don't use object sharing inside I/O threads, as a fix for a well known instability of VM introduced with the new object sharing code

src/redis.c

@@ -760,6 +760,7 @@ void initServer() {
     signal(SIGPIPE, SIG_IGN);
     setupSigSegvAction();
 
+    server.mainthread = pthread_self();
     server.devnull = fopen("/dev/null","w");
     if (server.devnull == NULL) {
         redisLog(REDIS_WARNING, "Can't open /dev/null: %s", server.neterr);