holoskii / rendering Goto Github PK

In several places atomics are incremented with code like this:

finishedPixels.store(finishedPixels.load() + 1);

This is not atomic, it's three separate statements (read, modify, write). Consider what happens if you have two threads modifying the same variable:

1. Thread 1 calls finishedPixels.load() and reads (for example) the value 2
2. Thread 2 also calls finishedPixels.load() and also reads 2
3. Thread 1 increments the value to 3 and calls finishedPixels.store(3)
4. Thread 2 increments the value to 3 and also calls finishedPixels.store(3).

The value is now 3 instead of the expected 4, just as if you had used a plain non-atomic variable - this is what atomic operations exist to avoid.

std::atomic overloads the ++ and -- operators, so you can increment/decrement your values as one unsplittable (-> atomic) operation.