Start of server

The main function of Redis server is in server.c.

// server.c

int main(int argc, char **argv) {
    struct timeval tv;
    int j;
	
	 /* Set some constants of the server */ 
    /* We need to initialize our libraries, and the server configuration. */
#ifdef INIT_SETPROCTITLE_REPLACEMENT
    spt_init(argc, argv);
#endif
    setlocale(LC_COLLATE,"");
    tzset(); /* Populates 'timezone' global. */
    // The processing of OutOfMemory is mainly to print to the log
    zmalloc_set_oom_handler(redisOutOfMemoryHandler);
    srand(time(NULL)^getpid());
    gettimeofday(&tv,NULL);

    char hashseed[16];
    getRandomHexChars(hashseed,sizeof(hashseed));
    dictSetHashFunctionSeed((uint8_t*)hashseed);
    // Determine whether it is sentinel mode
    server.sentinel_mode = checkForSentinelMode(argc,argv);
    // Initialize constant configuration of Redis server
    initServerConfig();
    moduleInitModulesSystem();

    /* Store the executable path and arguments in a safe place in order
     * to be able to restart the server later. */
    server.executable = getAbsolutePath(argv[0]);
    server.exec_argv = zmalloc(sizeof(char*)*(argc+1));
    server.exec_argv[argc] = NULL;
    for (j = 0; j < argc; j++) server.exec_argv[j] = zstrdup(argv[j]);

    /* We need to init sentinel right now as parsing the configuration file
     * in sentinel mode will have the effect of populating the sentinel
     * data structures with master nodes to monitor. */
    if (server.sentinel_mode) {
        // If it is sentinel mode, perform sentinel configuration initialization
        initSentinelConfig();
        initSentinel();
    }
	
	// The following is the processing of commands and parameters to determine whether the commands started by the server or other commands are executed
    /* 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. */
    // argv[0] is the executed program name
    // Is the redis check RDB RDB file checking tool executed
    if (strstr(argv[0],"redis-check-rdb") != NULL)
        redis_check_rdb_main(argc,argv,NULL);
    // Whether the executed is the redis check AOF AOF file repair tool
    else if (strstr(argv[0],"redis-check-aof") != NULL)
        redis_check_aof_main(argc,argv);
    
    // Command operation to determine whether it is only output prompt
    if (argc >= 2) {
        j = 1; /* First option to parse in argv[] */
        sds options = sdsempty();
        char *configfile = NULL;

        /* 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);
            }
        }
        
        // Gets the path to the specified profile
        /* First argument is the config file name? */
        if (argv[j][0] != '-' || argv[j][1] != '-') {
            configfile = argv[j];
            server.configfile = getAbsolutePath(configfile);
            /* Replace the config file in server.exec_argv with
             * its absolute path. */
            zfree(server.exec_argv[j]);
            server.exec_argv[j] = zstrdup(server.configfile);
            j++;
        }

        /* 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 file name
         * is parsed, if any. */
        while(j != argc) {
            if (argv[j][0] == '-' && argv[j][1] == '-') {
                /* Option name */
                if (!strcmp(argv[j], "--check-rdb")) {
                    /* Argument has no options, need to skip for parsing. */
                    j++;
                    continue;
                }
                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++;
        }
        if (server.sentinel_mode && configfile && *configfile == '-') {
            serverLog(LL_WARNING,
                "Sentinel config from STDIN not allowed.");
            serverLog(LL_WARNING,
                "Sentinel needs config file on disk to save state.  Exiting...");
            exit(1);
        }
        resetServerSaveParams();
        loadServerConfig(configfile,options);
        sdsfree(options);
    }

    serverLog(LL_WARNING, "oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo");
    serverLog(LL_WARNING,
        "Redis version=%s, bits=%d, commit=%s, modified=%d, pid=%d, just started",
            REDIS_VERSION,
            (sizeof(long) == 8) ? 64 : 32,
            redisGitSHA1(),
            strtol(redisGitDirty(),NULL,10) > 0,
            (int)getpid());

    if (argc == 1) {
        serverLog(LL_WARNING, "Warning: no config file specified, using the default config. In order to specify a config file use %s /path/to/%s.conf", argv[0], server.sentinel_mode ? "sentinel" : "redis");
    } else {
        serverLog(LL_WARNING, "Configuration loaded");
    }

    // Define whether upstart or systemd takes over the redis process
    server.supervised = redisIsSupervised(server.supervised_mode);
    int background = server.daemonize && !server.supervised;
    // Whether to execute in the background
    if (background) daemonize();

    // Initialize service
    initServer();
    if (background || server.pidfile) createPidFile();
    redisSetProcTitle(argv[0]);
    redisAsciiArt();
    checkTcpBacklogSettings();

    // Print some warnings or prompts
    if (!server.sentinel_mode) {
        /* Things not needed when running in Sentinel mode. */
        serverLog(LL_WARNING,"Server initialized");
    #ifdef __linux__
        linuxMemoryWarnings();
    #endif
        moduleLoadFromQueue();
        loadDataFromDisk();
        if (server.cluster_enabled) {
            if (verifyClusterConfigWithData() == C_ERR) {
                serverLog(LL_WARNING,
                    "You can't have keys in a DB different than DB 0 when in "
                    "Cluster mode. Exiting.");
                exit(1);
            }
        }
        if (server.ipfd_count > 0)
            serverLog(LL_NOTICE,"Ready to accept connections");
        if (server.sofd > 0)
            serverLog(LL_NOTICE,"The server is now ready to accept connections at %s", server.unixsocket);
    } else {
        sentinelIsRunning();
    }

    /* Warning the user about suspicious maxmemory setting. */
    if (server.maxmemory > 0 && server.maxmemory < 1024*1024) {
        serverLog(LL_WARNING,"WARNING: You specified a maxmemory value that is less than 1MB (current value is %llu bytes). Are you sure this is what you really want?", server.maxmemory);
    }

    // Set the event handling before each event cycle waiting
    aeSetBeforeSleepProc(server.el,beforeSleep);
    // Set the event handling after each event cycle waiting
    aeSetAfterSleepProc(server.el,afterSleep);
    // Enter event loop
    aeMain(server.el);
    aeDeleteEventLoop(server.el);
    return 0;
}

The order of the whole startup is approximately:

1. Set some global variables, such as hash seed.
2. Resolve the command and command line parameters. If you are not executing redis server or other redis server commands (such as -- version, etc.), specify the corresponding command and exit.
3. Prepare to start the service, call initServer() to initialize the service, start listening to the corresponding port, and add the time / file event to be monitored to EventLoop.
4. Set the event processing before and after the event cycle waiting of EventLoop, and then enter the aeMain() event listening and cycling. The default IO multiplexing is epoll.

Among them, ae.c is the encapsulated event cycle call, while ae_epl. C and ae_select.c are the codes that encapsulate epoll and select, so that they all have a unified interface.

Server initialization initServer()

// server.c

// Initialize the server, listen to the port, set the event callback, apply for the required memory, etc
void initServer(void) {
    int j;
	
	 // Set signal processing 
    signal(SIGHUP, SIG_IGN);
    signal(SIGPIPE, SIG_IGN);
    setupSignalHandlers();

    if (server.syslog_enabled) {
        openlog(server.syslog_ident, LOG_PID | LOG_NDELAY | LOG_NOWAIT,
            server.syslog_facility);
    }
	
	 // Set and initialize variables for some values of server variables
    server.hz = server.config_hz;
    server.pid = getpid();// Process id
    server.current_client = NULL;
    server.clients = listCreate();
    server.clients_index = raxNew();
    server.clients_to_close = listCreate();
    server.slaves = listCreate();
    server.monitors = listCreate();
    server.clients_pending_write = listCreate();
    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.clients_paused = 0;
    server.system_memory_size = zmalloc_get_memory_size();
    
    // Create an object that can be shared, mainly objects of SDS structure
    createSharedObjects();
    // Set the limit on the number of files (socket, pipe, etc.) to be opened according to the maximum number of clients, etc
    adjustOpenFilesLimit();
    // Create EventLoop
    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);

    // Listen to TCP port
    /* Open the TCP listening socket for the user commands. */
    if (server.port != 0 &&
        listenToPort(server.port,server.ipfd,&server.ipfd_count) == C_ERR)
        exit(1);

	 // Listen to UNIX socket
    /* 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);
    }

    // Judge whether the listening port is successful
    /* Abort if there are no listening sockets at all. */
    if (server.ipfd_count == 0 && server.sofd < 0) {
        serverLog(LL_WARNING, "Configured to not listen anywhere, exiting.");
        exit(1);
    }

    /* Create the Redis databases, and initialize other internal state. */
    // Initialize the default database, 16 by default
    for (j = 0; j < server.dbnum; j++) {
        server.db[j].dict = dictCreate(&dbDictType,NULL);
        server.db[j].expires = dictCreate(&keyptrDictType,NULL);
        server.db[j].blocking_keys = dictCreate(&keylistDictType,NULL);
        server.db[j].ready_keys = dictCreate(&objectKeyPointerValueDictType,NULL);
        server.db[j].watched_keys = dictCreate(&keylistDictType,NULL);
        server.db[j].id = j;
        server.db[j].avg_ttl = 0;
        server.db[j].defrag_later = listCreate();
    }
    evictionPoolAlloc(); /* Initialize the LRU keys pool. */
    server.pubsub_channels = dictCreate(&keylistDictType,NULL);
    server.pubsub_patterns = listCreate();
    listSetFreeMethod(server.pubsub_patterns,freePubsubPattern);
    listSetMatchMethod(server.pubsub_patterns,listMatchPubsubPattern);
    server.cronloops = 0;
    server.rdb_child_pid = -1;
    server.aof_child_pid = -1;
    server.rdb_child_type = RDB_CHILD_TYPE_NONE;
    server.rdb_bgsave_scheduled = 0;
    server.child_info_pipe[0] = -1;
    server.child_info_pipe[1] = -1;
    server.child_info_data.magic = 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_rdb_cow_bytes = 0;
    server.stat_aof_cow_bytes = 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. */
    // Time event. Although 1 millisecond is set here, it is to ensure that every EventLoop can execute after it has time or timeout
    if (aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
        serverPanic("Can't create event loop timers.");
        exit(1);
    }

    // Set epoll event and callback for fd of listening port, for TCP socket
    /* Create an event handler for accepting new connections in TCP and Unix
     * domain sockets. */
    for (j = 0; j < server.ipfd_count; j++) {
        if (aeCreateFileEvent(server.el, server.ipfd[j], AE_READABLE,
            acceptTcpHandler,NULL) == AE_ERR)
            {
                serverPanic(
                    "Unrecoverable error creating server.ipfd file event.");
            }
    }
    // Set epoll events and callbacks for fd of Unix socket, for Unix socket
    if (server.sofd > 0 && aeCreateFileEvent(server.el,server.sofd,AE_READABLE,
        acceptUnixHandler,NULL) == AE_ERR) serverPanic("Unrecoverable error creating server.sofd file event.");


    // Event callback for pipeline
    /* 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.");
    }

    // Open AOF or not
    /* Open the AOF file if needed. */
    if (server.aof_state == AOF_ON) {
        server.aof_fd = open(server.aof_filename,
                               O_WRONLY|O_APPEND|O_CREAT,0644);
        if (server.aof_fd == -1) {
            serverLog(LL_WARNING, "Can't open the append-only file: %s",
                strerror(errno));
            exit(1);
        }
    }

    // Memory limit for 32-bit systems, limited to 3G
    /* 32 bit instances are limited to 4GB of address space, so if there is
     * no explicit limit in the user provided configuration we set a limit
     * at 3 GB using maxmemory with 'noeviction' policy'. This avoids
     * useless crashes of the Redis instance for out of memory. */
    if (server.arch_bits == 32 && server.maxmemory == 0) {
        serverLog(LL_WARNING,"Warning: 32 bit instance detected but no memory limit set. Setting 3 GB maxmemory limit with 'noeviction' policy now.");
        server.maxmemory = 3072LL*(1024*1024); /* 3 GB */
        server.maxmemory_policy = MAXMEMORY_NO_EVICTION;
    }

    // Open redis cluster
    if (server.cluster_enabled) clusterInit();
    replicationScriptCacheInit();
    scriptingInit(1);
    slowlogInit();
    latencyMonitorInit();
    bioInit();
    server.initial_memory_usage = zmalloc_used_memory();
}

initServer() mainly does the following:

• Obtain some system restrictions, such as the maximum number of files opened and the maximum 3G memory usage under 32-bit system.
• Start listening to the corresponding TCP socket, Unix socket, etc., and add them to the EventLoop to listen for read events.
• Add the ServerCron function to the time event.
• Initialize various other functions.