第一个是asyncio.Future,另外一个是concurrent.futures.Future
前者几乎兼容后者,区别在于:
- asyncio.Future.result,asyncio.Future.exception不存在一个超时选项,并且如果被中断的时候future还没有结束,会触发一个exception
2.如果回调函数用asyncio.Future.add_done_callback()方法注册了,结果一定会通过event_loop的asyncio.AbstractEventLoop.call_soon_threadsafe()来返回
- asyncio.Future类里面没有wait()和as_completed()方法(concurrent.futures.Future有)
This class is not thread safe.
concurrent.futures.Future的方法
cancel()
Attempt to cancel the call. If the call is currently being executed and cannot be cancelled then the method will return False, otherwise the call will be cancelled and the method will return True
cancelled
Return True if the call was successfully cancelled.
running
Return True if the call is currently being executed and cannot be cancelled.
done
Return True if the call was successfully cancelled or finished running.
result(timeout=None)
Return the value returned by the call. If the call hasn’t yet completed then this method will wait up to timeoutseconds. If the call hasn’t completed in timeout seconds, then a concurrent.futures.TimeoutError will be raised. timeout can be an int or float. If timeout is not specified or None, there is no limit to the wait time.
If the future is cancelled before completing then CancelledError will be raised.If the call raised, this method will raise the same exception.
exception(timeout=None)
Return the exception raised by the call. If the call hasn’t yet completed then this method will wait up to timeout seconds. If the call hasn’t completed in timeout seconds, then a concurrent.futures.TimeoutErrorwill be raised. timeout can be an int or float. If timeout is not specified or None, there is no limit to the wait time.
If the future is cancelled before completing then CancelledError will be raised.
If the call completed without raising, None is returned.
add_done_callback(fn)
Attaches the callable fn to the future. fn will be called, with the future as its only argument, when the future is cancelled or finishes running.
Added callables are called in the order that they were added and are always called in a thread belonging to the process that added them. If the callable raises an Exception
subclass, it will be logged and ignored. If the callable raises a BaseException
subclass, the behavior is undefined.
If the future has already completed or been cancelled, fn will be called immediately.
The following Future methods are meant for use in unit tests and Executor
implementations.
set_running_or_notify_cancel()
This method should only be called by Executor implementations before executing the work associated with the Future and by unit tests.
If the method returns False then the Future was cancelled, i.e. Future.cancel()
was called and returned True
. Any threads waiting on the Future completing (i.e. through as_completed()
or wait()) will be woken up.
If the method returns True then the Future
was not cancelled and has been put in the running state, i.e. calls to Future.running() will return True.
This method can only be called once and cannot be called after Future.set_result() or Future.set_exception() have been called.
set_result(result)
Sets the result of the work associated with the Future to result.
This method should only be used by Executor implementations and unit tests.
set_exception
(exception)
Sets the result of the work associated with the Future to the Exception exception.
This method should only be used by Executor implementations and unit tests.
asyncio.Future的方法
cancel()
Cancel the future and schedule callbacks.
If the future is already done or cancelled, return False. Otherwise, change the future’s state to cancelled, schedule the callbacks and return True.
cancelled()
Return True if the future was cancelled.
done()
Return True if the future is done.
Done means either that a result / exception are available, or that the future was cancelled.
result()
Return the result this future represents.
If the future has been cancelled, raises CancelledError. If the future’s result isn’t yet available, raises InvalidStateError. If the future is done and has an exception set, this exception is raised.
exception()
Return the exception that was set on this future.
The exception (or None if no exception was set) is returned only if the future is done. If the future has been cancelled, raises CancelledError. If the future isn’t done yet, raises InvalidStateError.
add_done_callback(fn)
Add a callback to be run when the future becomes done.
The callback is called with a single argument - the future object. If the future is already done when this is called, the callback is scheduled with call_soon().
Use functools.partial to pass parameters to the callback. For example, fut.add_done_callback(functools.partial(print, "Future:", flush=True)) will call print("Future:", fut, flush=True).
remove_done_callback(fn)
Remove all instances of a callback from the “call when done” list.
Returns the number of callbacks removed.
set_result(result)
Mark the future done and set its result.
If the future is already done when this method is called, raises InvalidStateError.
set_exception(exception)
Mark the future done and set an exception.
If the future is already done when this method is called, raises InvalidStateError.
