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@ -1895,10 +1895,7 @@ Another option, if the iteration operation isn’t lightweight, is to work on an
```go hl_lines="2 3 4 5 6 7"
func (c *Cache) AverageBalance() float64 {
c.mu.RLock()
m := make(map[string]float64, len(c.balances)) // Copies the map
for k, v := range c.balances {
m[k] = v
}
m := maps.Clone(c.balances)
c.mu.RUnlock()
sum := 0.

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@ -7,10 +7,6 @@ comments: true
このページは『100 Go Mistakes』の内容をまとめたものです。一方で、コミュニティに開かれたページでもあります。「ありがちな間違い」が新たに追加されるべきだとお考えでしたら [community mistake issue](https://github.com/teivah/100-go-mistakes/issues/new?assignees=&labels=community+mistake&template=community_mistake.md&title=) を作成してください。
???+ Tip "Jobs"
Is your company hiring? [Sponsor](https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&tier_id=386213&preview=true) the Japanese version of this repository and let a significant audience of Go developers (~1k unique visitors per week) know about your opportunities in this section.
![](img/inside-cover.png)
???+ warning "注意"

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@ -7,11 +7,6 @@ comments: true
Esta página é um resumo dos erros do [100 Go Mistakes and How to Avoid Them book](book.md). Enquanto isso, também está aberto à comunidade. Se você acredita que um erro comum do Go deve ser adicionado, crie uma [issue](https://github.com/teivah/100-go-mistakes/issues/new?assignees=&labels=community+mistake&template=community_mistake.md&title=).
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Sua empresa está contratando? [Patrocine](https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&tier_id=386213&preview=true) este repositório e informe um público significativo de desenvolvedores Go (cerca de 1 mil visitantes únicos por semana) sobre suas oportunidades nesta seção.
![](img/inside-cover.png)
???+ warning "Beta"

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@ -5,10 +5,6 @@ comments: true
# 100 个 Go 常见错误及如何避免
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Is your company hiring? [Sponsor](https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&tier_id=386213&preview=true) the Chinese version of this repository and let a significant audience of Go developers (~1k unique visitors per week) know about your opportunities in this section.
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## 代码及工程组织

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@ -4845,18 +4845,15 @@ the use case. However, we should see the two options as complementary. </p>
<p>Another option, if the iteration operation isn’t lightweight, is to work on an actual copy of the data and protect only the copy:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-58-1"><a id="__codelineno-58-1" name="__codelineno-58-1" href="#__codelineno-58-1"></a><span class="kd">func</span><span class="w"> </span><span class="p">(</span><span class="nx">c</span><span class="w"> </span><span class="o">*</span><span class="nx">Cache</span><span class="p">)</span><span class="w"> </span><span class="nx">AverageBalance</span><span class="p">()</span><span class="w"> </span><span class="kt">float64</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-58-2"><a id="__codelineno-58-2" name="__codelineno-58-2" href="#__codelineno-58-2"></a><span class="hll"><span class="w"> </span><span class="nx">c</span><span class="p">.</span><span class="nx">mu</span><span class="p">.</span><span class="nx">RLock</span><span class="p">()</span>
</span></span><span id="__span-58-3"><a id="__codelineno-58-3" name="__codelineno-58-3" href="#__codelineno-58-3"></a><span class="hll"><span class="w"> </span><span class="nx">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nb">make</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">float64</span><span class="p">,</span><span class="w"> </span><span class="nb">len</span><span class="p">(</span><span class="nx">c</span><span class="p">.</span><span class="nx">balances</span><span class="p">))</span><span class="w"> </span><span class="c1">// Copies the map</span>
</span></span><span id="__span-58-4"><a id="__codelineno-58-4" name="__codelineno-58-4" href="#__codelineno-58-4"></a><span class="hll"><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">k</span><span class="p">,</span><span class="w"> </span><span class="nx">v</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">range</span><span class="w"> </span><span class="nx">c</span><span class="p">.</span><span class="nx">balances</span><span class="w"> </span><span class="p">{</span>
</span></span><span id="__span-58-5"><a id="__codelineno-58-5" name="__codelineno-58-5" href="#__codelineno-58-5"></a><span class="hll"><span class="w"> </span><span class="nx">m</span><span class="p">[</span><span class="nx">k</span><span class="p">]</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">v</span>
</span></span><span id="__span-58-6"><a id="__codelineno-58-6" name="__codelineno-58-6" href="#__codelineno-58-6"></a><span class="hll"><span class="w"> </span><span class="p">}</span>
</span></span><span id="__span-58-7"><a id="__codelineno-58-7" name="__codelineno-58-7" href="#__codelineno-58-7"></a><span class="hll"><span class="w"> </span><span class="nx">c</span><span class="p">.</span><span class="nx">mu</span><span class="p">.</span><span class="nx">RUnlock</span><span class="p">()</span>
</span></span><span id="__span-58-8"><a id="__codelineno-58-8" name="__codelineno-58-8" href="#__codelineno-58-8"></a>
</span><span id="__span-58-9"><a id="__codelineno-58-9" name="__codelineno-58-9" href="#__codelineno-58-9"></a><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mf">0.</span>
</span><span id="__span-58-10"><a id="__codelineno-58-10" name="__codelineno-58-10" href="#__codelineno-58-10"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">balance</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">range</span><span class="w"> </span><span class="nx">m</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-58-11"><a id="__codelineno-58-11" name="__codelineno-58-11" href="#__codelineno-58-11"></a><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="nx">balance</span>
</span><span id="__span-58-12"><a id="__codelineno-58-12" name="__codelineno-58-12" href="#__codelineno-58-12"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-58-13"><a id="__codelineno-58-13" name="__codelineno-58-13" href="#__codelineno-58-13"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="nb">float64</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
</span><span id="__span-58-14"><a id="__codelineno-58-14" name="__codelineno-58-14" href="#__codelineno-58-14"></a><span class="p">}</span>
</span></span><span id="__span-58-3"><a id="__codelineno-58-3" name="__codelineno-58-3" href="#__codelineno-58-3"></a><span class="hll"><span class="w"> </span><span class="nx">m</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">maps</span><span class="p">.</span><span class="nx">Clone</span><span class="p">(</span><span class="nx">c</span><span class="p">.</span><span class="nx">balances</span><span class="p">)</span>
</span></span><span id="__span-58-4"><a id="__codelineno-58-4" name="__codelineno-58-4" href="#__codelineno-58-4"></a><span class="hll"><span class="w"> </span><span class="nx">c</span><span class="p">.</span><span class="nx">mu</span><span class="p">.</span><span class="nx">RUnlock</span><span class="p">()</span>
</span></span><span id="__span-58-5"><a id="__codelineno-58-5" name="__codelineno-58-5" href="#__codelineno-58-5"></a><span class="hll">
</span></span><span id="__span-58-6"><a id="__codelineno-58-6" name="__codelineno-58-6" href="#__codelineno-58-6"></a><span class="hll"><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mf">0.</span>
</span></span><span id="__span-58-7"><a id="__codelineno-58-7" name="__codelineno-58-7" href="#__codelineno-58-7"></a><span class="hll"><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">balance</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="k">range</span><span class="w"> </span><span class="nx">m</span><span class="w"> </span><span class="p">{</span>
</span></span><span id="__span-58-8"><a id="__codelineno-58-8" name="__codelineno-58-8" href="#__codelineno-58-8"></a><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">+=</span><span class="w"> </span><span class="nx">balance</span>
</span><span id="__span-58-9"><a id="__codelineno-58-9" name="__codelineno-58-9" href="#__codelineno-58-9"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-58-10"><a id="__codelineno-58-10" name="__codelineno-58-10" href="#__codelineno-58-10"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">sum</span><span class="w"> </span><span class="o">/</span><span class="w"> </span><span class="nb">float64</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="nx">m</span><span class="p">))</span>
</span><span id="__span-58-11"><a id="__codelineno-58-11" name="__codelineno-58-11" href="#__codelineno-58-11"></a><span class="p">}</span>
</span></code></pre></div>
<p>Once we have made a deep copy, we release the mutex. The iterations are done on the copy outside of the critical section.</p>
<p>In summary, we have to be careful with the boundaries of a mutex lock. In this section, we have seen why assigning an existing map (or an existing slice) to a map isn’t enough to protect against data races. The new variable, whether a map or a slice, is backed by the same data set. There are two leading solutions to prevent this: protect the whole function, or work on a copy of the actual data. In all cases, let’s be cautious when designing critical sections and make sure the boundaries are accurately defined.</p>
@ -4866,6 +4863,47 @@ the use case. However, we should see the two options as complementary. </p>
<summary>TL;DR</summary>
<p>To accurately use <code>sync.WaitGroup</code>, call the <code>Add</code> method before spinning up goroutines.</p>
</details>
<p>In the following example, we will initialize a wait group, start three goroutines that will update a counter atomically, and then wait for them to complete. We want to wait for these three goroutines to print the value of the counter (which should be 3):</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-59-1"><a id="__codelineno-59-1" name="__codelineno-59-1" href="#__codelineno-59-1"></a><span class="nx">wg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span><span class="p">{}</span>
</span><span id="__span-59-2"><a id="__codelineno-59-2" name="__codelineno-59-2" href="#__codelineno-59-2"></a><span class="kd">var</span><span class="w"> </span><span class="nx">v</span><span class="w"> </span><span class="kt">uint64</span>
</span><span id="__span-59-3"><a id="__codelineno-59-3" name="__codelineno-59-3" href="#__codelineno-59-3"></a><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="p">&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-59-4"><a id="__codelineno-59-4" name="__codelineno-59-4" href="#__codelineno-59-4"></a><span class="w"> </span><span class="k">go</span><span class="w"> </span><span class="kd">func</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-59-5"><a id="__codelineno-59-5" name="__codelineno-59-5" href="#__codelineno-59-5"></a><span class="w"> </span><span class="nx">wg</span><span class="p">.</span><span class="nx">Add</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
</span><span id="__span-59-6"><a id="__codelineno-59-6" name="__codelineno-59-6" href="#__codelineno-59-6"></a><span class="w"> </span><span class="nx">atomic</span><span class="p">.</span><span class="nx">AddUint64</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">v</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span>
</span><span id="__span-59-7"><a id="__codelineno-59-7" name="__codelineno-59-7" href="#__codelineno-59-7"></a><span class="w"> </span><span class="nx">wg</span><span class="p">.</span><span class="nx">Done</span><span class="p">()</span>
</span><span id="__span-59-8"><a id="__codelineno-59-8" name="__codelineno-59-8" href="#__codelineno-59-8"></a><span class="w"> </span><span class="p">}()</span>
</span><span id="__span-59-9"><a id="__codelineno-59-9" name="__codelineno-59-9" href="#__codelineno-59-9"></a><span class="p">}</span>
</span><span id="__span-59-10"><a id="__codelineno-59-10" name="__codelineno-59-10" href="#__codelineno-59-10"></a><span class="nx">wg</span><span class="p">.</span><span class="nx">Wait</span><span class="p">()</span>
</span><span id="__span-59-11"><a id="__codelineno-59-11" name="__codelineno-59-11" href="#__codelineno-59-11"></a><span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span>
</span></code></pre></div>
<p>If we run this example, we get a non-deterministic value: the code can print any value from 0 to 3. Also, if we enable the <code>-race</code> flag, Go will even catch a data race.</p>
<p>The problem is that <code>wg.Add(1)</code> is called within the newly created goroutine, not in the parent goroutine. Hence, there is no guarantee that we have indicated to the wait group that we want to wait for three goroutines before calling <code>wg.Wait()</code>.</p>
<p>To fix this issue, we can call <code>wg.Add</code> before the loop:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-60-1"><a id="__codelineno-60-1" name="__codelineno-60-1" href="#__codelineno-60-1"></a><span class="nx">wg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span><span class="p">{}</span>
</span><span id="__span-60-2"><a id="__codelineno-60-2" name="__codelineno-60-2" href="#__codelineno-60-2"></a><span class="kd">var</span><span class="w"> </span><span class="nx">v</span><span class="w"> </span><span class="kt">uint64</span>
</span><span id="__span-60-3"><a id="__codelineno-60-3" name="__codelineno-60-3" href="#__codelineno-60-3"></a><span class="nx">wg</span><span class="p">.</span><span class="nx">Add</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
</span><span id="__span-60-4"><a id="__codelineno-60-4" name="__codelineno-60-4" href="#__codelineno-60-4"></a><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="p">&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-60-5"><a id="__codelineno-60-5" name="__codelineno-60-5" href="#__codelineno-60-5"></a><span class="w"> </span><span class="k">go</span><span class="w"> </span><span class="kd">func</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-60-6"><a id="__codelineno-60-6" name="__codelineno-60-6" href="#__codelineno-60-6"></a><span class="w"> </span><span class="nx">atomic</span><span class="p">.</span><span class="nx">AddUint64</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">v</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span>
</span><span id="__span-60-7"><a id="__codelineno-60-7" name="__codelineno-60-7" href="#__codelineno-60-7"></a><span class="w"> </span><span class="nx">wg</span><span class="p">.</span><span class="nx">Done</span><span class="p">()</span>
</span><span id="__span-60-8"><a id="__codelineno-60-8" name="__codelineno-60-8" href="#__codelineno-60-8"></a><span class="w"> </span><span class="p">}()</span>
</span><span id="__span-60-9"><a id="__codelineno-60-9" name="__codelineno-60-9" href="#__codelineno-60-9"></a><span class="p">}</span>
</span><span id="__span-60-10"><a id="__codelineno-60-10" name="__codelineno-60-10" href="#__codelineno-60-10"></a><span class="nx">wg</span><span class="p">.</span><span class="nx">Wait</span><span class="p">()</span>
</span><span id="__span-60-11"><a id="__codelineno-60-11" name="__codelineno-60-11" href="#__codelineno-60-11"></a><span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span>
</span></code></pre></div>
<p>Or inside the loop but not in the newly created goroutine:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-61-1"><a id="__codelineno-61-1" name="__codelineno-61-1" href="#__codelineno-61-1"></a><span class="nx">wg</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">sync</span><span class="p">.</span><span class="nx">WaitGroup</span><span class="p">{}</span>
</span><span id="__span-61-2"><a id="__codelineno-61-2" name="__codelineno-61-2" href="#__codelineno-61-2"></a><span class="kd">var</span><span class="w"> </span><span class="nx">v</span><span class="w"> </span><span class="kt">uint64</span>
</span><span id="__span-61-3"><a id="__codelineno-61-3" name="__codelineno-61-3" href="#__codelineno-61-3"></a><span class="k">for</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="p">&lt;</span><span class="w"> </span><span class="mi">3</span><span class="p">;</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-61-4"><a id="__codelineno-61-4" name="__codelineno-61-4" href="#__codelineno-61-4"></a><span class="w"> </span><span class="nx">wg</span><span class="p">.</span><span class="nx">Add</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
</span><span id="__span-61-5"><a id="__codelineno-61-5" name="__codelineno-61-5" href="#__codelineno-61-5"></a><span class="w"> </span><span class="k">go</span><span class="w"> </span><span class="kd">func</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-61-6"><a id="__codelineno-61-6" name="__codelineno-61-6" href="#__codelineno-61-6"></a><span class="w"> </span><span class="nx">atomic</span><span class="p">.</span><span class="nx">AddUint64</span><span class="p">(</span><span class="o">&amp;</span><span class="nx">v</span><span class="p">,</span><span class="w"> </span><span class="mi">1</span><span class="p">)</span>
</span><span id="__span-61-7"><a id="__codelineno-61-7" name="__codelineno-61-7" href="#__codelineno-61-7"></a><span class="w"> </span><span class="nx">wg</span><span class="p">.</span><span class="nx">Done</span><span class="p">()</span>
</span><span id="__span-61-8"><a id="__codelineno-61-8" name="__codelineno-61-8" href="#__codelineno-61-8"></a><span class="w"> </span><span class="p">}()</span>
</span><span id="__span-61-9"><a id="__codelineno-61-9" name="__codelineno-61-9" href="#__codelineno-61-9"></a><span class="p">}</span>
</span><span id="__span-61-10"><a id="__codelineno-61-10" name="__codelineno-61-10" href="#__codelineno-61-10"></a><span class="nx">wg</span><span class="p">.</span><span class="nx">Wait</span><span class="p">()</span>
</span><span id="__span-61-11"><a id="__codelineno-61-11" name="__codelineno-61-11" href="#__codelineno-61-11"></a><span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">v</span><span class="p">)</span>
</span></code></pre></div>
<p><a href="https://github.com/teivah/100-go-mistakes/tree/master/src/09-concurrency-practice/71-wait-group/main.go"><span class="twemoji"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg></span> Source code</a></p>
<h3 id="forgetting-about-synccond-72">Forgetting about <code>sync.Cond</code> (#72)</h3>
<details class="info" open="open">
@ -4893,76 +4931,26 @@ the use case. However, we should see the two options as complementary. </p>
</details>
<p>Many common functions in the standard library accept a <code>time.Duration</code>, which is an alias for the <code>int64</code> type. However, one <code>time.Duration</code> unit represents one nanosecond, instead of one millisecond, as commonly seen in other programming languages. As a result, passing numeric types instead of using the <code>time.Duration</code> API can lead to unexpected behavior.</p>
<p>A developer with experience in other languages might assume that the following code creates a new <code>time.Ticker</code> that delivers ticks every second, given the value <code>1000</code>:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-59-1"><a id="__codelineno-59-1" name="__codelineno-59-1" href="#__codelineno-59-1"></a><span class="nx">ticker</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="mi">1000</span><span class="p">)</span>
</span><span id="__span-59-2"><a id="__codelineno-59-2" name="__codelineno-59-2" href="#__codelineno-59-2"></a><span class="k">for</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-59-3"><a id="__codelineno-59-3" name="__codelineno-59-3" href="#__codelineno-59-3"></a><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-59-4"><a id="__codelineno-59-4" name="__codelineno-59-4" href="#__codelineno-59-4"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ticker</span><span class="p">.</span><span class="nx">C</span><span class="p">:</span>
</span><span id="__span-59-5"><a id="__codelineno-59-5" name="__codelineno-59-5" href="#__codelineno-59-5"></a><span class="w"> </span><span class="c1">// Do something</span>
</span><span id="__span-59-6"><a id="__codelineno-59-6" name="__codelineno-59-6" href="#__codelineno-59-6"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-59-7"><a id="__codelineno-59-7" name="__codelineno-59-7" href="#__codelineno-59-7"></a><span class="p">}</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-62-1"><a id="__codelineno-62-1" name="__codelineno-62-1" href="#__codelineno-62-1"></a><span class="nx">ticker</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="mi">1000</span><span class="p">)</span>
</span><span id="__span-62-2"><a id="__codelineno-62-2" name="__codelineno-62-2" href="#__codelineno-62-2"></a><span class="k">for</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-62-3"><a id="__codelineno-62-3" name="__codelineno-62-3" href="#__codelineno-62-3"></a><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-62-4"><a id="__codelineno-62-4" name="__codelineno-62-4" href="#__codelineno-62-4"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ticker</span><span class="p">.</span><span class="nx">C</span><span class="p">:</span>
</span><span id="__span-62-5"><a id="__codelineno-62-5" name="__codelineno-62-5" href="#__codelineno-62-5"></a><span class="w"> </span><span class="c1">// Do something</span>
</span><span id="__span-62-6"><a id="__codelineno-62-6" name="__codelineno-62-6" href="#__codelineno-62-6"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-62-7"><a id="__codelineno-62-7" name="__codelineno-62-7" href="#__codelineno-62-7"></a><span class="p">}</span>
</span></code></pre></div>
<p>However, because 1,000 <code>time.Duration</code> units = 1,000 nanoseconds, ticks are delivered every 1,000 nanoseconds = 1 microsecond, not every second as assumed.</p>
<p>We should always use the <code>time.Duration</code> API to avoid confusion and unexpected behavior:
<div class="language-go highlight"><pre><span></span><code><span id="__span-60-1"><a id="__codelineno-60-1" name="__codelineno-60-1" href="#__codelineno-60-1"></a><span class="nx">ticker</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Microsecond</span><span class="p">)</span>
</span><span id="__span-60-2"><a id="__codelineno-60-2" name="__codelineno-60-2" href="#__codelineno-60-2"></a><span class="c1">// Or</span>
</span><span id="__span-60-3"><a id="__codelineno-60-3" name="__codelineno-60-3" href="#__codelineno-60-3"></a><span class="nx">ticker</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="mi">1000</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">Nanosecond</span><span class="p">)</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-63-1"><a id="__codelineno-63-1" name="__codelineno-63-1" href="#__codelineno-63-1"></a><span class="nx">ticker</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Microsecond</span><span class="p">)</span>
</span><span id="__span-63-2"><a id="__codelineno-63-2" name="__codelineno-63-2" href="#__codelineno-63-2"></a><span class="c1">// Or</span>
</span><span id="__span-63-3"><a id="__codelineno-63-3" name="__codelineno-63-3" href="#__codelineno-63-3"></a><span class="nx">ticker</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTicker</span><span class="p">(</span><span class="mi">1000</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">Nanosecond</span><span class="p">)</span>
</span></code></pre></div></p>
<p><a href="https://github.com/teivah/100-go-mistakes/tree/master/src/10-standard-lib/75-wrong-time-duration/main.go"><span class="twemoji"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg></span> Source code</a></p>
<h3 id="timeafter-and-memory-leaks-76"><code>time.After</code> and memory leaks (#76)</h3>
<details class="info" open="open">
<summary>TL;DR</summary>
<p>Avoiding calls to <code>time.After</code> in repeated functions (such as loops or HTTP handlers) can avoid peak memory consumption. The resources created by <code>time.After</code> are released only when the timer expires.</p>
<details class="warning" open="open">
<summary>Warning</summary>
<p>This mistake isn't relevant anymore from Go 1.23 (<a href="https://go.dev/wiki/Go123Timer">details</a>).</p>
</details>
<p>Developers often use <code>time.After</code> in loops or HTTP handlers repeatedly to implement the timing function. But it can lead to unintended peak memory consumption due to the delayed release of resources, just like the following code:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-61-1"><a id="__codelineno-61-1" name="__codelineno-61-1" href="#__codelineno-61-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">consumer</span><span class="p">(</span><span class="nx">ch</span><span class="w"> </span><span class="o">&lt;-</span><span class="kd">chan</span><span class="w"> </span><span class="nx">Event</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-61-2"><a id="__codelineno-61-2" name="__codelineno-61-2" href="#__codelineno-61-2"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-61-3"><a id="__codelineno-61-3" name="__codelineno-61-3" href="#__codelineno-61-3"></a><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-61-4"><a id="__codelineno-61-4" name="__codelineno-61-4" href="#__codelineno-61-4"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="nx">event</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ch</span><span class="p">:</span>
</span><span id="__span-61-5"><a id="__codelineno-61-5" name="__codelineno-61-5" href="#__codelineno-61-5"></a><span class="w"> </span><span class="nx">handle</span><span class="p">(</span><span class="nx">event</span><span class="p">)</span>
</span><span id="__span-61-6"><a id="__codelineno-61-6" name="__codelineno-61-6" href="#__codelineno-61-6"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">time</span><span class="p">.</span><span class="nx">After</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">Hour</span><span class="p">):</span>
</span><span id="__span-61-7"><a id="__codelineno-61-7" name="__codelineno-61-7" href="#__codelineno-61-7"></a><span class="w"> </span><span class="nx">log</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;warning: no messages received&quot;</span><span class="p">)</span>
</span><span id="__span-61-8"><a id="__codelineno-61-8" name="__codelineno-61-8" href="#__codelineno-61-8"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-61-9"><a id="__codelineno-61-9" name="__codelineno-61-9" href="#__codelineno-61-9"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-61-10"><a id="__codelineno-61-10" name="__codelineno-61-10" href="#__codelineno-61-10"></a><span class="p">}</span>
</span></code></pre></div>
<p>The source code of the function time.After is as follows:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-62-1"><a id="__codelineno-62-1" name="__codelineno-62-1" href="#__codelineno-62-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">After</span><span class="p">(</span><span class="nx">d</span><span class="w"> </span><span class="nx">Duration</span><span class="p">)</span><span class="w"> </span><span class="o">&lt;-</span><span class="kd">chan</span><span class="w"> </span><span class="nx">Time</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-62-2"><a id="__codelineno-62-2" name="__codelineno-62-2" href="#__codelineno-62-2"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="nx">NewTimer</span><span class="p">(</span><span class="nx">d</span><span class="p">).</span><span class="nx">C</span>
</span><span id="__span-62-3"><a id="__codelineno-62-3" name="__codelineno-62-3" href="#__codelineno-62-3"></a><span class="p">}</span>
</span></code></pre></div>
<p>As we see, it returns receive-only channel.</p>
<p>When <code>time.After</code> is used in a loop or repeated context, a new channel is created in each iteration. If these channels are not properly closed or if their associated timers are not stopped, they can accumulate and consume memory. The resources associated with each timer and channel are only released when the timer expires or the channel is closed.</p>
<p>To avoid this happening, We can use context's timeout setting instead of <code>time.After</code>, like below:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-63-1"><a id="__codelineno-63-1" name="__codelineno-63-1" href="#__codelineno-63-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">consumer</span><span class="p">(</span><span class="nx">ch</span><span class="w"> </span><span class="o">&lt;-</span><span class="kd">chan</span><span class="w"> </span><span class="nx">Event</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-63-2"><a id="__codelineno-63-2" name="__codelineno-63-2" href="#__codelineno-63-2"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-63-3"><a id="__codelineno-63-3" name="__codelineno-63-3" href="#__codelineno-63-3"></a><span class="w"> </span><span class="nx">ctx</span><span class="p">,</span><span class="w"> </span><span class="nx">cancel</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">context</span><span class="p">.</span><span class="nx">WithTimeout</span><span class="p">(</span><span class="nx">context</span><span class="p">.</span><span class="nx">Background</span><span class="p">(),</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">Hour</span><span class="p">)</span>
</span><span id="__span-63-4"><a id="__codelineno-63-4" name="__codelineno-63-4" href="#__codelineno-63-4"></a><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-63-5"><a id="__codelineno-63-5" name="__codelineno-63-5" href="#__codelineno-63-5"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="nx">event</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ch</span><span class="p">:</span>
</span><span id="__span-63-6"><a id="__codelineno-63-6" name="__codelineno-63-6" href="#__codelineno-63-6"></a><span class="w"> </span><span class="nx">cancel</span><span class="p">()</span>
</span><span id="__span-63-7"><a id="__codelineno-63-7" name="__codelineno-63-7" href="#__codelineno-63-7"></a><span class="w"> </span><span class="nx">handle</span><span class="p">(</span><span class="nx">event</span><span class="p">)</span>
</span><span id="__span-63-8"><a id="__codelineno-63-8" name="__codelineno-63-8" href="#__codelineno-63-8"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ctx</span><span class="p">.</span><span class="nx">Done</span><span class="p">():</span>
</span><span id="__span-63-9"><a id="__codelineno-63-9" name="__codelineno-63-9" href="#__codelineno-63-9"></a><span class="w"> </span><span class="nx">log</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;warning: no messages received&quot;</span><span class="p">)</span>
</span><span id="__span-63-10"><a id="__codelineno-63-10" name="__codelineno-63-10" href="#__codelineno-63-10"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-63-11"><a id="__codelineno-63-11" name="__codelineno-63-11" href="#__codelineno-63-11"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-63-12"><a id="__codelineno-63-12" name="__codelineno-63-12" href="#__codelineno-63-12"></a><span class="p">}</span>
</span></code></pre></div>
<p>We can also use <code>time.NewTimer</code> like so:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-64-1"><a id="__codelineno-64-1" name="__codelineno-64-1" href="#__codelineno-64-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">consumer</span><span class="p">(</span><span class="nx">ch</span><span class="w"> </span><span class="o">&lt;-</span><span class="kd">chan</span><span class="w"> </span><span class="nx">Event</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-64-2"><a id="__codelineno-64-2" name="__codelineno-64-2" href="#__codelineno-64-2"></a><span class="w"> </span><span class="nx">timerDuration</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="o">*</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">Hour</span>
</span><span id="__span-64-3"><a id="__codelineno-64-3" name="__codelineno-64-3" href="#__codelineno-64-3"></a><span class="w"> </span><span class="nx">timer</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">time</span><span class="p">.</span><span class="nx">NewTimer</span><span class="p">(</span><span class="nx">timerDuration</span><span class="p">)</span>
</span><span id="__span-64-4"><a id="__codelineno-64-4" name="__codelineno-64-4" href="#__codelineno-64-4"></a>
</span><span id="__span-64-5"><a id="__codelineno-64-5" name="__codelineno-64-5" href="#__codelineno-64-5"></a><span class="w"> </span><span class="k">for</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-64-6"><a id="__codelineno-64-6" name="__codelineno-64-6" href="#__codelineno-64-6"></a><span class="w"> </span><span class="nx">timer</span><span class="p">.</span><span class="nx">Reset</span><span class="p">(</span><span class="nx">timerDuration</span><span class="p">)</span>
</span><span id="__span-64-7"><a id="__codelineno-64-7" name="__codelineno-64-7" href="#__codelineno-64-7"></a><span class="w"> </span><span class="k">select</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-64-8"><a id="__codelineno-64-8" name="__codelineno-64-8" href="#__codelineno-64-8"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="nx">event</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">ch</span><span class="p">:</span>
</span><span id="__span-64-9"><a id="__codelineno-64-9" name="__codelineno-64-9" href="#__codelineno-64-9"></a><span class="w"> </span><span class="nx">handle</span><span class="p">(</span><span class="nx">event</span><span class="p">)</span>
</span><span id="__span-64-10"><a id="__codelineno-64-10" name="__codelineno-64-10" href="#__codelineno-64-10"></a><span class="w"> </span><span class="k">case</span><span class="w"> </span><span class="o">&lt;-</span><span class="nx">timer</span><span class="p">.</span><span class="nx">C</span><span class="p">:</span>
</span><span id="__span-64-11"><a id="__codelineno-64-11" name="__codelineno-64-11" href="#__codelineno-64-11"></a><span class="w"> </span><span class="nx">log</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="s">&quot;warning: no messages received&quot;</span><span class="p">)</span>
</span><span id="__span-64-12"><a id="__codelineno-64-12" name="__codelineno-64-12" href="#__codelineno-64-12"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-64-13"><a id="__codelineno-64-13" name="__codelineno-64-13" href="#__codelineno-64-13"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-64-14"><a id="__codelineno-64-14" name="__codelineno-64-14" href="#__codelineno-64-14"></a><span class="p">}</span>
</span></code></pre></div>
<p><a href="https://github.com/teivah/100-go-mistakes/tree/master/src/10-standard-lib/76-time-after/main.go"><span class="twemoji"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg></span> Source code</a></p>
<h3 id="json-handling-common-mistakes-77">JSON handling common mistakes (#77)</h3>
<ul>
<li>Unexpected behavior because of type embedding</li>
@ -5016,34 +5004,34 @@ the use case. However, we should see the two options as complementary. </p>
<p>To avoid unexpected behaviors in HTTP handler implementations, make sure you don’t miss the <code>return</code> statement if you want a handler to stop after <code>http.Error</code>.</p>
</details>
<p>Consider the following HTTP handler that handles an error from <code>foo</code> using <code>http.Error</code>:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-65-1"><a id="__codelineno-65-1" name="__codelineno-65-1" href="#__codelineno-65-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">handler</span><span class="p">(</span><span class="nx">w</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">ResponseWriter</span><span class="p">,</span><span class="w"> </span><span class="nx">req</span><span class="w"> </span><span class="o">*</span><span class="nx">http</span><span class="p">.</span><span class="nx">Request</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-65-2"><a id="__codelineno-65-2" name="__codelineno-65-2" href="#__codelineno-65-2"></a><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">foo</span><span class="p">(</span><span class="nx">req</span><span class="p">)</span>
</span><span id="__span-65-3"><a id="__codelineno-65-3" name="__codelineno-65-3" href="#__codelineno-65-3"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">nil</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-65-4"><a id="__codelineno-65-4" name="__codelineno-65-4" href="#__codelineno-65-4"></a><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">Error</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusInternalServerError</span><span class="p">)</span>
</span><span id="__span-65-5"><a id="__codelineno-65-5" name="__codelineno-65-5" href="#__codelineno-65-5"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-65-6"><a id="__codelineno-65-6" name="__codelineno-65-6" href="#__codelineno-65-6"></a>
</span><span id="__span-65-7"><a id="__codelineno-65-7" name="__codelineno-65-7" href="#__codelineno-65-7"></a><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="s">&quot;all good&quot;</span><span class="p">))</span>
</span><span id="__span-65-8"><a id="__codelineno-65-8" name="__codelineno-65-8" href="#__codelineno-65-8"></a><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">WriteHeader</span><span class="p">(</span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusCreated</span><span class="p">)</span>
</span><span id="__span-65-9"><a id="__codelineno-65-9" name="__codelineno-65-9" href="#__codelineno-65-9"></a><span class="p">}</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-64-1"><a id="__codelineno-64-1" name="__codelineno-64-1" href="#__codelineno-64-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">handler</span><span class="p">(</span><span class="nx">w</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">ResponseWriter</span><span class="p">,</span><span class="w"> </span><span class="nx">req</span><span class="w"> </span><span class="o">*</span><span class="nx">http</span><span class="p">.</span><span class="nx">Request</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-64-2"><a id="__codelineno-64-2" name="__codelineno-64-2" href="#__codelineno-64-2"></a><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">foo</span><span class="p">(</span><span class="nx">req</span><span class="p">)</span>
</span><span id="__span-64-3"><a id="__codelineno-64-3" name="__codelineno-64-3" href="#__codelineno-64-3"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">nil</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-64-4"><a id="__codelineno-64-4" name="__codelineno-64-4" href="#__codelineno-64-4"></a><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">Error</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusInternalServerError</span><span class="p">)</span>
</span><span id="__span-64-5"><a id="__codelineno-64-5" name="__codelineno-64-5" href="#__codelineno-64-5"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-64-6"><a id="__codelineno-64-6" name="__codelineno-64-6" href="#__codelineno-64-6"></a>
</span><span id="__span-64-7"><a id="__codelineno-64-7" name="__codelineno-64-7" href="#__codelineno-64-7"></a><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="s">&quot;all good&quot;</span><span class="p">))</span>
</span><span id="__span-64-8"><a id="__codelineno-64-8" name="__codelineno-64-8" href="#__codelineno-64-8"></a><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">WriteHeader</span><span class="p">(</span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusCreated</span><span class="p">)</span>
</span><span id="__span-64-9"><a id="__codelineno-64-9" name="__codelineno-64-9" href="#__codelineno-64-9"></a><span class="p">}</span>
</span></code></pre></div>
<p>If we run this code and <code>err != nil</code>, the HTTP response would be:</p>
<div class="language-text highlight"><pre><span></span><code><span id="__span-66-1"><a id="__codelineno-66-1" name="__codelineno-66-1" href="#__codelineno-66-1"></a>foo
</span><span id="__span-66-2"><a id="__codelineno-66-2" name="__codelineno-66-2" href="#__codelineno-66-2"></a>all good
<div class="language-text highlight"><pre><span></span><code><span id="__span-65-1"><a id="__codelineno-65-1" name="__codelineno-65-1" href="#__codelineno-65-1"></a>foo
</span><span id="__span-65-2"><a id="__codelineno-65-2" name="__codelineno-65-2" href="#__codelineno-65-2"></a>all good
</span></code></pre></div>
<p>The response contains both the error and success messages, and also the first HTTP status code, 500. There would also be a warning log indicating that we attempted to write the status code multiple times:</p>
<div class="language-text highlight"><pre><span></span><code><span id="__span-67-1"><a id="__codelineno-67-1" name="__codelineno-67-1" href="#__codelineno-67-1"></a>2023/10/10 16:45:33 http: superfluous response.WriteHeader call from main.handler (main.go:20)
<div class="language-text highlight"><pre><span></span><code><span id="__span-66-1"><a id="__codelineno-66-1" name="__codelineno-66-1" href="#__codelineno-66-1"></a>2023/10/10 16:45:33 http: superfluous response.WriteHeader call from main.handler (main.go:20)
</span></code></pre></div>
<p>The mistake in this code is that <code>http.Error</code> does not stop the handler's execution, which means the success message and status code get written in addition to the error. Beyond an incorrect response, failing to return after writing an error can lead to the unwanted execution of code and unexpected side-effects. The following code adds the <code>return</code> statement following the <code>http.Error</code> and exhibits the desired behavior when ran:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-68-1"><a id="__codelineno-68-1" name="__codelineno-68-1" href="#__codelineno-68-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">handler</span><span class="p">(</span><span class="nx">w</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">ResponseWriter</span><span class="p">,</span><span class="w"> </span><span class="nx">req</span><span class="w"> </span><span class="o">*</span><span class="nx">http</span><span class="p">.</span><span class="nx">Request</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-68-2"><a id="__codelineno-68-2" name="__codelineno-68-2" href="#__codelineno-68-2"></a><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">foo</span><span class="p">(</span><span class="nx">req</span><span class="p">)</span>
</span><span id="__span-68-3"><a id="__codelineno-68-3" name="__codelineno-68-3" href="#__codelineno-68-3"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">nil</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-68-4"><a id="__codelineno-68-4" name="__codelineno-68-4" href="#__codelineno-68-4"></a><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">Error</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusInternalServerError</span><span class="p">)</span>
</span><span id="__span-68-5"><a id="__codelineno-68-5" name="__codelineno-68-5" href="#__codelineno-68-5"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="c1">// Adds the return statement</span>
</span><span id="__span-68-6"><a id="__codelineno-68-6" name="__codelineno-68-6" href="#__codelineno-68-6"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-68-7"><a id="__codelineno-68-7" name="__codelineno-68-7" href="#__codelineno-68-7"></a>
</span><span id="__span-68-8"><a id="__codelineno-68-8" name="__codelineno-68-8" href="#__codelineno-68-8"></a><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="s">&quot;all good&quot;</span><span class="p">))</span>
</span><span id="__span-68-9"><a id="__codelineno-68-9" name="__codelineno-68-9" href="#__codelineno-68-9"></a><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">WriteHeader</span><span class="p">(</span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusCreated</span><span class="p">)</span>
</span><span id="__span-68-10"><a id="__codelineno-68-10" name="__codelineno-68-10" href="#__codelineno-68-10"></a><span class="p">}</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-67-1"><a id="__codelineno-67-1" name="__codelineno-67-1" href="#__codelineno-67-1"></a><span class="kd">func</span><span class="w"> </span><span class="nx">handler</span><span class="p">(</span><span class="nx">w</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">ResponseWriter</span><span class="p">,</span><span class="w"> </span><span class="nx">req</span><span class="w"> </span><span class="o">*</span><span class="nx">http</span><span class="p">.</span><span class="nx">Request</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-67-2"><a id="__codelineno-67-2" name="__codelineno-67-2" href="#__codelineno-67-2"></a><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="nx">foo</span><span class="p">(</span><span class="nx">req</span><span class="p">)</span>
</span><span id="__span-67-3"><a id="__codelineno-67-3" name="__codelineno-67-3" href="#__codelineno-67-3"></a><span class="w"> </span><span class="k">if</span><span class="w"> </span><span class="nx">err</span><span class="w"> </span><span class="o">!=</span><span class="w"> </span><span class="kc">nil</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-67-4"><a id="__codelineno-67-4" name="__codelineno-67-4" href="#__codelineno-67-4"></a><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">Error</span><span class="p">(</span><span class="nx">w</span><span class="p">,</span><span class="w"> </span><span class="s">&quot;foo&quot;</span><span class="p">,</span><span class="w"> </span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusInternalServerError</span><span class="p">)</span>
</span><span id="__span-67-5"><a id="__codelineno-67-5" name="__codelineno-67-5" href="#__codelineno-67-5"></a><span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="c1">// Adds the return statement</span>
</span><span id="__span-67-6"><a id="__codelineno-67-6" name="__codelineno-67-6" href="#__codelineno-67-6"></a><span class="w"> </span><span class="p">}</span>
</span><span id="__span-67-7"><a id="__codelineno-67-7" name="__codelineno-67-7" href="#__codelineno-67-7"></a>
</span><span id="__span-67-8"><a id="__codelineno-67-8" name="__codelineno-67-8" href="#__codelineno-67-8"></a><span class="w"> </span><span class="nx">_</span><span class="p">,</span><span class="w"> </span><span class="nx">_</span><span class="w"> </span><span class="p">=</span><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">Write</span><span class="p">([]</span><span class="nb">byte</span><span class="p">(</span><span class="s">&quot;all good&quot;</span><span class="p">))</span>
</span><span id="__span-67-9"><a id="__codelineno-67-9" name="__codelineno-67-9" href="#__codelineno-67-9"></a><span class="w"> </span><span class="nx">w</span><span class="p">.</span><span class="nx">WriteHeader</span><span class="p">(</span><span class="nx">http</span><span class="p">.</span><span class="nx">StatusCreated</span><span class="p">)</span>
</span><span id="__span-67-10"><a id="__codelineno-67-10" name="__codelineno-67-10" href="#__codelineno-67-10"></a><span class="p">}</span>
</span></code></pre></div>
<p><a href="https://github.com/teivah/100-go-mistakes/tree/master/src/10-standard-lib/80-http-return/main.go"><span class="twemoji"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M12 .297c-6.63 0-12 5.373-12 12 0 5.303 3.438 9.8 8.205 11.385.6.113.82-.258.82-.577 0-.285-.01-1.04-.015-2.04-3.338.724-4.042-1.61-4.042-1.61C4.422 18.07 3.633 17.7 3.633 17.7c-1.087-.744.084-.729.084-.729 1.205.084 1.838 1.236 1.838 1.236 1.07 1.835 2.809 1.305 3.495.998.108-.776.417-1.305.76-1.605-2.665-.3-5.466-1.332-5.466-5.93 0-1.31.465-2.38 1.235-3.22-.135-.303-.54-1.523.105-3.176 0 0 1.005-.322 3.3 1.23.96-.267 1.98-.399 3-.405 1.02.006 2.04.138 3 .405 2.28-1.552 3.285-1.23 3.285-1.23.645 1.653.24 2.873.12 3.176.765.84 1.23 1.91 1.23 3.22 0 4.61-2.805 5.625-5.475 5.92.42.36.81 1.096.81 2.22 0 1.606-.015 2.896-.015 3.286 0 .315.21.69.825.57C20.565 22.092 24 17.592 24 12.297c0-6.627-5.373-12-12-12"/></svg></span> Source code</a></p>
<h3 id="using-the-default-http-client-and-server-81">Using the default HTTP client and server (#81)</h3>
@ -5065,38 +5053,38 @@ the use case. However, we should see the two options as complementary. </p>
<p>Enabling the <code>-race</code> flag is highly recommended when writing concurrent applications. Doing so allows you to catch potential data races that can lead to software bugs.</p>
</details>
<p>In Go, the race detector isn’t a static analysis tool used during compilation; instead, it’s a tool to find data races that occur at runtime. To enable it, we have to enable the -race flag while compiling or running a test. For example:</p>
<div class="language-bash highlight"><pre><span></span><code><span id="__span-69-1"><a id="__codelineno-69-1" name="__codelineno-69-1" href="#__codelineno-69-1"></a>go<span class="w"> </span><span class="nb">test</span><span class="w"> </span>-race<span class="w"> </span>./...
<div class="language-bash highlight"><pre><span></span><code><span id="__span-68-1"><a id="__codelineno-68-1" name="__codelineno-68-1" href="#__codelineno-68-1"></a>go<span class="w"> </span><span class="nb">test</span><span class="w"> </span>-race<span class="w"> </span>./...
</span></code></pre></div>
<p>Once the race detector is enabled, the compiler instruments the code to detect data races. Instrumentation refers to a compiler adding extra instructions: here, tracking all memory accesses and recording when and how they occur.</p>
<p>Enabling the race detector adds an overhead in terms of memory and execution time; hence, it's generally recommended to enable it only during local testing or continuous integration, not production.</p>
<p>If a race is detected, Go raises a warning. For example:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-70-1"><a id="__codelineno-70-1" name="__codelineno-70-1" href="#__codelineno-70-1"></a><span class="kn">package</span><span class="w"> </span><span class="nx">main</span>
</span><span id="__span-70-2"><a id="__codelineno-70-2" name="__codelineno-70-2" href="#__codelineno-70-2"></a>
</span><span id="__span-70-3"><a id="__codelineno-70-3" name="__codelineno-70-3" href="#__codelineno-70-3"></a><span class="kn">import</span><span class="w"> </span><span class="p">(</span>
</span><span id="__span-70-4"><a id="__codelineno-70-4" name="__codelineno-70-4" href="#__codelineno-70-4"></a><span class="w"> </span><span class="s">&quot;fmt&quot;</span>
</span><span id="__span-70-5"><a id="__codelineno-70-5" name="__codelineno-70-5" href="#__codelineno-70-5"></a><span class="p">)</span>
</span><span id="__span-70-6"><a id="__codelineno-70-6" name="__codelineno-70-6" href="#__codelineno-70-6"></a>
</span><span id="__span-70-7"><a id="__codelineno-70-7" name="__codelineno-70-7" href="#__codelineno-70-7"></a><span class="kd">func</span><span class="w"> </span><span class="nx">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-70-8"><a id="__codelineno-70-8" name="__codelineno-70-8" href="#__codelineno-70-8"></a><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span>
</span><span id="__span-70-9"><a id="__codelineno-70-9" name="__codelineno-70-9" href="#__codelineno-70-9"></a><span class="w"> </span><span class="k">go</span><span class="w"> </span><span class="kd">func</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">}()</span>
</span><span id="__span-70-10"><a id="__codelineno-70-10" name="__codelineno-70-10" href="#__codelineno-70-10"></a><span class="w"> </span><span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
</span><span id="__span-70-11"><a id="__codelineno-70-11" name="__codelineno-70-11" href="#__codelineno-70-11"></a><span class="p">}</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-69-1"><a id="__codelineno-69-1" name="__codelineno-69-1" href="#__codelineno-69-1"></a><span class="kn">package</span><span class="w"> </span><span class="nx">main</span>
</span><span id="__span-69-2"><a id="__codelineno-69-2" name="__codelineno-69-2" href="#__codelineno-69-2"></a>
</span><span id="__span-69-3"><a id="__codelineno-69-3" name="__codelineno-69-3" href="#__codelineno-69-3"></a><span class="kn">import</span><span class="w"> </span><span class="p">(</span>
</span><span id="__span-69-4"><a id="__codelineno-69-4" name="__codelineno-69-4" href="#__codelineno-69-4"></a><span class="w"> </span><span class="s">&quot;fmt&quot;</span>
</span><span id="__span-69-5"><a id="__codelineno-69-5" name="__codelineno-69-5" href="#__codelineno-69-5"></a><span class="p">)</span>
</span><span id="__span-69-6"><a id="__codelineno-69-6" name="__codelineno-69-6" href="#__codelineno-69-6"></a>
</span><span id="__span-69-7"><a id="__codelineno-69-7" name="__codelineno-69-7" href="#__codelineno-69-7"></a><span class="kd">func</span><span class="w"> </span><span class="nx">main</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-69-8"><a id="__codelineno-69-8" name="__codelineno-69-8" href="#__codelineno-69-8"></a><span class="w"> </span><span class="nx">i</span><span class="w"> </span><span class="o">:=</span><span class="w"> </span><span class="mi">0</span>
</span><span id="__span-69-9"><a id="__codelineno-69-9" name="__codelineno-69-9" href="#__codelineno-69-9"></a><span class="w"> </span><span class="k">go</span><span class="w"> </span><span class="kd">func</span><span class="p">()</span><span class="w"> </span><span class="p">{</span><span class="w"> </span><span class="nx">i</span><span class="o">++</span><span class="w"> </span><span class="p">}()</span>
</span><span id="__span-69-10"><a id="__codelineno-69-10" name="__codelineno-69-10" href="#__codelineno-69-10"></a><span class="w"> </span><span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
</span><span id="__span-69-11"><a id="__codelineno-69-11" name="__codelineno-69-11" href="#__codelineno-69-11"></a><span class="p">}</span>
</span></code></pre></div>
<p>Running this code with the <code>-race</code> logs the following warning:</p>
<div class="language-bash highlight"><pre><span></span><code><span id="__span-71-1"><a id="__codelineno-71-1" name="__codelineno-71-1" href="#__codelineno-71-1"></a><span class="o">==================</span>
</span><span id="__span-71-2"><a id="__codelineno-71-2" name="__codelineno-71-2" href="#__codelineno-71-2"></a>WARNING:<span class="w"> </span>DATA<span class="w"> </span>RACE
</span><span id="__span-71-3"><a id="__codelineno-71-3" name="__codelineno-71-3" href="#__codelineno-71-3"></a><span class="hll">Write<span class="w"> </span>at<span class="w"> </span>0x00c000026078<span class="w"> </span>by<span class="w"> </span>goroutine<span class="w"> </span><span class="m">7</span>:<span class="w"> </span><span class="c1"># (1)</span>
</span></span><span id="__span-71-4"><a id="__codelineno-71-4" name="__codelineno-71-4" href="#__codelineno-71-4"></a><span class="w"> </span>main.main.func1<span class="o">()</span>
</span><span id="__span-71-5"><a id="__codelineno-71-5" name="__codelineno-71-5" href="#__codelineno-71-5"></a><span class="w"> </span>/tmp/app/main.go:9<span class="w"> </span>+0x4e
</span><span id="__span-71-6"><a id="__codelineno-71-6" name="__codelineno-71-6" href="#__codelineno-71-6"></a>
</span><span id="__span-71-7"><a id="__codelineno-71-7" name="__codelineno-71-7" href="#__codelineno-71-7"></a><span class="hll">Previous<span class="w"> </span><span class="nb">read</span><span class="w"> </span>at<span class="w"> </span>0x00c000026078<span class="w"> </span>by<span class="w"> </span>main<span class="w"> </span>goroutine:<span class="w"> </span><span class="c1"># (2)</span>
</span></span><span id="__span-71-8"><a id="__codelineno-71-8" name="__codelineno-71-8" href="#__codelineno-71-8"></a><span class="w"> </span>main.main<span class="o">()</span>
</span><span id="__span-71-9"><a id="__codelineno-71-9" name="__codelineno-71-9" href="#__codelineno-71-9"></a><span class="w"> </span>/tmp/app/main.go:10<span class="w"> </span>+0x88
</span><span id="__span-71-10"><a id="__codelineno-71-10" name="__codelineno-71-10" href="#__codelineno-71-10"></a>
</span><span id="__span-71-11"><a id="__codelineno-71-11" name="__codelineno-71-11" href="#__codelineno-71-11"></a><span class="hll">Goroutine<span class="w"> </span><span class="m">7</span><span class="w"> </span><span class="o">(</span>running<span class="o">)</span><span class="w"> </span>created<span class="w"> </span>at:<span class="w"> </span><span class="c1"># (3)</span>
</span></span><span id="__span-71-12"><a id="__codelineno-71-12" name="__codelineno-71-12" href="#__codelineno-71-12"></a><span class="w"> </span>main.main<span class="o">()</span>
</span><span id="__span-71-13"><a id="__codelineno-71-13" name="__codelineno-71-13" href="#__codelineno-71-13"></a><span class="w"> </span>/tmp/app/main.go:9<span class="w"> </span>+0x7a
</span><span id="__span-71-14"><a id="__codelineno-71-14" name="__codelineno-71-14" href="#__codelineno-71-14"></a><span class="o">==================</span>
<div class="language-bash highlight"><pre><span></span><code><span id="__span-70-1"><a id="__codelineno-70-1" name="__codelineno-70-1" href="#__codelineno-70-1"></a><span class="o">==================</span>
</span><span id="__span-70-2"><a id="__codelineno-70-2" name="__codelineno-70-2" href="#__codelineno-70-2"></a>WARNING:<span class="w"> </span>DATA<span class="w"> </span>RACE
</span><span id="__span-70-3"><a id="__codelineno-70-3" name="__codelineno-70-3" href="#__codelineno-70-3"></a><span class="hll">Write<span class="w"> </span>at<span class="w"> </span>0x00c000026078<span class="w"> </span>by<span class="w"> </span>goroutine<span class="w"> </span><span class="m">7</span>:<span class="w"> </span><span class="c1"># (1)</span>
</span></span><span id="__span-70-4"><a id="__codelineno-70-4" name="__codelineno-70-4" href="#__codelineno-70-4"></a><span class="w"> </span>main.main.func1<span class="o">()</span>
</span><span id="__span-70-5"><a id="__codelineno-70-5" name="__codelineno-70-5" href="#__codelineno-70-5"></a><span class="w"> </span>/tmp/app/main.go:9<span class="w"> </span>+0x4e
</span><span id="__span-70-6"><a id="__codelineno-70-6" name="__codelineno-70-6" href="#__codelineno-70-6"></a>
</span><span id="__span-70-7"><a id="__codelineno-70-7" name="__codelineno-70-7" href="#__codelineno-70-7"></a><span class="hll">Previous<span class="w"> </span><span class="nb">read</span><span class="w"> </span>at<span class="w"> </span>0x00c000026078<span class="w"> </span>by<span class="w"> </span>main<span class="w"> </span>goroutine:<span class="w"> </span><span class="c1"># (2)</span>
</span></span><span id="__span-70-8"><a id="__codelineno-70-8" name="__codelineno-70-8" href="#__codelineno-70-8"></a><span class="w"> </span>main.main<span class="o">()</span>
</span><span id="__span-70-9"><a id="__codelineno-70-9" name="__codelineno-70-9" href="#__codelineno-70-9"></a><span class="w"> </span>/tmp/app/main.go:10<span class="w"> </span>+0x88
</span><span id="__span-70-10"><a id="__codelineno-70-10" name="__codelineno-70-10" href="#__codelineno-70-10"></a>
</span><span id="__span-70-11"><a id="__codelineno-70-11" name="__codelineno-70-11" href="#__codelineno-70-11"></a><span class="hll">Goroutine<span class="w"> </span><span class="m">7</span><span class="w"> </span><span class="o">(</span>running<span class="o">)</span><span class="w"> </span>created<span class="w"> </span>at:<span class="w"> </span><span class="c1"># (3)</span>
</span></span><span id="__span-70-12"><a id="__codelineno-70-12" name="__codelineno-70-12" href="#__codelineno-70-12"></a><span class="w"> </span>main.main<span class="o">()</span>
</span><span id="__span-70-13"><a id="__codelineno-70-13" name="__codelineno-70-13" href="#__codelineno-70-13"></a><span class="w"> </span>/tmp/app/main.go:9<span class="w"> </span>+0x7a
</span><span id="__span-70-14"><a id="__codelineno-70-14" name="__codelineno-70-14" href="#__codelineno-70-14"></a><span class="o">==================</span>
</span></code></pre></div>
<ol>
<li>Indicates that goroutine 7 was writing</li>
@ -5110,17 +5098,17 @@ the use case. However, we should see the two options as complementary. </p>
<li>When these goroutines were created: goroutine 7 was created in main().</li>
</ul>
<p>In addition, if a specific file contains tests that lead to data races, we can exclude it <span class="twemoji" title="temporarily! 😉"><svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24"><path d="M11 9h2V7h-2m1 13c-4.41 0-8-3.59-8-8s3.59-8 8-8 8 3.59 8 8-3.59 8-8 8m0-18A10 10 0 0 0 2 12a10 10 0 0 0 10 10 10 10 0 0 0 10-10A10 10 0 0 0 12 2m-1 15h2v-6h-2v6Z"/></svg></span> from race detection using the <code>!race</code> build tag:</p>
<div class="language-go highlight"><pre><span></span><code><span id="__span-72-1"><a id="__codelineno-72-1" name="__codelineno-72-1" href="#__codelineno-72-1"></a><span class="c1">//go:build !race</span>
</span><span id="__span-72-2"><a id="__codelineno-72-2" name="__codelineno-72-2" href="#__codelineno-72-2"></a>
</span><span id="__span-72-3"><a id="__codelineno-72-3" name="__codelineno-72-3" href="#__codelineno-72-3"></a><span class="kn">package</span><span class="w"> </span><span class="nx">main</span>
</span><span id="__span-72-4"><a id="__codelineno-72-4" name="__codelineno-72-4" href="#__codelineno-72-4"></a>
</span><span id="__span-72-5"><a id="__codelineno-72-5" name="__codelineno-72-5" href="#__codelineno-72-5"></a><span class="kn">import</span><span class="w"> </span><span class="p">(</span>
</span><span id="__span-72-6"><a id="__codelineno-72-6" name="__codelineno-72-6" href="#__codelineno-72-6"></a><span class="w"> </span><span class="s">&quot;testing&quot;</span>
</span><span id="__span-72-7"><a id="__codelineno-72-7" name="__codelineno-72-7" href="#__codelineno-72-7"></a><span class="p">)</span>
</span><span id="__span-72-8"><a id="__codelineno-72-8" name="__codelineno-72-8" href="#__codelineno-72-8"></a>
</span><span id="__span-72-9"><a id="__codelineno-72-9" name="__codelineno-72-9" href="#__codelineno-72-9"></a><span class="kd">func</span><span class="w"> </span><span class="nx">TestFoo</span><span class="p">(</span><span class="nx">t</span><span class="w"> </span><span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">T</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-72-10"><a id="__codelineno-72-10" name="__codelineno-72-10" href="#__codelineno-72-10"></a><span class="w"> </span><span class="c1">// ...</span>
</span><span id="__span-72-11"><a id="__codelineno-72-11" name="__codelineno-72-11" href="#__codelineno-72-11"></a><span class="p">}</span>
<div class="language-go highlight"><pre><span></span><code><span id="__span-71-1"><a id="__codelineno-71-1" name="__codelineno-71-1" href="#__codelineno-71-1"></a><span class="c1">//go:build !race</span>
</span><span id="__span-71-2"><a id="__codelineno-71-2" name="__codelineno-71-2" href="#__codelineno-71-2"></a>
</span><span id="__span-71-3"><a id="__codelineno-71-3" name="__codelineno-71-3" href="#__codelineno-71-3"></a><span class="kn">package</span><span class="w"> </span><span class="nx">main</span>
</span><span id="__span-71-4"><a id="__codelineno-71-4" name="__codelineno-71-4" href="#__codelineno-71-4"></a>
</span><span id="__span-71-5"><a id="__codelineno-71-5" name="__codelineno-71-5" href="#__codelineno-71-5"></a><span class="kn">import</span><span class="w"> </span><span class="p">(</span>
</span><span id="__span-71-6"><a id="__codelineno-71-6" name="__codelineno-71-6" href="#__codelineno-71-6"></a><span class="w"> </span><span class="s">&quot;testing&quot;</span>
</span><span id="__span-71-7"><a id="__codelineno-71-7" name="__codelineno-71-7" href="#__codelineno-71-7"></a><span class="p">)</span>
</span><span id="__span-71-8"><a id="__codelineno-71-8" name="__codelineno-71-8" href="#__codelineno-71-8"></a>
</span><span id="__span-71-9"><a id="__codelineno-71-9" name="__codelineno-71-9" href="#__codelineno-71-9"></a><span class="kd">func</span><span class="w"> </span><span class="nx">TestFoo</span><span class="p">(</span><span class="nx">t</span><span class="w"> </span><span class="o">*</span><span class="nx">testing</span><span class="p">.</span><span class="nx">T</span><span class="p">)</span><span class="w"> </span><span class="p">{</span>
</span><span id="__span-71-10"><a id="__codelineno-71-10" name="__codelineno-71-10" href="#__codelineno-71-10"></a><span class="w"> </span><span class="c1">// ...</span>
</span><span id="__span-71-11"><a id="__codelineno-71-11" name="__codelineno-71-11" href="#__codelineno-71-11"></a><span class="p">}</span>
</span></code></pre></div>
<h3 id="not-using-test-execution-modes-parallel-and-shuffle-84">Not using test execution modes (parallel and shuffle) (#84)</h3>
<details class="info" open="open">

4
site/ja/index.html
View file

@ -3362,10 +3362,6 @@
<h1 id="go">Go言語でありがちな間違い</h1>
<p>このページは『100 Go Mistakes』の内容をまとめたものです。一方で、コミュニティに開かれたページでもあります。「ありがちな間違い」が新たに追加されるべきだとお考えでしたら <a href="https://github.com/teivah/100-go-mistakes/issues/new?assignees=&amp;labels=community+mistake&amp;template=community_mistake.md&amp;title=">community mistake issue</a> を作成してください。</p>
<details class="tip" open="open">
<summary>Jobs</summary>
<p>Is your company hiring? <a href="https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&amp;tier_id=386213&amp;preview=true">Sponsor</a> the Japanese version of this repository and let a significant audience of Go developers (~1k unique visitors per week) know about your opportunities in this section.</p>
</details>
<p><a class="glightbox" href="../img/inside-cover.png" data-type="image" data-width="auto" data-height="auto" data-desc-position="bottom"><img alt="" src="../img/inside-cover.png" /></a></p>
<details class="warning" open="open">
<summary>注意</summary>

4
site/pt-br/index.html
View file

@ -3428,10 +3428,6 @@
<h1 id="erros-comuns-de-go">Erros comuns de Go</h1>
<p>Esta página é um resumo dos erros do <a href="../book/">100 Go Mistakes and How to Avoid Them book</a>. Enquanto isso, também está aberto à comunidade. Se você acredita que um erro comum do Go deve ser adicionado, crie uma <a href="https://github.com/teivah/100-go-mistakes/issues/new?assignees=&amp;labels=community+mistake&amp;template=community_mistake.md&amp;title=">issue</a>.</p>
<details class="tip" open="open">
<summary>Jobs</summary>
<p>Sua empresa está contratando? <a href="https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&amp;tier_id=386213&amp;preview=true">Patrocine</a> este repositório e informe um público significativo de desenvolvedores Go (cerca de 1 mil visitantes únicos por semana) sobre suas oportunidades nesta seção.</p>
</details>
<p><a class="glightbox" href="../img/inside-cover.png" data-type="image" data-width="auto" data-height="auto" data-desc-position="bottom"><img alt="" src="../img/inside-cover.png" /></a></p>
<details class="warning" open="open">
<summary>Beta</summary>

2
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View file

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BIN
site/sitemap.xml.gz
View file

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4
site/zh/index.html
View file

@ -3181,10 +3181,6 @@
<h1 id="100-go">100 个 Go 常见错误及如何避免</h1>
<details class="tip" open="open">
<summary>Jobs</summary>
<p>Is your company hiring? <a href="https://github.com/sponsors/teivah/sponsorships?sponsor=teivah&amp;tier_id=386213&amp;preview=true">Sponsor</a> the Chinese version of this repository and let a significant audience of Go developers (~1k unique visitors per week) know about your opportunities in this section.</p>
</details>
<p><a class="glightbox" href="../img/inside-cover.png" data-type="image" data-width="auto" data-height="auto" data-desc-position="bottom"><img alt="" src="../img/inside-cover.png" /></a></p>
<h2 id="_1">代码及工程组织</h2>
<h3 id="1">意外的变量隐藏 (#1)</h3>