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 15c4227cc627cc79e5de0362a1dd6d56ec242644..a11b36c7176621b8fd5807265091d368606a2850 100644 (file)
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -1031,7 +1031,7 @@ 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;
@@ -1056,8 +1056,8 @@ ExecAppendAsyncEventWait(AppendState *node)
    }
 
    /*
-    * No need for further processing if there are no configured events other
-    * than the postmaster death event.
+    * No need for further processing if none of the subplans configured any
+    * events.
     */
    if (GetNumRegisteredWaitEvents(node->as_eventset) == 1)
    {
@@ -1066,6 +1066,21 @@ ExecAppendAsyncEventWait(AppendState *node)
        return;
    }
 
+   /*
+    * 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;
@@ -1107,6 +1122,13 @@ ExecAppendAsyncEventWait(AppendState *node)
                ExecAsyncNotify(areq);
            }
        }
+
+       /* Handle standard interrupts */
+       if ((w->events & WL_LATCH_SET) != 0)
+       {
+           ResetLatch(MyLatch);
+           CHECK_FOR_INTERRUPTS();
+       }
    }
 }