JobGraphStoreWatcher (Flink : 2.0-preview1 API)

All Known Implementing Classes:

NoOpJobGraphStoreWatcher, ZooKeeperJobGraphStoreWatcher
```
public interface JobGraphStoreWatcher
```
A watcher on JobGraphStore. It could monitor all the changes on the job graph store and notify the JobGraphStore via JobGraphStore.JobGraphListener.
Important: The JobGraphStoreWatcher could not guarantee that there is no JobGraphStore.JobGraphListener callbacks happen after stop(). So the implementor is responsible for filtering out these spurious callbacks.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`void`	`start(JobGraphStore.JobGraphListener jobGraphListener)`	Start the watcher on `JobGraphStore`.
`void`	`stop()`	Stop the watcher on `JobGraphStore`.

- Method Detail
  - start
```
void start(JobGraphStore.JobGraphListener jobGraphListener)
    throws Exception
```
    Start the watcher on JobGraphStore.
    
    Parameters:
    
    jobGraphListener - use jobGraphListener to notify the DefaultJobGraphStore
    
    Throws:
    
    Exception - when start internal services
  - stop
```
void stop()
   throws Exception
```
    Stop the watcher on JobGraphStore.
    
    Throws:
    
    Exception - when stop internal services