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Teiva Harsanyi 2024-03-08 00:04:31 +01:00
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71
docs/index.md
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@ -2186,6 +2186,77 @@ func handler(w http.ResponseWriter, req *http.Request) {
Enabling the `-race` flag is highly recommended when writing concurrent applications. Doing so allows you to catch potential data races that can lead to software bugs.
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:
```bash
go test -race ./...
```
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.
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.
If a race is detected, Go raises a warning. For example:
```go
package main
import (
"fmt"
)
func main() {
i := 0
go func() { i++ }()
fmt.Println(i)
}
```
Runnig this code with the `-race` logs the following warning:
```bash hl_lines="3 7 11"
==================
WARNING: DATA RACE
Write at 0x00c000026078 by goroutine 7: # (1)
main.main.func1()
/tmp/app/main.go:9 +0x4e
Previous read at 0x00c000026078 by main goroutine: # (2)
main.main()
/tmp/app/main.go:10 +0x88
Goroutine 7 (running) created at: # (3)
main.main()
/tmp/app/main.go:9 +0x7a
==================
```
1. Indicates that goroutine 7 was writing
2. Indicates that the main goroutine was reading
3. Indicates when the goroutine 7 was created
Let’s make sure we are comfortable reading these messages. Go always logs the following:
* The concurrent goroutines that are incriminated: here, the main goroutine and goroutine 7.
* Where accesses occur in the code: in this case, lines 9 and 10.
* When these goroutines were created: goroutine 7 was created in main().
In addition, if a specific file contains tests that lead to data races, we can (temporarily! :wink:) exclude it from race detection using the `!race` build tag:
```go
//go:build !race
package main
import (
"testing"
)
func TestFoo(t *testing.T) {
// ...
}
```
### Not using test execution modes (parallel and shuffle) (#84)
???+ info "TL;DR"

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mkdocs.yml
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@ -22,6 +22,7 @@ theme:
- announce.dismiss
- navigation.tracking
- toc.follow
- content.code.annotate
palette:
# Palette toggle for light mode
- scheme: default

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site/404.html
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@ -861,7 +861,7 @@
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site/5-interface-pollution/index.html
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site/56-concurrency-faster/index.html
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@ -1261,7 +1261,7 @@
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site/89-benchmarks/index.html
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@ -1403,7 +1403,7 @@
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site/9-generics/index.html
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@ -1260,7 +1260,7 @@
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site/98-profiling-execution-tracing/index.html
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@ -1447,7 +1447,7 @@ world” is executed, which occupies the four CPU cores for approximately 40 ms.
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site/book/index.html
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site/chapter-1/index.html
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site/index.html
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@ -4945,6 +4945,64 @@ the use case. However, we should see the two options as complementary. </p>
<summary>TL;DR</summary>
<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>./...
</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>
</span></code></pre></div>
<p>Runnig 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>
</span></code></pre></div>
<ol>
<li>Indicates that goroutine 7 was writing</li>
<li>Indicates that the main goroutine was reading</li>
<li>Indicates when the goroutine 7 was created</li>
</ol>
<p>Let’s make sure we are comfortable reading these messages. Go always logs the following:</p>
<ul>
<li>The concurrent goroutines that are incriminated: here, the main goroutine and goroutine 7.</li>
<li>Where accesses occur in the code: in this case, lines 9 and 10.</li>
<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 (temporarily! <img alt="😉" class="twemoji" src="https://cdn.jsdelivr.net/gh/jdecked/twemoji@15.0.3/assets/svg/1f609.svg" title=":wink:" />) exclude it 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>
</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">
<summary>TL;DR</summary>
@ -5226,7 +5284,7 @@ the use case. However, we should see the two options as complementary. </p>
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@ -2,72 +2,72 @@
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