[PATCH] pthread_once hangs when init routine throws an exception [BZ #18435]

[Martin Sebor]

> I understand the purpose here, but I also think it's a bad design and
> not useful in portable code, which cannot make any assumptions about
> the underlying system objects used by the C++ standard library of even
> that "underlying" objects exist. I think the whole native_handle() API
> just encourages non-portable constructs and implementation lock-in
> that is harmful both to implementors (less freedom to improve) and
> applications (trapped by implementation-specific assumptions).

You're right, it does have that effect. It was a conscious
design choice made by the authors of the C++ threads library.
IIRC, some of the early design alternative included:

1) providing a rich set of functions that exposes the union of
    functionality of the underlying implementations; functions
    that don't have a native equivalent simply fail (the Rogue
    Wave Threads library does that)

2) providing a narrow interface (the C11 threads library takes
    this approach, though I don't think it precludes (3))

3) providing a narrow interface that exposes the common subset
    of functionality and give users a means to access the wrapped
    native objects

The challenge with (1) is that it can be difficult to both
specify and use portably because sometimes there are similar
underlying APIs but with subtle differences.

The problem with (2) is that it tends to be overly constraining
for non-trivial uses.

So C++ chose (3).

Martin