From 8a83338769fa9c7c4c2588c1bd6178b62b5eaef4 Mon Sep 17 00:00:00 2001
From: Andrew Noyes <andrew@weaselab.dev>
Date: Sat, 23 Aug 2025 09:02:45 -0400
Subject: [PATCH] Add "force concurrent execution" to style guide

---
 style.md | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

diff --git a/style.md b/style.md
index 03d489a..145b844 100644
--- a/style.md
+++ b/style.md
@@ -417,6 +417,27 @@ TEST_CASE("Server accepts connections") {
   - `std::latch`, `std::barrier`, futures/promises
   - RAII guards and resource management
 
+### Multithreading Test Correctness
+- **Force concurrent execution** - Thread creation takes time, so work often completes sequentially before threads start
+- **Use std::latch to synchronize thread startup** - Ensures all threads begin racing simultaneously
+```cpp
+// BAD: Race likely over before threads start
+std::atomic<int> counter{0};
+for (int i = 0; i < 4; ++i) {
+  threads.emplace_back([&]() { counter++; }); // Probably sequential
+}
+
+// GOOD: Force threads to race simultaneously
+std::atomic<int> counter{0};
+std::latch start_latch{4};
+for (int i = 0; i < 4; ++i) {
+  threads.emplace_back([&]() {
+    start_latch.count_down_and_wait(); // All threads start together
+    counter++; // Now they actually race
+  });
+}
+```
+
 ---
 
 ## Build Integration