OpenMP pragmas and options

The OMP_PARALLEL pragma defines a parallel region, which is a region of the program that is executed by multiple threads in parallel.This is the fundamental construct that starts parallel execution.

Syntax

#pragma OMP PARALLEL [clause1, clause2...] new-line structured block

where [clause1, clause2...] indicates that the clauses are optional. There can be zero (0) or more clauses, where clause may be one of the following:

The following clauses are not currently supported in this initial release of the OMP PARALLEL pragma for HP C.

The OMP FOR pragma for HP C identifies a construct that specifies a region in which the iterations of the associated loop should be executed in parallel. The iterations of the loop are distributed across threads that already exist.

This initial release of OMP FOR in the HP C compiler only supports static scheduling. In the case of multiple schedule clauses, the first clause is considered and the rest are silently ignored.

Syntax

#pragma OMP FOR [clause1,clause2...] newline
for-loop

where [clause1, clause2...] indicates that the clauses are optional. There can be zero (0) or more clauses, where clause may be one of the following:

	NOTE: chunksize should be an integer constant. Expressions in the place of chunksize are not currently supported.

The following clauses are not currently supported in this initial release of the OMP FOR pragma for HP C.

The OMP SECTION/SECTIONS pragmas identify a construct that specifies a set of constructs to be divided among threads in a team. Each section is executed once by a thread in the team.

Syntax

#pragma OMP SECTIONS [clause1, clause2...]new-line
{
#pragma OMP SECTION new-line
structured-block
#pragma OMP SECTION new-line
structured-block
.
.
.
}

where [clause1, clause2...] indicates that the clauses are optional. There can be zero (0) or more clauses, where clause may be one of the following:

The following clauses are not currently supported in this initial release of the OMP SECTION/SECTIONS pragmas for HP C.

The OMP PARALLEL FOR pragma for HP C is a shortcut for an OMP PARALLEL region that contains a single OMP FOR pragma.

Syntax

#pragma OMP PARALLEL FOR clause1,clause2... new-line
for-loop

OMP PARALLEL FOR admits all the allowable clauses of the OMP PARALLEL pragma and the OMP FOR pragma. The PRIVATE clause is supported.

The OMP PARALLEL SECTIONS pragma for HP C is a shortcut for specifying a parallel region containing a single OMP SECTIONS pragma.

Syntax

#pragma OMP PARALLEL SECTIONS [clause1, clause2...]new-line
{
[ #pragma OMP SECTION new-line
structured-block
[#pragma OMP SECTION new-line
structured-block
.
.
.
}

OMP PARALLEL SECTIONS admits all the allowable clauses of the OMP PARALLEL pragma and the OMP SECTIONS pragma. The PRIVATE clause is supported.

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

Syntax

#pragma OMP CRITICAL [(name)] new-line
structured-block

The critical section name parameter is optional. All unnamed critical sections globally map to a single name; this is provided by the HP C compiler.

The OMP_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.

Syntax

#pragma OMP BARRIER new-line

The smallest statement to contain a barrier must be a block or a compound statement. OMP BARRIER is valid only inside a parallel region and outside the scope of a OMP FOR, OMP SECTION/SECTIONS, OMP CRITICAL, OMP ORDERED, and OMP MASTER.

The OMP ORDERED pragma indicates that the following structured block should be executed in the same order in which iterations would be executed in a sequential loop.

Syntax

#pragma OMP ORDERED new-line
structured-block

The OMP ORDERED pragmas must be called within theOMP FOR and/or OMP PARALLEL FOR loops.

The OMP MASTER pragma for HP C directs that the structured block following it should be executed by the master thread(thread 0) of the team.

Syntax

#pragma OMP MASTER new-line
structured block

Other threads in the team do not execute the associated statement.