HP C/aC++ for PA-RISC Software manual OMP Barrier Pragma, OMP Critical Pragma, OMP for Pragma

The atomic directive ensures that a specific memory location is updated atomically, rather than exposing it to the possibility of multiple, simultaneous writing threads.

OMP BARRIER Pragma

#pragma omp barrier

The barrier pragma synchronizes all the threads in a team. When encountered, each thread waits until all the threads in the team have reached that point.

The smallest statement to contain a barrier must be a block or a compound statement. barrier is valid only inside a parallel region and outside the scope of for, section, sections, critical, ordered, and master.

OMP CRITICAL Pragma

#pragma omp critical [(name)] structured-block

The critical pragma identifies a construct that restricts the execution of the associated structured block to one thread at a time.

The name parameter is optional. All unnamed critical sections map to the same name.

OMP FOR Pragma

#pragma omp for [clause1,clause2, ...]

for-loop

where [clause1, clause2, ...] indicates that the clauses are optional. There can be zero or more clauses.

clause may be one of the following:

•private(list)

•firstprivate(list)

•lastprivate(list)

•ordered

•schedule(kind[,chunksize])

•nowait

See “OpenMP Clauses” (page 114) for more information.

OMP FLUSH Pragma

#pragma omp flush [(list)]

where (list) names the variables that will be synchronized.

The flush pragma, whether explicit or implied, specifies a cross-thread sequence point at which the implementation is required to ensure that all the threads in a team have a consistent view of certain objects in the memory. A flush directive without a list is implied for the following directives:

•barrier

•an entry to and exit from critical

•at entry to and exit from ordered

•at entry to and exit from parallel

•at entry to and exit from parallel for

•at entry to and exit from parallel sections

Other Pragmas 111