一、概括:

wordcount作业提交流程,主要集中在JobSubmitter.submitJobInternal中，包括检测输出目录合法性，设置作业提交信息（主机和用户），获得JobID，向HDFS中拷贝作业所需文件（Job.jar Job.xml split文件等）最后执行作业提交。这里以WordCount为例介绍提交流程.

二、wordcount流程代码

public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {

        //step 1: 获取job对象
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration);

        String input = "data/wc.data";
        String output = "out/";
        FileUtils.deleteTarget(output, configuration);

        //step 2: 设置jar的相关信息
        job.setJarByClass(WordCountApp.class);

        //step 3:设置自定义的mapper和reducer信息
        job.setMapperClass(MyMapper.class);
        job.setReducerClass(MyReducer.class);

        //step 4:设置mapper阶段输出的key和value类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);

        //step 5:设置reducer阶段输出的key和value类型
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        //step 6:设置输入输出路径
        FileInputFormat.setInputPaths(job, new Path(input));
        FileOutputFormat.setOutputPath(job, new Path(output));

        //step 7:提交job
        boolean result = job.waitForCompletion(true);//此处进入作业提交流程，然后循环监控作业状态 
        System.exit(result ? 0 : 1);
    }

三、流程主要代码讲解

• waitForCompletion方法中主要是提交作业和监控状态，这里我们主要分析作业提交

public boolean waitForCompletion(boolean verbose
                                   ) throws IOException, InterruptedException,
                                            ClassNotFoundException {
    if (state == JobState.DEFINE) {
      //提交作业
      submit();
    }
    if (verbose) {
      //监控job，并实时打印任务状态
      monitorAndPrintJob();
    } else {
      // get the completion poll interval from the client.
      int completionPollIntervalMillis = 
        Job.getCompletionPollInterval(cluster.getConf());
      while (!isComplete()) {
        try {
          Thread.sleep(completionPollIntervalMillis);
        } catch (InterruptedException ie) {
        }
      }
    }
    return isSuccessful();
  }

• submit方法中主要是:1.连接集群。2.作业提交

public void submit() 
         throws IOException, InterruptedException, ClassNotFoundException {
    ensureState(JobState.DEFINE);
    setUseNewAPI();
    //连接集群（lcoal ，Yarn）
    connect();
    final JobSubmitter submitter = 
        getJobSubmitter(cluster.getFileSystem(), cluster.getClient());
    status = ugi.doAs(new PrivilegedExceptionAction<JobStatus>() {
      public JobStatus run() throws IOException, InterruptedException, 
      ClassNotFoundException {
         //提交作业
        return submitter.submitJobInternal(Job.this, cluster);
      }
    });
    state = JobState.RUNNING;
    LOG.info("The url to track the job: " + getTrackingURL());
   }

• 连接集群时会通过conf构造一个cluster实例，重要的是cluster的初始化部份

private synchronized void connect()
          throws IOException, InterruptedException, ClassNotFoundException {
    if (cluster == null) {
      cluster = 
        ugi.doAs(new PrivilegedExceptionAction<Cluster>() {
                   public Cluster run()
                          throws IOException, InterruptedException, 
                                 ClassNotFoundException {
                     return new Cluster(getConfiguration());
                   }
                 });
    }
  }

public Cluster(Configuration conf) throws IOException {
    this(null, conf);
  }

  public Cluster(InetSocketAddress jobTrackAddr, Configuration conf) 
      throws IOException {
    this.conf = conf;
    this.ugi = UserGroupInformation.getCurrentUser();
    initialize(jobTrackAddr, conf);
  }

private void initialize(InetSocketAddress jobTrackAddr, Configuration conf)
      throws IOException {

    synchronized (frameworkLoader) {
      for (ClientProtocolProvider provider : frameworkLoader) {
        LOG.debug("Trying ClientProtocolProvider : "
            + provider.getClass().getName());
        ClientProtocol clientProtocol = null; 
        try {
          if (jobTrackAddr == null) {
            //实际上是根据你的配置创建YarnRunner对象，还是LocalJobRunner对象
            clientProtocol = provider.create(conf);
          } else {
            clientProtocol = provider.create(jobTrackAddr, conf);
          }
          //初始化cluster内部成员变量
          if (clientProtocol != null) {
            clientProtocolProvider = provider;
            client = clientProtocol;
            LOG.debug("Picked " + provider.getClass().getName()
                + " as the ClientProtocolProvider");
            break;
          }
          else {
            LOG.debug("Cannot pick " + provider.getClass().getName()
                + " as the ClientProtocolProvider - returned null protocol");
          }
        } 
        catch (Exception e) {
          LOG.info("Failed to use " + provider.getClass().getName()
              + " due to error: " + e.getMessage());
        }
      }
    }

    if (null == clientProtocolProvider || null == client) {
      throw new IOException(
          "Cannot initialize Cluster. Please check your configuration for "
              + MRConfig.FRAMEWORK_NAME
              + " and the correspond server addresses.");
    }
  }

• YARNRunner 构造方法

public YARNRunner(Configuration conf, ResourceMgrDelegate resMgrDelegate,
      ClientCache clientCache) {
    this.conf = conf;
    try {
      this.resMgrDelegate = resMgrDelegate;
      this.clientCache = clientCache;
      this.defaultFileContext = FileContext.getFileContext(this.conf);
    } catch (UnsupportedFileSystemException ufe) {
      throw new RuntimeException("Error in instantiating YarnClient", ufe);
    }
  }

• ResourceMgrDelegate构造方法

public ResourceMgrDelegate(YarnConfiguration conf) {
    super(ResourceMgrDelegate.class.getName());
    this.conf = conf;
    //实际上是创建YarnClientImpl对象
    this.client = YarnClient.createYarnClient();
    init(conf);
    //实际上是创建rmClient对象
    start();
  }

• 接下来看JobSubmitter.submitJobInternal

JobStatus submitJobInternal(Job job, Cluster cluster) 
  throws ClassNotFoundException, InterruptedException, IOException {
    
    //检测输出目录合法性，是否已存在，或未设置
    //validate the jobs output specs 
    checkSpecs(job);

    Configuration conf = job.getConfiguration();
    addMRFrameworkToDistributedCache(conf);
    //获取staging路径，用以存放作业执行过程中用到的文件，默认位置/tmp/hadoop-yarn/staging/hadoop/.staging ，可通过yarn.app.mapreduce.am.staging-dir修改
    Path jobStagingArea = JobSubmissionFiles.getStagingDir(cluster, conf);
    //configure the command line options correctly on the submitting dfs
    //主机名和地址设置 
    InetAddress ip = InetAddress.getLocalHost();
    if (ip != null) {
      submitHostAddress = ip.getHostAddress();
      submitHostName = ip.getHostName();
      conf.set(MRJobConfig.JOB_SUBMITHOST,submitHostName);
      conf.set(MRJobConfig.JOB_SUBMITHOSTADDR,submitHostAddress);
    }
     //获取新的JobID，此处需要RPC调用
    JobID jobId = submitClient.getNewJobID();
    job.setJobID(jobId);
    //获取提交的job目录：/tmp/hadoop-yarn/staging/root/.staging/job_xxxxxx
    Path submitJobDir = new Path(jobStagingArea, jobId.toString());
    JobStatus status = null;
    try {
      conf.set(MRJobConfig.USER_NAME,
          UserGroupInformation.getCurrentUser().getShortUserName());
      conf.set("hadoop.http.filter.initializers", 
          "org.apache.hadoop.yarn.server.webproxy.amfilter.AmFilterInitializer");
      conf.set(MRJobConfig.MAPREDUCE_JOB_DIR, submitJobDir.toString());
      LOG.debug("Configuring job " + jobId + " with " + submitJobDir 
          + " as the submit dir");
      // get delegation token for the dir
      TokenCache.obtainTokensForNamenodes(job.getCredentials(),
          new Path[] { submitJobDir }, conf);
      
      populateTokenCache(conf, job.getCredentials());

      // generate a secret to authenticate shuffle transfers
      if (TokenCache.getShuffleSecretKey(job.getCredentials()) == null) {
        KeyGenerator keyGen;
        try {
         
          int keyLen = CryptoUtils.isShuffleEncrypted(conf) 
              ? conf.getInt(MRJobConfig.MR_ENCRYPTED_INTERMEDIATE_DATA_KEY_SIZE_BITS, 
                  MRJobConfig.DEFAULT_MR_ENCRYPTED_INTERMEDIATE_DATA_KEY_SIZE_BITS)
              : SHUFFLE_KEY_LENGTH;
          keyGen = KeyGenerator.getInstance(SHUFFLE_KEYGEN_ALGORITHM);
          keyGen.init(keyLen);
        } catch (NoSuchAlgorithmException e) {
          throw new IOException("Error generating shuffle secret key", e);
        }
        SecretKey shuffleKey = keyGen.generateKey();
        TokenCache.setShuffleSecretKey(shuffleKey.getEncoded(),
            job.getCredentials());
      }
      //向集群中拷贝所需文件，包含-files, -libjars and -archives和你作业的jar包
      copyAndConfigureFiles(job, submitJobDir);
      
      //设置job.xml路径
      Path submitJobFile = JobSubmissionFiles.getJobConfPath(submitJobDir);
     
      // Create the splits for the job
      LOG.debug("Creating splits at " + jtFs.makeQualified(submitJobDir));
       // 写分片文件(job.split文件、job.splitmetainfo文件)到提交的目录
       //获取map数量
      int maps = writeSplits(job, submitJobDir);
      conf.setInt(MRJobConfig.NUM_MAPS, maps);
      LOG.info("number of splits:" + maps);

      // write "queue admins of the queue to which job is being submitted"
      // to job file.
      //设置队列名
      String queue = conf.get(MRJobConfig.QUEUE_NAME,
          JobConf.DEFAULT_QUEUE_NAME);
      AccessControlList acl = submitClient.getQueueAdmins(queue);
      conf.set(toFullPropertyName(queue,
          QueueACL.ADMINISTER_JOBS.getAclName()), acl.getAclString());

      // removing jobtoken referrals before copying the jobconf to HDFS
      // as the tasks don't need this setting, actually they may break
      // because of it if present as the referral will point to a
      // different job.
      TokenCache.cleanUpTokenReferral(conf);

      if (conf.getBoolean(
          MRJobConfig.JOB_TOKEN_TRACKING_IDS_ENABLED,
          MRJobConfig.DEFAULT_JOB_TOKEN_TRACKING_IDS_ENABLED)) {
        // Add HDFS tracking ids
        ArrayList<String> trackingIds = new ArrayList<String>();
        for (Token<? extends TokenIdentifier> t :
            job.getCredentials().getAllTokens()) {
          trackingIds.add(t.decodeIdentifier().getTrackingId());
        }
        conf.setStrings(MRJobConfig.JOB_TOKEN_TRACKING_IDS,
            trackingIds.toArray(new String[trackingIds.size()]));
      }

      // Set reservation info if it exists
      ReservationId reservationId = job.getReservationId();
      if (reservationId != null) {
        conf.set(MRJobConfig.RESERVATION_ID, reservationId.toString());
      }

      // Write job file to submit dir
      //将本job信息写入job.xml 到提交的目录
      writeConf(conf, submitJobFile);
      
      //
      // Now, actually submit the job (using the submit name)
      //
      printTokens(jobId, job.getCredentials());
      //真正提交job到RM，底层是通过rmClient提交应用
      status = submitClient.submitJob(
          jobId, submitJobDir.toString(), job.getCredentials());
      if (status != null) {
        return status;
      } else {
        throw new IOException("Could not launch job");
      }
    } finally {
      if (status == null) {
        LOG.info("Cleaning up the staging area " + submitJobDir);
        if (jtFs != null && submitJobDir != null)
          //删除提交的目录
          jtFs.delete(submitJobDir, true);
      }
    }
  }

• writeSplits方法中主要的writeNewSplits方法

private <T extends InputSplit>
  int writeNewSplits(JobContext job, Path jobSubmitDir) throws IOException,
      InterruptedException, ClassNotFoundException {
    Configuration conf = job.getConfiguration();
    //反射获取输入的inputFormat类型，默认是TextInputFormat
    InputFormat<?, ?> input =
      ReflectionUtils.newInstance(job.getInputFormatClass(), conf);
    //inputFomat对读取的文件进行分片操作
    List<InputSplit> splits = input.getSplits(job);
    T[] array = (T[]) splits.toArray(new InputSplit[splits.size()]);

    // sort the splits into order based on size, so that the biggest
    // go first
    //对分片进行排序，把分片大的放数组前面
    Arrays.sort(array, new SplitComparator());
    //将分片文件写入提交的目录中去
    JobSplitWriter.createSplitFiles(jobSubmitDir, conf, 
        jobSubmitDir.getFileSystem(conf), array);
    return array.length;
  }

• 默认是走的TextInputFormat的getSplit方法

public List<InputSplit> getSplits(JobContext job) throws IOException {
    Stopwatch sw = new Stopwatch().start();
    //分片最小size，默认为1
    long minSize = Math.max(getFormatMinSplitSize(), getMinSplitSize(job));
    //分片最大size，默认为Long.MAX_VALUE
    long maxSize = getMaxSplitSize(job);

    // generate splits
    List<InputSplit> splits = new ArrayList<InputSplit>();
    //获取文件的文件状态
    List<FileStatus> files = listStatus(job);
    for (FileStatus file: files) {
      Path path = file.getPath();
      long length = file.getLen();
      //如果文件大小不为0
      if (length != 0) {
        //获取文件block地址
        BlockLocation[] blkLocations;
        if (file instanceof LocatedFileStatus) {
          blkLocations = ((LocatedFileStatus) file).getBlockLocations();
        } else {
          FileSystem fs = path.getFileSystem(job.getConfiguration());
          blkLocations = fs.getFileBlockLocations(file, 0, length);
        }
        //判断文件是否可分割
        if (isSplitable(job, path)) {
          //获取文件blocksize，默认128M
          long blockSize = file.getBlockSize();
          //计算splitSize，具体就是取中间那个。
          long splitSize = computeSplitSize(blockSize, minSize, maxSize);

          long bytesRemaining = length;
          //如果bytesRemaining)/splitSize>1.1就执行
          while (((double) bytesRemaining)/splitSize > SPLIT_SLOP) {
            int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining);
            splits.add(makeSplit(path, length-bytesRemaining, splitSize,
                        blkLocations[blkIndex].getHosts(),
                        blkLocations[blkIndex].getCachedHosts()));
            bytesRemaining -= splitSize;
          }
          //添加最后一个块信息到splits数组中
          if (bytesRemaining != 0) {
            int blkIndex = getBlockIndex(blkLocations, length-bytesRemaining);
            splits.add(makeSplit(path, length-bytesRemaining, bytesRemaining,
                       blkLocations[blkIndex].getHosts(),
                       blkLocations[blkIndex].getCachedHosts()));
          }
        } else { // not splitable
          //不可分的，直接作为一个块加到splits数组中
          splits.add(makeSplit(path, 0, length, blkLocations[0].getHosts(),
                      blkLocations[0].getCachedHosts()));
        }
      } else { 
        //Create empty hosts array for zero length files
        splits.add(makeSplit(path, 0, length, new String[0]));
      }
    }
    // Save the number of input files for metrics/loadgen
    job.getConfiguration().setLong(NUM_INPUT_FILES, files.size());
    sw.stop();
    if (LOG.isDebugEnabled()) {
      LOG.debug("Total # of splits generated by getSplits: " + splits.size()
          + ", TimeTaken: " + sw.elapsedMillis());
    }
    return splits;
  }