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quay/util/asyncwrapper.py

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2019-11-12 16:09:47 +00:00
import queue
from functools import wraps
from concurrent.futures import Executor, Future, CancelledError
class AsyncExecutorWrapper(object):
""" This class will wrap a syncronous library transparently in a way which
will move all calls off to an asynchronous Executor, and will change all
returned values to be Future objects.
"""
SYNC_FLAG_FIELD = '__AsyncExecutorWrapper__sync__'
def __init__(self, delegate, executor):
""" Wrap the specified synchronous delegate instance, and submit() all
method calls to the specified Executor instance.
"""
self._delegate = delegate
self._executor = executor
def __getattr__(self, attr_name):
maybe_callable = getattr(self._delegate, attr_name) # Will raise proper attribute error
if callable(maybe_callable):
# Build a callable which when executed places the request
# onto a queue
@wraps(maybe_callable)
def wrapped_method(*args, **kwargs):
if getattr(maybe_callable, self.SYNC_FLAG_FIELD, False):
sync_result = Future()
try:
sync_result.set_result(maybe_callable(*args, **kwargs))
except Exception as ex:
sync_result.set_exception(ex)
return sync_result
try:
return self._executor.submit(maybe_callable, *args, **kwargs)
except queue.Full as ex:
queue_full = Future()
queue_full.set_exception(ex)
return queue_full
return wrapped_method
else:
return maybe_callable
@classmethod
def sync(cls, f):
""" Annotate the given method to flag it as synchronous so that AsyncExecutorWrapper
will return the result immediately without submitting it to the executor.
"""
setattr(f, cls.SYNC_FLAG_FIELD, True)
return f
class NullExecutorCancelled(CancelledError):
def __init__(self):
super(NullExecutorCancelled, self).__init__('Null executor always fails.')
class NullExecutor(Executor):
""" Executor instance which always returns a Future completed with a
CancelledError exception. """
def submit(self, _, *args, **kwargs):
always_fail = Future()
always_fail.set_exception(NullExecutorCancelled())
return always_fail