Re: [PATCH v7 1/4] spinlock: A new lockref structure for locklessupdate of refcount

From: Linus Torvalds
Date: Sat Aug 31 2013 - 13:17:15 EST

On Fri, Aug 30, 2013 at 8:06 PM, George Spelvin <linux@xxxxxxxxxxx> wrote:
> Just noticing that you are adding several functions that return a boolean
> value as an int. And a "gotref" local variable.
> Is that just not wanting to bother with thse newfangled C99 innovations,
> or do you dislike the "bool" type for some reason?

I don't use "bool" in code I write. I don't think it adds any actual
value, and I think the data type is badly designed and of dubious
value in C. It has very few actual advantages.

That said, it's not like I *hate* the type, and I won't remove bool
from code other people write. I just think it's superfluous and
stupid, and another case of C++ people thinking too much "this is a
cool feature" without then actually doing it well. The C people then
picked it up because it was less onerous than some other C++ features,
and all the compilers had the logic anyway.

If "bool" had real advantages (like having a dense array
representation, for example), that would be one thing. It doesn't.
Sure, now you can take an address of a bool (which you couldn't
generally do efficiently if it really was a bit array), but it also
means that in practice, "bool" is normally nothing but "char" with
some really odd and special implicit type casting rules.

I doubt most people really even understand how "bool" casting works.

And bool is actually really *dangerous* to use if you don't understand
it. There are people who use "bool", but then because they want to be
portable, they have a compatibility #ifdef or other configuration
thing that does something like

typedef int bool;
#define true 1
#define false 0

and it will actually work. Most of the time. And then the semantic
differences from a _real_ C compiler that supports the C99 _Bool/bool
type are really really subtle.

IOW, bool has very few real upsides, and it has a real downside: it's
subtle, and people really never even seem to _realize_ just how subtle
it is. I suspect that if you ask ten random average C programmers if
the above is equivalent to stdbool.h, nine of them will say "sure".

And they'd be *COMPLETELY* wrong.

So no. I'm definitely not a fan of bool. I think there are better
types, and I think there are better ways to document things.

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