5.2.4. vlcp.event.future


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Created on 2016/9/28


Future is a helper class to simplify the process of retrieving a result from other routines. The implementation is straight-forward: first check the return value, if not set, wait for the event. Multiple routines can wait for the same Future object.

The interface is similar to asyncio, but:

  • Cancel is not supported - you should terminate the sender routine instead. But RoutineFuture supports close() (and cancel() which is the same)

  • Callback is not supported - start a subroutine to wait for the result instead.

  • result() returns None if the result is not ready; exception() is not supported.

  • New wait() async function: get the result, or wait for the result until available. It is always the recommended way to use a future; result() is not recommended.

    wait() will NOT cancel the Future (or RoutineFuture) when the waiting coroutine is closed. This is different from asyncio.Future. To ensure that the future closes after awaited, use wait_and_close() of RoutineFuture.

  • ensure_result() returns a context manager: this should be used in the sender routine, to ensure that a result is always set after exit the with scope. If the result is not set, it is set to None; if an exception is raised, it is set with set_exception.

Since v2.0, you can directly use await future to wait for the result

class vlcp.event.future.Future(scheduler)

Basic future object


Initialize self. See help(type(self)) for accurate signature.

Returns:True if the result is available; False otherwise.
ensure_result(supress_exception=False, defaultresult=None)

Context manager to ensure returning the result

Returns:None if the result is not ready, the result from set_result, or raise the exception from set_exception. If the result can be None, it is not possible to tell if the result is available; use done() to determine that.

Set an exception to Future object, wake up all the waiters

Parameters:exception – exception to set

Set the result to Future object, wake up all the waiters

Parameters:result – result to set
Parameters:container – DEPRECATED container of current routine
Returns:The result, or raise the exception from set_exception.
exception vlcp.event.future.FutureCancelledException
class vlcp.event.future.FutureEvent(*args, **kwargs)
class vlcp.event.future.RoutineFuture(subprocess, container)

Quick wrapper to create a subroutine and return the result to a Future object

__init__(subprocess, container)

Start the subprocess

  • subprocess – a generator process, which returns the result to future on exit
  • container – the routine container to run the subprocess with

Same as close()


Terminate the subprocess


wait for result; always close no matter success or failed