VikingCoder on In the C++ bag of tricks: scoped locks

Comment on In the C++ bag of tricks: scoped locks

You're also consuming the variable name i, which everyone else is probably using.

Speaking of which, this means you can't have one of your locks scoped inside another one.

Solvable by creating a Preprocessor macro which creates a unique and complex-named identifier.

  #define LOCKED(lk) for(int UNIQUE_ID=0; UNIQUE_ID<1 && !lk_lock(lk); lk_unlock(lk), UNIQUE_ID++)

Use __LINE__ to help make the id unique.

VikingCoder 12y

Then you still can't forget and do this:

    lock(lk_var) lock(lk_var2)
    {
        lk_var = lk_var2;
    }

Or this:

    lock(lk_var) { lock(lk_var2 { lk_var = lk_var2; } }

Using the pre-processor to solve a regular, every day, hum-drum, solved-a-billion-times RAII problem is bad news.

JoeAltmaier 12y

SUre you could. The{} make it work.

VikingCoder 12y

EDIT: I sit corrected. My post is wrong.

No, you can't, and no they don't.

    lock(lk_var) {
        lock(lk_var2) {
            var = var2;
        }
    }

That expands to:

    for(int i=0; (i < 1) && !lk_lock(lk_var); lk_unlock(lk_var), i++)
    {
        for(int i=0; (i < 1) && !lk_lock(lk_var2); lk_unlock(lk_var2), i++)
        {
            var = var2;
        }
    }

You end up with an i scoped inside another i.

plorkyeran 12y

C++ has variable shadowing, so that works correctly.

    for (int i = 0; i < 5; ++i) {
        for (int i = 0; i < 5; ++i) {
            printf("hello\n");
        }
    }

prints hello 25 times.

VikingCoder 12y

Oh right. My brain was stuck in another language. Wow, I forgot how much I'd forgotten about C++.

JoeAltmaier 12y

Actually that's just C (name nesting)

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