Loops in Subroutines

• Orphan1 (source):
  main program: "time loop", not parallel
  loops in smooth_x/smooth_y can be parallelised
  large overhead: fork/join in every call
• Orphan2 (source):
  create threads once with PARALLEL block around time loop

  • all threads execute this loops
  • index variable t private by default
  DO in subroutines for distribution of loop iterations

  • not lexically inside a PARALLEL directive ("orphaned")
  • already created threads are used
  • synchronisation of threads (implicit barrier) at END DO
• Orphan3 (source):
  END DO NOWAIT : no barrier at the end of DO
  can be used to reduce thread waiting times
  Warning: erroneous in our example (even if used only for one loop)!
  explicit synchronisation: BARRIER
• Orphan4 (source):
  commands executed by only one thread:

  • SINGLE / END SINGLE
  all threads wait at the end
  simultaneous prints by several threads ok, but output may be scrambled