Handle interrupts while waiting on Append's async subplans

We did not wake up on interrupts while waiting on async events on an
async-capable append node. For example, if you tried to cancel the
query, nothing would happen until one of the async subplans becomes
readable. To fix, add WL_LATCH_SET to the WaitEventSet.

Backpatch down to v14 where async Append execution was introduced.

Discussion: https://www.postgresql.org/message-id/37a40570-f558-40d3-b5ea-5c2079b3b30b@iki.fi

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index 241b3aaa146fdd0818b4104ec0dd5ac698a32a43..e48a547e237880cefca9879d3b4407b9c643f3c6 100644 (file)
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1020,7 +1020,7 @@ ExecAppendAsyncRequest(AppendState *node, TupleTableSlot **result)
 static void
 ExecAppendAsyncEventWait(AppendState *node)
 {
-       int                     nevents = node->as_nasyncplans + 1;
+       int                     nevents = node->as_nasyncplans + 2;
        long            timeout = node->as_syncdone ? -1 : 0;
        WaitEvent       occurred_event[EVENT_BUFFER_SIZE];
        int                     noccurred;
@@ -1047,13 +1047,28 @@ ExecAppendAsyncEventWait(AppendState *node)
                }
 
                /*
-                * If there are no configured events other than the postmaster death
-                * event, we don't need to wait or poll.
+                * No need for further processing if none of the subplans configured
+                * any events.
                 */
                if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
                        noccurred = 0;
                else
                {
+                       /*
+                        * Add the process latch to the set, so that we wake up to process
+                        * the standard interrupts with CHECK_FOR_INTERRUPTS().
+                        *
+                        * NOTE: For historical reasons, it's important that this is added
+                        * to the WaitEventSet after the ExecAsyncConfigureWait() calls.
+                        * Namely, postgres_fdw calls "GetNumRegisteredWaitEvents(set) ==
+                        * 1" to check if any other events are in the set.  That's a poor
+                        * design, it's questionable for postgres_fdw to be doing that in
+                        * the first place, but we cannot change it now.  The pattern has
+                        * possibly been copied to other extensions too.
+                        */
+                       AddWaitEventToSet(node->as_eventset, WL_LATCH_SET, PGINVALID_SOCKET,
+                                                         MyLatch, NULL);
+
                        /* Return at most EVENT_BUFFER_SIZE events in one call. */
                        if (nevents > EVENT_BUFFER_SIZE)
                                nevents = EVENT_BUFFER_SIZE;
@@ -1102,6 +1117,13 @@ ExecAppendAsyncEventWait(AppendState *node)
                                ExecAsyncNotify(areq);
                        }
                }
+
+               /* Handle standard interrupts */
+               if ((w->events & WL_LATCH_SET) != 0)
+               {
+                       ResetLatch(MyLatch);
+                       CHECK_FOR_INTERRUPTS();
+               }
        }
 }