Allow parallel custom and foreign scans.

This patch doesn't put the new infrastructure to use anywhere, and
indeed it's not clear how it could ever be used for something like
postgres_fdw which has to send an SQL query and wait for a reply,
but there might be FDWs or custom scan providers that are CPU-bound,
so let's give them a way to join club parallel.

KaiGai Kohei, reviewed by me.

1 files changed, 62 insertions, 0 deletions

diff --git a/src/backend/executor/nodeForeignscan.c b/src/backend/executor/nodeForeignscan.c
index 64a07bcc771..388c9227498 100644
--- a/src/backend/executor/nodeForeignscan.c
+++ b/src/backend/executor/nodeForeignscan.c
@@ -282,3 +282,65 @@ ExecReScanForeignScan(ForeignScanState *node)
 
 	ExecScanReScan(&node->ss);
 }
+
+/* ----------------------------------------------------------------
+ *		ExecForeignScanEstimate
+ *
+ *		Informs size of the parallel coordination information, if any
+ * ----------------------------------------------------------------
+ */
+void
+ExecForeignScanEstimate(ForeignScanState *node, ParallelContext *pcxt)
+{
+	FdwRoutine *fdwroutine = node->fdwroutine;
+
+	if (fdwroutine->EstimateDSMForeignScan)
+	{
+		node->pscan_len = fdwroutine->EstimateDSMForeignScan(node, pcxt);
+		shm_toc_estimate_chunk(&pcxt->estimator, node->pscan_len);
+		shm_toc_estimate_keys(&pcxt->estimator, 1);
+	}
+}
+
+/* ----------------------------------------------------------------
+ *		ExecForeignScanInitializeDSM
+ *
+ *		Initialize the parallel coordination information
+ * ----------------------------------------------------------------
+ */
+void
+ExecForeignScanInitializeDSM(ForeignScanState *node, ParallelContext *pcxt)
+{
+	FdwRoutine *fdwroutine = node->fdwroutine;
+
+	if (fdwroutine->InitializeDSMForeignScan)
+	{
+		int			plan_node_id = node->ss.ps.plan->plan_node_id;
+		void	   *coordinate;
+
+		coordinate = shm_toc_allocate(pcxt->toc, node->pscan_len);
+		fdwroutine->InitializeDSMForeignScan(node, pcxt, coordinate);
+		shm_toc_insert(pcxt->toc, plan_node_id, coordinate);
+	}
+}
+
+/* ----------------------------------------------------------------
+ *		ExecForeignScanInitializeDSM
+ *
+ *		Initialization according to the parallel coordination information
+ * ----------------------------------------------------------------
+ */
+void
+ExecForeignScanInitializeWorker(ForeignScanState *node, shm_toc *toc)
+{
+	FdwRoutine *fdwroutine = node->fdwroutine;
+
+	if (fdwroutine->InitializeWorkerForeignScan)
+	{
+		int			plan_node_id = node->ss.ps.plan->plan_node_id;
+		void	   *coordinate;
+
+		coordinate = shm_toc_lookup(toc, plan_node_id);
+		fdwroutine->InitializeWorkerForeignScan(node, toc, coordinate);
+	}
+}