Taskwait construct
==================
.. index:: taskwait

Apart from implicit synchronization (task data dependences), OmpSs-2 also offers a mechanism that allow users to synchronize task execution.
The ``taskwait`` construct is an stand-alone 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)``: It 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.

.. highlight:: c

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;
 }