Task class

Andrew,

I don't know if this should work or not, but some questions...

What happens when you call Task_create()?  Do you get a NULL handle returned, or is an error thrown?  

When is the constructor calling Task_create() being invoked?  This needs to be after the Task module has been started up (within SYS/BIOS' module startup sequence) which usually happens before constructors are called during startup, before main().  But this can vary on some device families.  What device are you running on?

Scott

Right now this entire design is till in the concept stage.  I may move task creation to a member function of the class and invoke it when the system is ready.  I can't get the code to compile as it does not like the fact that the task function is a member function of a class.  I gotta fix that first, then I can move forward.  From what I've read you have to declare the function in an extern "C"  block.  I can't find an example so I'm poking around blind on how to do this.

Right now I have nothing carved in stone.  I have a concept in my head on how I would like a class to encapsulate a task.  I just gotta figure out how to do it.

Andrew,
can you post the complete error message? There are type checks for functions that you pass to Task_create, and extern "C" might not be enough to make the signature of taskFxn compatible. 

Hi

Member functions cannot have C linkage (C linkage specifications for member functions are simply ignored). You need to make taskFxn a global function, ideally static so that it is local to the translation unit (namespaces won't work). The idiomatic way is to pass a pointer to your class object as a "user" or "context" parameter, unless the callback mechanism doesn't provide such a parameter, in which case it is broken anyway. For tasks, you have two such parameters, "arg0" and "arg1", so you can choose "arg0":

class MyTask
{
    [...]
  public:
    void Run();
    [...]
};

extern "C" {
  void taskFxn(UArg arg0, UArg arg1)
  {
    MyTask *task = reinterpret_cast<MyTask*>(arg0);
    if(task)
    {
      task->Run();
    }
  }
}

You would then need to pass Task_Params to Task_create and set the arg0 member of that parameter struct to a valid pointer to a MyTask object.

Edwin McKay said:

Thanks this should help. Can I place the TSK_Create in the constructor of the MyClass? I am trying to mimic a Object Oriented OS that we used to use. We would simply derive from the Task Class and the virtual "run' function would be called. Or did place the TIBios call some place else?

That depends a lot on your use case. I don't think I would put the call into the constructor, for the following reasons:

1. If you compile without exception support, there's no way to report an error.
2. If you don't carefully restrict how instances of your task class are created, you might end up with temporaries calling TSK_Create.
3. You would be coupling your task abstraction to a concrete BIOS implementation, which may or may not be a bad thing.

I think I would apply the strategy pattern to provide the task with the platform-dependent functions, if I needed any.

In any case, you will have to pay close attention to lifetime management of the task object. If you can use shared_ptr (or some alternative implementation), that will probably make your task (no pun intended) easier.