Language Reference

SMP and Thread-Safing Directives

The XL Fortran compiler provides a compiler option, -qsmp=auto, which instructs the compiler to automatically parallelize Fortran DO loops. This includes both DO loops coded explicitly by the user and DO loops generated by the compiler for array language constructs (for example, loops generated by WHERE, FORALL, and for array assignment). However, the compiler will only automatically parallelize loops that are independent; that is, loops whose iterations can be computed independently of any other iteration.

While automatic parallelization will be sufficient for some users, the SMP and thread-safing directives give you the option of providing additional information about the source code to the compiler. The compiler will use information given to it either during automatic parallelization, or to determine that certain parts of the program should be parallelized. For example, the PARALLEL DO directive specifies that the DO loop that is immediately following it should be run in parallel.

In XL Fortran these are the SMP and thread-safing directives that you can use:

• Assertive. These directives provide information to the compiler about the source code that the compiler would not necessarily be able to determine on its own.
  • ASSERT - See ASSERT
  • CNCALL - See CNCALL
  • INDEPENDENT - See INDEPENDENT
  • PERMUTATION - See PERMUTATION
• Prescriptive. These directives instruct the compiler that it should apply some transformation to your code.
  • ATOMIC - See ATOMIC
  • BARRIER - See BARRIER
  • CRITICAL - See CRITICAL / END CRITICAL
  • DO (work-sharing) - See DO / END DO
  • DO SERIAL - See DO SERIAL
  • FLUSH - See FLUSH
  • MASTER - See MASTER / END MASTER
  • ORDERED - See ORDERED / END ORDERED
  • PARALLEL - See PARALLEL / END PARALLEL
  • PARALLEL DO - See PARALLEL DO / END PARALLEL DO
  • PARALLEL SECTIONS - See PARALLEL SECTIONS / END PARALLEL SECTIONS
  • PARALLEL WORKSHARE - See PARALLEL WORKSHARE / END PARALLEL WORKSHARE
  • SCHEDULE - See SCHEDULE
  • SECTIONS - See SECTIONS / END SECTIONS
  • SINGLE -- See SINGLE / END SINGLE
  • WORKSHARE - See WORKSHARE
• Thread-safing. These directives allocate thread-specific variables and COMMON areas at run time.
  • THREADLOCAL - See THREADLOCAL
  • THREADPRIVATE - See THREADPRIVATE