Examples of org.apache.slider.core.persist.ConfPersister

org.apache.slider.core.persist.ConfPersister
Class to implement persistence of a configuration. This code contains the logic to acquire and release locks. # writelock MUST be acquired exclusively for writes. This is done by creating the file with no overwrite # shared readlock MUST be acquired for reads. This is done by creating the readlock file with overwrite forbidden -but treating a failure as a sign that the lock exists, and therefore the operation can continue. # releaselock is only released if the client created it. # after acquiring either lock, client must check for the alternate lock existing. If it is, release lock and fail. There's one small race here: multiple readers; first reader releases lock while second is in use. Strict Fix: client checks for readlock after read completed. If it is not there, problem: fail. But this massively increases the risk of false negatives. This isn't 100% perfect, because of the condition where the owner releases a lock, a writer grabs its lock & writes to it, the reader gets slightly contaminated data: own-share-delete-write-own-release(shared)-delete We are assuming that the rate of change is low enough that this is rare, and of limited damage. ONCE A CLUSTER IS RUNNING, ONLY THE AM MAY PERSIST UPDATES VIA ITS APIs That is: outside the AM, a writelock MUST only be acquired after verifying there is no running application.

  public AggregateConf loadPersistedClusterDescription(String clustername) throws
                                                                           IOException,
      SliderException,
                                                                           LockAcquireFailedException {
    Path clusterDirectory = sliderFileSystem.buildClusterDirPath(clustername);
    ConfPersister persister = new ConfPersister(sliderFileSystem, clusterDirectory);
    AggregateConf instanceDescription = new AggregateConf();
    persister.load(instanceDescription);
    return instanceDescription;
  }

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  public AggregateConf loadPersistedClusterDescription(String clustername) throws
                                                                           IOException,
      SliderException,
                                                                           LockAcquireFailedException {
    Path clusterDirectory = sliderFileSystem.buildClusterDirPath(clustername);
    ConfPersister persister = new ConfPersister(sliderFileSystem, clusterDirectory);
    AggregateConf instanceDescription = new AggregateConf();
    persister.load(instanceDescription);
    return instanceDescription;
  }

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  public void persist(Path appconfdir) throws
      IOException,
      SliderException,
      LockAcquireFailedException {
    coreFS.createClusterDirectories(instancePaths);
    ConfPersister persister =
      new ConfPersister(coreFS, getInstanceDir());
    ConfDirSnapshotAction action = null;
    if (appconfdir != null) {
      action = new ConfDirSnapshotAction(appconfdir);
    }
    persister.save(instanceDescription, action);
  }

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    CoreFileSystem sliderFileSystem,
    Path clusterDirectory) throws
                           IOException,
      SliderException {
    AggregateConf instanceDefinition = new AggregateConf();
    ConfPersister persister =
      new ConfPersister(sliderFileSystem, clusterDirectory);
    try {
      persister.load(instanceDefinition);
    } catch (LockAcquireFailedException e) {
      log.debug("Lock acquisition failure of {}", clusterDirectory, e);


      throw new BadClusterStateException(
        "Application at %s is locked for reading",

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   */
  public static void updateInstanceDefinition(CoreFileSystem coreFS,
                                              Path dir,
                                              AggregateConf instanceDefinition)
      throws SliderException, IOException, LockAcquireFailedException {
    ConfPersister persister =
      new ConfPersister(coreFS, dir);
    persister.save(instanceDefinition, null);
  }

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