Skip to content

HTTPS clone URL

Subversion checkout URL

You can clone with
or
.
Download ZIP
Fetching contributors…

Cannot retrieve contributors at this time

350 lines (285 sloc) 12.125 kB
"""``tornado.gen`` is a generator-based interface to make it easier to
work in an asynchronous environment. Code using the ``gen`` module
is technically asynchronous, but it is written as a single generator
instead of a collection of separate functions.
For example, the following asynchronous handler::
class AsyncHandler(RequestHandler):
@asynchronous
def get(self):
http_client = AsyncHTTPClient()
http_client.fetch("http://example.com",
callback=self.on_fetch)
def on_fetch(self, response):
do_something_with_response(response)
self.render("template.html")
could be written with ``gen`` as::
class GenAsyncHandler(RequestHandler):
@asynchronous
@gen.engine
def get(self):
http_client = AsyncHTTPClient()
response = yield gen.Task(http_client.fetch, "http://example.com")
do_something_with_response(response)
self.render("template.html")
`Task` works with any function that takes a ``callback`` keyword
argument. You can also yield a list of ``Tasks``, which will be
started at the same time and run in parallel; a list of results will
be returned when they are all finished::
def get(self):
http_client = AsyncHTTPClient()
response1, response2 = yield [gen.Task(http_client.fetch, url1),
gen.Task(http_client.fetch, url2)]
For more complicated interfaces, `Task` can be split into two parts:
`Callback` and `Wait`::
class GenAsyncHandler2(RequestHandler):
@asynchronous
@gen.engine
def get(self):
http_client = AsyncHTTPClient()
http_client.fetch("http://example.com",
callback=(yield gen.Callback("key"))
response = yield gen.Wait("key")
do_something_with_response(response)
self.render("template.html")
The ``key`` argument to `Callback` and `Wait` allows for multiple
asynchronous operations to be started at different times and proceed
in parallel: yield several callbacks with different keys, then wait
for them once all the async operations have started.
The result of a `Wait` or `Task` yield expression depends on how the callback
was run. If it was called with no arguments, the result is ``None``. If
it was called with one argument, the result is that argument. If it was
called with more than one argument or any keyword arguments, the result
is an `Arguments` object, which is a named tuple ``(args, kwargs)``.
"""
import functools
import operator
import sys
import types
class KeyReuseError(Exception): pass
class UnknownKeyError(Exception): pass
class LeakedCallbackError(Exception): pass
class BadYieldError(Exception): pass
def engine(func):
"""Decorator for asynchronous generators.
Any generator that yields objects from this module must be wrapped
in this decorator. The decorator only works on functions that are
already asynchronous. For `~tornado.web.RequestHandler`
``get``/``post``/etc methods, this means that both the `tornado.gen.engine`
and `tornado.web.asynchronous` decorators must be used (in either order).
In most other cases, it means that it doesn't make sense to use
``gen.engine`` on functions that don't already take a callback argument.
"""
@functools.wraps(func)
def wrapper(*args, **kwargs):
gen = func(*args, **kwargs)
if isinstance(gen, types.GeneratorType):
Runner(gen).run()
return
assert gen is None, gen
# no yield, so we're done
return wrapper
class YieldPoint(object):
"""Base class for objects that may be yielded from the generator."""
def start(self, runner):
"""Called by the runner after the generator has yielded.
No other methods will be called on this object before ``start``.
"""
raise NotImplementedError()
def is_ready(self):
"""Called by the runner to determine whether to resume the generator.
Returns a boolean; may be called more than once.
"""
raise NotImplementedError()
def get_result(self):
"""Returns the value to use as the result of the yield expression.
This method will only be called once, and only after `is_ready`
has returned true.
"""
raise NotImplementedError()
class Callback(YieldPoint):
"""Returns a callable object that will allow a matching `Wait` to proceed.
The key may be any value suitable for use as a dictionary key, and is
used to match ``Callbacks`` to their corresponding ``Waits``. The key
must be unique among outstanding callbacks within a single run of the
generator function, but may be reused across different runs of the same
function (so constants generally work fine).
The callback may be called with zero or one arguments; if an argument
is given it will be returned by `Wait`.
"""
def __init__(self, key):
self.key = key
def start(self, runner):
self.runner = runner
runner.register_callback(self.key)
def is_ready(self):
return True
def get_result(self):
return self.runner.result_callback(self.key)
class Wait(YieldPoint):
"""Returns the argument passed to the result of a previous `Callback`."""
def __init__(self, key):
self.key = key
def start(self, runner):
self.runner = runner
def is_ready(self):
return self.runner.is_ready(self.key)
def get_result(self):
return self.runner.pop_result(self.key)
class WaitAll(YieldPoint):
"""Returns the results of multiple previous `Callbacks`.
The argument is a sequence of `Callback` keys, and the result is
a list of results in the same order.
`WaitAll` is equivalent to yielding a list of `Wait` objects.
"""
def __init__(self, keys):
self.keys = keys
def start(self, runner):
self.runner = runner
def is_ready(self):
return all(self.runner.is_ready(key) for key in self.keys)
def get_result(self):
return [self.runner.pop_result(key) for key in self.keys]
class Task(YieldPoint):
"""Runs a single asynchronous operation.
Takes a function (and optional additional arguments) and runs it with
those arguments plus a ``callback`` keyword argument. The argument passed
to the callback is returned as the result of the yield expression.
A `Task` is equivalent to a `Callback`/`Wait` pair (with a unique
key generated automatically)::
result = yield gen.Task(func, args)
func(args, callback=(yield gen.Callback(key)))
result = yield gen.Wait(key)
"""
def __init__(self, func, *args, **kwargs):
assert "callback" not in kwargs
self.args = args
self.kwargs = kwargs
self.func = func
def start(self, runner):
self.runner = runner
self.key = object()
runner.register_callback(self.key)
self.kwargs["callback"] = runner.result_callback(self.key)
self.func(*self.args, **self.kwargs)
def is_ready(self):
return self.runner.is_ready(self.key)
def get_result(self):
return self.runner.pop_result(self.key)
class Multi(YieldPoint):
"""Runs multiple asynchronous operations in parallel.
Takes a list of ``Tasks`` or other ``YieldPoints`` and returns a list of
their responses. It is not necessary to call `Multi` explicitly,
since the engine will do so automatically when the generator yields
a list of ``YieldPoints``.
"""
def __init__(self, children):
assert all(isinstance(i, YieldPoint) for i in children)
self.children = children
def start(self, runner):
for i in self.children:
i.start(runner)
def is_ready(self):
return all(i.is_ready() for i in self.children)
def get_result(self):
return [i.get_result() for i in self.children]
class _NullYieldPoint(YieldPoint):
def start(self, runner):
pass
def is_ready(self):
return True
def get_result(self):
return None
class Runner(object):
"""Internal implementation of `tornado.gen.engine`.
Maintains information about pending callbacks and their results.
"""
def __init__(self, gen):
self.gen = gen
self.yield_point = _NullYieldPoint()
self.pending_callbacks = set()
self.results = {}
self.running = False
self.finished = False
self.exc_info = None
def register_callback(self, key):
"""Adds ``key`` to the list of callbacks."""
if key in self.pending_callbacks:
raise KeyReuseError("key %r is already pending" % key)
self.pending_callbacks.add(key)
def is_ready(self, key):
"""Returns true if a result is available for ``key``."""
if key not in self.pending_callbacks:
raise UnknownKeyError("key %r is not pending" % key)
return key in self.results
def set_result(self, key, result):
"""Sets the result for ``key`` and attempts to resume the generator."""
self.results[key] = result
self.run()
def pop_result(self, key):
"""Returns the result for ``key`` and unregisters it."""
self.pending_callbacks.remove(key)
return self.results.pop(key)
def run(self):
"""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:
if self.exc_info is None:
try:
if not self.yield_point.is_ready():
return
next = self.yield_point.get_result()
except Exception:
self.exc_info = sys.exc_info()
try:
if self.exc_info is not None:
exc_info = self.exc_info
self.exc_info = None
yielded = self.gen.throw(*exc_info)
else:
yielded = self.gen.send(next)
except StopIteration:
self.finished = True
if self.pending_callbacks:
raise LeakedCallbackError(
"finished without waiting for callbacks %r" %
self.pending_callbacks)
return
except Exception:
self.finished = True
raise
if isinstance(yielded, list):
yielded = Multi(yielded)
if isinstance(yielded, YieldPoint):
self.yield_point = yielded
self.yield_point.start(self)
else:
self.exc_info = (BadYieldError("yielded unknown object %r" % yielded),)
finally:
self.running = False
def result_callback(self, key):
def inner(*args, **kwargs):
if kwargs or len(args) > 1:
result = Arguments(args, kwargs)
elif args:
result = args[0]
else:
result = None
self.set_result(key, result)
return inner
# in python 2.6+ this could be a collections.namedtuple
class Arguments(tuple):
"""The result of a yield expression whose callback had more than one
argument (or keyword arguments).
The `Arguments` object can be used as a tuple ``(args, kwargs)``
or an object with attributes ``args`` and ``kwargs``.
"""
__slots__ = ()
def __new__(cls, args, kwargs):
return tuple.__new__(cls, (args, kwargs))
args = property(operator.itemgetter(0))
kwargs = property(operator.itemgetter(1))
Jump to Line
Something went wrong with that request. Please try again.