content: /*
   * The Alluxio Open Foundation licenses this work under the Apache License, version 2.0
   * (the "License"). You may not use this work except in compliance with the License, which is
   * available at www.apache.org/licenses/LICENSE-2.0
   *
   * This software is distributed on an "AS IS" basis, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND,
   * either express or implied, as more fully set forth in the License.
   *
   * See the NOTICE file distributed with this work for information regarding copyright ownership.
   */
  
  package alluxio.master.file.meta;
  
  import alluxio.concurrent.LockMode;
  
  import com.google.common.base.Preconditions;
  
  import java.util.List;
  import java.util.concurrent.locks.Lock;
  import javax.annotation.concurrent.NotThreadSafe;
  
  /**
   * Manages the locks for a list of inodes, based off an existing lock list. This does not
   * modify the base lock list, and when this lock list is closed, the base lock list is not closed.
   * The purpose of this class is to allow lock lists to be temporarily extended and then restored.
   *
   * The base lock list can end with either an inode or edge, and can be read locked or write locked.
   *
   * Modification is only supported for the non-base part of the lock list.
   */
  @NotThreadSafe
  public class CompositeInodeLockList implements InodeLockList {
    /** The base lock list for this composite list. */
    private final InodeLockList mBaseLockList;
    /** An extension lock list for taking additional locks on top of the locks in mBaseLockList. */
    private final InodeLockList mSubLockList;
  
    /** The size of the base lock list, saved for fast lookup. */
    private final int mBaseListSize;
  
    /**
     * Constructs a new lock list, using an existing lock list as the base list.
     *
     * @param baseLockList the base {@link InodeLockList} to use
     * @param useTryLock whether or not use {@link Lock#tryLock()} or {@link Lock#lock()}
     */
    public CompositeInodeLockList(InodeLockList baseLockList, boolean useTryLock) {
      mBaseLockList = baseLockList;
      mBaseListSize = baseLockList.numInodes();
      mSubLockList = new SimpleInodeLockList(baseLockList.getInodeLockManager(), useTryLock);
    }
  
    @Override
    public void lockRootEdge(LockMode mode) {
      throw new UnsupportedOperationException(
          "lockRootEdge is not supported for composite lock lists");
    }
  
    @Override
    public void lockInode(Inode inode, LockMode mode) {
      mode = nextLockMode(mode);
      mSubLockList.lockInode(inode, mode);
    }
  
    @Override
    public void lockEdge(Inode inode, String childName, LockMode mode) {
      mode = nextLockMode(mode);
      if (mSubLockList.isEmpty()) {
        Preconditions.checkState(inode.getId() == mBaseLockList.get(mBaseListSize - 1).getId());
      }
      mSubLockList.lockEdge(inode, childName, mode);
    }
  
    @Override
    public void unlockLastInode() {
      if (!mSubLockList.isEmpty()) {
        mSubLockList.unlockLastInode();
      }
    }
  
    @Override
    public void unlockLastEdge() {
      if (!mSubLockList.isEmpty()) {
        mSubLockList.unlockLastEdge();
      }
    }
  
    @Override
    public void downgradeToReadLocks() {
      if (canDowngradeLast()) {
        mSubLockList.downgradeToReadLocks();
      }
    }
  
    @Override
    public void downgradeLastEdge() {
      if (canDowngradeLast()) {
        mSubLockList.downgradeLastEdge();
      }
    }
  
    @Override
    public void pushWriteLockedEdge(Inode inode, String childName) {
      if (canDowngradeLast()) {
        mSubLockList.pushWriteLockedEdge(inode, childName);
        return;
      }
      // Can't downgrade, just acquire new locks instead.
      mSubLockList.lockInode(inode, LockMode.WRITE);
      mSubLockList.lockEdge(inode, childName, LockMode.WRITE);
    }
  
    private boolean canDowngradeLast() {
      return !mSubLockList.isEmpty() && mBaseLockList.getLockMode() == LockMode.READ;
    }
  
    private LockMode nextLockMode(LockMode mode) {
      if (mBaseLockList.getLockMode() == LockMode.WRITE) {
        return LockMode.WRITE;
      }
      return mode;
    }
  
    @Override
    public LockMode getLockMode() {
      return mSubLockList.isEmpty() ? mBaseLockList.getLockMode() : mSubLockList.getLockMode();
    }
  
    @Override
    public List<Inode> getLockedInodes() {
      List<Inode> inodes = mBaseLockList.getLockedInodes();
      inodes.addAll(mSubLockList.getLockedInodes());
      return inodes;
    }
  
    @Override
    public Inode get(int index) {
      return index < mBaseListSize ? mBaseLockList.get(index)
          : mSubLockList.get(index - mBaseListSize);
    }
  
    @Override
    public int numInodes() {
      return mBaseListSize + mSubLockList.numInodes();
    }
  
    @Override
    public boolean endsInInode() {
      return mSubLockList.isEmpty() ? mBaseLockList.endsInInode() : mSubLockList.endsInInode();
    }
  
    @Override
    public boolean isEmpty() {
      return mBaseLockList.isEmpty() && mSubLockList.isEmpty();
    }
  
    @Override
    public InodeLockManager getInodeLockManager() {
      return mBaseLockList.getInodeLockManager();
    }
  
    @Override
    public void close() {
      mSubLockList.close();
    }
  }
  