Kill diskless fork child asap when the last replica drop (#1227)

We originally checked the replica connection to whether to kill the
diskless child only when rdbPipeReadHandler is triggered. Actually
we can check it when the replica is disconnected, so that we don't
have to wait for rdbPipeReadHandler to be triggered and can kill
the forkless child as soon as possible.

In this way, when the child or rdbPipeReadHandler is stuck for some
reason, we can kill the child faster and release the fork resources.

Signed-off-by: Binbin <[email protected]>

src/networking.c

@@ -1555,12 +1555,17 @@ void unlinkClient(client *c) {
          * in which case it needs to be cleaned from that list */
         if (c->flag.replica && c->repl_state == REPLICA_STATE_WAIT_BGSAVE_END && server.rdb_pipe_conns) {
             int i;
+            int still_alive = 0;
             for (i = 0; i < server.rdb_pipe_numconns; i++) {
                 if (server.rdb_pipe_conns[i] == c->conn) {
                     rdbPipeWriteHandlerConnRemoved(c->conn);
                     server.rdb_pipe_conns[i] = NULL;
-                    break;
                 }
+                if (server.rdb_pipe_conns[i]) still_alive++;
+            }
+            if (still_alive == 0) {
+                serverLog(LL_NOTICE, "Diskless rdb transfer, last replica dropped, killing fork child.");
+                killRDBChild();
             }
         }
         /* Only use shutdown when the fork is active and we are the parent. */
@@ -1781,6 +1786,7 @@ void freeClient(client *c) {
         if (server.saveparamslen == 0 && c->repl_state == REPLICA_STATE_WAIT_BGSAVE_END &&
             server.child_type == CHILD_TYPE_RDB && server.rdb_child_type == RDB_CHILD_TYPE_DISK &&
             anyOtherReplicaWaitRdb(c) == 0) {
+            serverLog(LL_NOTICE, "Background saving, persistence disabled, last replica dropped, killing fork child.");
             killRDBChild();
         }
         if (c->repl_state == REPLICA_STATE_SEND_BULK) {

src/replication.c

@@ -1669,7 +1669,9 @@ void rdbPipeReadHandler(struct aeEventLoop *eventLoop, int fd, void *clientData,
                 if (!conn) continue;
                 stillUp++;
             }
-            serverLog(LL_NOTICE, "Diskless rdb transfer, done reading from pipe, %d replicas still up.", stillUp);
+            if (stillUp) {
+                serverLog(LL_NOTICE, "Diskless rdb transfer, done reading from pipe, %d replicas still up.", stillUp);
+            }
             /* Now that the replicas have finished reading, notify the child that it's safe to exit.
              * When the server detects the child has exited, it can mark the replica as online, and
              * start streaming the replication buffers. */
@@ -1678,7 +1680,6 @@ void rdbPipeReadHandler(struct aeEventLoop *eventLoop, int fd, void *clientData,
             return;
         }
 
-        int stillAlive = 0;
         for (i = 0; i < server.rdb_pipe_numconns; i++) {
             ssize_t nwritten;
             connection *conn = server.rdb_pipe_conns[i];
@@ -1708,15 +1709,10 @@ void rdbPipeReadHandler(struct aeEventLoop *eventLoop, int fd, void *clientData,
                 server.rdb_pipe_numconns_writing++;
                 connSetWriteHandler(conn, rdbPipeWriteHandler);
             }
-            stillAlive++;
         }
 
-        if (stillAlive == 0) {
-            serverLog(LL_WARNING, "Diskless rdb transfer, last replica dropped, killing fork child.");
-            killRDBChild();
-        }
         /*  Remove the pipe read handler if at least one write handler was set. */
-        if (server.rdb_pipe_numconns_writing || stillAlive == 0) {
+        if (server.rdb_pipe_numconns_writing) {
             aeDeleteFileEvent(server.el, server.rdb_pipe_read, AE_READABLE);
             break;
         }