diff --git a/src/backend/tcop/utility.c b/src/backend/tcop/utility.c index 230eed559cd..7341ef8513c 100644 --- a/src/backend/tcop/utility.c +++ b/src/backend/tcop/utility.c @@ -787,6 +787,23 @@ standard_ProcessUtility(PlannedStmt *pstmt, ListenStmt *stmt = (ListenStmt *) parsetree; CheckRestrictedOperation("LISTEN"); + + /* + * We don't allow LISTEN in background processes, as there is + * no mechanism for them to collect NOTIFY messages, so they'd + * just block cleanout of the async SLRU indefinitely. + * (Authors of custom background workers could bypass this + * restriction by calling Async_Listen directly, but then it's + * on them to provide some mechanism to process the message + * queue.) Note there seems no reason to forbid UNLISTEN. + */ + if (MyBackendType != B_BACKEND) + ereport(ERROR, + (errcode(ERRCODE_FEATURE_NOT_SUPPORTED), + /* translator: %s is name of a SQL command, eg LISTEN */ + errmsg("cannot execute %s within a background process", + "LISTEN"))); + Async_Listen(stmt->conditionname); } break;