Re: [boost] Boost.Threads, N2178, N2184, et al

From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2007-03-26 17:26:44

> On Mar 26, 2007, at 2:04 PM, Peter Dimov wrote:
>
>> Howard Hinnant wrote:
>>
>>> Fair point.  Perhaps we should go back to a more fundamental
>>> question:
>>>
>>> std::thread t(f);
>>> ...
>>> t.cancel();  // Logically is this a const or non-const operation on
>>> the thread executing t/f?
>>
>> I prefer to first ask "does it matter"? If you can't observe the
>> cancelation
>> state of t and if you are assured that t.cancel is valid no matter
>> what else
>> is going on with t, what difference does a const/non-const label
>> make to the
>> external observer?
>>
>> (Internally there is a flag being set, of course.)
>
> I believe it matters because other threads can detect whether the
> child thread has been canceled or not.  Canceled may be a valid
> state.  But it is a different and detectable state.

Perhaps shared_ptr/weak_ptr is a good analogy. I can have shared_ptr<int 
const>, and if this is the last reference to expire it'll delete the int 
(despite that mutable operations on the int are disallowed.) I can also have 
a weak_ptr<int const> to the same object, and I can detect the fact that it 
has been destroyed. Yet the object has no "destroyed" state.

Emil Dotchevski