MB-58961: Simplify cursor-registering logging logic in ActiveStream

In a couple of places we access the newly registered cursor by ensuring
that the cursor cannot be removed during our access.
No need of that extra logic though, all the code paths involved acquire
the AS::streamLock already.

Change-Id: Iefbc50b902999fd3234fe475a67f7c818f27f6ac
Reviewed-on: https://review.couchbase.org/c/kv_engine/+/199153
Tested-by: Paolo Cocchi <[email protected]>
Reviewed-by: Vesko Karaganev <[email protected]>
Well-Formed: Restriction Checker

Author: paolococchi

engines/ep/src/dcp/active_stream.cc

@@ -261,26 +261,18 @@ void ActiveStream::registerCursor(CheckpointManager& chkptmgr,
         curChkSeqno = result.nextSeqno;
         cursor = result.cursor;
 
-        // Note: We have just registered a cursor and then unlocked the CM at
-        // return. Might cursor-drop kick in before we even try to access the
-        // cursor for logging here?
-        std::optional<queue_op> op{};
-        {
-            const auto lockedCursor = result.cursor.lock();
-            if (lockedCursor) {
-                op = (*lockedCursor->getPos())->getOperation();
-            }
-        }
+        const auto lockedCursor = result.cursor.lock();
+        Expects(lockedCursor);
         log(spdlog::level::level_enum::info,
-            "{} ActiveStream::registerCursor name \"{}\", wantedSeqno:{}, "
-            "result{{tryBackfill:{}, nextSeqno:{}, op:{}}}, "
-            "pendingBackfill:{}",
+            "{} ActiveStream::registerCursor name \"{}\", "
+            "lastProcessedSeqno:{}, result{{tryBackfill:{}, nextSeqno:{}, "
+            "op:{}}}, pendingBackfill:{}",
             logPrefix,
             name_,
             lastProcessedSeqno,
             result.tryBackfill,
             result.nextSeqno,
-            op ? ::to_string(*op) : "N/A",
+            ::to_string((*lockedCursor->getPos())->getOperation()),
             pendingBackfill);
     } catch (std::exception& error) {
         log(spdlog::level::level_enum::warn,
@@ -1777,27 +1769,19 @@ void ActiveStream::scheduleBackfill_UNLOCKED(DcpProducer& producer,
             return;
         }
 
-        // Note: We have just registered a cursor and then unlocked the CM at
-        // return. Might cursor-drop kick in before we even try to access the
-        // cursor for logging here?
-        std::optional<queue_op> op{};
-        {
-            const auto lockedCursor = registerResult.cursor.lock();
-            if (lockedCursor) {
-                op = (*lockedCursor->getPos())->getOperation();
-            }
-        }
+        const auto lockedCursor = registerResult.cursor.lock();
+        Expects(lockedCursor);
         log(spdlog::level::level_enum::info,
             "{} ActiveStream::scheduleBackfill_UNLOCKED register cursor with "
-            "name \"{}\" wantedSeqno:{}, result{{tryBackfill:{}, "
+            "name \"{}\" lastProcessedSeqno:{}, result{{tryBackfill:{}, "
             "nextSeqno:{}}}, "
             "op:{}",
             logPrefix,
             name_,
             lastReadSeqno.load(),
             registerResult.tryBackfill,
             registerResult.nextSeqno,
-            op ? ::to_string(*op) : "N/A");
+            ::to_string((*lockedCursor->getPos())->getOperation()));
 
         curChkSeqno = registerResult.nextSeqno;
         tryBackfill = registerResult.tryBackfill;