Function ExecSquelchShareInputScan

src/backend/executor/nodeShareInputScan.c:620–679

* This is called when the node above us has finished and will not need any more * rows from us. */

 * rows from us.
 */
void
ExecSquelchShareInputScan(ShareInputScanState *node, bool force)
{
	EState	   *estate = node->ss.ps.state;
	ShareInputScan *sisc = (ShareInputScan *) node->ss.ps.plan;
	shareinput_local_state *local_state = node->local_state;

	if (node->ss.ps.squelched)
		return;

	/* clean up tuple table */
	ExecClearTuple(node->ss.ps.ps_ResultTupleSlot);

	/*
	 * If this ShareInputScan is shared within the same slice then its
	 * subtree may still need to be executed and the motions in the subtree
	 * cannot yet be stopped. Thus, don't recurse in this case.
	 *
	 * In squelching a cross-slice ShareInputScan writer, we need to ensure
	 * we don't block any reader on other slices as a result of not
	 * materializing the shared plan.
	 *
	 * Note that we emphatically can't "fake" an empty tuple store and just
	 * go ahead waking up the readers because that can lead to wrong results.
	 */
	if (sisc->cross_slice && node->ref)
	{
		if (currentSliceId == sisc->producer_slice_id || estate->es_plannedstmt->numSlices == 1)
		{
			/*
			 * We are the producer. If we haven't materialized the tuplestore
			 * yet, we need to do it now, even though we won't need the data
			 * for anything. There might be other consumers that need it, and
			 * they will hang waiting for us forever otherwise.
			 */
			if (!local_state->ready)
			{
				elog((Debug_shareinput_xslice ? LOG : DEBUG1), "SISC WRITER (shareid=%d, slice=%d): initializing because squelched",
					 sisc->share_id, currentSliceId);
				init_tuplestore_state(node);
			}
		}
		else
		{
			/* We are a consumer. Let the producer know that we're done. */
			Assert(!local_state->closed);

			local_state->ndone++;

			if (local_state->ndone == local_state->nsharers)
			{
				shareinput_reader_notifydone(node->ref, sisc->nconsumers);
				local_state->closed = true;
			}
			release_shareinput_reference(node->ref, true);
			node->ref = NULL;
		}
	}