HI Stavros,

Maybe the answer for your question is what do you mean by "real time". In computing science "Real time" mean that a task had to answers to an external signal, like in embeded robotics system, as soon as possible. In that context, the kernel is one of an important element while he has to be preemptible.

In that case Fortran is still a very used langage. that evolve regulary.C++ is an object oriented langage that manipulate abstractions and need for that a good training. It's also a complex langage that to be warned specificaly with the pointers.

Here at INRA MetaGenoPolis we use delphy an object pascal strongly typed.

Personnaly I use C++ because I write code in C++ since 1986, and notabily for a real time kernel. but I have also written a real time kernel in pascal.

So to conclude :

• will my program be distributed ;
• what langage I controle better ;
• Is the kernel that will support your programs real time with premption.

Sincerely.

Pierre Léonard

  C was developed as a language to write an operating system: UNIX.  Due to that it had to handle signals, and have an interrupt handler.  That is likely what is meant.

  Fortran does not have a user definable interrupt handler, however, since the Fortran 2003 standard, Fortran has a defined way to call C routines.  Because of this, one can write the main body of the program in Fortran, and define the signal handling in a C routine.  

  I have often mixed languages when the two languages were better at different part of the problem. 

  It is possible that the people who have espoused this either only know one of the languages, or feel programs have to be written in a single language, perhaps from a support perspective.  You probably should ask them what they feel the deficiencies are.  (Maybe there is not a Fortran compiler for the real-time systems they are targeting, for example automotive sensors.  That would certainly be a convincing argument.)

Salut Pierre et merci pour ta reponse

My understanding about kernel architecture and their operations is poor. I can only express my need from a programmer's point of view and less from the machine point of view. But here's an example of what I think you are expressing in your comments, found on rt.wiki.kernel.org. If kernel code is executing when some event takes place that requires a high priority thread to start executing, the high priority thread can not preempt the running kernel code, until the kernel code explicitly yields control. In the worst case, the latency could potentially be hundreds milliseconds or more. What we'd want in a real-time system is for the kernel to be able to voluntarily yield control to a higher priority task waiting to execute thus minimising latency. Our real-time latency including the computational burden can't exceed some seconds from the moment that the outside data set is received till the moment our outcomes in the form of messages are transmitted to the remote user. In our case fortran is very good for handling the computational part . But it is only a feeling that I need to establisherd factually, that C/C++ handle better the flow and distribution of real-time data with a small as possible latency. But why?

It really depends on which level you are programming. If you are running your software on a hardware directly without any OS in between (or even if you are using any sort of embedded system) there are parts where you need to control the hardware directly. For this you need access to actual memory addresses. C (and C++) provide this through pointers. Although Fortran has a concept of pointers this is not equivalent to C pointers. In Fortran pointers cannot  be used to control the hardware.

So, depending on how close you need to get to the hardware Fortran cannot solve all you problems. You will need some sort of a system programming language like C, and sometimes even a few lines of assembler. C or C++ can give you comparable performance to Fortran if you are using it right. But, it is a lot easier to get bad performance with C and C++ than it is with Fortran. If you are a lot more comfortable with Fortran you should do your computation with it and only use another language where this is really necessary.

Hi James,

As said by me and Simon the most important is the kernel , OS, whatever you name it and it's capacity to stop a task in order to start a new task if that last have a higher priority.

If Stravos had, for example an vrtx OS (real time), the last question is what are the langage available with the SDK.

And for a kernel you can use other langage than C for example Pascal in 1983, we wroten a complete UNIX V7 and after SIII in pascal.

And finally there is an important aspect to see that is the facility to write a program in a langage and you can find some scaling with the cocomo software

Pierre Léonard

Thank you guys.

This is really very valuable input.