On 21/12/2016 08:20, Gedare Bloom wrote:
I haven't fully understood the distinction. I get that C11 are individually (and collectively) smaller. I don't entirely get what is their time-space tradeoff or when they are less desirable.
There are a few advantages to self-contained resources like mutexes for an API like C11 and POSIX.
1. All major POSIX implementations work this way. The libstdc++ code base assumes it, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78677. The standard does say POSIX create calls can return an error however it seems to be assumed this does not happen. A change in RTEMS brings us closer to the major implementations in this regard.
2. Performance. Sebastian's work with LibBSD, which is documented in the recent v3 SMP report highlighted the cost in the object look up in various hot parts of the kernel. This alone is a significant piece of data.
3. Deterministic resourcing. If you can link an application and it fits in memory the resource is allocated. There is no need to account and adjust a configuration parameter in another area of the system. This combines well with function section linking where we only have the referenced code in the target executable which means only the referenced resources are included.
4. Self-contained objects help dynamic loaded resource configuration. You do not know what can or could be loaded dynamically and how resources may be used or shared. A central base image configuration leads to possible conflicts in resource allocation. The unlimited patch back in the mid-90's was one solution to this problem, self-contains objects is another.
I would like to see a table that compares/contrasts these in a simple way to evaluate. I will try to look closely at these different approaches in a few weeks.
I hope the list above helps. Chris _______________________________________________ devel mailing list devel@rtems.org http://lists.rtems.org/mailman/listinfo/devel
