WIP: Add 'expedited' decorator for urgent messages

[ZwFink]

This patch adds the @expedited decorator to enable urgent inter-PE messages to skip the message queue. This patch also lays the groundwork for adding additional entry method options such as priorities.

Example of usage:

from charm4py import charm, Chare, Array, expedited


class Test(Chare):
    """
    A chare array to test the element proxy.
    """

    def __init__(self):
        self.count = 0

    @expedited
    def say(self, msg):
        """
        Helper method which is called by invoking the element proxy.
        This method is expected to be called on only the chare for
        which the proxy is created.
        """

        self.count += 1
        print("Say", msg, "called on", self.thisIndex, "on PE", charm.myPe())
        if self.count == 2:
            assert self.thisIndex == (3,)
            exit()

    def start(self):
        proxy = self.thisProxy[3]
        proxy.say("bye")
        proxy.say("bye")


def main(args):
    arr_proxy = Array(Test, 6)
    arr_proxy[0].start()


charm.start(main)

[lgtm-com]

This pull request introduces 1 alert when merging d813e1d into 0b9a2be - view on LGTM.com

new alerts:

• 1 for Unused local variable

[lgtm-com]

This pull request introduces 1 alert when merging eae8497 into 0b9a2be - view on LGTM.com

new alerts:

• 1 for Unused local variable