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non-blocking-channel-operations
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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example မြန်မာဘာသာ: Non-Blocking Channel Operations</title>
<link rel=stylesheet href="site.css">
</head>
<script>
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<body>
<div class="example" id="non-blocking-channel-operations">
<h2><a href="./">Go by Example မြန်မာဘာသာ</a>: Non-Blocking Channel Operations</h2>
<table>
<tr>
<td class="docs">
<p>Channel တွေပေါ်မှာ အခြေခံ ပို့တာ(send)နဲ့ လက်ခံတာ (receive) တွေက blocking ဖြစ်ပါတယ်။
ဒါပေမယ့် <code>select</code> နဲ့ <code>default</code> clause ကိုသုံးပြီး <code>non-blocking</code> ပို့တာ၊
လက်ခံတာ၊ ဒါ့အပြင် non-blocking multi-way <code>select</code> တွေကိုတောင်
implement လုပ်နိုင်ပါတယ်။</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://go.dev/play/p/CAqWfTEZtgl"><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">
</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">messages</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="nx">signals</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">(</span><span class="kd">chan</span> <span class="kt">bool</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>ဒါက non-blocking လက်ခံမှုပါ။ <code>messages</code> မှာ တန်ဖိုးတစ်ခု အဆင်သင့်ရှိနေရင်
<code>select</code> က အဲဒီတန်ဖိုးနဲ့အတူ <code><-messages</code> <code>case</code> ကို ယူပါလိမ့်မယ်။
မရှိဘူးဆိုရင်တော့ ချက်ချင်း <code>default</code> case ကို ယူပါလိမ့်မယ်။</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">msg</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">messages</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">"received message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
<span class="k">default</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">"no message received"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Non-blocking ပို့မှုကလည်း အပေါ်ကလိုဘဲ အလုပ်လုပ်ပါတယ်။ ဒီမှာ <code>msg</code> ကို
<code>messages</code> channel ဆီ ပို့လို့မရပါဘူး၊ ဘာလို့လဲဆိုတော့
channel မှာ buffer မရှိသလို လက်ခံမယ့်သူလည်း မရှိလို့ပါ။
ဒါကြောင့် <code>default</code> case ကို ရွေးချယ်ပါတယ်။</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">msg</span> <span class="o">:=</span> <span class="s">"hi"</span>
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">messages</span> <span class="o"><-</span> <span class="nx">msg</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">"sent message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
<span class="k">default</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">"no message sent"</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>default</code> clause ရဲ့အပေါ်မှာ <code>case</code> အများကြီးသုံးပြီး
multi-way non-blocking select ကို implement လုပ်နိုင်ပါတယ်။
ဒီမှာ <code>messages</code> နဲ့ <code>signals</code> နှစ်ခုလုံးကနေ non-blocking လက်ခံဖို့ ကြိုးစားပါတယ်။</p>
</td>
<td class="code">
<pre class="chroma">
<span class="k">select</span> <span class="p">{</span>
<span class="k">case</span> <span class="nx">msg</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">messages</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">"received message"</span><span class="p">,</span> <span class="nx">msg</span><span class="p">)</span>
<span class="k">case</span> <span class="nx">sig</span> <span class="o">:=</span> <span class="o"><-</span><span class="nx">signals</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">"received signal"</span><span class="p">,</span> <span class="nx">sig</span><span class="p">)</span>
<span class="k">default</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">"no activity"</span><span class="p">)</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="gp">$</span> go run non-blocking-channel-operations.go
<span class="go">no message received
</span><span class="go">no message sent
</span><span class="go">no activity</span></pre>
</td>
</tr>
</table>
<p class="next">
နောက်ဥပမာ: <a href="closing-channels">Closing Channels</a>.
</p>
<p class="footer">
by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> နှင့် <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>
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