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# Copyright (c) 2012 The Chromium Authors. All rights reserved.
# Use of this source code is governed by a BSD-style license that can be
# found in the LICENSE file.
import sys
_no_value = object()
def All(futures, except_pass=None):
'''Creates a Future which returns a list of results from each Future in
|futures|.
If any Future raises an error other than those in |except_pass| the returned
Future will raise as well.
'''
def resolve():
resolved = []
for f in futures:
try:
resolved.append(f.Get())
# "except None" will simply not catch any errors.
except except_pass:
pass
return resolved
return Future(callback=resolve)
def Race(futures, except_pass=None):
'''Returns a Future which resolves to the first Future in |futures| that
either succeeds or throws an error apart from those in |except_pass|.
If all Futures throw errors in |except_pass| then the returned Future
will re-throw one of those errors, for a nice stack trace.
'''
def resolve():
first_future = None
for future in futures:
if first_future is None:
first_future = future
try:
return future.Get()
# "except None" will simply not catch any errors.
except except_pass:
pass
# Everything failed, propagate the first error even though it was
# caught by |except_pass|.
return first_future.Get()
return Future(callback=resolve)
class Future(object):
'''Stores a value, error, or callback to be used later.
'''
def __init__(self, value=_no_value, callback=None, exc_info=None):
self._value = value
self._callback = callback
self._exc_info = exc_info
if (self._value is _no_value and
self._callback is None and
self._exc_info is None):
raise ValueError('Must have either a value, error, or callback.')
def Then(self, callback):
'''Creates and returns a future that runs |callback| on the value of this
future.
'''
def then():
return callback(self.Get())
return Future(callback=then)
def Get(self):
'''Gets the stored value, error, or callback contents.
'''
if self._value is not _no_value:
return self._value
if self._exc_info is not None:
self._Raise()
try:
self._value = self._callback()
return self._value
except:
self._exc_info = sys.exc_info()
self._Raise()
def _Raise(self):
exc_info = self._exc_info
raise exc_info[0], exc_info[1], exc_info[2]
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