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<div class="tutorial-container" style="max-width: 960px; margin: 80px auto 40px; padding: 0 20px;"><div class="tutorial-sidebar"><h3>目录</h3><a href="0.html">1. 简介</a><a href="1.html">2. Python历史</a><a href="2.html">3. 安装Python</a><a href="3.html">3.1. Python解释器</a><a href="4.html">4. 第一个Python程序</a><a href="5.html">4.1. 使用文本编辑器</a><a href="6.html">4.2. 输入和输出</a><a href="7.html">5. Python基础</a><a href="8.html">5.1. 数据类型和变量</a><a href="9.html">5.2. 字符串和编码</a><a href="10.html">5.3. 使用list和tuple</a><a href="11.html">5.4. 条件判断</a><a href="12.html">5.5. 模式匹配</a><a href="13.html">5.6. 循环</a><a href="14.html">5.7. 使用dict和set</a><a href="15.html">6. 函数</a><a href="16.html">6.1. 调用函数</a><a href="17.html">6.2. 定义函数</a><a href="18.html">6.3. 函数的参数</a><a href="19.html">6.4. 递归函数</a><a href="20.html">7. 高级特性</a><a href="21.html">7.1. 切片</a><a href="22.html">7.2. 迭代</a><a href="23.html">7.3. 列表生成式</a><a href="24.html">7.4. 生成器</a><a href="25.html">7.5. 迭代器</a><a href="26.html">8. 函数式编程</a><a href="27.html">8.1. 高阶函数</a><a href="28.html">8.1.1. map/reduce</a><a href="29.html">8.1.2. filter</a><a href="30.html">8.1.3. sorted</a><a href="31.html">8.2. 返回函数</a><a href="32.html">8.3. 匿名函数</a><a href="33.html">8.4. 装饰器</a><a href="34.html">8.5. 偏函数</a><a href="35.html">9. 模块</a><a href="36.html">9.1. 使用模块</a><a href="37.html">9.2. 安装第三方模块</a><a href="38.html">10. 面向对象编程</a><a href="39.html">10.1. 类和实例</a><a href="40.html">10.2. 访问限制</a><a href="41.html">10.3. 继承和多态</a><a href="42.html">10.4. 获取对象信息</a><a href="43.html">10.5. 实例属性和类属性</a><a href="44.html">11. 面向对象高级编程</a><a href="45.html">11.1. 使用__slots__</a><a href="46.html">11.2. 使用@property</a><a href="47.html">11.3. 多重继承</a><a href="48.html">11.4. 定制类</a><a href="49.html">11.5. 使用枚举类</a><a href="50.html">11.6. 使用元类</a><a href="51.html">12. 错误、调试和测试</a><a href="52.html">12.1. 错误处理</a><a href="53.html">12.2. 调试</a><a href="54.html">12.3. 单元测试</a><a href="55.html">12.4. 文档测试</a><a href="56.html">13. IO编程</a><a href="57.html">13.1. 文件读写</a><a href="58.html">13.2. StringIO和BytesIO</a><a href="59.html">13.3. 操作文件和目录</a><a href="60.html">13.4. 序列化</a><a href="61.html">14. 进程和线程</a><a href="62.html">14.1. 多进程</a><a href="63.html">14.2. 多线程</a><a href="64.html">14.3. ThreadLocal</a><a href="65.html">14.4. 进程 vs. 线程</a><a href="66.html">14.5. 分布式进程</a><a href="67.html">15. 正则表达式</a><a href="68.html">16. 常用内建模块</a><a href="69.html">16.1. datetime</a><a href="70.html">16.2. collections</a><a href="71.html">16.3. argparse</a><a href="72.html">16.4. base64</a><a href="73.html">16.5. struct</a><a href="74.html">16.6. hashlib</a><a href="75.html">16.7. hmac</a><a href="76.html">16.8. itertools</a><a href="77.html">16.9. contextlib</a><a href="78.html">16.10. urllib</a><a href="79.html">16.11. XML</a><a href="80.html">16.12. HTMLParser</a><a href="81.html">16.13. venv</a><a href="82.html">17. 常用第三方模块</a><a href="83.html">17.1. Pillow</a><a href="84.html">17.2. requests</a><a href="85.html">17.3. chardet</a><a href="86.html">17.4. psutil</a><a href="87.html">18. 图形界面</a><a href="88.html">18.1. 海龟绘图</a><a href="89.html">19. 网络编程</a><a href="90.html">19.1. TCP/IP简介</a><a href="91.html">19.2. TCP编程</a><a href="92.html">19.3. UDP编程</a><a href="93.html">20. 电子邮件</a><a href="94.html">20.1. SMTP发送邮件</a><a href="95.html">20.2. POP3收取邮件</a><a href="96.html">21. 访问数据库</a><a href="97.html">21.1. 使用SQLite</a><a href="98.html">21.2. 使用MySQL</a><a href="99.html">21.3. 使用SQLAlchemy</a><a href="100.html">22. Web开发</a><a href="101.html">22.1. HTTP协议简介</a><a href="102.html">22.2. HTML简介</a><a href="103.html">22.3. WSGI接口</a><a href="104.html">22.4. 使用Web框架</a><a href="105.html">22.5. 使用模板</a><a href="106.html">23. 异步IO</a><a href="107.html">23.1. 协程</a><a href="108.html">23.2. 使用asyncio</a><a href="109.html">23.3. 使用aiohttp</a><a href="110.html">24. FAQ</a><a href="111.html">25. 期末总结</a></div><div class="tutorial-content"><h1>14.3. ThreadLocal</h1><div class="tutorial-body"><p>但是局部变量也有问题，就是在函数调用的时候，传递起来很麻烦：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">def</span> <span class="hljs-title function_">process_student</span>(<span class="hljs-params">name</span>):

std = Student(name)

<span class="hljs-comment"># std是局部变量，但是每个函数都要用它，因此必须传进去：</span>

do_task_1(std)

do_task_2(std)

<span class="hljs-keyword">def</span> <span class="hljs-title function_">do_task_1</span>(<span class="hljs-params">std</span>):

do_subtask_1(std)

do_subtask_2(std)

<span class="hljs-keyword">def</span> <span class="hljs-title function_">do_task_2</span>(<span class="hljs-params">std</span>):

do_subtask_2(std)

</code></pre>

<p>每个函数一层一层调用都这么传参数那还得了？用全局变量？也不行，因为每个线程处理不同的<code>Student</code>对象，不能共享。</p>

<p>如果用一个全局<code>dict</code>存放所有的<code>Student</code>对象，然后以<code>thread</code>自身作为<code>key</code>获得线程对应的<code>Student</code>对象如何？</p>

<pre class="hljs"><code class="language-python">global_dict = {}

<span class="hljs-keyword">def</span> <span class="hljs-title function_">std_thread</span>(<span class="hljs-params">name</span>):

std = Student(name)

<span class="hljs-comment"># 把std放到全局变量global_dict中：</span>

global_dict[threading.current_thread()] = std

do_task_1()

do_task_2()

<span class="hljs-keyword">def</span> <span class="hljs-title function_">do_task_1</span>():

<span class="hljs-comment"># 不传入std，而是根据当前线程查找：</span>

std = global_dict[threading.current_thread()]

...

<span class="hljs-keyword">def</span> <span class="hljs-title function_">do_task_2</span>():

<span class="hljs-comment"># 任何函数都可以查找出当前线程的std变量：</span>

std = global_dict[threading.current_thread()]

...

</code></pre>

<p>这种方式理论上是可行的，它最大的优点是消除了<code>std</code>对象在每层函数中的传递问题，但是，每个函数获取<code>std</code>的代码有点丑。</p>

<p>有没有更简单的方式？</p>

<p><code>ThreadLocal</code>应运而生，不用查找<code>dict</code>，<code>ThreadLocal</code>帮你自动做这件事：</p>

<pre class="hljs"><code class="language-python"><span class="hljs-keyword">import</span> threading

<span class="hljs-comment"># 创建全局ThreadLocal对象:</span>

local_school = threading.local()

<span class="hljs-keyword">def</span> <span class="hljs-title function_">process_student</span>():

<span class="hljs-comment"># 获取当前线程关联的student:</span>

std = local_school.student

<span class="hljs-built_in">print</span>(<span class="hljs-string">'Hello, %s (in %s)'</span> % (std, threading.current_thread().name))

<span class="hljs-keyword">def</span> <span class="hljs-title function_">process_thread</span>(<span class="hljs-params">name</span>):

<span class="hljs-comment"># 绑定ThreadLocal的student:</span>

local_school.student = name

process_student()

t1 = threading.Thread(target= process_thread, args=(<span class="hljs-string">'Alice'</span>,), name=<span class="hljs-string">'Thread-A'</span>)

t2 = threading.Thread(target= process_thread, args=(<span class="hljs-string">'Bob'</span>,), name=<span class="hljs-string">'Thread-B'</span>)

t1.start()

t2.start()

t1.join()

t2.join()

</code></pre>

<pre class="hljs"><code class="language-plain">Hello, Alice (in Thread-A)

Hello, Bob (in Thread-B)

</code></pre>

<p>全局变量<code>local_school</code>就是一个<code>ThreadLocal</code>对象，每个<code>Thread</code>对它都可以读写<code>student</code>属性，但互不影响。你可以把<code>local_school</code>看成全局变量，但每个属性如<code>local_school.student</code>都是线程的局部变量，可以任意读写而互不干扰，也不用管理锁的问题，<code>ThreadLocal</code>内部会处理。</p>

<p>可以理解为全局变量<code>local_school</code>是一个<code>dict</code>，不但可以用<code>local_school.student</code>，还可以绑定其他变量，如<code>local_school.teacher</code>等等。</p>

<p><code>ThreadLocal</code>最常用的地方就是为每个线程绑定一个数据库连接，HTTP请求，用户身份信息等，这样一个线程的所有调用到的处理函数都可以非常方便地访问这些资源。</p>

<p>一个<code>ThreadLocal</code>变量虽然是全局变量，但每个线程都只能读写自己线程的独立副本，互不干扰。<code>ThreadLocal</code>解决了参数在一个线程中各个函数之间互相传递的问题。</p>

<p><a href="use_threadlocal.py">use_threadlocal.py</a></p>

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</a></div><div style="display: flex; justify-content: space-between; margin-top: 32px; padding-top: 20px; border-top: 1px solid var(--border, #e5e7eb);"><a href="63.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">← 14.2. 多线程</a><a href="65.html" style="color: var(--primary, #3b82f6); text-decoration: none; font-weight: 500;">14.4. 进程 vs. 线程 →</a></div><p style="margin-top: 16px; font-size: 13px; color: var(--text-secondary, #999);">原文：<a href="https://liaoxuefeng.com/books/python/process-thread/threadlocal/index.html" style="color: var(--primary, #3b82f6);">廖雪峰 - 14.3. ThreadLocal</a></p></div></div>

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