Update cpp.md

Signed-off-by: Dennis Eichhorn <spl1nes.com@googlemail.com>

standards/cpp.md

@@ -161,6 +161,31 @@ void add_arrays(float* a, float* b, float* result, size_t size) {
 }
 ```
 
+### Locks vs lockless
+
+Locked version
+
+```c++
+pthread_mutex_t mtx = PTHREAD_MUTEX_INITIALIZER;
+int counter = 0;
+
+void increment_counter() {
+    pthread_mutex_lock(&mtx);
+    ++counter;
+    pthread_mutex_unlock(&mtx);
+}
+```
+
+Lockless version
+
+```c++
+atomic_int counter = 0;
+
+void increment_counter() {
+    atomic_fetch_add(&counter, 1);  // Atomic operation, no locking needed
+}
+```
+
 ### Cache line sharing between CPU cores
 
 When working with multi-threading you may choose to use atomic variables and atomic operations to reduce the locking in your application. You may think that a variable value `a[0]` used by thread 1 on core 1 and a variable value `a[1]` used by thread 2 on core 2 will have no performance impact. However, this is wrong. Core 1 and core 2 both have different L1 and L2 caches BUT the CPU doesn't just load individual variables, it loads entire cache lines (e.g. 64 bytes). This means that if you define `int a[2]`, it has a high chance of being on the same cache line and therfore thread 1 and thread 2 both have to wait on each other when doing atomic writes.