Taskwait construct

Apart from implicit synchronization (task data dependences), OmpSs-2 also offers a mechanism that allow users to synchronize task execution. The taskwait construct is a standalone directive (with no code block associated) and specifies a wait on the deep completion of all descendant tasks, including the non-direct children tasks.

The syntax of the taskwait construct is the following:

#pragma oss taskwait [clauses]

The valid clauses for the taskwait construct are the following:

• on(list-of-variables): Specifies to wait only for the subset (not all of them) of descendant tasks that declared a dependency on any of the variables that appear on the list of variables.

The on clause allows to wait only on the tasks that produces some data in the same way as the inout clause. It suspends the current task until all previous tasks with any dependency on the expression are completed. The following example illustrates its use:

int compute1(void);
int compute2(void);

int main()
{
  int result1, result2;

  #pragma oss task out(result1)
  result1 = compute1();

  #pragma oss task out(result2)
  result2 = compute2();

  #pragma oss taskwait on(result1)
  printf("result1 = %d\n", result1);

  #pragma oss taskwait on(result2)
  printf("result2 = %d\n", result2);

  return 0;
}