Allow custom and foreign scans to have shutdown callbacks.

This is expected to be useful mostly when performing such scans in
parallel, because in that case it allows (in combination with commit
acf555bc53acb589b5a2827e65d655fa8c9adee0) nodes below a Gather to get
control just before the DSM segment goes away.

KaiGai Kohei, except that I rewrote the documentation.  Reviewed by
Claudio Freire.

Discussion: http://postgr.es/m/CADyhKSXJK0jUJ8rWv4AmKDhsUh124_rEn39eqgfC5D8fu6xVuw@mail.gmail.com

7 files changed, 36 insertions, 0 deletions

diff --git a/src/backend/executor/execProcnode.c b/src/backend/executor/execProcnode.c
index 5ccc2e846dc..ef6f35a5a0b 100644
--- a/src/backend/executor/execProcnode.c
+++ b/src/backend/executor/execProcnode.c
@@ -822,6 +822,12 @@ ExecShutdownNode(PlanState *node)
 		case T_GatherState:
 			ExecShutdownGather((GatherState *) node);
 			break;
+		case T_ForeignScanState:
+			ExecShutdownForeignScan((ForeignScanState *) node);
+			break;
+		case T_CustomScanState:
+			ExecShutdownCustomScan((CustomScanState *) node);
+			break;
 		default:
 			break;
 	}
diff --git a/src/backend/executor/nodeCustom.c b/src/backend/executor/nodeCustom.c
index 16343a56df7..d4647482905 100644
--- a/src/backend/executor/nodeCustom.c
+++ b/src/backend/executor/nodeCustom.c
@@ -202,3 +202,12 @@ ExecCustomScanInitializeWorker(CustomScanState *node, shm_toc *toc)
 		methods->InitializeWorkerCustomScan(node, toc, coordinate);
 	}
 }
+
+void
+ExecShutdownCustomScan(CustomScanState *node)
+{
+	const CustomExecMethods *methods = node->methods;
+
+	if (methods->ShutdownCustomScan)
+		methods->ShutdownCustomScan(node);
+}
diff --git a/src/backend/executor/nodeForeignscan.c b/src/backend/executor/nodeForeignscan.c
index 86a77e356c0..3b6d1390eb4 100644
--- a/src/backend/executor/nodeForeignscan.c
+++ b/src/backend/executor/nodeForeignscan.c
@@ -353,3 +353,19 @@ ExecForeignScanInitializeWorker(ForeignScanState *node, shm_toc *toc)
 		fdwroutine->InitializeWorkerForeignScan(node, toc, coordinate);
 	}
 }
+
+/* ----------------------------------------------------------------
+ *		ExecShutdownForeignScan
+ *
+ *		Gives FDW chance to stop asynchronous resource consumption
+ *		and release any resources still held.
+ * ----------------------------------------------------------------
+ */
+void
+ExecShutdownForeignScan(ForeignScanState *node)
+{
+	FdwRoutine *fdwroutine = node->fdwroutine;
+
+	if (fdwroutine->ShutdownForeignScan)
+		fdwroutine->ShutdownForeignScan(node);
+}
diff --git a/src/include/executor/nodeCustom.h b/src/include/executor/nodeCustom.h
index 19d5d047b5c..c2f2ca1eede 100644
--- a/src/include/executor/nodeCustom.h
+++ b/src/include/executor/nodeCustom.h
@@ -37,5 +37,6 @@ extern void ExecCustomScanInitializeDSM(CustomScanState *node,
 							ParallelContext *pcxt);
 extern void ExecCustomScanInitializeWorker(CustomScanState *node,
 							   shm_toc *toc);
+extern void ExecShutdownCustomScan(CustomScanState *node);
 
 #endif   /* NODECUSTOM_H */
diff --git a/src/include/executor/nodeForeignscan.h b/src/include/executor/nodeForeignscan.h
index f0e942a8bcb..1b167b8143a 100644
--- a/src/include/executor/nodeForeignscan.h
+++ b/src/include/executor/nodeForeignscan.h
@@ -28,5 +28,6 @@ extern void ExecForeignScanInitializeDSM(ForeignScanState *node,
 							 ParallelContext *pcxt);
 extern void ExecForeignScanInitializeWorker(ForeignScanState *node,
 								shm_toc *toc);
+extern void ExecShutdownForeignScan(ForeignScanState *node);
 
 #endif   /* NODEFOREIGNSCAN_H */
diff --git a/src/include/foreign/fdwapi.h b/src/include/foreign/fdwapi.h
index 523d4155756..6ca44f734f9 100644
--- a/src/include/foreign/fdwapi.h
+++ b/src/include/foreign/fdwapi.h
@@ -151,6 +151,7 @@ typedef void (*InitializeDSMForeignScan_function) (ForeignScanState *node,
 typedef void (*InitializeWorkerForeignScan_function) (ForeignScanState *node,
 																shm_toc *toc,
 														   void *coordinate);
+typedef void (*ShutdownForeignScan_function) (ForeignScanState *node);
 typedef bool (*IsForeignScanParallelSafe_function) (PlannerInfo *root,
 															 RelOptInfo *rel,
 														 RangeTblEntry *rte);
@@ -224,6 +225,7 @@ typedef struct FdwRoutine
 	EstimateDSMForeignScan_function EstimateDSMForeignScan;
 	InitializeDSMForeignScan_function InitializeDSMForeignScan;
 	InitializeWorkerForeignScan_function InitializeWorkerForeignScan;
+	ShutdownForeignScan_function ShutdownForeignScan;
 } FdwRoutine;
 
 
diff --git a/src/include/nodes/extensible.h b/src/include/nodes/extensible.h
index 7e860b0dca7..0b02cc18e99 100644
--- a/src/include/nodes/extensible.h
+++ b/src/include/nodes/extensible.h
@@ -139,6 +139,7 @@ typedef struct CustomExecMethods
 	void		(*InitializeWorkerCustomScan) (CustomScanState *node,
 														   shm_toc *toc,
 														   void *coordinate);
+	void		(*ShutdownCustomScan) (CustomScanState *node);
 
 	/* Optional: print additional information in EXPLAIN */
 	void		(*ExplainCustomScan) (CustomScanState *node,