[Xenomai] C++ std::thread and xenomai pthread

Jeff Webb jeff.webb at nta-inc.net
Thu Aug 14 23:01:47 CEST 2014


On 08/14/2014 02:27 PM, Matthew Lindner wrote:
> Can you elaborate? Did you check to see if it was using xenomai
> pthreads and was staying in primary mode?

It's been a while since I wrote the code, so it's hard for me to remember the details.  This is why I was reluctant to say more.  I have used the code quite a bit since then, so I am confident it works fine, but I haven't needed to look at the implementation in a while.

Yes, I made sure it was using Xenomai pthreads, stayed in primary mode, and the latency measurements were good.  I don't remember whether creating a std::thread using one of the class constructors works as expected, but I use a factory function, since I usually want to create threads with POSIX scheduling attributes anyway.  In my applications, I usually do something like this:

   std::thread rt_thread(posix_util::create_thread(
                         mq_test, SCHED_FIFO, 16));
   rt_thread.join();

I won't include all of the details here, but it looks like the tricky part goes something like this:

inline
std::thread create_thread(std::function<void()> const& f)
{
     std::thread t;
     auto pthread_t_ptr = (pthread_t*)(void*)(&t);
     *pthread_t_ptr = create_pthread(f);
     return t;
}

The sequence is this:

   1) A dummy std::thread object is created.
   2) The create_pthread function then uses pthread_create to make a standard pthread and return it.
   3) The std::thread object is modified to use the standard pthread object.
   
So, this does not answer the question of whether recompiling libstdc++ is necessary because I use pthread_create instead of the class constructor.  Perhaps the class constructor did not work because of the recompilation issue and that is another reason for this approach -- I'm not sure.

That's about all I can add at this point -- you can do some experiments to see how things work for yourself.  I hope this helps.

-Jeff





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