Source code for traits_futures.wrappers

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#
# This software is provided without warranty under the terms of the BSD
# license included in LICENSE.txt and may be redistributed only under
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"""
Wrappers for the background task callable and the foreground future.

These are used by the TraitsExecutor machinery.
"""

import logging

from traits.api import Bool, HasStrictTraits, HasTraits, Instance, observe

from traits_futures.i_task_specification import IFuture

logger = logging.getLogger(__name__)




class FutureWrapper(HasStrictTraits):
    """
    Wrapper for the IFuture.

    Passes on messages received for this future.
    """

    #: The Traits Futures future being wrapped
    future = Instance(IFuture)

    #: Object that receives messages from the background task.
    receiver = Instance(HasTraits)

    #: Bool recording whether the future has completed or not. The
    #: executor listens to this trait to decide when it can clean up
    #: its own internal state.
    done = Bool(False)

    @observe("receiver:message")
    def _dispatch_to_future(self, event):
        """
        Pass on a message to the future.
        """
        message = event.new
        done = self.future.receive(message)
        if done:
            self.done = True





def run_background_task(task, sender, cancelled):
    """
    Wrapper for callables submitted to the underlying executor.

    Parameters
    ----------
    task
        Callable representing the background task. This will be called
        with arguments ``send`` and ``cancelled``.
    sender : IMessageSender
        Object used to send messages.
    cancelled
        Zero-argument callable returning bool. This can be called to check
        whether cancellation has been requested.
    """
    try:
        with sender:
            task(sender.send, cancelled)
    except BaseException:
        # We'll only ever get here in the case of a coding error. But in
        # case that happens, it's useful to have the exception logged to
        # help the developer.
        logger.exception("Unexpected exception in background task.")
        raise