2.2 Input/Output

In the parallel context, there are several limitations on open files. First, several threads may run on one processor, so Fortran Logical Unit Numbers are shared by all the threads on a processor. Second, open files are left behind when a thread migrates to another processor--it is a crashing error to open a file, migrate, then try to read from the file.

Because of these restrictions, it is best to open files only when needed, and close them as soon as possible. In particular, it is best if there are no open files whenever you make blocking calls.