Giraph源码分析――启动ZooKeeper服务 - 数据库编程

），然后退出for循环，发现hostNameTaskMap的size等于1，直接退出while循环。那么此处就选了test162 0。

最后，创建了文件：_bsp/_defaultZkManagerDir/job_201403301409_0006/zkServerList_test162 0

onlineZooKeeperServers()，根据zkServerList_test162 0文件，Task 0 先生成zoo.cfg配置文件，使用ProcessBuilder来创建ZooKeeper服务进程，然后Task 0 再通过socket连接到ZooKeeper服务进程上，最后创建文件 _bsp/_defaultZkManagerDir/job_201403301409_0006/_zkServer/test162 0 来标记master任务已完成。worker一直在进行循环检测master是否生成好 _bsp/_defaultZkManagerDir/job_201403301409_0006/_zkServer/test162 0，即worker等待直到master上的ZooKeeper服务已经启动完成。

启动ZooKeeper服务的命令如下：

3) determineGraphFunctions()。

GraphTaskManager类中有CentralizedServiceMaster对象和CentralizedServiceWorker 对象，分别对应于master和worker。每个BSP compute node扮演的角色判定逻辑如下：

a) If not split master, everyone does the everything and/or running ZooKeeper.

b) If split master/worker, masters also run ZooKeeper

c) If split master/worker == true and giraph.zkList is set, the master will not instantiate a ZK instance, but will assume a quorum is already active on the cluster for Giraph to use.

该判定在GraphTaskManager 类中的静态方法determineGraphFunctions()中定义，片段代码如下：

 private static GraphFunctions determineGraphFunctions(
      ImmutableClassesGiraphConfiguration conf,
      ZooKeeperManager zkManager) {
    // What functions should this mapper do 
    if (!splitMasterWorker) {
      if ((zkManager != null) && zkManager.runsZooKeeper()) {
        functions = GraphFunctions.ALL;
      } else {
        functions = GraphFunctions.ALL_EXCEPT_ZOOKEEPER;
      }
    } else {
      if (zkAlreadyProvided) {
        int masterCount = conf.getZooKeeperServerCount();
        if (taskPartition < masterCount) {
          functions = GraphFunctions.MASTER_ONLY;
        } else {
          functions = GraphFunctions.WORKER_ONLY;
        }
      } else {
        if ((zkManager != null) && zkManager.runsZooKeeper()) {
          functions = GraphFunctions.MASTER_ZOOKEEPER_ONLY;
        } else {
          functions = GraphFunctions.WORKER_ONLY;
        }
      }
    }
    return functions;
  }

默认的，Giraph会区分master和worker。会在master上面启动zookeeper服务，不会在worker上启动ZooKeeper服务。那么Task 0 就是master+ZooKeeper，其他Tasks就是workers。

Giraph源码分析――启动ZooKeeper服务(三)