Can changing a value from X to X in C++ lead to a data race?

No, changing a value from X to X in C++ does not inherently lead to a data race. A data race occurs when multiple threads access and potentially modify the same memory location concurrently without proper synchronization, and at least one of the accesses is a write operation.

In the case you mentioned, where the value is not changed (i.e., going from X to X), there is no write operation occurring, so there is no possibility of a data race.

However, if there are concurrent operations on the same memory location where at least one of the operations is a write, data races can occur. It's important to properly synchronize access to shared data in multithreaded scenarios using techniques like mutexes, atomic operations, or other synchronization primitives to prevent data races and ensure correct behavior.

Therefore, while changing a value from X to X itself does not lead to a data race, it's crucial to consider the broader context of concurrent access and modifications to shared memory in your code to ensure thread safety and avoid potential data race conditions.