net.java.truevfs.ext.pacemaker.PaceManager.scala Maven / Gradle / Ivy

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Constrains the number of concurrently mounted archive file systems in order to save some heap space. This module provides a JMX interface for monitoring and management. Add the JAR artifact of this module to the run time class path to make its services available for service location in the client API modules.

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/*
 * Copyright (C) 2005-2015 Schlichtherle IT Services.
 * All rights reserved. Use is subject to license terms.
 */
package net.java.truevfs.ext.pacemaker

import net.java.truecommons.logging._
import net.java.truevfs.comp.jmx._
import net.java.truevfs.ext.pacemaker.PaceManager._
import net.java.truevfs.kernel.spec._

/** A pace manager.
  * This class is thread-safe.
  *
  * @author Christian Schlichtherle
  */
private class PaceManager(mediator: PaceMediator, manager: FsManager)
extends JmxManager[PaceMediator](mediator, manager) {

  private val cachedMountPoints = mediator.cachedMountPoints
  private val evictedMountPoints = mediator.evictedMountPoints

  def maximumSize = mediator.maximumSize
  def maximumSize_=(maximumSize: Int) { mediator.maximumSize = maximumSize }

  override def newView = new PaceManagerView(this)

  /**
   * Records access to a file system after the fact and tries to unmount the
   * least-recently accessed file systems which exceed the maximum number
   * of mounted file systems.
   * A file system is never unmounted if there any open streams or channels
   * associated with it or if any of its child file systems is mounted.
   *
   * @param mountPoint the mount point of the accessed file system.
   */
  def recordAccess(mountPoint: FsMountPoint) {
    cachedMountPoints recordAccess mountPoint
    unmountEvictedArchiveFileSystems()
  }

  private def unmountEvictedArchiveFileSystems() {
    val iterator = evictedMountPoints.iterator
    if (iterator.hasNext) {
      val builder = new FsSyncExceptionBuilder
      do {
        val evictedMountPoint = iterator next ()
        val evictedMountPointFilter = FsPrefixMountPointFilter forPrefix evictedMountPoint
        // Check that neither the evicted file system nor any of its child file
        // systems is actually mounted.
        if (!(cachedMountPoints exists evictedMountPointFilter.accept)) {
          try {
            new FsSync()
              .manager(manager)
              .filter(FsControllerFilter forPrefix evictedMountPoint)
              .run()
            iterator remove ()
          } catch {
            case e: FsSyncException =>
              e.getCause match {
                case _: FsOpenResourceException =>
                  // Do NOT remove evicted controller - the sync shall get
                  // retried at the next call to this method!
                  //it remove ()

                  // This is pretty much a normal situation, so just log the
                  // exception at the TRACE level.
                  logger trace ("ignoring", e)
                case _ =>
                  // Prevent retrying this operation - it would most likely
                  // yield the same result.
                  iterator remove ()

                  // Mark the exception for subsequent rethrowing at the end of
                  // this method.
                  builder warn e
              }
          }
        }
      } while (iterator.hasNext)
      builder check ()
    }
  }
}

private object PaceManager {

  val logger = new LocalizedLogger(classOf[PaceManager])
}