多线程python的实现及多线程有序性介绍

ゝ一纸荒年。 2024-03-24 19:23 99阅读 0赞

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本文主要介绍了多线程python的实现及多线程有序性，多线程一般用于同时调用多个函数，cpu时间片轮流分配给多个任务

多线程一般用于同时调用多个函数，cpu时间片轮流分配给多个任务**。** 优点是提高cpu的使用率，使计算机减少处理多个任务的总时间；缺点是如果有全局变量，调用多个函数会使全局变量被多个函数修改，造成计算错误，这使需要使用join方法或者设置局部变量来解决问题。

python使用threading模块来实现多线程，threading.join()方法是保证调用join的子线程完成后，才会分配cpu给其他的子线程，从而保证线程运行的有序性。

### 一、多线程运行无序问题 ###

我们首先创建三个实例，t1,t2,t3 t1实例调用function1函数，t2和t3函数调用function11函数，他们都是对全局变量l1进行操作

**代码如下：**

<table> 
 <tbody> 
 <tr> 
 <td> 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 </td> 
 <td> <code>import</code> <code>threading,time</code> <code>l1 </code><code>=</code> <code>[]</code> <code>#创建RLock锁，acquire几次，release几次</code> <code>lock </code><code>=</code> <code>threading.RLock()</code> <code>def</code> <code>function1(x,y):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>for</code> <code>i </code><code>in</code> <code>range</code><code>(x):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>l1.append(i)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>if</code> <code>i </code><code>=</code><code>=</code> <code>0</code><code>:</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>time.sleep(</code><code>1</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>end_time </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"t{} is finished in {}s"</code><code>.</code><code>format</code><code>(y,end_time </code><code>-</code><code>time1 ))</code> <code>def</code> <code>function11(x,y):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>for</code> <code>i </code><code>in</code> <code>range</code><code>(x):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>l1.append(i)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>end_time </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"t{} is finished in {}s"</code><code>.</code><code>format</code><code>(y, end_time </code><code>-</code><code>time1))</code> <code>#2.创建子线程：thread类</code> <code>if</code> <code>__name__ </code><code>=</code><code>=</code> <code>'__main__'</code><code>:</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t1 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function1, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>1</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t2 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function11, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>2</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t3 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function11, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>3</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>time1 </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"time starts in {}"</code><code>.</code><code>format</code><code>(time1))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t1.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t2.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t3.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(l1)</code> </td> 
 </tr> 
 </tbody> 
</table>

**结果如下：**

> runfile('E:/桌面/temp.py', wdir='E:/桌面')  
> time starts in 1656474963.9487  
> t2 is finished in 0.0s  
> t3 is finished in 0.0s  
> \[0, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99\]  
> t1 is finished in 1.0152690410614014s

我们可以看到，全局变量中开头有两个0，而不是按着0，1，2，3的方式按序填充，所以可以得知全局变量在多线程中是被多个函数**无序**调用的。为了保证多线程有序调用全局变量，我们可以利用threading.join()的方法。

### 二、“join方法”解决多线程运行无序问题 ###

我们重写了function1函数，并命名为function2，t1调用function2函数。t2,t3不变。

**代码如下：**

<table> 
 <tbody> 
 <tr> 
 <td> 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 </td> 
 <td> <code>import</code> <code>threading,time</code> <code>l1 </code><code>=</code> <code>[]</code> <code>#创建RLock锁，acquire几次，release几次</code> <code>lock </code><code>=</code> <code>threading.RLock()</code> <code>def</code> <code>function1(x,y):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>for</code> <code>i </code><code>in</code> <code>range</code><code>(x):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>l1.append(i)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>if</code> <code>i </code><code>=</code><code>=</code> <code>0</code><code>:</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>time.sleep(</code><code>1</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>end_time </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"t{} is finished in {}s"</code><code>.</code><code>format</code><code>(y,end_time </code><code>-</code><code>time1))</code> <code>def</code> <code>function11(x,y):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>for</code> <code>i </code><code>in</code> <code>range</code><code>(x):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>l1.append(i)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>end_time </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"t{} is finished in {}s"</code><code>.</code><code>format</code><code>(y,end_time </code><code>-</code><code>time1))</code> <code>def</code> <code>function2(x,y):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>for</code> <code>i </code><code>in</code> <code>range</code><code>(x):</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>l1.append(i)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>if</code> <code>i </code><code>=</code><code>=</code> <code>0</code><code>:</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</code><code>time.sleep(</code><code>1</code><code>)</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>end_time </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"t{} is finished in {}s"</code><code>.</code><code>format</code><code>(y,end_time </code><code>-</code><code>time1))</code> <code>#2.创建子线程：thread类</code> <code>if</code> <code>__name__ </code><code>=</code><code>=</code> <code>'__main__'</code><code>:</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t1 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function2, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>1</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t2 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function11, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>2</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t3 </code><code>=</code> <code>threading.Thread(target</code><code>=</code> <code>function11, args </code><code>=</code> <code>(</code><code>100</code><code>,</code><code>3</code><code>))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>time1 </code><code>=</code> <code>time.time()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(</code><code>"time starts in {}"</code><code>.</code><code>format</code><code>(time1))</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t1.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t1.join()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t2.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>t3.start()</code> <code>&nbsp;&nbsp;&nbsp;&nbsp;</code><code>print</code><code>(l1)</code> </td> 
 </tr> 
 </tbody> 
</table>

**结果如下:**

> runfile('E:/桌面/temp.py', wdir='E:/桌面')  
> time starts in 1656476057.441827  
> t1 is finished in 1.0155227184295654s  
> t2 is finished in 1.0155227184295654s  
> t3 is finished in 1.0155227184295654s  
> \[0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99\]

由此可见，threading.join()方法可以解决多线程**无序**问题

### 三、threading.Thread()的常用参数 ###

1.group：默认值None，为了实现ThreadGroup类而保留  
2.target：在start方法中调用的可调用对象，即需要开启线程的可调用对象，比如函数、方法  
3.name：默认为“Thread-N”，字符串形式的线程名称  
4.args：默认为空元组，参数target中传入的可调用对象的参数元组  
5.kwargs：默认为空字典\{\}，参数target中传入的可调用对象的关键字参数字典  
6.daemon：默认为None

### 结语 ###

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