Future-proof the recursion inside ExecShutdownNode().

tglsfdc · tglsfdc · commit c35ba141de1f · 2022-09-19T12:16:07.000-04:00
The API contract for planstate_tree_walker() callbacks is that they take a PlanState pointer and a context pointer. Somebody figured they could save a couple lines of code by ignoring that, and passing ExecShutdownNode itself as the walker even though it has but one argument. Somewhat remarkably, we've gotten away with that so far. However, it seems clear that the upcoming C2x standard means to forbid such cases, and compilers that actively break such code likely won't be far behind. So spend the extra few lines of code to do it honestly with a separate walker function. In HEAD, we might as well go further and remove ExecShutdownNode's useless return value. I left that as-is in back branches though, to forestall complaints about ABI breakage. Back-patch, with the thought that this might become of practical importance before our stable branches are all out of service. It doesn't seem to be fixing any live bug on any currently known platform, however. Discussion: https://postgr.es/m/208054.1663534665@sss.pgh.pa.us
diff --git a/src/backend/executor/execMain.c b/src/backend/executor/execMain.c
@@ -1691,7 +1691,7 @@ ExecutePlan(EState *estate,
 	 * point.
 	 */
 	if (!(estate->es_top_eflags & EXEC_FLAG_BACKWARD))
-		(void) ExecShutdownNode(planstate);
+		ExecShutdownNode(planstate);
 
 	if (use_parallel_mode)
 		ExitParallelMode();
diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
@@ -121,6 +121,7 @@
 
 static TupleTableSlot *ExecProcNodeFirst(PlanState *node);
 static TupleTableSlot *ExecProcNodeInstr(PlanState *node);
+static bool ExecShutdownNode_walker(PlanState *node, void *context);
 
 
 /* ------------------------------------------------------------------------
@@ -768,8 +769,14 @@ ExecEndNode(PlanState *node)
  * Give execution nodes a chance to stop asynchronous resource consumption
  * and release any resources still held.
  */
-bool
+void
 ExecShutdownNode(PlanState *node)
+{
+	(void) ExecShutdownNode_walker(node, NULL);
+}
+
+static bool
+ExecShutdownNode_walker(PlanState *node, void *context)
 {
 	if (node == NULL)
 		return false;
@@ -789,7 +796,7 @@ ExecShutdownNode(PlanState *node)
 	if (node->instrument && node->instrument->running)
 		InstrStartNode(node->instrument);
 
-	planstate_tree_walker(node, ExecShutdownNode, NULL);
+	planstate_tree_walker(node, ExecShutdownNode_walker, context);
 
 	switch (nodeTag(node))
 	{
diff --git a/src/include/executor/executor.h b/src/include/executor/executor.h
@@ -239,7 +239,7 @@ extern PlanState *ExecInitNode(Plan *node, EState *estate, int eflags);
 extern void ExecSetExecProcNode(PlanState *node, ExecProcNodeMtd function);
 extern Node *MultiExecProcNode(PlanState *node);
 extern void ExecEndNode(PlanState *node);
-extern bool ExecShutdownNode(PlanState *node);
+extern void ExecShutdownNode(PlanState *node);
 extern void ExecSetTupleBound(int64 tuples_needed, PlanState *child_node);
 
 
