concurrency

Exploring concurrent programming.

Sample codes demo concurrency via async, multithreading and multiprocessing methods in:

• py: Python
• cs: C# / .NET
• cpp: C++

Concurrency in Python

I. Multithreading and Multiprocessing

py/sample_thread.py allows testing multithreading and multiprocessing for different tasks, including I/O-bound and CPU-bound.

Example: CPU-Bound Tasks

The following tests demonstrates that for CPU-bound tasks in Python, multithreading doesn't help, while multiprocessing helps.

1. CPU-Bound, Sequential: ~15s (benchmark)

2. CPU-Bound, Multithreading: ~15s (no gain)

3. CPU-Bound, Multiprocessing: ~5s (huge gain)

II. Asynchronous I/O

py/sample_async.py leverages Python's asyncio.

Concurrency in C# / .NET

/cs/ConsoleApp provides a menu of different concurrency methods. Tasks print their unique IDs (0 - 9), also color coded for two concurrent tasks. The main method prints a heartbeat character (♥), allowing to recocognize the methods that don't block the main thread:

1. Independent I/O-bound tasks

2. Independent CPU-bound tasks

3. I/O-bound operations over a collection

4. CPU-bound operations over a collection

Concurrency in C++

/cpp/main.cpp demos concurrency in C++, with the following options. The task IDs, colors, and heartbeat (♥) are similar to the C# demo.

1. Synchronous

2. Multithreading via std::async

3. Multithreading via std::thread

Thread-Safe in C++

thread_safe.cpp demos and benchmarks two common thread-safe methods in C++:

1. With lock: Using mutex which, at the expense of higher overhead, ensures that only one thread can access a section of the code at a time.

2. Lock-free: Using atomic which is generally faster, at the expense of higher complexity and being applicable to a limited set of data types. Its magic is related to hardware-level CPU instructions.

Also, the lock-free version includes cache alignment that avoids "False Sharing", which is a performance-degrading issue if independent variables reside on the same CPU cache line.

The benchmarking result favors the lock-free method in this particular test, as expected: