exceptions``
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|
argument to suppress this logging for selected exception types.
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|
.. deprecated:: 4.3
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Use `multi` instead.
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"""
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|
if isinstance(children, dict):
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keys = list(children.keys()) # type: Optional[List]
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children_seq = children.values() # type: Iterable
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|
else:
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keys = None
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children_seq = children
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children_futs = list(map(convert_yielded, children_seq))
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|
assert all(is_future(i) or isinstance(i, _NullFuture) for i in children_futs)
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|
unfinished_children = set(children_futs)
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|
future = _create_future()
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|
if not children_futs:
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future_set_result_unless_cancelled(future, {} if keys is not None else [])
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|
|
def callback(fut: Future) -> None:
|
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unfinished_children.remove(fut)
|
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if not unfinished_children:
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result_list = []
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for f in children_futs:
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try:
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result_list.append(f.result())
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|
except Exception as e:
|
|
if future.done():
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|
if not isinstance(e, quiet_exceptions):
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|
app_log.error(
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"Multiple exceptions in yield list", exc_info=True
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)
|
|
else:
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future_set_exc_info(future, sys.exc_info())
|
|
if not future.done():
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|
if keys is not None:
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future_set_result_unless_cancelled(
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future, dict(zip(keys, result_list))
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)
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|
else:
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future_set_result_unless_cancelled(future, result_list)
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|
|
listening = set() # type: Set[Future]
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|
for f in children_futs:
|
|
if f not in listening:
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listening.add(f)
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future_add_done_callback(f, callback)
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return future
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|
|
|
|
def maybe_future(x: Any) -> Future:
|
|
"""Converts ``x`` into a `.Future`.
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|
|
If ``x`` is already a `.Future`, it is simply returned; otherwise
|
|
it is wrapped in a new `.Future`. This is suitable for use as
|
|
``result = yield gen.maybe_future(f())`` when you don't know whether
|
|
``f()`` returns a `.Future` or not.
|
|
|
|
.. deprecated:: 4.3
|
|
This function only handles ``Futures``, not other yieldable objects.
|
|
Instead of `maybe_future`, check for the non-future result types
|
|
you expect (often just ``None``), and ``yield`` anything unknown.
|
|
"""
|
|
if is_future(x):
|
|
return x
|
|
else:
|
|
fut = _create_future()
|
|
fut.set_result(x)
|
|
return fut
|
|
|
|
|
|
def with_timeout(
|
|
timeout: Union[float, datetime.timedelta],
|
|
future: _Yieldable,
|
|
quiet_exceptions: "Union[Type[Exception], Tuple[Type[Exception], ...]]" = (),
|
|
) -> Future:
|
|
"""Wraps a `.Future` (or other yieldable object) in a timeout.
|
|
|
|
Raises `tornado.util.TimeoutError` if the input future does not
|
|
complete before ``timeout``, which may be specified in any form
|
|
allowed by `.IOLoop.add_timeout` (i.e. a `datetime.timedelta` or
|
|
an absolute time relative to `.IOLoop.time`)
|
|
|
|
If the wrapped `.Future` fails after it has timed out, the exception
|
|
will be logged unless it is either of a type contained in
|
|
``quiet_exceptions`` (which may be an exception type or a sequence of
|
|
types), or an ``asyncio.CancelledError``.
|
|
|
|
The wrapped `.Future` is not canceled when the timeout expires,
|
|
permitting it to be reused. `asyncio.wait_for` is similar to this
|
|
function but it does cancel the wrapped `.Future` on timeout.
|
|
|
|
.. versionadded:: 4.0
|
|
|
|
.. versionchanged:: 4.1
|
|
Added the ``quiet_exceptions`` argument and the logging of unhandled
|
|
exceptions.
|
|
|
|
.. versionchanged:: 4.4
|
|
Added support for yieldable objects other than `.Future`.
|
|
|
|
.. versionchanged:: 6.0.3
|
|
``asyncio.CancelledError`` is now always considered "quiet".
|
|
|
|
"""
|
|
# It's tempting to optimize this by cancelling the input future on timeout
|
|
# instead of creating a new one, but A) we can't know if we are the only
|
|
# one waiting on the input future, so cancelling it might disrupt other
|
|
# callers and B) concurrent futures can only be cancelled while they are
|
|
# in the queue, so cancellation cannot reliably bound our waiting time.
|
|
future_converted = convert_yielded(future)
|
|
result = _create_future()
|
|
chain_future(future_converted, result)
|
|
io_loop = IOLoop.current()
|
|
|
|
def error_callback(future: Future) -> None:
|
|
try:
|
|
future.result()
|
|
except asyncio.CancelledError:
|
|
pass
|
|
except Exception as e:
|
|
if not isinstance(e, quiet_exceptions):
|
|
app_log.error(
|
|
"Exception in Future %r after timeout", future, exc_info=True
|
|
)
|
|
|
|
def timeout_callback() -> None:
|
|
if not result.done():
|
|
result.set_exception(TimeoutError("Timeout"))
|
|
# In case the wrapped future goes on to fail, log it.
|
|
future_add_done_callback(future_converted, error_callback)
|
|
|
|
timeout_handle = io_loop.add_timeout(timeout, timeout_callback)
|
|
if isinstance(future_converted, Future):
|
|
# We know this future will resolve on the IOLoop, so we don't
|
|
# need the extra thread-safety of IOLoop.add_future (and we also
|
|
# don't care about StackContext here.
|
|
future_add_done_callback(
|
|
future_converted, lambda future: io_loop.remove_timeout(timeout_handle)
|
|
)
|
|
else:
|
|
# concurrent.futures.Futures may resolve on any thread, so we
|
|
# need to route them back to the IOLoop.
|
|
io_loop.add_future(
|
|
future_converted, lambda future: io_loop.remove_timeout(timeout_handle)
|
|
)
|
|
return result
|
|
|
|
|
|
def sleep(duration: float) -> "Future[None]":
|
|
"""Return a `.Future` that resolves after the given number of seconds.
|
|
|
|
When used with ``yield`` in a coroutine, this is a non-blocking
|
|
analogue to `time.sleep` (which should not be used in coroutines
|
|
because it is blocking)::
|
|
|
|
yield gen.sleep(0.5)
|
|
|
|
Note that calling this function on its own does nothing; you must
|
|
wait on the `.Future` it returns (usually by yielding it).
|
|
|
|
.. versionadded:: 4.1
|
|
"""
|
|
f = _create_future()
|
|
IOLoop.current().call_later(
|
|
duration, lambda: future_set_result_unless_cancelled(f, None)
|
|
)
|
|
return f
|
|
|
|
|
|
class _NullFuture(object):
|
|
"""_NullFuture resembles a Future that finished with a result of None.
|
|
|
|
It's not actually a `Future` to avoid depending on a particular event loop.
|
|
Handled as a special case in the coroutine runner.
|
|
|
|
We lie and tell the type checker that a _NullFuture is a Future so
|
|
we don't have to leak _NullFuture into lots of public APIs. But
|
|
this means that the type checker can't warn us when we're passing
|
|
a _NullFuture into a code path that doesn't understand what to do
|
|
with it.
|
|
"""
|
|
|
|
def result(self) -> None:
|
|
return None
|
|
|
|
def done(self) -> bool:
|
|
return True
|
|
|
|
|
|
# _null_future is used as a dummy value in the coroutine runner. It differs
|
|
# from moment in that moment always adds a delay of one IOLoop iteration
|
|
# while _null_future is processed as soon as possible.
|
|
_null_future = typing.cast(Future, _NullFuture())
|
|
|
|
moment = typing.cast(Future, _NullFuture())
|
|
moment.__doc__ = """A special object which may be yielded to allow the IOLoop to run for
|
|
one iteration.
|
|
|
|
This is not needed in normal use but it can be helpful in long-running
|
|
coroutines that are likely to yield Futures that are ready instantly.
|
|
|
|
Usage: ``yield gen.moment``
|
|
|
|
In native coroutines, the equivalent of ``yield gen.moment`` is
|
|
``await asyncio.sleep(0)``.
|
|
|
|
.. versionadded:: 4.0
|
|
|
|
.. deprecated:: 4.5
|
|
``yield None`` (or ``yield`` with no argument) is now equivalent to
|
|
``yield gen.moment``.
|
|
"""
|
|
|
|
|
|
class Runner(object):
|
|
"""Internal implementation of `tornado.gen.coroutine`.
|
|
|
|
Maintains information about pending callbacks and their results.
|
|
|
|
The results of the generator are stored in ``result_future`` (a
|
|
`.Future`)
|
|
"""
|
|
|
|
def __init__(
|
|
self,
|
|
gen: "Generator[_Yieldable, Any, _T]",
|
|
result_future: "Future[_T]",
|
|
first_yielded: _Yieldable,
|
|
) -> None:
|
|
self.gen = gen
|
|
self.result_future = result_future
|
|
self.future = _null_future # type: Union[None, Future]
|
|
self.running = False
|
|
self.finished = False
|
|
self.io_loop = IOLoop.current()
|
|
if self.handle_yield(first_yielded):
|
|
gen = result_future = first_yielded = None # type: ignore
|
|
self.run()
|
|
|
|
def run(self) -> None:
|
|
"""Starts or resumes the generator, running until it reaches a
|
|
yield point that is not ready.
|
|
"""
|
|
if self.running or self.finished:
|
|
return
|
|
try:
|
|
self.running = True
|
|
while True:
|
|
future = self.future
|
|
if future is None:
|
|
raise Exception("No pending future")
|
|
if not future.done():
|
|
return
|
|
self.future = None
|
|
try:
|
|
exc_info = None
|
|
|
|
try:
|
|
value = future.result()
|
|
except Exception:
|
|
exc_info = sys.exc_info()
|
|
future = None
|
|
|
|
if exc_info is not None:
|
|
try:
|
|
yielded = self.gen.throw(*exc_info) # type: ignore
|
|
finally:
|
|
# Break up a reference to itself
|
|
# for faster GC on CPython.
|
|
exc_info = None
|
|
else:
|
|
yielded = self.gen.send(value)
|
|
|
|
except (StopIteration, Return) as e:
|
|
self.finished = True
|
|
self.future = _null_future
|
|
future_set_result_unless_cancelled(
|
|
self.result_future, _value_from_stopiteration(e)
|
|
)
|
|
self.result_future = None # type: ignore
|
|
return
|
|
except Exception:
|
|
self.finished = True
|
|
self.future = _null_future
|
|
future_set_exc_info(self.result_future, sys.exc_info())
|
|
self.result_future = None # type: ignore
|
|
return
|
|
if not self.handle_yield(yielded):
|
|
return
|
|
yielded = None
|
|
finally:
|
|
self.running = False
|
|
|
|
def handle_yield(self, yielded: _Yieldable) -> bool:
|
|
try:
|
|
self.future = convert_yielded(yielded)
|
|
except BadYieldError:
|
|
self.future = Future()
|
|
future_set_exc_info(self.future, sys.exc_info())
|
|
|
|
if self.future is moment:
|
|
self.io_loop.add_callback(self.run)
|
|
return False
|
|
elif self.future is None:
|
|
raise Exception("no pending future")
|
|
elif not self.future.done():
|
|
|
|
def inner(f: Any) -> None:
|
|
# Break a reference cycle to speed GC.
|
|
f = None # noqa: F841
|
|
self.run()
|
|
|
|
self.io_loop.add_future(self.future, inner)
|
|
return False
|
|
return True
|
|
|
|
def handle_exception(
|
|
self, typ: Type[Exception], value: Exception, tb: types.TracebackType
|
|
) -> bool:
|
|
if not self.running and not self.finished:
|
|
self.future = Future()
|
|
future_set_exc_info(self.future, (typ, value, tb))
|
|
self.run()
|
|
return True
|
|
else:
|
|
return False
|
|
|
|
|
|
# Convert Awaitables into Futures.
|
|
try:
|
|
_wrap_awaitable = asyncio.ensure_future
|
|
except AttributeError:
|
|
# asyncio.ensure_future was introduced in Python 3.4.4, but
|
|
# Debian jessie still ships with 3.4.2 so try the old name.
|
|
_wrap_awaitable = getattr(asyncio, "async")
|
|
|
|
|
|
def convert_yielded(yielded: _Yieldable) -> Future:
|
|
"""Convert a yielded object into a `.Future`.
|
|
|
|
The default implementation accepts lists, dictionaries, and
|
|
Futures. This has the side effect of starting any coroutines that
|
|
did not start themselves, similar to `asyncio.ensure_future`.
|
|
|
|
If the `~functools.singledispatch` library is available, this function
|
|
may be extended to support additional types. For example::
|
|
|
|
@convert_yielded.register(asyncio.Future)
|
|
def _(asyncio_future):
|
|
return tornado.platform.asyncio.to_tornado_future(asyncio_future)
|
|
|
|
.. versionadded:: 4.1
|
|
|
|
"""
|
|
if yielded is None or yielded is moment:
|
|
return moment
|
|
elif yielded is _null_future:
|
|
return _null_future
|
|
elif isinstance(yielded, (list, dict)):
|
|
return multi(yielded) # type: ignore
|
|
elif is_future(yielded):
|
|
return typing.cast(Future, yielded)
|
|
elif isawaitable(yielded):
|
|
return _wrap_awaitable(yielded) # type: ignore
|
|
else:
|
|
raise BadYieldError("yielded unknown object %r" % (yielded,))
|
|
|
|
|
|
convert_yielded = singledispatch(convert_yielded)
|