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

From: Howard Hinnant (hinnant_at_[hidden])
Date: 2007-08-22 14:13:24

On Aug 22, 2007, at 12:49 PM, Peter Dimov wrote:

> Howard Hinnant wrote:
>
>> Vendor C, with the best of intentions, decides that the release build
>> of the std::lib should contain this checking (std::lib vendors
>> including debug checks in release builds should sound familiar to  
>> many
>> of you).  Now we have goal #3, but have lost goal #1, and there is no
>> wrapper we can use to get it back.
>>
>> How do we prevent, or at least discourage, Vendor C from taking this
>> path?
>
> Shouldn't Vendor C be allowed this freedom? If its customers prefer  
> paying
> the price of a pointer in exchange for the ever-present checks, why  
> should
> the vendor be prevented from delivering the product they want? We can
> explain the rationale for the design and our suggested  
> implementation in
> non-normative notes and let the vendors make the informed decision.

Today I don't use list::size() in portable code.  Why?  Because we  
gave the vendor too much freedom.

Being a vendor myself, I appreciate vendor freedom.  But I try to  
recognize where the line is between vendor freedom, and the client's  
ability to use the library.

If it comes to pass that std::condition<std::mutex> (or some unchecked  
variant) sometimes has a size penalty over the native condition  
variable, I will write shared_mutex/upgrade_mutex in terms of  
pthread_cond_t and pthread_mutex_t instead of the code shown here:

    http://home.twcny.rr.com/hinnant/cpp_extensions/shared_mutex

class shared_mutex
{
     typedef mutex mutex_t;
     typedef condition<unchecked<mutex_t>> cond_t;

     mutex_t  mut_;
     cond_t   gate1_;
     cond_t   gate2_;
     unsigned state_;
    ...

I've already done it (just to explore the consequences).  It isn't  
pretty.  But clients of shared_mutex don't care how messy it is to  
implement.  Only I, the maintainer of that code care.  And the  
client's concerns trump my own.

When we get to the point that I won't eat my own dog food, goal #1 is  
lost.

-Howard