Let us describe here the solution we have adopted. This is really a first attempt, and there is definitely room for improvement. However, we believe that it provides reasonable capabilities for now, considering that NetSolve is still at an early stage of development. As we noted, we need to ship code over to the computational server. Since NetSolve works in a heterogeneous environment, it is not possible to migrate compiled code. Thus, we require that the user have his subroutine or function in a separate file, written either in C or Fortran. We send this file to the computational server. The server compiles it and is then able to use this user-supplied function.

The security implementation is quite simple. When compiling the user's function, we use the nm UNIX command to disallow any system call. The approach is very restrictive for the user, but typically the subroutine that has to be passed needs only to perform computations. If course, there are a lot of hacker ways to go around this problem, and our system currently does not pretend to be a real security manager. We are investigating Java to deal with this user-supplied function issue.