Re: [c++-pthreads] Re: I'm Lost

[Kevlin Henney <kevlin@xxxxxxxxxxxxx>]

In message <42E7709F.AE07F97A@xxxxxx>, Alexander Terekhov 
<terekhov@xxxxxx> writes
> Wil Evers wrote:
> [...]
> > I'd say it's time to face the truth, which is that POSIX cancellation
> > semantics are incompatible with commonly established C++ coding
> > practices.
>
> It's incompatible with cancel-unaware C++ code. Note that it's
> incompatible with cancel-unaware C code as well, but that didn't
> stop POSIX and ongoing creation of cancel-safe code in both C
> and C++ languages. Very many tons of cancel-safe code.

To the best of my knowledge there have been zero lines of cancel-safe 
C++ code written against the C++ binding of POSIX threads.

Of course, C and C++ have an intimate relationship, but that does not 
mean to say that they are the same or that C++ must slavishly follow the 
same model that C has decided on. There is a question of 
interoperability, but that is not the same as portability. The 
discussion so far seems to have taken the latter view, which is subtly 
different.

If the C++ binding chooses to throw exceptions for cancellation, no C++ 
code will be broken by silent changes. Code written in C++ that is 
correct against the C binding will continue to be correct against that 
binding. But should the program be modified to take advantage of a C++ 
binding, that guarantee no longer holds. However, this is unsurprising 
and is to be expected of any migration between APIs. Of course, it makes 
sense to minimise gratuitous differences, but minimal difference is not 
the same as no difference.

Kevlin
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