# Shared memory example in python

You can allocate shared memory segment that can be accessed from separate
processes.

In python, this can be done using `sysv_ipc` module
(`sudo pip install sysv_ipc`).

# General idea
One process allocates memory segment, it must define segment size (size must be
multiple of PAGE_SIZE). Segment can then be accessed using unique ID. ID can be
selected randomly.

`memory = sysv_ipc.SharedMemory(1235, flags=sysv_ipc.IPC_CREX, size=sysv_ipc.PAGE_SIZE * 4)`

When shared memory is no longer needed, it must be freed.

`memory.remove()`

Other process can then attach to this segment, using ID:

`memory = sysv_ipc.SharedMemory(1235)`

Each process can then read and write to shared memory.

# Example code

In the example code, `reader.py` maintains shared memory segment. It allocates
segment on startup and frees it when finishing. It enters infinite loop in which it prints current contents of shared memory segment. Use `^C` to interrupt loop, free memory and exit.

`writer.py` can be used to modify contents of memory. It takes address and value as arguments, writes data into segment and exits.

Tested on Ubuntu 18.04.