Redis 源码分析 RedisServer 启动过程

// 时区设置
setlocale(LC_COLLATE,"");
tzset(); /* Populates 'timezone' global. */
zmalloc_set_oom_handler(redisOutOfMemoryHandler);
srand(time(NULL)^getpid());
srandom(time(NULL)^getpid());
gettimeofday(&tv,NULL);
init_genrand64(((long long) tv.tv_sec * 1000000 + tv.tv_usec) ^ getpid());
crc64_init();

void dictSetHashFunctionSeed(uint8_t *seed) {
    memcpy(dict_hash_function_seed,seed,sizeof(dict_hash_function_seed));
}

/* The default hashing function uses SipHash implementation
 * in siphash.c. */
uint64_t siphash(const uint8_t *in, const size_t inlen, const uint8_t *k);
uint64_t siphash_nocase(const uint8_t *in, const size_t inlen, const uint8_t *k);

uint64_t dictGenHashFunction(const void *key, int len) {
    return siphash(key,len,dict_hash_function_seed);
}

server.sentinel_mode = checkForSentinelMode(argc,argv);

/* Returns 1 if there is --sentinel among the arguments or if
 * argv[0] contains "redis-sentinel". */
int checkForSentinelMode(int argc, char **argv) {
    int j;

    if (strstr(argv[0],"redis-sentinel") != NULL) return 1;
    for (j = 1; j < argc; j++)
        if (!strcmp(argv[j],"--sentinel")) return 1;
    return 0;
}

void initServerConfig(void) {
    int j;

    updateCachedTime(1);
    getRandomHexChars(server.runid,CONFIG_RUN_ID_SIZE);
    server.runid[CONFIG_RUN_ID_SIZE] = '\0';
    changeReplicationId();
    clearReplicationId2();
    server.hz = CONFIG_DEFAULT_HZ; /* Initialize it ASAP, even if it may get
                                      updated later after loading the config.
                                      This value may be used before the server
                                      is initialized. */
    server.timezone = getTimeZone(); /* Initialized by tzset(). */
    server.configfile = NULL;
    server.executable = NULL;
    server.arch_bits = (sizeof(long) == 8) ? 64 : 32;
    server.bindaddr_count = 0;
    server.unixsocketperm = CONFIG_DEFAULT_UNIX_SOCKET_PERM;
    server.ipfd.count = 0;
    server.tlsfd.count = 0;
    server.sofd = -1;
    server.active_expire_enabled = 1;
    server.skip_checksum_validation = 0;
    server.saveparams = NULL;
    server.loading = 0;
    server.loading_rdb_used_mem = 0;
    server.logfile = zstrdup(CONFIG_DEFAULT_LOGFILE);
    server.aof_state = AOF_OFF;
    server.aof_rewrite_base_size = 0;
    server.aof_rewrite_scheduled = 0;
    server.aof_flush_sleep = 0;
    server.aof_last_fsync = time(NULL);
    atomicSet(server.aof_bio_fsync_status,C_OK);
    server.aof_rewrite_time_last = -1;
    server.aof_rewrite_time_start = -1;
    server.aof_lastbgrewrite_status = C_OK;
    server.aof_delayed_fsync = 0;
    server.aof_fd = -1;
    server.aof_selected_db = -1; /* Make sure the first time will not match */
    server.aof_flush_postponed_start = 0;
    server.pidfile = NULL;
    server.active_defrag_running = 0;
    server.notify_keyspace_events = 0;
    server.blocked_clients = 0;
    memset(server.blocked_clients_by_type,0,
           sizeof(server.blocked_clients_by_type));
    server.shutdown_asap = 0;
    server.cluster_configfile = zstrdup(CONFIG_DEFAULT_CLUSTER_CONFIG_FILE);
    server.cluster_module_flags = CLUSTER_MODULE_FLAG_NONE;
    server.migrate_cached_sockets = dictCreate(&migrateCacheDictType,NULL);
    server.next_client_id = 1; /* Client IDs, start from 1 .*/
    server.loading_process_events_interval_bytes = (1024*1024*2);

    unsigned int lruclock = getLRUClock();
    atomicSet(server.lruclock,lruclock);
    resetServerSaveParams();

    appendServerSaveParams(60*60,1);  /* save after 1 hour and 1 change */
    appendServerSaveParams(300,100);  /* save after 5 minutes and 100 changes */
    appendServerSaveParams(60,10000); /* save after 1 minute and 10000 changes */

    /* Replication related */
    server.masterauth = NULL;
    server.masterhost = NULL;
    server.masterport = 6379;
    server.master = NULL;
    server.cached_master = NULL;
    server.master_initial_offset = -1;
    server.repl_state = REPL_STATE_NONE;
    server.repl_transfer_tmpfile = NULL;
    server.repl_transfer_fd = -1;
    server.repl_transfer_s = NULL;
    server.repl_syncio_timeout = CONFIG_REPL_SYNCIO_TIMEOUT;
    server.repl_down_since = 0; /* Never connected, repl is down since EVER. */
    server.master_repl_offset = 0;

    /* Replication partial resync backlog */
    server.repl_backlog = NULL;
    server.repl_backlog_histlen = 0;
    server.repl_backlog_idx = 0;
    server.repl_backlog_off = 0;
    server.repl_no_slaves_since = time(NULL);

    /* Failover related */
    server.failover_end_time = 0;
    server.force_failover = 0;
    server.target_replica_host = NULL;
    server.target_replica_port = 0;
    server.failover_state = NO_FAILOVER;

    /* Client output buffer limits */
    for (j = 0; j < CLIENT_TYPE_OBUF_COUNT; j++)
        server.client_obuf_limits[j] = clientBufferLimitsDefaults[j];

    /* Linux OOM Score config */
    for (j = 0; j < CONFIG_OOM_COUNT; j++)
        server.oom_score_adj_values[j] = configOOMScoreAdjValuesDefaults[j];

    /* Double constants initialization */
    R_Zero = 0.0;
    R_PosInf = 1.0/R_Zero;
    R_NegInf = -1.0/R_Zero;
    R_Nan = R_Zero/R_Zero;

    /* Command table -- we initialize it here as it is part of the
     * initial configuration, since command names may be changed via
     * redis.conf using the rename-command directive. */
    server.commands = dictCreate(&commandTableDictType,NULL);
    server.orig_commands = dictCreate(&commandTableDictType,NULL);
    populateCommandTable();
    server.delCommand = lookupCommandByCString("del");
    server.multiCommand = lookupCommandByCString("multi");
    server.lpushCommand = lookupCommandByCString("lpush");
    server.lpopCommand = lookupCommandByCString("lpop");
    server.rpopCommand = lookupCommandByCString("rpop");
    server.zpopminCommand = lookupCommandByCString("zpopmin");
    server.zpopmaxCommand = lookupCommandByCString("zpopmax");
    server.sremCommand = lookupCommandByCString("srem");
    server.execCommand = lookupCommandByCString("exec");
    server.expireCommand = lookupCommandByCString("expire");
    server.pexpireCommand = lookupCommandByCString("pexpire");
    server.xclaimCommand = lookupCommandByCString("xclaim");
    server.xgroupCommand = lookupCommandByCString("xgroup");
    server.rpoplpushCommand = lookupCommandByCString("rpoplpush");
    server.lmoveCommand = lookupCommandByCString("lmove");

    /* Debugging */
    server.watchdog_period = 0;

    /* By default we want scripts to be always replicated by effects
     * (single commands executed by the script), and not by sending the
     * script to the slave / AOF. This is the new way starting from
     * Redis 5. However it is possible to revert it via redis.conf. */
    server.lua_always_replicate_commands = 1;

    /* Client Pause related */
    server.client_pause_type = CLIENT_PAUSE_OFF;
    server.client_pause_end_time = 0;   

    initConfigValues();
}

    /* Check if we need to start in redis-check-rdb/aof mode. We just execute
     * the program main. However the program is part of the Redis executable
     * so that we can easily execute an RDB check on loading errors. */
    if (strstr(argv[0],"redis-check-rdb") != NULL)
        redis_check_rdb_main(argc,argv,NULL);
    else if (strstr(argv[0],"redis-check-aof") != NULL)
        redis_check_aof_main(argc,argv);

   if (argc >= 2) {
        j = 1; /* First option to parse in argv[] */
        sds options = sdsempty();

        /* Handle special options --help and --version */
        if (strcmp(argv[1], "-v") == 0 ||
            strcmp(argv[1], "--version") == 0) version();
        if (strcmp(argv[1], "--help") == 0 ||
            strcmp(argv[1], "-h") == 0) usage();
        if (strcmp(argv[1], "--test-memory") == 0) {
            if (argc == 3) {
                memtest(atoi(argv[2]),50);
                exit(0);
            } else {
                fprintf(stderr,"Please specify the amount of memory to test in megabytes.\n");
                fprintf(stderr,"Example: ./redis-server --test-memory 4096\n\n");
                exit(1);
            }
        }
        /* Parse command line options
         * Precedence wise, File, stdin, explicit options -- last config is the one that matters.
         *
         * First argument is the config file name? */
        if (argv[1][0] != '-') {
            /* Replace the config file in server.exec_argv with its absolute path. */
            server.configfile = getAbsolutePath(argv[1]);
            zfree(server.exec_argv[1]);
            server.exec_argv[1] = zstrdup(server.configfile);
            j = 2; // Skip this arg when parsing options
        }
        while(j < argc) {
            /* Either first or last argument - Should we read config from stdin? */
            if (argv[j][0] == '-' && argv[j][1] == '\0' && (j == 1 || j == argc-1)) {
                config_from_stdin = 1;
            }
            /* All the other options are parsed and conceptually appended to the
             * configuration file. For instance --port 6380 will generate the
             * string "port 6380\n" to be parsed after the actual config file
             * and stdin input are parsed (if they exist). */
            else if (argv[j][0] == '-' && argv[j][1] == '-') {
                /* Option name */
                if (sdslen(options)) options = sdscat(options,"\n");
                options = sdscat(options,argv[j]+2);
                options = sdscat(options," ");
            } else {
                /* Option argument */
                options = sdscatrepr(options,argv[j],strlen(argv[j]));
                options = sdscat(options," ");
            }
            j++;
        }

        // 读取配置文件
        loadServerConfig(server.configfile, config_from_stdin, options);
        if (server.sentinel_mode) loadSentinelConfigFromQueue();
        sdsfree(options);
    }

int background = server.daemonize && !server.supervised;
// 是否是后台运行
if (background) daemonize();

// 执行后台运行的方法
void daemonize(void) {
    int fd;

    if (fork() != 0) exit(0); /* parent exits */
    setsid(); /* create a new session */

    /* Every output goes to /dev/null. If Redis is daemonized but
     * the 'logfile' is set to 'stdout' in the configuration file
     * it will not log at all. */
    if ((fd = open("/dev/null", O_RDWR, 0)) != -1) {
        dup2(fd, STDIN_FILENO);
        dup2(fd, STDOUT_FILENO);
        dup2(fd, STDERR_FILENO);
        if (fd > STDERR_FILENO) close(fd);
    }
}

int
daemon_init(const char *pname, int facility)
{
        int                i;
        pid_t        pid;

        if ( (pid = Fork()) < 0) //创建一个子进程
                return (-1);
        else if (pid)
                _exit(0);                        /* parent terminates 父进程退出*/

        //子进程继续运行
        //此进程是子进程,所以肯定不是组长进程

        /* child 1 continues... */

        if (setsid() < 0)                        /* become session leader 创建会话,成为会话首进程,新的进程组的组长进程*/
                return (-1);

        Signal(SIGHUP, SIG_IGN); //把挂起信号设置为忽略
        if ( (pid = Fork()) < 0) //再创建一个子进程
                return (-1);
        else if (pid) //父进程退出
                _exit(0);                        /* child 1 terminates */

        //第二个子进程继续运行,因为第二个子进程已经不是会话首进程了,所以永远不会获得控制终端

        /* child 2 continues... */

        daemon_proc = 1;                        /* for err_XXX() functions 再error.c中定义的变量*/

        chdir("/");                                /* change working directory 调整工作目录到根目录 */

        /* close off file descriptors */
        for (i = 0; i < MAXFD; i++) //关闭所有文件描述符
                close(i);

        /* redirect stdin, stdout, and stderr to /dev/null 定义标准输入,标准输出和标准错误到/dev/null */
        open("/dev/null", O_RDONLY);
        open("/dev/null", O_RDWR);
        open("/dev/null", O_RDWR);

        openlog(pname, LOG_PID, facility); //打开日志文件

        return (0);                                /* success 函数运行成功 */
}

    signal(SIGHUP, SIG_IGN);
    signal(SIGPIPE, SIG_IGN);

void setupSignalHandlers(void) {
    struct sigaction act;

    /* When the SA_SIGINFO flag is set in sa_flags then sa_sigaction is used.
     * Otherwise, sa_handler is used. */
    sigemptyset(&act.sa_mask);
    act.sa_flags = 0;
    act.sa_handler = sigShutdownHandler;
    sigaction(SIGTERM, &act, NULL);
    sigaction(SIGINT, &act, NULL);

    sigemptyset(&act.sa_mask);
    act.sa_flags = SA_NODEFER | SA_RESETHAND | SA_SIGINFO;
    act.sa_sigaction = sigsegvHandler;
    if(server.crashlog_enabled) {
        sigaction(SIGSEGV, &act, NULL);
        sigaction(SIGBUS, &act, NULL);
        sigaction(SIGFPE, &act, NULL);
        sigaction(SIGILL, &act, NULL);
        sigaction(SIGABRT, &act, NULL);
    }
    return;
}

    if (server.syslog_enabled) {
        openlog(server.syslog_ident, LOG_PID | LOG_NDELAY | LOG_NOWAIT,
            server.syslog_facility);
    }

    /* Initialization after setting defaults from the config system. */
    server.aof_state = server.aof_enabled ? AOF_ON : AOF_OFF;
    server.hz = server.config_hz;
    server.pid = getpid();
    server.in_fork_child = CHILD_TYPE_NONE;
    server.main_thread_id = pthread_self();
    server.current_client = NULL;
    server.errors = raxNew();
    server.fixed_time_expire = 0;
    server.clients = listCreate();
    server.clients_index = raxNew();
    server.clients_to_close = listCreate();
    server.slaves = listCreate();
    server.monitors = listCreate();
    server.clients_pending_write = listCreate();
    server.clients_pending_read = listCreate();
    server.clients_timeout_table = raxNew();
    server.replication_allowed = 1;
    server.slaveseldb = -1; /* Force to emit the first SELECT command. */
    server.unblocked_clients = listCreate();
    server.ready_keys = listCreate();
    server.clients_waiting_acks = listCreate();
    server.get_ack_from_slaves = 0;
    server.client_pause_type = 0;
    server.paused_clients = listCreate();
    server.events_processed_while_blocked = 0;
    server.system_memory_size = zmalloc_get_memory_size();
    server.blocked_last_cron = 0;
    server.blocking_op_nesting = 0;

    createSharedObjects();

    /* Shared command responses */
    shared.crlf = createObject(OBJ_STRING,sdsnew("\r\n"));
    shared.ok = createObject(OBJ_STRING,sdsnew("+OK\r\n"));
    shared.emptybulk = createObject(OBJ_STRING,sdsnew("$0\r\n\r\n"));
    shared.czero = createObject(OBJ_STRING,sdsnew(":0\r\n"));
    shared.cone = createObject(OBJ_STRING,sdsnew(":1\r\n"));
    shared.emptyarray = createObject(OBJ_STRING,sdsnew("*0\r\n"));
    shared.pong = createObject(OBJ_STRING,sdsnew("+PONG\r\n"));
    shared.queued = createObject(OBJ_STRING,sdsnew("+QUEUED\r\n"));
    shared.emptyscan = createObject(OBJ_STRING,sdsnew("*2\r\n$1\r\n0\r\n*0\r\n"));
    shared.space = createObject(OBJ_STRING,sdsnew(" "));
    shared.colon = createObject(OBJ_STRING,sdsnew(":"));
    shared.plus = createObject(OBJ_STRING,sdsnew("+"));

    adjustOpenFilesLimit();

    const char *clk_msg = monotonicInit();
    serverLog(LL_NOTICE, "monotonic clock: %s", clk_msg);
    server.el = aeCreateEventLoop(server.maxclients+CONFIG_FDSET_INCR);
    if (server.el == NULL) {
        serverLog(LL_WARNING,
            "Failed creating the event loop. Error message: '%s'",
            strerror(errno));
        exit(1);
    }
    server.db = zmalloc(sizeof(redisDb)*server.dbnum);

    /* Open the TCP listening socket for the user commands. */
    if (server.port != 0 &&
        listenToPort(server.port,&server.ipfd) == C_ERR) {
        serverLog(LL_WARNING, "Failed listening on port %u (TCP), aborting.", server.port);
        exit(1);
    }
    if (server.tls_port != 0 &&
        listenToPort(server.tls_port,&server.tlsfd) == C_ERR) {
        serverLog(LL_WARNING, "Failed listening on port %u (TLS), aborting.", server.tls_port);
        exit(1);
    }

    /* Open the listening Unix domain socket. */
    if (server.unixsocket != NULL) {
        unlink(server.unixsocket); /* don't care if this fails */
        server.sofd = anetUnixServer(server.neterr,server.unixsocket,
            server.unixsocketperm, server.tcp_backlog);
        if (server.sofd == ANET_ERR) {
            serverLog(LL_WARNING, "Opening Unix socket: %s", server.neterr);
            exit(1);
        }
        anetNonBlock(NULL,server.sofd);
        anetCloexec(server.sofd);
    }

/* Create a new eviction pool. */
void evictionPoolAlloc(void) {
    struct evictionPoolEntry *ep;
    int j;

    ep = zmalloc(sizeof(*ep)*EVPOOL_SIZE);
    for (j = 0; j < EVPOOL_SIZE; j++) {
        ep[j].idle = 0;
        ep[j].key = NULL;
        ep[j].cached = sdsnewlen(NULL,EVPOOL_CACHED_SDS_SIZE);
        ep[j].dbid = 0;
    }
    EvictionPoolLRU = ep;
}

    server.rdb_child_type = RDB_CHILD_TYPE_NONE;
    server.rdb_pipe_conns = NULL;
    server.rdb_pipe_numconns = 0;
    server.rdb_pipe_numconns_writing = 0;
    server.rdb_pipe_buff = NULL;
    server.rdb_pipe_bufflen = 0;
    server.rdb_bgsave_scheduled = 0;
    server.child_info_pipe[0] = -1;
    server.child_info_pipe[1] = -1;
    server.child_info_nread = 0;
    aofRewriteBufferReset();
    server.aof_buf = sdsempty();
    server.lastsave = time(NULL); /* At startup we consider the DB saved. */
    server.lastbgsave_try = 0;    /* At startup we never tried to BGSAVE. */
    server.rdb_save_time_last = -1;
    server.rdb_save_time_start = -1;
    server.dirty = 0;

    resetServerStats();
    /* A few stats we don't want to reset: server startup time, and peak mem. */
    server.stat_starttime = time(NULL);
    server.stat_peak_memory = 0;
    server.stat_current_cow_bytes = 0;
    server.stat_current_cow_updated = 0;
    server.stat_current_save_keys_processed = 0;
    server.stat_current_save_keys_total = 0;
    server.stat_rdb_cow_bytes = 0;
    server.stat_aof_cow_bytes = 0;
    server.stat_module_cow_bytes = 0;
    server.stat_module_progress = 0;
    for (int j = 0; j < CLIENT_TYPE_COUNT; j++)
        server.stat_clients_type_memory[j] = 0;
    server.cron_malloc_stats.zmalloc_used = 0;
    server.cron_malloc_stats.process_rss = 0;
    server.cron_malloc_stats.allocator_allocated = 0;
    server.cron_malloc_stats.allocator_active = 0;
    server.cron_malloc_stats.allocator_resident = 0;
    server.lastbgsave_status = C_OK;
    server.aof_last_write_status = C_OK;
    server.aof_last_write_errno = 0;
    server.repl_good_slaves_count = 0;

    /* Create the timer callback, this is our way to process many background
     * operations incrementally, like clients timeout, eviction of unaccessed
     * expired keys and so forth. */
    if (aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
        serverPanic("Can't create event loop timers.");
        exit(1);
    }

    /* Create an event handler for accepting new connections in TCP and Unix
     * domain sockets. */
    if (createSocketAcceptHandler(&server.ipfd, acceptTcpHandler) != C_OK) {
        serverPanic("Unrecoverable error creating TCP socket accept handler.");
    }
    if (createSocketAcceptHandler(&server.tlsfd, acceptTLSHandler) != C_OK) {
        serverPanic("Unrecoverable error creating TLS socket accept handler.");
    }
    if (server.sofd > 0 && aeCreateFileEvent(server.el,server.sofd,AE_READABLE,
        acceptUnixHandler,NULL) == AE_ERR) serverPanic("Unrecoverable error creating server.sofd file event.");


    /* Register a readable event for the pipe used to awake the event loop
     * when a blocked client in a module needs attention. */
    if (aeCreateFileEvent(server.el, server.module_blocked_pipe[0], AE_READABLE,
        moduleBlockedClientPipeReadable,NULL) == AE_ERR) {
            serverPanic(
                "Error registering the readable event for the module "
                "blocked clients subsystem.");
    }

/* Initialize the slow log. This function should be called a single time
 * at server startup. */
void slowlogInit(void) {
    server.slowlog = listCreate();
    server.slowlog_entry_id = 0;
    listSetFreeMethod(server.slowlog,slowlogFreeEntry);
}

/* Initialize the background system, spawning the thread. */
void bioInit(void) {
    pthread_attr_t attr;
    pthread_t thread;
    size_t stacksize;
    int j;

    /* Initialization of state vars and objects */
    for (j = 0; j < BIO_NUM_OPS; j++) {
        pthread_mutex_init(&bio_mutex[j],NULL);
        pthread_cond_init(&bio_newjob_cond[j],NULL);
        pthread_cond_init(&bio_step_cond[j],NULL);
        bio_jobs[j] = listCreate();
        bio_pending[j] = 0;
    }

    /* Set the stack size as by default it may be small in some system */
    pthread_attr_init(&attr);
    pthread_attr_getstacksize(&attr,&stacksize);
    if (!stacksize) stacksize = 1; /* The world is full of Solaris Fixes */
    while (stacksize < REDIS_THREAD_STACK_SIZE) stacksize *= 2;
    pthread_attr_setstacksize(&attr, stacksize);

    /* Ready to spawn our threads. We use the single argument the thread
     * function accepts in order to pass the job ID the thread is
     * responsible of. */
    for (j = 0; j < BIO_NUM_OPS; j++) {
        void *arg = (void*)(unsigned long) j;
        if (pthread_create(&thread,&attr,bioProcessBackgroundJobs,arg) != 0) {
            serverLog(LL_WARNING,"Fatal: Can't initialize Background Jobs.");
            exit(1);
        }
        bio_threads[j] = thread;
    }
}

void moduleLoadFromQueue(void) {
    listIter li;
    listNode *ln;

    listRewind(server.loadmodule_queue,&li);
    while((ln = listNext(&li))) {
        struct moduleLoadQueueEntry *loadmod = ln->value;
        if (moduleLoad(loadmod->path,(void **)loadmod->argv,loadmod->argc)
            == C_ERR)
        {
            serverLog(LL_WARNING,
                "Can't load module from %s: server aborting",
                loadmod->path);
            exit(1);
        }
    }

/* Function called at startup to load RDB or AOF file in memory. */
void loadDataFromDisk(void) {
    long long start = ustime();
    if (server.aof_state == AOF_ON) {
        if (loadAppendOnlyFile(server.aof_filename) == C_OK)
            serverLog(LL_NOTICE,"DB loaded from append only file: %.3f seconds",(float)(ustime()-start)/1000000);
    } else {
        rdbSaveInfo rsi = RDB_SAVE_INFO_INIT;
        errno = 0; /* Prevent a stale value from affecting error checking */
        if (rdbLoad(server.rdb_filename,&rsi,RDBFLAGS_NONE) == C_OK) {
            serverLog(LL_NOTICE,"DB loaded from disk: %.3f seconds",
                (float)(ustime()-start)/1000000);

            /* Restore the replication ID / offset from the RDB file. */
            if ((server.masterhost ||
                (server.cluster_enabled &&
                nodeIsSlave(server.cluster->myself))) &&
                rsi.repl_id_is_set &&
                rsi.repl_offset != -1 &&
                /* Note that older implementations may save a repl_stream_db
                 * of -1 inside the RDB file in a wrong way, see more
                 * information in function rdbPopulateSaveInfo. */
                rsi.repl_stream_db != -1)
            {
                memcpy(server.replid,rsi.repl_id,sizeof(server.replid));
                server.master_repl_offset = rsi.repl_offset;
                /* If we are a slave, create a cached master from this
                 * information, in order to allow partial resynchronizations
                 * with masters. */
                replicationCacheMasterUsingMyself();
                selectDb(server.cached_master,rsi.repl_stream_db);
            }
        } else if (errno != ENOENT) {
            serverLog(LL_WARNING,"Fatal error loading the DB: %s. Exiting.",strerror(errno));
            exit(1);
        }
    }
}

    aeSetBeforeSleepProc(server.el,beforeSleep);
    aeSetAfterSleepProc(server.el,afterSleep);

void beforeSleep(struct aeEventLoop *eventLoop) {
    UNUSED(eventLoop);

    size_t zmalloc_used = zmalloc_used_memory();
    if (zmalloc_used > server.stat_peak_memory)
        server.stat_peak_memory = zmalloc_used;

    /* Just call a subset of vital functions in case we are re-entering
     * the event loop from processEventsWhileBlocked(). Note that in this
     * case we keep track of the number of events we are processing, since
     * processEventsWhileBlocked() wants to stop ASAP if there are no longer
     * events to handle. */
    if (ProcessingEventsWhileBlocked) {
        uint64_t processed = 0;
        processed += handleClientsWithPendingReadsUsingThreads();
        processed += tlsProcessPendingData();
        processed += handleClientsWithPendingWrites();
        processed += freeClientsInAsyncFreeQueue();
        server.events_processed_while_blocked += processed;
        return;
    }

    /* Handle precise timeouts of blocked clients. */
    handleBlockedClientsTimeout();

    /* We should handle pending reads clients ASAP after event loop. */
    handleClientsWithPendingReadsUsingThreads();

    /* Handle TLS pending data. (must be done before flushAppendOnlyFile) */
    tlsProcessPendingData();

    /* If tls still has pending unread data don't sleep at all. */
    aeSetDontWait(server.el, tlsHasPendingData());

    /* Call the Redis Cluster before sleep function. Note that this function
     * may change the state of Redis Cluster (from ok to fail or vice versa),
     * so it's a good idea to call it before serving the unblocked clients
     * later in this function. */
    if (server.cluster_enabled) clusterBeforeSleep();

    /* Run a fast expire cycle (the called function will return
     * ASAP if a fast cycle is not needed). */
    if (server.active_expire_enabled && server.masterhost == NULL)
        activeExpireCycle(ACTIVE_EXPIRE_CYCLE_FAST);

    /* Unblock all the clients blocked for synchronous replication
     * in WAIT. */
    if (listLength(server.clients_waiting_acks))
        processClientsWaitingReplicas();

    /* Check if there are clients unblocked by modules that implement
     * blocking commands. */
    if (moduleCount()) moduleHandleBlockedClients();

    /* Try to process pending commands for clients that were just unblocked. */
    if (listLength(server.unblocked_clients))
        processUnblockedClients();

    /* Send all the slaves an ACK request if at least one client blocked
     * during the previous event loop iteration. Note that we do this after
     * processUnblockedClients(), so if there are multiple pipelined WAITs
     * and the just unblocked WAIT gets blocked again, we don't have to wait
     * a server cron cycle in absence of other event loop events. See #6623.
     * 
     * We also don't send the ACKs while clients are paused, since it can
     * increment the replication backlog, they'll be sent after the pause
     * if we are still the master. */
    if (server.get_ack_from_slaves && !checkClientPauseTimeoutAndReturnIfPaused()) {
        robj *argv[3];

        argv[0] = shared.replconf;
        argv[1] = shared.getack;
        argv[2] = shared.special_asterick; /* Not used argument. */
        replicationFeedSlaves(server.slaves, server.slaveseldb, argv, 3);
        server.get_ack_from_slaves = 0;
    }

    /* We may have recieved updates from clients about their current offset. NOTE:
     * this can't be done where the ACK is recieved since failover will disconnect 
     * our clients. */
    updateFailoverStatus();

    /* Send the invalidation messages to clients participating to the
     * client side caching protocol in broadcasting (BCAST) mode. */
    trackingBroadcastInvalidationMessages();

    /* Write the AOF buffer on disk */
    if (server.aof_state == AOF_ON)
        flushAppendOnlyFile(0);

    /* Handle writes with pending output buffers. */
    handleClientsWithPendingWritesUsingThreads();

    /* Close clients that need to be closed asynchronous */
    freeClientsInAsyncFreeQueue();

    /* Try to process blocked clients every once in while. Example: A module
     * calls RM_SignalKeyAsReady from within a timer callback (So we don't
     * visit processCommand() at all). */
    handleClientsBlockedOnKeys();

    /* Before we are going to sleep, let the threads access the dataset by
     * releasing the GIL. Redis main thread will not touch anything at this
     * time. */
    if (moduleCount()) moduleReleaseGIL();

    /* Do NOT add anything below moduleReleaseGIL !!! */
}

void aeMain(aeEventLoop *eventLoop) {
    eventLoop->stop = 0;
    while (!eventLoop->stop) {
        aeProcessEvents(eventLoop, AE_ALL_EVENTS|
                                   AE_CALL_BEFORE_SLEEP|
                                   AE_CALL_AFTER_SLEEP);
    }
}

/* After sleep callback. */
if (eventLoop->aftersleep != NULL && flags & AE_CALL_AFTER_SLEEP)
    eventLoop->aftersleep(eventLoop);

// 写：sendReplyToClient
// 读：readQueryFromClient