菜鸡学习zookeeper源码（一）查找入口

第一步寻找入口

? ? ? ? ? 相信有很多人跟我一样都想看一看一些优秀的开源项目的代码，但是呢，由于各种原因都没有坚持下去，可能是因为没时间，坚持不下去，不知道该怎么看等等，好了废话不多说。直接开始看。第一步寻找zookeeper源码的入口，zookeeper的代码有很多，千头万绪总有一个开始的位置，这步我是借鉴网上的一个例子，直接找的是zookeeper的启动文件：zookeeper.sh? zookeeper.sh是zookeeper的启动文件。从这个文件中，我们可以看到

、这个文件中出现频率最高的就是org.apache.zookeeper.server.quorum.QuorumPeerMain这个java类 我就姑且任务这个是zookeeper启动类 从这个类开始看

开始分析QuorumPeerMain

? 优秀的开源代码就是比较好点，上面有很多注释，从注释上看QuorumPeerMain 这个类是配置相关的类。下面是关于这个类的一些注释信息

/**
 *
 * <h2>Configuration file</h2>
 *
 * When the main() method of this class is used to start the program, the first
 * argument is used as a path to the config file, which will be used to obtain
 * configuration information. This file is a Properties file, so keys and
 * values are separated by equals (=) and the key/value pairs are separated
 * by new lines. The following is a general summary of keys used in the
 * configuration file. For full details on this see the documentation in
 * docs/index.html
 * <ol>
 * <li>dataDir - The directory where the ZooKeeper data is stored.</li>
 * <li>dataLogDir - The directory where the ZooKeeper transaction log is stored.</li>
 * <li>clientPort - The port used to communicate with clients.</li>
 * <li>tickTime - The duration of a tick in milliseconds. This is the basic
 * unit of time in ZooKeeper.</li>
 * <li>initLimit - The maximum number of ticks that a follower will wait to
 * initially synchronize with a leader.</li>
 * <li>syncLimit - The maximum number of ticks that a follower will wait for a
 * message (including heartbeats) from the leader.</li>
 * <li>server.<i>id</i> - This is the host:port[:port] that the server with the
 * given id will use for the quorum protocol.</li>
 * </ol>
 * In addition to the config file. There is a file in the data directory called
 * "myid" that contains the server id as an ASCII decimal value.
 *
 */

从上面看，感觉这个类主要是进行一些配置文件的解析操作，然后我们进行看下这个QuorumPeerMain类的main方法

 public static void main(String[] args) {
        QuorumPeerMain main = new QuorumPeerMain();
        try {
            // 从字面看是 开始进行初始化并进行运行操作
            //后面进行验证一下是不是 
            main.initializeAndRun(args);
        } catch (IllegalArgumentException e) {
            LOG.error("Invalid arguments, exiting abnormally", e);
            LOG.info(USAGE);
            System.err.println(USAGE);
            ZKAuditProvider.addServerStartFailureAuditLog();
            ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
        } catch (ConfigException e) {
            LOG.error("Invalid config, exiting abnormally", e);
            System.err.println("Invalid config, exiting abnormally");
            ZKAuditProvider.addServerStartFailureAuditLog();
            ServiceUtils.requestSystemExit(ExitCode.INVALID_INVOCATION.getValue());
        } catch (DatadirException e) {
            LOG.error("Unable to access datadir, exiting abnormally", e);
            System.err.println("Unable to access datadir, exiting abnormally");
            ZKAuditProvider.addServerStartFailureAuditLog();
            ServiceUtils.requestSystemExit(ExitCode.UNABLE_TO_ACCESS_DATADIR.getValue());
        } catch (AdminServerException e) {
            LOG.error("Unable to start AdminServer, exiting abnormally", e);
            System.err.println("Unable to start AdminServer, exiting abnormally");
            ZKAuditProvider.addServerStartFailureAuditLog();
            ServiceUtils.requestSystemExit(ExitCode.ERROR_STARTING_ADMIN_SERVER.getValue());
        } catch (Exception e) {
            LOG.error("Unexpected exception, exiting abnormally", e);
            ZKAuditProvider.addServerStartFailureAuditLog();
            ServiceUtils.requestSystemExit(ExitCode.UNEXPECTED_ERROR.getValue());
        }
        LOG.info("Exiting normally");
        ServiceUtils.requestSystemExit(ExitCode.EXECUTION_FINISHED.getValue());
    }

    
 protected void initializeAndRun(String[] args) throws ConfigException, IOException, AdminServerException {
        QuorumPeerConfig config = new QuorumPeerConfig();
        if (args.length == 1) {
            // 进行解析配置文件信息 
            config.parse(args[0]);
        }

        // Start and schedule the the purge task
        DatadirCleanupManager purgeMgr = new DatadirCleanupManager(
            config.getDataDir(),
            config.getDataLogDir(),
            config.getSnapRetainCount(),
            config.getPurgeInterval());
        purgeMgr.start();

        if (args.length == 1 && config.isDistributed()) {
            runFromConfig(config);
        } else {
            LOG.warn("Either no config or no quorum defined in config, running in standalone mode");
            // there is only server in the quorum -- run as standalone
            ZooKeeperServerMain.main(args);
        }
    }

这块其实可以直接看?purgeMgr.start() 这个方法 或者 runFromConfig(config);但是我自己就是想看下是怎么进行解析参数的，我就点击进去看下参数解析。

参数解析操作

public void parse(String path) throws ConfigException {
        LOG.info("Reading configuration from: " + path);

        try {
            File configFile = (new VerifyingFileFactory.Builder(LOG)
                .warnForRelativePath()
                .failForNonExistingPath()
                .build()).create(path);

            Properties cfg = new Properties();
            try (FileInputStream in = new FileInputStream(configFile)) {
                cfg.load(in);
                configFileStr = path;
            }

            /* Read entire config file as initial configuration */
            initialConfig = new String(Files.readAllBytes(configFile.toPath()));

            parseProperties(cfg);
        } catch (IOException e) {
            throw new ConfigException("Error processing " + path, e);
        } catch (IllegalArgumentException e) {
            throw new ConfigException("Error processing " + path, e);
        }

        if (dynamicConfigFileStr != null) {
            try {
                Properties dynamicCfg = new Properties();
                try (FileInputStream inConfig = new FileInputStream(dynamicConfigFileStr)) {
                    dynamicCfg.load(inConfig);
                    if (dynamicCfg.getProperty("version") != null) {
                        throw new ConfigException("dynamic file shouldn't have version inside");
                    }

                    String version = getVersionFromFilename(dynamicConfigFileStr);
                    // If there isn't any version associated with the filename,
                    // the default version is 0.
                    if (version != null) {
                        dynamicCfg.setProperty("version", version);
                    }
                }
                setupQuorumPeerConfig(dynamicCfg, false);

            } catch (IOException e) {
                throw new ConfigException("Error processing " + dynamicConfigFileStr, e);
            } catch (IllegalArgumentException e) {
                throw new ConfigException("Error processing " + dynamicConfigFileStr, e);
            }
            File nextDynamicConfigFile = new File(configFileStr + nextDynamicConfigFileSuffix);
            if (nextDynamicConfigFile.exists()) {
                try {
                    Properties dynamicConfigNextCfg = new Properties();
                    try (FileInputStream inConfigNext = new FileInputStream(nextDynamicConfigFile)) {
                        dynamicConfigNextCfg.load(inConfigNext);
                    }
                    boolean isHierarchical = false;
                    for (Entry<Object, Object> entry : dynamicConfigNextCfg.entrySet()) {
                        String key = entry.getKey().toString().trim();
                        if (key.startsWith("group") || key.startsWith("weight")) {
                            isHierarchical = true;
                            break;
                        }
                    }
                    lastSeenQuorumVerifier = createQuorumVerifier(dynamicConfigNextCfg, isHierarchical);
                } catch (IOException e) {
                    LOG.warn("NextQuorumVerifier is initiated to null");
                }
            }
        }
    }

从上面看就是一个比较简单的从配置文件中读取配置信息的方法，没有什么特殊的逻辑

?purgeMgr.start();

这个方法点击进去看，说是进行一些清理动作，进行追踪代码可以看到后面进行执行了一个PurgeTask任务，这个任务像是在清理一些快照和一些日志信息，具体快照和日志里有什么，我们后面继续看，这块就直接跳过。

启动服务

    if (args.length == 1 && config.isDistributed()) {
            runFromConfig(config);
        } else {
            LOG.warn("Either no config or no quorum defined in config, running in standalone mode");
            // there is only server in the quorum -- run as standalone
            ZooKeeperServerMain.main(args);
        }

下面就到了两个分支的操作

一个是runFromConfig 一个是ZooKeeperServerMain的启动 这个我们下面接着看