PGI Fortran Reference manual - The Portland Group

OpenMP Directives for FortranUsageThe ATOMIC directive is semantically equivalent to enclosing the following single statement ina CRITICAL / END CRITICAL directive pair.The statements must be one of the following forms:x = x operator exprx = expr operator xx = intrinsic (x, expr)x = intrinsic (expr, x)where x is a scalar variable of intrinsic type, expr is a scalar expression that does not referencex, intrinsic is one of MAX, MIN, IAND, IOR, or IEOR, and operator is one of +, *,-, /, .AND., .OR., .EQV., or .NEQV..8.7.2. BARRIERThe OpenMP BARRIER directive defines a point in a program where each thread waits for allother threads to arrive before continuing with program execution.Syntax!$OMP BARRIERUsageThere may be occasions in a parallel region when it is necessary that all threads complete workto that point before any thread is allowed to continue. The BARRIER directive synchronizes allthreads at such a point in a program. Multiple barrier points are allowed within a parallel region.The BARRIER directive must either be executed by all threads executing the parallel region or bynone of them.8.7.3. CRITICAL ... END CRITICALThe CRITICAL...END CRITICAL directive requires a thread to wait until no other thread isexecuting within a critical section.Syntax!$OMP CRITICAL [(name)]< Fortran code executed in body of critical section >!$OMP END CRITICAL [(name)]UsageWithin a parallel region, there may exist subregions of code that will not execute properly whenexecuted by multiple threads simultaneously. This issue is often due to a shared variable that iswritten and then read again.PGI Fortran Reference Guide 165