Any C code that may need to be used in a threaded context should use this macro should to prevent
Fortran code being run simultaneously in two separate threads, with consequent danger of
unsynchronised memory access. The macro locks the global CNF mutex, then executes the code
specified in the argument, and then unlocks the mutex. If the mutex is currently locked by another
thread (e.g. due to the use of F77_LOCK in the other thread), then the calling thread blocks
until the other thread releases the mutex.
Any arbitrary C code. Typically, this will be an invocation of a Fortran subroutine.
F77_LOCK( result = F77_CALL(sim)( nel, data, status ); )
macro invokes the cnfLock and cnfUnlock functions to lock and unlock the global mutex.