Process events with processEventsWhileBlocked() when blocked.

When we are blocked and a few events a processed from time to time, it
is smarter to call the event handler a few times in order to handle the
accept, read, write, close cycle of a client in a single pass, otherwise
there is too much latency added for clients to receive a reply while the
server is busy in some way (for example during the DB loading).

src/aof.c

@@ -560,7 +560,7 @@ int loadAppendOnlyFile(char *filename) {
         /* Serve the clients from time to time */
         if (!(loops++ % 1000)) {
             loadingProgress(ftello(fp));
-            aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);
+            processEventsWhileBlocked();
         }
 
         if (fgets(buf,sizeof(buf),fp) == NULL) {

src/networking.c

@@ -1621,3 +1621,26 @@ int clientsArePaused(void) {
     }
     return server.clients_paused;
 }
+
+/* This function is called by Redis in order to process a few events from
+ * time to time while blocked into some not interruptible operation.
+ * This allows to reply to clients with the -LOADING error while loading the
+ * data set at startup or after a full resynchronization with the master
+ * and so forth.
+ *
+ * It calls the event loop in order to process a few events. Specifically we
+ * try to call the event loop for times as long as we receive acknowledge that
+ * some event was processed, in order to go forward with the accept, read,
+ * write, close sequence needed to serve a client.
+ *
+ * The function returns the total number of events processed. */
+int processEventsWhileBlocked(void) {
+    int iterations = 4; /* See the function top-comment. */
+    int count = 0;
+    while (iterations--) {
+        int events = aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);
+        if (!events) break;
+        count += events;
+    }
+    return count;
+}

src/rdb.c

@@ -1072,7 +1072,7 @@ void rdbLoadProgressCallback(rio *r, const void *buf, size_t len) {
         if (server.masterhost && server.repl_state == REDIS_REPL_TRANSFER)
             replicationSendNewlineToMaster();
         loadingProgress(r->processed_bytes);
-        aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);
+        processEventsWhileBlocked();
     }
 }
 

src/redis.h

@@ -1006,6 +1006,7 @@ void disconnectSlaves(void);
 int listenToPort(int port, int *fds, int *count);
 void pauseClients(mstime_t duration);
 int clientsArePaused(void);
+int processEventsWhileBlocked(void);
 
 #ifdef __GNUC__
 void addReplyErrorFormat(redisClient *c, const char *fmt, ...)

src/scripting.c

@@ -452,8 +452,7 @@ void luaMaskCountHook(lua_State *lua, lua_Debug *ar) {
          * here when the EVAL command will return. */
          aeDeleteFileEvent(server.el, server.lua_caller->fd, AE_READABLE);
     }
-    if (server.lua_timedout)
-        aeProcessEvents(server.el, AE_FILE_EVENTS|AE_DONT_WAIT);
+    if (server.lua_timedout) processEventsWhileBlocked();
     if (server.lua_kill) {
         redisLog(REDIS_WARNING,"Lua script killed by user with SCRIPT KILL.");
         lua_pushstring(lua,"Script killed by user with SCRIPT KILL...");