Week-2

Python Application Builder

POSIX IPC Implementation

The whole python synthesis was converted into POSIX_IPC implementation instead of shared memory implementation.

How to execute:

Just download this directory and run using the following command in terminal:

python3 main.py

Dependencies:

pip install opencv-python
pip install posix_ipc

Example (5 Blocks):

The current example has a color filter and edge detector which read from the same wire on which the camera writes. Then both the color filter and the edge detector write to wires that are read and displayed by the screen block. The video can be found below:

Other Improvements

Spawning Independent Processes Without Copying Memory:

As in multiprocessing processes, the whole process memory is copied into the child process. In this improvement I will try to run independent processes so they are lightweight and don’t inherit memory from the parent process. Running independent command line processes requires string arguments and not objects. So, I wrote a custom serializer/deserializer which converts all arguments to a string which can then be passed onto command line and then deserialized back to arguments.

Fixing Memory Leaks:

The POSIX_IPC uses kernel level commands to share memory between processes. The main issue here was that if I kill the Python processes using the parent process, it would cause memory leak because the shared memory is not released. This is written in the POSIX_IPC documentation:

“You must call close_fd() or os.close() explicitly; the file descriptor is not closed automatically when a SharedMemory object is garbage collected.”

So I came up with a way to signal every process to safely terminate and release the shared memory. Each process will regularly check if the parent process is still alive, if it has exited, all processes will know and then they can safely unlink and de-allocate the shared memory preventing any memory leaks.

Complete Prototype:

The complete working prototype can be found here.