Redis源码阅读笔记-服务器启动和初始化

服务器的启动

Redis服务器的main函数是在server.c中。

// server.c

int main(int argc, char **argv) {
    struct timeval tv;
    int j;
	
	 /* 对服务器一些常量等进行设置 */ 
    /* 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. */
    // OutOfMemory时的处理，主要是打印到日志中
    zmalloc_set_oom_handler(redisOutOfMemoryHandler);
    srand(time(NULL)^getpid());
    gettimeofday(&tv,NULL);

    char hashseed[16];
    getRandomHexChars(hashseed,sizeof(hashseed));
    dictSetHashFunctionSeed((uint8_t*)hashseed);
    // 判断是不是sentinel模式（哨兵模式）
    server.sentinel_mode = checkForSentinelMode(argc,argv);
    // 初始化Redis server的常量配置
    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) {
        // 若是是sentinel模式，则进行sentinel的配置初始化
        initSentinelConfig();
        initSentinel();
    }
	
	// 下面是对命令和参数进行处理，判断是不是执行server启动的命令，或者其余命令
    /* 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] 为执行的程序名称
    // 执行的是否为redis-check-rdb RDB文件检查工具
    if (strstr(argv[0],"redis-check-rdb") != NULL)
        redis_check_rdb_main(argc,argv,NULL);
    // 执行的是否为redis-check-aof  AOF文件修复工具
    else if (strstr(argv[0],"redis-check-aof") != NULL)
        redis_check_aof_main(argc,argv);
    
    // 判断是否只是输出提示的的命令操做
    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);
            }
        }
        
        // 获取指定配置文件的路径
        /* 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");
    }

    // 定义是upstart仍是systemd接管redis进程
    server.supervised = redisIsSupervised(server.supervised_mode);
    int background = server.daemonize && !server.supervised;
    // 是否在后台执行
    if (background) daemonize();

    // 初始化服务
    initServer();
    if (background || server.pidfile) createPidFile();
    redisSetProcTitle(argv[0]);
    redisAsciiArt();
    checkTcpBacklogSettings();

    // 打印部分警告或者提示
    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);
    }

    // 设置每次事件循环等待前的事件处理
    aeSetBeforeSleepProc(server.el,beforeSleep);
    // 设置每次事件循环等待后的事件处理
    aeSetAfterSleepProc(server.el,afterSleep);
    // 进入事件循环
    aeMain(server.el);
    aeDeleteEventLoop(server.el);
    return 0;
}

整个启动的顺序大概是：

1. 设置部分全局变量，好比hash种子等。
2. 解析命令和命令行参数，若是执行的不是redis-server或者是redis-server的其余(好比--version等)命令，则指定对应命令后退出。
3. 准备启动服务，调用initServer()初始化服务，会开始监听对应的端口，和把要监控的时间/文件事件添加到EventLoop中。
4. 设置EventLoop的 事件循环等待前的事件处理 和 事件循环等待后的事件处理，而后进入aeMain()事件的监听和循环，默认的IO多路复用是epoll。

其中ae.c是封装好的事件循环调用，而ae_epoll.c和ae_select.c等则是封装epoll和select等的代码，使它们都由一个统一的接口。

服务器初始化initServer()

// server.c

// 初始化服务器，监听端口，设置事件回调，申请须要的内存等
void initServer(void) {
    int j;
	
	 // 设置信号的处理 
    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);
    }
	
	 // 为server变量的部分值设置和初始化变量
    server.hz = server.config_hz;
    server.pid = getpid();// 进程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();
    
    // 建立一个能够共享的对象，主要是SDS结构的对象
    createSharedObjects();
    // 根据最大客户端数等，设置文件(socket, pipe等)打开数量限制
    adjustOpenFilesLimit();
    // 建立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);

    // 监听TCP端口
    /* 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);

	 // 监听Unix scoket
    /* 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);
    }

    // 判断是否监听端口成功
    /* 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. */
    // 初始化默认的数据库，默认为16个
    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. */
    // 时间事件，虽然这里设置了1毫秒，可是是为了保证每一个EventLoop有时间或者timeout后，都能执行
    if (aeCreateTimeEvent(server.el, 1, serverCron, NULL, NULL) == AE_ERR) {
        serverPanic("Can't create event loop timers.");
        exit(1);
    }

    // 为监听的端口的fd设置epoll事件和回调， 针对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.");
            }
    }
    // 为Unix socket的fd设置epoll事件和回调， 针对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.");


    // 针对管道的事件回调
    /* 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.");
    }

    // 是否打开AOF
    /* 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);
        }
    }

    // 针对32位系统的内存限制，限制为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;
    }

    // 是否打开redis集群
    if (server.cluster_enabled) clusterInit();
    replicationScriptCacheInit();
    scriptingInit(1);
    slowlogInit();
    latencyMonitorInit();
    bioInit();
    server.initial_memory_usage = zmalloc_used_memory();
}

initServer()主要作了：

• 获取系统部分限制，好比文件最大打开数和32位系统下限制最大3G内存使用。
• 开始监听对应的TCP socket、Unix socket等，并将它们加入到EventLoop中监听读事件。
• 将ServerCron函数加加入到时间事件中。
• 初始化其余各类功能。