CloseHook (Solr 9.0.0 core API)

```
public interface CloseHook
```
Used to request notification when the core is closed.
Call SolrCore.addCloseHook(org.apache.solr.core.CloseHook) during the SolrCoreAware.inform(SolrCore) method to add a close hook to your object.
The close hook can be useful for releasing objects related to the request handler (for instance, if you have a JDBC DataSource or something like that)

Method Summary

All Methods Instance Methods Default Methods
Modifier and Type	Method	Description
`default void`	`postClose(SolrCore core)`	Method called when the given SolrCore object has been shut down and update handlers and searchers are closed Use this method for post-close clean up operations e.g.
`default void`	`preClose(SolrCore core)`	Method called when the given SolrCore object is closing / shutting down but before the update handler and searcher(s) are actually closed Important: Keep the method implementation as short as possible.

- Method Detail
  - preClose
```
default void preClose(SolrCore core)
```
    Method called when the given SolrCore object is closing / shutting down but before the update handler and searcher(s) are actually closed
    Important: Keep the method implementation as short as possible. If it were to use any heavy i/o , network connections - it might be a better idea to launch in a separate Thread so as to not to block the process of shutting down a given SolrCore instance.
    
    Parameters:
    
    core - SolrCore object that is shutting down / closing
  - postClose
```
default void postClose(SolrCore core)
```
    Method called when the given SolrCore object has been shut down and update handlers and searchers are closed
    Use this method for post-close clean up operations e.g. deleting the index from disk.
    The core's passed to the method is already closed and therefore, its update handler or searcher should *NOT* be used
    Important: Keep the method implementation as short as possible. If it were to use any heavy i/o , network connections - it might be a better idea to launch in a separate Thread so as to not to block the process of shutting down a given SolrCore instance.
    
    Parameters:
    
    core - SolrCore object that is shutting down / closing