Source code for traits_futures.i_task_specification

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"""
Interface for a job specification. The job specification is the object
that the TraitsExecutor knows how to deal with.
"""

from abc import ABC, abstractmethod


class ITaskSpecification(ABC):
    """
    Specify background task callable and foreground future for a task.

    An object implementing the ITaskSpecification interface describes how to
    create a background task and a corresponding foreground future to execute a
    particular type of background task. It's consumed by the TraitsExecutor
    when submitting background tasks, and implemented by BackgroundCall,
    BackgroundIteration and others.
    """

    @abstractmethod
    def background_task(self):
        """
        Return the callable that will be invoked as the background task.

        This callable should be pickleable and should have the signature

            task(send, cancelled)

        Any exception raised while executing the callable, or result returned
        by the callable, will be recorded in the corresponding future.

        The ``send`` argument can be used by the background task to send
        messages back to the main thread of execution. It's a callable that can
        be used either in the form ``send(message_type)`` or in the form
        ``send(message_type, message_args)``. Here ``message_type`` is a simple
        constant (typically a string), and ``message_args`` is a single Python
        object containing optional arguments for the message. The arguments to
        ``send`` should typically be both immutable and pickleable. ``send``
        returns no useful result.

        The ``cancelled`` argument may be used by the background task to check
        whether cancellation has been requested. When called with no arguments,
        it returns either ``True`` to indicate that cancellation has been
        requested, or ``False``.

        Note that there's no obligation for the background task to check the
        cancellation status.

        Returns
        -------
        task : callable
        """

    @abstractmethod
    def future(self):
        """
        Return a Future for the background task.

        Returns
        -------
        future : IFuture
            Future object that can be used to monitor the status of the
            background task.
        """