import time
class AsyncResultTimeout(Exception):
pass
class AsyncResult(object):
"""AsyncResult is an object that represent a computation that occurs in
the background and will eventually have a result. Use the .value property
to access the result (which will block if the result has not yet arrived)
"""
__slots__ = ["_conn", "_is_ready", "_is_exc", "_callbacks", "_obj", "_ttl"]
def __init__(self, conn):
self._conn = conn
self._is_ready = False
self._is_exc = None
self._obj = None
self._callbacks = []
self._ttl = None
def __repr__(self):
if self._is_ready:
state = "ready"
elif self._is_exc:
state = "error"
elif self.expired:
state = "expired"
else:
state = "pending"
return "<AsyncResult object (%s) at 0x%08x>" % (state, id(self))
def __call__(self, is_exc, obj):
if self.expired:
return
self._is_ready = True
self._is_exc = is_exc
self._obj = obj
for cb in self._callbacks:
cb(self)
del self._callbacks[:]
def wait(self):
"""wait for the result to arrive. if the AsyncResult object has an
expiry set, and the result does not arrive within that timeout,
an AsyncResultTimeout exception is raised"""
if self._is_ready:
return
if self._ttl is None:
while not self._is_ready:
self._conn.serve()
else:
while True:
timeout = self._ttl - time.time()
self._conn.poll(timeout = max(timeout, 0))
if self._is_ready:
break
if timeout <= 0:
raise AsyncResultTimeout("result expired")
def add_callback(self, func):
"""adds a callback to be invoked when the result arrives. the
callback function takes a single argument, which is the current
AsyncResult (self)"""
if self._is_ready:
func(self)
else:
self._callbacks.append(func)
def set_expiry(self, timeout):
"""set the expiry time (in seconds, relative to now) or None for
unlimited time"""
if timeout is None:
self._ttl = None
else:
self._ttl = time.time() + timeout
@property
def ready(self):
"""a predicate of whether the result has arrived"""
if self.expired:
return False
if not self._is_ready:
self._conn.poll_all()
return self._is_ready
@property
def error(self):
"""a predicate of whether the returned result is an exception"""
if self.ready:
return self._is_exc
return False
@property
def expired(self):
"""a predicate of whether the async result has expired"""
if self._is_ready or self._ttl is None:
return False
else:
return time.time() > self._ttl
@property
def value(self):
"""returns the result of the operation. if the result has not yet
arrived, accessing this property will wait for it. if the result does
not arrive before the expiry time elapses, AsyncResultTimeout is
raised. if the returned result is an exception, it will be raised here.
otherwise, the result is returned directly."""
self.wait()
if self._is_exc:
raise self._obj
else:
return self._obj
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