Module org.elasticsearch.server
Package org.elasticsearch.common.file

Class AbstractFileWatchingService

java.lang.Object
org.elasticsearch.common.component.AbstractLifecycleComponent
org.elasticsearch.common.file.AbstractFileWatchingService
All Implemented Interfaces:
Closeable, AutoCloseable, ClusterStateListener, LifecycleComponent, Releasable
Direct Known Subclasses:
FileSettingsService
public abstract class AbstractFileWatchingService extends AbstractLifecycleComponent implements ClusterStateListener
A skeleton service for watching and reacting to a single file changing on disk

A file watching service watches for changes in a particular file on disk. There are three assumptions about the file structure:

  1. The file itself may or may not exist.
  2. The file's parent directory may or may not exist.
  3. The directory above the file's parent directory must always exist.

For example, if the watched file is under /usr/elastic/elasticsearch/conf/special/settings.yml, then /usr/elastic/elasticsearch/conf/ must exist, but special/ and special/settings.yml may be created, updated, or deleted during runtime.

What this class does not do is define what should happen after the file changes. An implementation class should override processFileChanges() to define the correct behavior.

  • Constructor Details

    • AbstractFileWatchingService

      public AbstractFileWatchingService(ClusterService clusterService, Path watchedFile)

  • Method Details

    • processFileChanges

      protected abstract void processFileChanges() throws InterruptedException, ExecutionException, IOException
      Any implementation of this class must implement this method in order to define what happens once the watched file changes.
      Throws:
      IOException - if there is an error reading the file itself
      ExecutionException - if there is an issue while applying the changes from the file
      InterruptedException - if the file processing is interrupted by another thread.

    • shouldRefreshFileState

      protected boolean shouldRefreshFileState(ClusterState clusterState)
      There may be an indication in cluster state that the file we are watching should be re-processed: for example, after cluster state has been restored from a snapshot. By default, we do nothing, but this method should be overridden if different behavior is desired.
      Parameters:
      clusterState - State of the cluster
      Returns:
      false, by default

    • addFileChangedListener

      public final void addFileChangedListener(FileChangedListener listener)

    • watchedFileDir

      public final Path watchedFileDir()

    • watchedFile

      public final Path watchedFile()

    • clusterChanged

      public final void clusterChanged(ClusterChangedEvent event)
      Description copied from interface: ClusterStateListener
      Called when cluster state changes.

      Cluster states are applied one-by-one which means they can be a performance bottleneck. Implementations of this method should therefore be fast, so please consider forking work into the background rather than doing everything inline.

      Specified by:
      clusterChanged in interface ClusterStateListener

    • doStart

      protected final void doStart()
      Description copied from class: AbstractLifecycleComponent
      Start this component. Typically that means doing things like launching background processes and registering listeners on other components. Other components have been initialized by this point, but may not yet be started.

      If this method throws an exception then the startup process will fail, but this component will not be stopped before it is closed.

      This method is called while synchronized on AbstractLifecycleComponent.lifecycle. It is only called once in the lifetime of a component, although it may not be called at all if the startup process encountered some kind of fatal error, such as the failure of some other component to initialize or start.

      Specified by:
      doStart in class AbstractLifecycleComponent

    • doStop

      protected final void doStop()
      Description copied from class: AbstractLifecycleComponent
      Stop this component. Typically that means doing the reverse of whatever AbstractLifecycleComponent.doStart() does.

      This method is called while synchronized on AbstractLifecycleComponent.lifecycle. It is only called once in the lifetime of a component, after calling AbstractLifecycleComponent.doStart(), although it will not be called at all if this component did not successfully start.

      Specified by:
      doStop in class AbstractLifecycleComponent

    • doClose

      protected final void doClose()
      Description copied from class: AbstractLifecycleComponent
      Close this component. Typically that means doing the reverse of whatever happened during initialization, such as releasing resources acquired there.

      This method is called while synchronized on AbstractLifecycleComponent.lifecycle. It is called once in the lifetime of a component. If the component was started then it will be stopped before it is closed, and once it is closed it will not be started or stopped.

      Specified by:
      doClose in class AbstractLifecycleComponent

    • watching

      public final boolean watching()

    • watcherThread

      protected final void watcherThread()