#!/usr/bin/env python3.9

from multiprocessing import shared_memory, resource_tracker
import os, random, signal, sys

#######################################################
def remove_shm_from_resource_tracker():
    """Monkey-patch multiprocessing.resource_tracker so SharedMemory won't be tracked

    More details at: https://bugs.python.org/issue38119
    """

    def fix_register(name, rtype):
        if rtype == "shared_memory":
            return
        return resource_tracker._resource_tracker.register(self, name, rtype)
    resource_tracker.register = fix_register

    def fix_unregister(name, rtype):
        if rtype == "shared_memory":
            return
        return resource_tracker._resource_tracker.unregister(self, name, rtype)
    resource_tracker.unregister = fix_unregister

    if "shared_memory" in resource_tracker._CLEANUP_FUNCS:
        del resource_tracker._CLEANUP_FUNCS["shared_memory"]
#######################################################
remove_shm_from_resource_tracker() ## turicas's monkeypatch protects
                                   ## shared memory from garbage collection
                                   ## by resource_tracker

sharedMemoryName = 'EricIdle'
sharedMemoryObjects = []
try:
    if sys.argv[ 1] == 'unlink':
        try:
            sharedMemoryObjects.append(
                shared_memory.SharedMemory(
                    name = sharedMemoryName,
                )
            )
        except FileNotFoundError:
            print( f'Shared memory {sharedMemoryName} does not exist.')
            sys.exit( 1)
        sharedMemoryObjects[ -1].close()
        sharedMemoryObjects[ -1].unlink()
        print( f'unlinked {sharedMemoryName}')
        sys.exit( 0)
except IndexError:
    pass

try:
    sharedMemoryObjects.append(
        shared_memory.SharedMemory(
            name = sharedMemoryName,
            create = True,
            size = 2**21,
        ),
    )
    print( f'Created shared memory {sharedMemoryName}.')
except FileExistsError:
    print( f'Not creating shared memory {sharedMemoryName}; already exists.')
    sharedMemoryObjects.append(
        shared_memory.SharedMemory(
            name = sharedMemoryName,
        )
    )

    

import time
while True:
    print( f'\n{sharedMemoryObjects[ -1]}')
    print( f'before: {bytes( sharedMemoryObjects[ -1].buf[ 0: 15])}')

    ba = bytes( 'asdfjkl;%s' % ( os.getpid()),  'utf-8')
    sharedMemoryObjects[ -1].buf[ 0:len( ba)] = ba

    ba = bytes( str( random.random())[ 2:6], 'utf-8')
    sharedMemoryObjects[ -1].buf[ 0:len( ba)] = ba

    print( f' after: {bytes( sharedMemoryObjects[ -1].buf[ 0: 15])}')
    time.sleep( 5)