Function ExecParallelCreateReaders

src/backend/executor/execParallel.c:874–894

* Set up tuple queue readers to read the results of a parallel subplan. * * This is separate from ExecInitParallelPlan() because we can launch the * worker processes and let them start doing something before we do this. */

 * worker processes and let them start doing something before we do this.
 */
void
ExecParallelCreateReaders(ParallelExecutorInfo *pei)
{
	int			nworkers = pei->pcxt->nworkers_launched;
	int			i;

	Assert(pei->reader == NULL);

	if (nworkers > 0)
	{
		pei->reader = (TupleQueueReader **)
			palloc(nworkers * sizeof(TupleQueueReader *));

		for (i = 0; i < nworkers; i++)
		{
			shm_mq_set_handle(pei->tqueue[i],
							  pei->pcxt->worker[i].bgwhandle);
			pei->reader[i] = CreateTupleQueueReader(pei->tqueue[i]);
		}
	}
}

/*
 * Re-initialize the parallel executor shared memory state before launching