Re: [boost] [thread] RFC standard proposed mutex, read-write mutex, condition

From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2007-08-25 16:16:48

On Aug 25, 2007, at 3:10 PM, Peter Dimov wrote:

> Howard Hinnant:
>
>> I'm strictly looking at this from the client's point of view.  I'm  
>> the
>> client.  I know what I want, and I want to be able to pick something
>> and know what it does.  I don't want to be stuck with something that
>> maybe does something, and maybe not.  It's like buying something with
>> absolutely no warranty.
>
> No, I don't agree. This is like saying that if the car you bought  
> promises
> 40 MPG and delivers 45, you'd return it because it doesn't meet the  
> spec.
>
> Bad analogies aside, giving the implementation the opportunity to  
> check the
> assumptions of your code is not as worthless as you make it to be.  
> It does
> not just "add a bunch of undefined behavior", it adds a license for  
> the
> implementation to turn the already erratic behavior into a predictable
> assertion failure.
>
> If the client has used the mutex constructor, this means that his  
> code has
> already made the assumption that the condition will be used with  
> that mutex.
> If you take away the Requires clause (the "bunch of undefined  
> behavior"),
> this will not make the code any more correct and can never be an
> improvement; it would be, at worst, a tie if the implementation did no
> checking.

The main philosophical difference between us is that I want to be able  
to choose "check", and be assured that I'm actually getting checking.   
And then I want to be able to choose "don't check".  And then not have  
to pay for it.  I want both choices.

What I want:

std::condition<std::constrain<std::mutex>> cv(mut);  // I *know* that  
if I mix bindings, I will get some kind of noise

And then I want to be able to change that code:

// I *know* that I'm not paying for checking
std::condition<std::mutex> cv(mut);  // Either with or without the  
"mut", I don't care

With your proposal I write:

std::condition<std::mutex>> cv(mut);

and I don't know whether I have checking or not.  All I know is that  
I've given permission for the implementation to check.  And if I write:

std::condition<std::mutex>> cv;

Then I don't know that I'm not still paying for checking.

I want your (1) and (3).  Your (2) gives me neither, not both.

-Howard