Create Rule “local-copies-to-avoid-race-condition/rule” (#6191)

* Create Rule “local-copies-to-avoid-race-condition/rule” * Update Rule “local-copies-to-avoid-race-condition/rule” * Merge branch 'SSWConsulting:main' into cms/sylhuang/SSW.Rules.Content/rule/local-copies-to-avoid-race-condition/rule * Update rules-to-better-code.md * Update Rule “local-copies-to-avoid-race-condition/rule” * Update rule.md --------- Co-authored-by: Tiago Araújo [SSW] <[email protected]>
SSWConsulting · Jul 31, 2023 · 6b5f5b4 · 6b5f5b4
1 parent 4002bfa
commit 6b5f5b4
Show file tree

Hide file tree

Showing 2 changed files with 43 additions and 0 deletions.
diff --git a/categories/software-development/rules-to-better-code.md b/categories/software-development/rules-to-better-code.md
@@ -80,6 +80,7 @@ index:
 - installing-3rd-party-libraries
 - package-audit-log
 - use-package-managers-appropriately
+- local-copies-to-resolve-race-condition
 
 ---
 

diff --git a/rules/local-copies-to-avoid-race-condition/rule.md b/rules/local-copies-to-avoid-race-condition/rule.md
@@ -0,0 +1,42 @@
+---
+type: rule
+title: Do you use local copies to resolve race condition?
+uri: local-copies-to-resolve-race-condition
+authors:
+  - title: Sylvia Huang
+    url: https://ssw.com.au/people/sylvia-huang
+created: 2023-07-31T01:19:28.222Z
+guid: f49d4f99-522e-433c-a7ab-0e59d78f03df
+---
+Code that looks perfectly fine in a single-threaded scenario could be vulnerable to race condition when some value is shared among multiple threads.
+
+<!--endintro-->
+
+Examine the following if-statement:
+
+```csharp
+if (A is null || (A.PropertyA == SOME_CONSTANT && B))
+{
+   // some logic
+}
+```
+::: bad
+Figure: Bad example - Vulnerable to race condition
+:::
+
+When the above code is run single-threaded, the second part of the if-condition would never be reached when A is null. However, if A is shared among multiple threads, the value of A could change from not null to null after passing the first check of if-condition, resulting in a [NRE](https://learn.microsoft.com/en-us/dotnet/api/system.nullreferenceexception?view=net-7.0) in the second check of if-condition.
+
+In order to make the code thread-safe, you should make a local copy of the shared value so that value change caused by another thread would no longer lead to crash.
+
+
+```csharp
+var copyA = A?.PropertyA;
+
+if (A is null || (copyA == SOME_CONSTANT && B))
+{
+   // some logic
+}
+```
+::: good
+Figure: Good example - Local copy to resolve race condition
+:::