forked from mmcgrana/gobyexample
-
Notifications
You must be signed in to change notification settings - Fork 0
/
Copy pathtimeouts
186 lines (149 loc) · 8.61 KB
/
timeouts
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
<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example: Timeouts</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'select';
}
if (e.key == "ArrowRight") {
window.location.href = 'non-blocking-channel-operations';
}
}
</script>
<body>
<div class="example" id="timeouts">
<h2><a href="./">Go by Example</a>: Timeouts</h2>
<table>
<tr>
<td class="docs">
<p><em>Timeouts</em> are important for programs that connect to
external resources or that otherwise need to bound
execution time. Implementing timeouts in Go is easy and
elegant thanks to channels and <code>select</code>.</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="http://play.golang.org/p/gyr0NbVKBVf"><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">"time"</span>
<span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</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>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>For our example, suppose we’re executing an external
call that returns its result on a channel <code>c1</code>
after 2s. Note that the channel is buffered, so the
send in the goroutine is nonblocking. This is a
common pattern to prevent goroutine leaks in case the
channel is never read.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">c1</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">string</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">c1</span> <span class="o"><-</span> <span class="s">"result 1"</span>
<span class="p">}()</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Here’s the <code>select</code> implementing a timeout.
<code>res := <-c1</code> awaits the result and <code><-time.After</code>
awaits a value to be sent after the timeout of
1s. Since <code>select</code> proceeds with the first
receive that’s ready, we’ll take the timeout case
if the operation takes more than the allowed 1s.</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c1</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">res</span><span class="p">)</span>
<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nf">After</span><span class="p">(</span><span class="mi">1</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</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="s">"timeout 1"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>If we allow a longer timeout of 3s, then the receive
from <code>c2</code> will succeed and we’ll print the result.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">c2</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">string</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>
<span class="k">go</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
<span class="nx">time</span><span class="p">.</span><span class="nf">Sleep</span><span class="p">(</span><span class="mi">2</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</span><span class="p">)</span>
<span class="nx">c2</span> <span class="o"><-</span> <span class="s">"result 2"</span>
<span class="p">}()</span>
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">res</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">c2</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">res</span><span class="p">)</span>
<span class="k">case</span> <span class="o"><-</span><span class="nx">time</span><span class="p">.</span><span class="nf">After</span><span class="p">(</span><span class="mi">3</span> <span class="o">*</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Second</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="s">"timeout 2"</span><span class="p">)</span>
<span class="p">}</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>Running this program shows the first operation timing
out and the second succeeding.</p>
</td>
<td class="code">
<pre class="chroma">
<span class="gp">$</span> go run timeouts.go
<span class="go">timeout 1
</span><span class="go">result 2</span></pre>
</td>
</tr>
</table>
<p class="next">
Next example: <a href="non-blocking-channel-operations">Non-Blocking Channel Operations</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
</p>
</div>
<script>
var codeLines = [];
codeLines.push('');codeLines.push('package main\u000A');codeLines.push('import (\u000A \"fmt\"\u000A \"time\"\u000A)\u000A');codeLines.push('func main() {\u000A');codeLines.push(' c1 :\u003D make(chan string, 1)\u000A go func() {\u000A time.Sleep(2 * time.Second)\u000A c1 \u003C- \"result 1\"\u000A }()\u000A');codeLines.push(' select {\u000A case res :\u003D \u003C-c1:\u000A fmt.Println(res)\u000A case \u003C-time.After(1 * time.Second):\u000A fmt.Println(\"timeout 1\")\u000A }\u000A');codeLines.push(' c2 :\u003D make(chan string, 1)\u000A go func() {\u000A time.Sleep(2 * time.Second)\u000A c2 \u003C- \"result 2\"\u000A }()\u000A select {\u000A case res :\u003D \u003C-c2:\u000A fmt.Println(res)\u000A case \u003C-time.After(3 * time.Second):\u000A fmt.Println(\"timeout 2\")\u000A }\u000A}\u000A');codeLines.push('');
</script>
<script src="site.js" async></script>
</body>
</html>