PGI Fortran Reference manual - The Portland Group

OpenMP Directives for FortranUsageA master thread is a single thread of control that begins an OpenMP program and which ispresent for the duration of the program. In a parallel region of code, there may be a sub-region ofcode that should execute only on the master thread. Instead of ending the parallel region beforethis subregion and then starting it up again after this subregion, the MASTER... END MASTERdirective pair allows the user to conveniently designate code that executes on the master threadand is skipped by the other threads.‣ There is no implied barrier on entry to or exit from a master section of code.‣ Nested master sections are ignored.‣ Branching into or out of a master section is not supported.ExamplesExample of Fortran MASTER...END MASTER directivePROGRAM MASTER_USEINTEGER A(0:1)INTEGER omp_get_thread_numA=-1!$OMP PARALLELA(omp_get_thread_num()) = omp_get_thread_num()!$OMP MASTERPRINT *, "YOU SHOULD ONLY SEE THIS ONCE"!$OMP END MASTER!$OMP END PARALLELPRINT *, "A(0)=", A(0), " A(1)=", A(1)END8.7.8. ORDEREDThe OpenMP ORDERED directive allows the user to identify a portion of code within anordered code block that must be executed in the original, sequential order, while allowing parallelexecution of statements outside the code block.Syntax!$OMP ORDERED< Fortran code block executed by processor >!$OMP END ORDEREDUsageThe ORDERED directive can appear only in the dynamic extent of a DO or PARALLELDO directive that includes the ORDERED clause. The structured code block between theORDERED / END ORDERED directives is executed by only one thread at a time, and in theorder of the loop iterations. This sequentializes the ordered code block while allowing parallelexecution of statements outside the code block. The following additional restrictions apply to theORDERED directive:‣ The ordered code block must be a structured block.PGI Fortran Reference Guide 170