Question about OpenSSL id_function() and pthreads

[Daniel Eischen]

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