/sys$common/syshlp/helplib.hlb FORTRAN, Logical Names, FOR$SPIN_WAIT  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  If defined during execution of a parallel processing application,
  this logical name controls the synchronization method used.  A
  value of 0 causes busy-waiting to be used, which maximizes
  synchronization response at the expense of wasted processor cycles.
  Positive values specify the number of busy-wait cycles to execute
  before relinquishing control of the processor.  The default is
  1000.  For more information, see the Compaq Fortran Performance Guide.