Subj : Re: pthread function behavior in C++ program
To   : comp.programming.threads
From : David Butenhof
Date : Fri Jun 10 2005 10:58 am

wij@seed.net.tw wrote:
> Torsten Robitzki wrote:
> 
>>...
>>I used "NPTL C++ cancellation" to search on google and the
>>results looks very promising.
> 
>  Now as understood, can I discard the use pthread_cleanup_push/pop in
> C++ codes?

POSIX specifically defines pthread_cleanup_push and pthread_cleanup_pop 
as a C construct that may not be appropriate for any other language 
binding. In particular, we expected (and would have liked to have 
required) that any language that implements real exceptions use the 
builtin mechanisms (e.g., C++ destructors and catch) instead of this C 
language hackery.

HOWEVER, as POSIX does not actually provide any C++ language binding, it 
can't say either whether you need those operations or whether they're 
supported. That is, you cannot write portable C++ threaded code that 
either uses them or does not. If you do, it might not work on some 
platforms. If you DON'T, it might not work on some platforms.

Similarly, as C++ says nothing about threads, you're left in a dark and 
sticky corner where any answer is entirely not just platform but release 
specific.

If you expect to be working exclusively with a C++ implementation that 
exposes cancellation as exceptions, then you definitely should use the 
native C++ mechanisms instead of pthread_cleanup_push/pop. On some 
implementations (e.g., Tru64 UNIX and OpenVMS), the C macros won't even 
work correctly (or possibly at all) from C++ (they're based language 
extensions to integrate with the native platform exceptions that the C++ 
compiler doesn't support).

Otherwise... you're best off completely avoiding cancellation in C++, if 
you can. If you can't, be really careful about determining what actually 
works, and why, on the platforms you need.

-- 
Dave Butenhof, David.Butenhof@hp.com
HP Utility Pricing software, POSIX thread consultant
Manageability Solutions Lab (MSL), Hewlett-Packard Company
110 Spit Brook Road, ZK2/3-Q18, Nashua, NH 03062

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