Simple but fast IPC method for a Python and C++ application?

Question

I have a GNU Radio application which utilizes both Python and C++ code. I want to be able to signal the C++ code of an event. If they were in the same scope I would normally use a simple boolean, but the code is separate to the point where some form of shared memory is required. The code in question is performance-critical so an efficient method is required.

I was initially thinking about a shared memory segment that is accessible by both Python and C++. Therefore I could set a flag in the python code and check it from C++. Since I just need a simple flag to pause the C++ code, would a semaphore suffice?

To be clear, I need to set a flag from Python and the C++ code will simply check this flag, and if it is set enter a busy loop.

So would trying to implement a shared memory segment between Python/C++ be a reasonable approach? How about a semaphore? On Linux, which is easier to implement?

Thanks!

Answer 1

Assuming this is two separate applications on one machine and you need decent real time performance you don't want to go with sockets. I would use a flag in shared memory, and probably use a semaphore to make sure both programs can't be accessing the flag at once. This library provides access to the semaphores and shared memory with Python and supports Python versions 2.4-3.1 (not 3.0): http://semanchuk.com/philip/posix_ipc

EDIT: Changed recommendation to using a semaphore protecting the flag in shared memory

Answer 2

Why not open a unix socket? Or use DBus

Answer 3

If Boost is an option, you could use Boost.Python and Boost.Interprocess . Boost.Python gives you a way for Python & C++ objects to interact and Boost.Interprocess gives you plenty of options for shared memory or synchronization primitives across process boundaries.

Answer 4

DBus looks promising. It supports signals, so you should be able to stop an application on demand. However, I'm not sure if it's performance will be enough for you.

Answer 5

You can try using custom signals. I don't know about Python code being able to send custom signals, but your C/C++ can certainly define custom signals with SIGIO.

If you have stringent response-time requirements, you might need to look beyond your application code and into some time of OS with support for real-time signals (rt-linux, muOs, etc.)