Python-zero-to-hero/chapter13.html at main · bocaletto-luca/Python-zero-to-hero · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8"/>
  <meta name="viewport" content="width=device-width, initial-scale=1"/>
  <meta name="description"
        content="Chapter 13 of Python Zero to Hero: explore concurrency & parallelism with threading, multiprocessing, futures and asyncio."/>
  <meta name="keywords"
        content="Python, concurrency, parallelism, threading, multiprocessing, concurrent.futures, asyncio, event loop"/>
  <meta name="author" content="Luca Bocaletto"/>
  <title>Chapter 13 – Concurrency & Parallelism | Python Zero to Hero</title>

  <!-- Bootstrap 5 CSS -->
  <link
    href="https://cdn.jsdelivr.net/npm/bootstrap@5.3.1/dist/css/bootstrap.min.css"
    rel="stylesheet"
    integrity="sha384-YSa3P1QY0VSei3nHevwltF1Jxv2pT3z5z0R6x35o1XQdYzdgQc8sYC+bS9v+g3Tc"
    crossorigin="anonymous"
  />

  <!-- Highlight.js CSS -->
  <link
    rel="stylesheet"
    href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.8.0/styles/github.min.css"
    integrity="sha512-94jnYVzi0AuOmT1JrLJiqxGWM1ZwVz4i1oF6XD2fXZj2lq+OJ9GSeUWLeFN5svoe0WyWkDi/gAhFI8QeYQj1Rg=="
    crossorigin="anonymous"
    referrerpolicy="no-referrer"
  />

  <style>
    body { padding-top: 4.5rem; }
    pre code { font-size: .9rem; }
    .btn-py { font-family: monospace; }
    .table th, .table td { vertical-align: middle; }
  </style>
</head>
<body>
  <!-- Navbar -->
  <nav class="navbar navbar-expand-lg navbar-dark bg-dark fixed-top">
    <div class="container">
      <a class="navbar-brand" href="index.html">Python Zero to Hero</a>
      <button class="navbar-toggler" type="button" data-bs-toggle="collapse"
              data-bs-target="#navContent" aria-controls="navContent"
              aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>
      <div class="collapse navbar-collapse" id="navContent">
        <ul class="navbar-nav ms-auto">
          <li class="nav-item"><a class="nav-link" href="chapter12.html">Chapter 12</a></li>
          <li class="nav-item"><a class="nav-link" href="index.html">Index</a></li>
          <li class="nav-item"><a class="nav-link" href="chapter14.html">Chapter 14</a></li>
          <li class="nav-item">
            <a class="nav-link" href="https://github.com/bocaletto-luca/python-zero-to-hero" target="_blank">
              GitHub Repo
            </a>
          </li>
        </ul>
      </div>
    </div>
  </nav>

  <!-- Main Content -->
  <main class="container">
    <!-- Header -->
    <header class="my-4">
      <h1 class="display-6">Chapter 13: Concurrency &amp; Parallelism</h1>
      <p class="text-muted">
        Learn to write concurrent and parallel Python code using threads, processes, futures and asyncio.
      </p>
      <a href="src/chapter13.py" download class="btn btn-outline-primary btn-sm btn-py">
        Download <code>chapter13.py</code>
      </a>
      <hr>
    </header>

    <!-- Objectives -->
    <section id="objectives" class="mb-5">
      <h2>Objectives</h2>
      <ul>
        <li>Use <code>threading.Thread</code> and <code>Lock</code> for simple threads.</li>
        <li>Leverage <code>multiprocessing.Process</code> and pools for CPU-bound work.</li>
        <li>Employ <code>concurrent.futures</code> for a unified interface.</li>
        <li>Write <code>asyncio</code> coroutines with <code>async</code>/<code>await</code>.</li>
        <li>Understand the Python GIL and when to use threads vs processes.</li>
      </ul>
    </section>

    <!-- 1. threading -->
    <section id="threading" class="mb-5">
      <h2>1. threading</h2>
      <p>Spawn lightweight threads:</p>
      <pre><code class="python">import threading

def worker(n):
    print(f"Thread {n} starting")
    # simulate work
    import time; time.sleep(0.5)
    print(f"Thread {n} done")

threads = []
for i in range(3):
    t = threading.Thread(target=worker, args=(i,))
    threads.append(t)
    t.start()

for t in threads:
    t.join()
</code></pre>
      <p>Protect shared data with a <code>Lock</code>:</p>
      <pre><code class="python">lock = threading.Lock()
counter = 0

def safe_increment():
    global counter
    with lock:
        temp = counter
        temp += 1
        counter = temp
</code></pre>
    </section>

    <!-- 2. multiprocessing -->
    <section id="multiprocessing" class="mb-5">
      <h2>2. multiprocessing</h2>
      <p>Run code in separate processes:</p>
      <pre><code class="python">from multiprocessing import Process, Pool

def f(x):
    return x*x

if __name__ == "__main__":
    # individual processes
    procs = [Process(target=worker, args=(i,)) for i in range(2)]
    for p in procs:
        p.start()
    for p in procs:
        p.join()

    # pool of workers
    with Pool(4) as pool:
        print(pool.map(f, [1,2,3,4]))
</code></pre>
      <p>Multiprocessing bypasses the GIL for CPU-bound tasks.</p>
    </section>

    <!-- 3. concurrent.futures -->
    <section id="futures" class="mb-5">
      <h2>3. concurrent.futures</h2>
      <p>Unified high-level API:</p>
      <pre><code class="python">from concurrent.futures import ThreadPoolExecutor, ProcessPoolExecutor

def square(x): return x*x

with ThreadPoolExecutor(max_workers=3) as executor:
    results = list(executor.map(square, range(5)))
    print("Threads:", results)

with ProcessPoolExecutor(max_workers=3) as executor:
    results = list(executor.map(square, range(5)))
    print("Processes:", results)
</code></pre>
    </section>

    <!-- 4. asyncio -->
    <section id="asyncio" class="mb-5">
      <h2>4. asyncio</h2>
      <p>Write asynchronous coroutines:</p>
      <pre><code class="python">import asyncio

async def say_after(delay, msg):
    await asyncio.sleep(delay)
    print(msg)

async def main():
    task1 = asyncio.create_task(say_after(1, "hello"))
    task2 = asyncio.create_task(say_after(2, "world"))
    print("Started tasks")
    await task1
    await task2

asyncio.run(main())
</code></pre>
      <p>Use <code>asyncio.gather()</code> to run coroutines concurrently.</p>
    </section>

    <!-- Exercises -->
    <section id="exercises" class="mb-5">
      <h2>Exercises</h2>
      <ol>
        <li>Write a threaded counter that increments a shared variable 10 000 times safely.</li>
        <li>Compute factorials of numbers 1–10 in parallel using a process pool.</li>
        <li>Use <code>ThreadPoolExecutor</code> to fetch URLs concurrently (use <code>requests</code>).</li>
        <li>Write an <code>asyncio</code> TCP echo server and client.</li>
      </ol>
    </section>

    <!-- Navigation -->
    <nav class="d-flex justify-content-between mb-5">
      <a href="chapter12.html" class="btn btn-outline-secondary">&larr; Chapter 12</a>
      <a href="chapter14.html" class="btn btn-primary">Chapter 14 &rarr;</a>
    </nav>
  </main>

  <!-- Footer -->
  <footer class="text-center py-4 border-top">
    <small>
      © 2025 Python Zero to Hero •
      <a href="https://github.com/bocaletto-luca/python-zero-to-hero" target="_blank">
        bocaletto-luca/python-zero-to-hero
      </a>
    </small>
  </footer>

  <!-- Bootstrap & Highlight.js -->
  <script
    src="https://cdn.jsdelivr.net/npm/bootstrap@5.3.1/dist/js/bootstrap.bundle.min.js"
    integrity="sha384-pQjTSprQoSWb8PQmxHkFvHUuI+13Z2VBxXc5xykxDc8/8aMbkwg/Sf5FCvbyT1Kg"
    crossorigin="anonymous"
  ></script>
  <script
    src="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/11.8.0/highlight.min.js"
    integrity="sha512-v+HDTvKi4ym72wvsLmDdWKH1Z9r7qmOZEk11Kd/PO5vQRO3KHSEt+XeajpxdsBUW5Fve4BJR+wHrHBW2ApwBMQ=="
    crossorigin="anonymous"
    referrerpolicy="no-referrer"
  ></script>
  <script>hljs.highlightAll();</script>
</body>
</html>