lock(Mutex,Function) -- make a function thread-safe

This function creates a thread-safe version of f. In particular, it takes a mutex and returns a new function that locks it when the function is called and unlocks it when complete, even if there is an error.

If mutex is omitted, then a mutex is created behind the scenes. Therefore, it's only necessary to define mutex before calling lock if you plan on sharing it between multiple functions.

Consider the following example.

You likely see that x ended up less than the expected value of 1000. This is an example of a race condition, as multiple threads were trying to modify the global variable x at the same time.

Let's try again using lock.