Re: thread-safety definition

[David Abrahams <dave@xxxxxxxxxxxxxxxxxxxx>]

Dave Butenhof <David.Butenhof@xxxxxx> writes:

> David Abrahams wrote:
>
>>Mathieu Lacage <Mathieu.Lacage@xxxxxxxxxxxxxxx> writes:
>>  
>>
>>>It looks like what everyone is trying to achieve here is a way for C++
>>> authors to write thread-safe libraries.    
>>>
>>I think you missed something, or maybe the main thing.  C++ authors
>>can already write thread-safe libraries.
>>
>>What I'm trying to achieve is to allow existing thread-safe library
>>code that wasn't written with POSIX cancellations in mind to be used
>>easily in a POSIX environment.
>>  
>>
> Right. And I maintain that this is trivial AS LONG AS you can
> guarantee that threads running that unsafe code will never be
> cancelled. (This seems reasonable, since obviously threads running
> that code had never previously been subject to cancellation!) And it's
> IMPOSSIBLE if you cannot guarantee that. 

Please don't shout, especially to emphasize something I disagree with
so fundamentally. ;-)

> The code must be analyzed and corrected, point by point; and the
> analysis (and possibly the correction as well) is easier if
> cancellation is a structured exception than if it's a return status
> handled in various "unique" ways by each routine.

If you make cancellations behave sufficiently like an ordinary C++
exception (either of Nathan's or Jason's models would do that I think)
then it's neither "IMPOSSIBLE" nor even difficult.  A great deal of
thread-safe exception-safe C++ library code would behave perfectly
well under those conditions.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com