2.6.3 barrier Directive

 

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The barrier directive synchronizes all the threads in a team. When encountered, each thread in the team waits until all of the others have reached this point. The syntax of the barrier directive is as follows:

#pragma omp barrier new-line  

After all threads in the team have encountered the barrier, each thread in the team begins executing the statements after the barrier directive in parallel. Note that because the barrier directive does not have a C language statement as part of its syntax, there are some restrictions on its placement within a program. See Appendix C for the formal grammar. The example below illustrates these restrictions.

/* ERROR - The barrier directive cannot be the immediate  
*          substatement of an if statement  
*/  
if (x!=0)  
   #pragma omp barrier  
...  
  
/* OK - The barrier directive is enclosed in a  
*      compound statement.  
*/  
if (x!=0) {  
   #pragma omp barrier  
}