Shared and private variables in a parallel environment
Some OpenMP clauses let you specify visibility context for selected
data variables. A brief summary of data scope attribute clauses are
listed below:
| Data scope attribute clause | Description |
|---|---|
| private | The private clause declares the variables in the list to be private to each thread in a team. |
| firstprivate | The firstprivate clause provides a superset of the functionality provided by the private clause. The private variable is initialized by the original value of the variable when the parallel construct is encountered. |
| lastprivate | The lastprivate clause provides a superset of the functionality provided by the private clause. The private variable is updated after the end of the parallel construct. |
| shared | The shared clause declares the variables in the list to be shared among all the threads in a team. All threads within a team access the same storage area for shared variables. |
| reduction | The reduction clause performs a reduction on the scalar variables that appear in the list, with a specified operator. |
| default | The default clause allows the user to affect the data-sharing attribute of the variables appeared in the parallel construct. |
For more information, see the OpenMP directive descriptions in Pragma directives for parallel processing in the XL C/C++ Compiler Reference. You can also refer to the OpenMP Application Program Interface Language Specification, which is available at http://www.openmp.org.
