🧵 File Downloader Threads – Python Multithreading Simulator

This project simulates concurrent file downloads using threads in Python, with controlled access to a shared file queue and performance metrics. The main goal is to demonstrate fundamental concepts such as concurrency, the GIL (Global Interpreter Lock), race conditions, and benchmarking with multiple threads.

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🔧 Technologies used

• Python 3.11
• Docker + Docker Compose
• threading.Thread + Lock
• CLI with argparse
• Makefile to simplify execution

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🧠 Explored concepts

✅ Concurrency with Threads

Download tasks are executed by multiple threads that share the same list of files. Each thread safely consumes one item at a time using a Lock to avoid race conditions.

❌ What is the GIL?

The GIL (Global Interpreter Lock) is an internal lock in CPython that allows only one thread to execute Python bytecode at a time, even on multicore systems.

However, in I/O-bound tasks (like the ones simulated here with sleep()), the GIL is temporarily released, allowing other threads to proceed. That’s why multithreading is still effective in scenarios such as:

• HTTP requests
• File access
• Waiting on databases

🔥 Multiprocessing

For CPU-bound tasks (e.g., heavy computation), the GIL becomes a bottleneck. In such cases, it's better to use multiprocessing, which creates independent processes, each with its own interpreter and GIL.

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🚀 How to run the project

1. Clone the repository

git clone https://github.com/your-username/file-downloader-threads.git
cd file-downloader-threads

2. Container's build

docker compose build

3. Up container

docker compose up -d

4. Access container

docker exec -it threaded_downloader bash

✅ Commands available in the Makefile

Dentro do container, execute:

make run                 # Run with 4 threads (default)
make run-threads T=8     # Run with 8 threads
make benchmark           # Show total execution time with 4 threads
make benchmark-threads T=1  # Benchmark

🧪 Example benchmark output

Downloads started...
...
⏱ Benchmark: 4 thread(s) completed in 3.91 seconds.

📊 Benchmark Results

📂 Project structure

.
├── cli.py               # Comand line interface
├── main.py              # Entrypoint to control threads
├── downloader.py        # Concurrent consume logic
├── fake_server.py       # Download simulator
├── logger.py            # Global print locker
├── Makefile             # Execution automation
├── Dockerfile
├── docker-compose.yml
└── README.md

🧩 Possible future improvements

• Add multiprocessing version for benchmark comparison
• Export results to CSV
• Simulate errors and implement retry logic
• Web interface or dashboard for real-time visualization