GBQueue.py

"""

Copyright (C) 2020  Eili Klein

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program.  If not, see <http://www.gnu.org/licenses/>.
    

"""

import multiprocessing as mp
import multiprocessing.queues as mpq

from queue import Empty, Full

import time


class MPQueue(mpq.Queue):

    DEFAULT_POLLING_TIMEOUT = 0.02

    # -- See StackOverflow Article :
    #   https://stackoverflow.com/questions/39496554/cannot-subclass-multiprocessing-queue-in-python-3-5
    #
    # -- tldr; mp.Queue is a _method_ that returns an mpq.Queue object.  That object
    # requires a context for proper operation, so this __init__ does that work as well.
    def __init__(self, *args, **kwargs):
        ctx = mp.get_context()
        super().__init__(*args, **kwargs, ctx=ctx)

    def safe_get(self, timeout=DEFAULT_POLLING_TIMEOUT):
        try:
            if timeout is None:
                return self.get(block=False)
            else:
                return self.get(block=True, timeout=timeout)
        except Empty:
            return None

    def safe_put(self, item, timeout=DEFAULT_POLLING_TIMEOUT):
        try:
            self.put(item, block=False, timeout=timeout)
            return True
        except Full:
            return False

    def drain(self):
        item = self.safe_get()
        while item:
            yield item
            item = self.safe_get()

    def safe_close(self):
        try:
            #num_left = sum(1 for __ in self.drain())
             
            self.close()
            self.join_thread()
        except:
            print("error closing Queue")
            pass
        #return num_left
        


class EventMessage:
    def __init__(self, msg_src, msg_type, msg):
        self.id = time.time()
        self.msg_src = msg_src
        self.msg_type = msg_type
        self.msg = msg

    def __str__(self):
        return f"{self.msg_src:10} - {self.msg_type:10} : {self.msg}"