forked from gobyexample-cn/gobyexample-cn.github.io
-
Notifications
You must be signed in to change notification settings - Fork 0
/
mutexes.html
246 lines (189 loc) · 10.8 KB
/
mutexes.html
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
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 互斥锁</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'atomic-counters';
}
if (e.key == "ArrowRight") {
window.location.href = 'stateful-goroutines';
}
}
</script>
<body>
<div class="example" id="mutexes">
<h2><a href="./">Go by Example 中文版</a>: 互斥锁</h2>
<table>
<tr>
<td class="docs">
<p>在前面的例子中，我们看到了如何使用原子操作(atomic-counters)来管理简单的计数器。
对于更加复杂的情况，我们可以使用一个<em><a href="http://zh.wikipedia.org/wiki/%E4%BA%92%E6%96%A5%E9%94%81">互斥量</a></em>
来在 Go 协程间安全的访问数据。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/GCobOgyGtJD"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="p">(</span>
<span class="s">"fmt"</span>
<span class="s">"sync"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Container 中定义了 counters 的 map ，由于我们希望从多个 goroutine 同时更新它，
因此我们添加了一个 互斥锁Mutex 来同步访问。
请注意不能复制互斥锁，如果需要传递这个 <code>struct</code>，应使用指针完成。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="kd">type</span> <span class="nx">Container</span> <span class="kd">struct</span> <span class="p">{</span>
<span class="nx">mu</span> <span class="nx">sync</span><span class="p">.</span><span class="nx">Mutex</span>
<span class="nx">counters</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>在访问 <code>counters</code> 之前锁定互斥锁；
使用 [defer]（defer） 在函数结束时解锁。</p>
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="p">(</span><span class="nx">c</span> <span class="o">*</span><span class="nx">Container</span><span class="p">)</span> <span class="nf">inc</span><span class="p">(</span><span class="nx">name</span> <span class="kt">string</span><span class="p">)</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">c</span><span class="p">.</span><span class="nx">mu</span><span class="p">.</span><span class="nf">Lock</span><span class="p">()</span>
<span class="k">defer</span> <span class="nx">c</span><span class="p">.</span><span class="nx">mu</span><span class="p">.</span><span class="nf">Unlock</span><span class="p">()</span>
<span class="nx">c</span><span class="p">.</span><span class="nx">counters</span><span class="p">[</span><span class="nx">name</span><span class="p">]</span><span class="o">++</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>请注意，互斥量的零值是可用的，因此这里不需要初始化。</p>
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">c</span> <span class="o">:=</span> <span class="nx">Container</span><span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="nx">counters</span><span class="p">:</span> <span class="kd">map</span><span class="p">[</span><span class="kt">string</span><span class="p">]</span><span class="kt">int</span><span class="p">{</span><span class="s">"a"</span><span class="p">:</span> <span class="mi">0</span><span class="p">,</span> <span class="s">"b"</span><span class="p">:</span> <span class="mi">0</span><span class="p">},</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"> <span class="kd">var</span> <span class="nx">wg</span> <span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这个函数在循环中递增对 name 的计数</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">doIncrement</span> <span class="o">:=</span> <span class="kd">func</span><span class="p">(</span><span class="nx">name</span> <span class="kt">string</span><span class="p">,</span> <span class="nx">n</span> <span class="kt">int</span><span class="p">)</span> <span class="p">{</span>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="nx">n</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">c</span><span class="p">.</span><span class="nf">inc</span><span class="p">(</span><span class="nx">name</span><span class="p">)</span>
<span class="p">}</span>
<span class="nx">wg</span><span class="p">.</span><span class="nf">Done</span><span class="p">()</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>同时运行多个 goroutines;
请注意，它们都访问相同的 <code>Container</code>，其中两个访问相同的计数器。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">wg</span><span class="p">.</span><span class="nf">Add</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="k">go</span> <span class="nf">doIncrement</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span> <span class="mi">10000</span><span class="p">)</span>
<span class="k">go</span> <span class="nf">doIncrement</span><span class="p">(</span><span class="s">"a"</span><span class="p">,</span> <span class="mi">10000</span><span class="p">)</span>
<span class="k">go</span> <span class="nf">doIncrement</span><span class="p">(</span><span class="s">"b"</span><span class="p">,</span> <span class="mi">10000</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>等待上面的 goroutines 都执行结束</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">wg</span><span class="p">.</span><span class="nf">Wait</span><span class="p">()</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">c</span><span class="p">.</span><span class="nx">counters</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>运行这个程序显示计数器更新和我们期望的一致</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go run mutexes.go
<span class="go">map[a:20000 b:10000]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>接下来我们将看一下，只使用协程和通道，
如何实现相同的任务状态管理。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="stateful-goroutines.html">状态协程</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
<script>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"sync\"\u000A)\u000A');codeLines.push('type Container struct {\u000A mu sync.Mutex\u000A counters map[string]int\u000A}\u000A');codeLines.push('func (c *Container) inc(name string) {\u000A');codeLines.push(' c.mu.Lock()\u000A defer c.mu.Unlock()\u000A c.counters[name]++\u000A}\u000A');codeLines.push('func main() {\u000A c :\u003D Container{\u000A');codeLines.push(' counters: map[string]int{\"a\": 0, \"b\": 0},\u000A }\u000A');codeLines.push(' var wg sync.WaitGroup\u000A');codeLines.push(' doIncrement :\u003D func(name string, n int) {\u000A for i :\u003D 0; i \u003C n; i++ {\u000A c.inc(name)\u000A }\u000A wg.Done()\u000A }\u000A');codeLines.push(' wg.Add(3)\u000A go doIncrement(\"a\", 10000)\u000A go doIncrement(\"a\", 10000)\u000A go doIncrement(\"b\", 10000)\u000A');codeLines.push(' wg.Wait()\u000A fmt.Println(c.counters)\u000A}\u000A');codeLines.push('');codeLines.push('');
</script>
<script src="site.js" async></script>
</body>
</html>