Multithreading Basics

import threading
import time

# Basic thread
def download(url, delay=1):
    print(f"  Downloading {url}...")
    time.sleep(delay * 0.01)  # Simulated delay
    print(f"  Done: {url}")

# Sequential
start = time.time()
download("file1.zip", 2)
download("file2.zip", 3)
print(f"  Sequential: {time.time() - start:.2f}s")

# Parallel with threads
start = time.time()
t1 = threading.Thread(target=download, args=("file3.zip", 2))
t2 = threading.Thread(target=download, args=("file4.zip", 3))
t1.start()
t2.start()
t1.join()
t2.join()
print(f"  Parallel: {time.time() - start:.2f}s")

# Thread pool (modern approach)
from concurrent.futures import ThreadPoolExecutor

urls = ["page1", "page2", "page3", "page4"]
with ThreadPoolExecutor(max_workers=4) as executor:
    executor.map(download, urls)
print("  All downloads complete!")

# Thread safety with Lock
counter = 0
lock = threading.Lock()

def safe_increment():
    global counter
    for _ in range(1000):
        with lock:
            counter += 1

threads = [threading.Thread(target=safe_increment) for _ in range(5)]
for t in threads: t.start()
for t in threads: t.join()
print(f"  Counter: {counter}")  # 5000 (correct!)