199 lines
6.5 KiB
Plaintext
Generated
199 lines
6.5 KiB
Plaintext
Generated
<!DOCTYPE html>
|
|
<html>
|
|
<head>
|
|
<meta charset="utf-8">
|
|
<title>Go by Example: Recover</title>
|
|
<link rel=stylesheet href="site.css">
|
|
</head>
|
|
<script>
|
|
onkeydown = (e) => {
|
|
|
|
if (e.key == "ArrowLeft") {
|
|
window.location.href = 'defer';
|
|
}
|
|
|
|
|
|
if (e.key == "ArrowRight") {
|
|
window.location.href = 'collection-functions';
|
|
}
|
|
|
|
}
|
|
</script>
|
|
<body>
|
|
<div class="example" id="recover">
|
|
<h2><a href="./">Go by Example</a>: Recover</h2>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>Go makes it possible to <em>recover</em> from a panic, by
|
|
using the <code>recover</code> built-in function. A <code>recover</code> can
|
|
stop a <code>panic</code> from aborting the program and let it
|
|
continue with execution instead.</p>
|
|
|
|
</td>
|
|
<td class="code empty leading">
|
|
|
|
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>An example of where this can be useful: a server
|
|
wouldn’t want to crash if one of the client connections
|
|
exhibits a critical error. Instead, the server would
|
|
want to close that connection and continue serving
|
|
other clients. In fact, this is what Go’s <code>net/http</code>
|
|
does by default for HTTP servers.</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/Sk-SVdofEIZ"><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="s">"fmt"</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>This function panics.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma">
|
|
<span class="kd">func</span> <span class="nf">mayPanic</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="nb">panic</span><span class="p">(</span><span class="s">"a problem"</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p><code>recover</code> must be called within a deferred function.
|
|
When the enclosing function panics, the defer will
|
|
activate and a <code>recover</code> call within it will catch
|
|
the panic.</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>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>The return value of <code>recover</code> is the error raised in
|
|
the call to <code>panic</code>.</p>
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma"> <span class="k">defer</span> <span class="kd">func</span><span class="p">()</span> <span class="p">{</span>
|
|
<span class="k">if</span> <span class="nx">r</span> <span class="o">:=</span> <span class="nb">recover</span><span class="p">();</span> <span class="nx">r</span> <span class="o">!=</span> <span class="kc">nil</span> <span class="p">{</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code leading">
|
|
|
|
<pre class="chroma"> <span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"Recovered. Error:\n"</span><span class="p">,</span> <span class="nx">r</span><span class="p">)</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="nf">mayPanic</span><span class="p">()</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
<p>This code will not run, because <code>mayPanic</code> panics.
|
|
The execution of <code>main</code> stops at the point of the
|
|
panic and resumes in the deferred closure.</p>
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<pre class="chroma">
|
|
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"After mayPanic()"</span><span class="p">)</span>
|
|
<span class="p">}</span>
|
|
</pre>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
<table>
|
|
|
|
<tr>
|
|
<td class="docs">
|
|
|
|
</td>
|
|
<td class="code">
|
|
|
|
<pre class="chroma"><span class="go">Recovered. Error:
|
|
</span><span class="go"> a problem</span></pre>
|
|
</td>
|
|
</tr>
|
|
|
|
</table>
|
|
|
|
|
|
<p class="next">
|
|
Next example: <a href="collection-functions">Collection Functions</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('');codeLines.push('package main\u000A');codeLines.push('import \"fmt\"\u000A');codeLines.push('func mayPanic() {\u000A panic(\"a problem\")\u000A}\u000A');codeLines.push('func main() {\u000A');codeLines.push(' defer func() {\u000A if r :\u003D recover(); r !\u003D nil {\u000A');codeLines.push(' fmt.Println(\"Recovered. Error:\\n\", r)\u000A }\u000A }()\u000A');codeLines.push(' mayPanic()\u000A');codeLines.push(' fmt.Println(\"After mayPanic()\")\u000A}\u000A');codeLines.push('');
|
|
</script>
|
|
<script src="site.js" async></script>
|
|
</body>
|
|
</html>
|