Package org.apache.hadoop.ha

Class HealthMonitor

java.lang.Object

org.apache.hadoop.ha.HealthMonitor

@Private
public class HealthMonitor
extends java.lang.Object

This class is a daemon which runs in a loop, periodically heartbeating with an HA service. It is responsible for keeping track of that service's health and exposing callbacks to the failover controller when the health status changes. Classes which need callbacks should implement the HealthMonitor.Callback interface.

Nested Class Summary

Nested Classes

Modifier and Type	Class	Description
static class	HealthMonitor.State

Method Summary

Modifier and Type	Method	Description
void	addCallback(org.apache.hadoop.ha.HealthMonitor.Callback cb)
void	addServiceStateCallback(org.apache.hadoop.ha.HealthMonitor.ServiceStateCallback cb)
protected HAServiceProtocol	createProxy()	Connect to the service to be monitored.
HAServiceProtocol	getProxy()
void	shutdown()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

addCallback

public void addCallback(org.apache.hadoop.ha.HealthMonitor.Callback cb)

addServiceStateCallback

public void addServiceStateCallback(org.apache.hadoop.ha.HealthMonitor.ServiceStateCallback cb)

shutdown

public void shutdown()

getProxy

public HAServiceProtocol getProxy()

Returns:

the current proxy object to the underlying service. Note that this may return null in the case that the service is not responding. Also note that, even if the last indicated state is healthy, the service may have gone down in the meantime.

createProxy

protected HAServiceProtocol createProxy()
                                 throws java.io.IOException

Connect to the service to be monitored. Stubbed out for easier testing.

Returns:

HAServiceProtocol.

Throws:

java.io.IOException - raised on errors performing I/O.