converted to python3

lib.py

import os
import mmap
import ctypes
import struct


class SHMWriter(object):

    def __init__(self, filename='/tmp/mmaptest'):
        self.filename = filename
        # Create new empty file to back memory map on disk
        self.fd = os.open('/tmp/mmaptest', os.O_CREAT | os.O_TRUNC | os.O_RDWR)

        # Zero out the file to insure it's the right size
        assert os.write(self.fd, b'\x00' * mmap.PAGESIZE) == mmap.PAGESIZE

        # Create the mmap instace with the following params:
        # fd: File descriptor which backs the mapping or -1 for anonymous mapping
        # length: Must in multiples of PAGESIZE (usually 4 KB)
        # flags: MAP_SHARED means other processes can share this mmap
        # prot: PROT_WRITE means this process can write to this mmap
        if os.name == 'nt':
            self.buf = mmap.mmap(0, 65536, 'GlobalSharedMemory)
        else:
            self.buf = mmap.mmap(self.fd, mmap.PAGESIZE,
                                 mmap.MAP_SHARED, mmap.PROT_WRITE)

        self.i = ctypes.c_int.from_buffer(self.buf)
        self.i.value = 0

        assert self.i.value == 0

        # Before we create a new value, we need to find the offset of the next free
        # memory address within the mmap
        self.offset = struct.calcsize(self.i._type_)

        # The offset should be uninitialized ('\x00')
        #assert self.buf[self.offset] == '\x00'

        # Now ceate a string containing 'foo' by first creating a c_char array
        r = b''
        self.s_type = ctypes.c_char * len(r)
        self.i.value = len(r)

        # Now create the ctypes instance
        self.s = self.s_type.from_buffer(self.buf, self.offset)

        # And finally set it
        self.s.raw = r

    def write(self, r):
        r = str(r).encode('utf-8')
        self.s_type = ctypes.c_char * len(r)
        self.s = self.s_type.from_buffer(self.buf, self.offset)
        self.s.raw = r
        self.i.value = len(r)