OpenMP Directives

PARALLEL Region Construct

Purpose:

A parallel region is a block of code that will be executed by multiple threads. This is the fundamental OpenMP parallel construct.

Format:

Fortran	!$OMP PARALLEL [clause ...] IF (scalar_logical_expression) PRIVATE (list) SHARED (list) DEFAULT (PRIVATE \| FIRSTPRIVATE \| SHARED \| NONE) FIRSTPRIVATE (list) REDUCTION (operator: list) COPYIN (list) NUM_THREADS (scalar-integer-expression) block !$OMP END PARALLEL
C/C++	#pragma omp parallel [clause ...] newline if (scalar_expression) private (list) shared (list) default (shared \| none) firstprivate (list) reduction (operator: list) copyin (list) num_threads (integer-expression) structured_block

Fortran

!$OMP PARALLEL [clause ...] 
               IF (scalar_logical_expression) 
               PRIVATE (list) 
               SHARED (list) 
               DEFAULT (PRIVATE | FIRSTPRIVATE | SHARED | NONE) 
               FIRSTPRIVATE (list) 
               REDUCTION (operator: list) 
               COPYIN (list) 
               NUM_THREADS (scalar-integer-expression)

   block

!$OMP END PARALLEL

C/C++

#pragma omp parallel [clause ...]  newline 
                     if (scalar_expression) 
                     private (list) 
                     shared (list) 
                     default (shared | none) 
                     firstprivate (list) 
                     reduction (operator: list) 
                     copyin (list) 
                     num_threads (integer-expression)

 
   structured_block

Notes:

When a thread reaches a PARALLEL directive, it creates a team of threads and becomes the master of the team. The master is a member of that team and has thread number 0 within that team.
Starting from the beginning of this parallel region, the code is duplicated and all threads will execute that code.
There is an implied barrier at the end of a parallel section. Only the master thread continues execution past this point.
If any thread terminates within a parallel region, all threads in the team will terminate, and the work done up until that point is undefined.