Date: Wed, 28 May 2003 20:46:26 -0400 (EDT) From: Daniel Eischen <eischen@pcnet.com> To: Craig Rodrigues <rodrigc@attbi.com> Cc: freebsd-threads@freebsd.org Subject: Re: Question about OpenSSL id_function() and pthreads Message-ID: <Pine.GSO.4.10.10305282038470.5688-100000@pcnet5.pcnet.com> In-Reply-To: <20030529003416.GA3712@attbi.com>
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On Wed, 28 May 2003, Craig Rodrigues wrote:
> On Wed, May 28, 2003 at 08:07:24PM -0400, Daniel Eischen wrote:
> > > I have some third party C++ code which tries to implements this function:
> > >
> > > static unsigned long
> > > idFunction()
> > > {
> > > #ifdef _WIN32
> > > return static_cast<unsigned long>(GetCurrentThreadId());
> > > #else
> > > return static_cast<unsigned long>(pthread_self());
> > > #endif
> > > }
> > >
> > >
> > > This code does not compile on FreeBSD-CURRENT:
> > >
> > > OpenSSLPluginI.cpp: In function `long unsigned int idFunction()':
> > > OpenSSLPluginI.cpp:151: invalid static_cast from type `pthread*' to type `long
> > > unsigned int'
> >
> > I don't know C++ well (much at all). What does static_cast do?
>
>
> static_cast, unlike C style casts, have restrictions which can
> result in compile-time errors.
>
> The full definition of static_cast is here:
> http://www.csci.csusb.edu/dick/c++std/cd2/expr.html#expr.static.cast
>
> A static_cast *cannot* convert a pointer type to an integral type
> (unsigned long), and will result in a compile time error.
To quote M. Warner Losh in a very recent thread ;-), "you lose".
> > The error message makes it look as if you are converting
> > a "pthread" * to "long unsigned int". Don't you just
> > want "unsigned long" instead?
>
> This function needs to return a unique numeric identifier
> based on a thread. pthread_self() returns a type of pthread_t.
> On Linux (where this code was written), pthread_t is:
>
> typedef unsigned long int pthread_t;
>
> So that is why this 3rd party code compiles and works fine on Linux.
>
> Obviously, this is not true on FreeBSD. The fact that
> this code relies on pthread_t being an integer type is bogus,
> but that's what you get for using 3rd party code. :)
Make an external function (in C) that converts the pthread_t
for you and use that to convert it.
This is a standards question, but is there a reason why
pthread_t can't be a pointer? We can always change the
thread libraries, but that would be a version bump and
doesn't help you right now.
--
Dan Eischen
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