MPI and global variables

Question

I have to implement an MPI program. There are some global variables (4 arrays of float numbers and other 6 single float variables) which are first inizialized by the main pr

Answer 1

As the other answers say, that's not how MPI works. Data is unique to each process and must be explicitly transferred between processes using the API available in the MPI specification.

However, there are programming models that allow this sort of behavior. If, when you say parallel computing, you mean multiple cores on one processor, you might be better served by using something like OpenMP to share your data between threads.

Alternatively, if you do in fact need to use multiple processors (either because your data is too big to fit in one processor's memory, or some other reason), you can take a look at one of the Parallel Global Address Space (PGAS) languages. In those models, you have memory that is globally available to all processes in an execution.

Last, there is a part of MPI that does allow you to expose memory from one process to other processes. It's the Remote Memory Access (RMA) or One-Sided chapter. It can be complex, but powerful if that's the kind of computing model you need.

All of these models will require changing the way your application works, but it sounds like they might map to your problem better.