Samza的ApplicationMaster

AMRMClientAsync handles communication with the ResourceManager and provides asynchronous updates on events such as container allocations and completions. It contains a thread that sends periodic heartbeats to the ResourceManager. It should be used by implementing a CallbackHandler:

 class MyCallbackHandler implements AMRMClientAsync.CallbackHandler {
   public void onContainersAllocated(List<Container> containers) {
     [run tasks on the containers]
   }
   
   public void onContainersCompleted(List<ContainerStatus> statuses) {
     [update progress, check whether app is done]
   }
   
   public void onNodesUpdated(List<NodeReport> updated) {}
   
   public void onReboot() {}
 }
 
 

 AMRMClientAsync asyncClient = 
     createAMRMClientAsync(appAttId, 1000, new MyCallbackhandler());
 asyncClient.init(conf);
 asyncClient.start();
 RegisterApplicationMasterResponse response = asyncClient
    .registerApplicationMaster(appMasterHostname, appMasterRpcPort,
       appMasterTrackingUrl);
 asyncClient.addContainerRequest(containerRequest);
 [... wait for application to complete]
 asyncClient.unregisterApplicationMaster(status, appMsg, trackingUrl);
 asyncClient.stop();

这个类是用来做为一个Client和RM进行通信，并且注册一个用于回调的对象来处理container 的allocation和completion事件。它启动一个线程，周期性地发送hearbeat至ResourceManager