omp critical

Syntax

structured-block

Arguments

Description

When this the omp critical pragma is used, a thread waits at the beginning of a critical section until no other thread in the team is executing a critical section having the same name. All unnamed critical sections are considered to have the same unspecified name.

Critical section names are global entities of the program.

The following example shows a queuing model in which a task is removed from the queue. To guard against multiple threads removing the same task from the queue, the operation to remove the task is placed in a critical section. Because there are two independent queues in this example, each queue is protected by these pragmas having different names, xaxis and yaxis, respectively:

#include <omp.h>
int dequeue(work_queue *a);
void work(int i, work_queue *a);

void critical_example(work_queue *x, work_queue *y) {
  int ix_next, iy_next;

  #pragma omp parallel shared(x, y) private(ix_next, iy_next) {
    #pragma omp critical (xaxis)
    ix_next = dequeue(x);
    work(ix_next, x);

    #pragma omp critical (yaxis)
    iy_next = dequeue(y);
    work(iy_next, y);
  }
}