platform/util/src/com/intellij/util/io/OpenChannelsCache.java

/*
 * Copyright 2000-2013 JetBrains s.r.o.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

/*
 * @author max
 */
package com.intellij.util.io;

import org.jetbrains.annotations.NonNls;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.RandomAccessFile;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class OpenChannelsCache { // TODO: Will it make sense to have a background thread, that flushes the cache by timeout?
  private final int myCacheSizeLimit;
  private final String myAccessMode;
  private final Map<File, ChannelDescriptor> myCache;

  public OpenChannelsCache(final int cacheSizeLimit, @NonNls String accessMode) {
    myCacheSizeLimit = cacheSizeLimit;
    myAccessMode = accessMode;
    myCache = new LinkedHashMap<File, ChannelDescriptor>(cacheSizeLimit, 0.5f, true);
  }

  public synchronized RandomAccessFile getChannel(File ioFile) throws FileNotFoundException {
    ChannelDescriptor descriptor = myCache.get(ioFile);
    if (descriptor == null) {
      dropOvercache();
      descriptor = new ChannelDescriptor(ioFile, myAccessMode);
      myCache.put(ioFile, descriptor);
    }
    descriptor.lock();
    return descriptor.getChannel();
  }

  private void dropOvercache() {
    int dropCount = myCache.size() - myCacheSizeLimit;

    if (dropCount >= 0) {
      List<File> keysToDrop = new ArrayList<File>();
      for (Map.Entry<File, ChannelDescriptor> entry : myCache.entrySet()) {
        if (dropCount < 0) break;
        if (!entry.getValue().isLocked()) {
          dropCount--;
          keysToDrop.add(entry.getKey());
        }
      }

      for (File file : keysToDrop) {
        closeChannel(file);
      }
    }
  }

  public synchronized void releaseChannel(File ioFile) {
    ChannelDescriptor descriptor = myCache.get(ioFile);
    assert descriptor != null;

    descriptor.unlock();
  }

  public synchronized void closeChannel(File ioFile) {
    final ChannelDescriptor descriptor = myCache.remove(ioFile);

    if (descriptor != null) {
      assert !descriptor.isLocked();

      AntivirusDetector.getInstance().execute(new Runnable() {
        @Override
        public void run() {
          try {
            descriptor.getChannel().close();
          }
          catch (IOException e) {
            throw new RuntimeException(e);
          }
        }
      });
    }
  }

  private static class ChannelDescriptor {
    private int lockCount = 0;
    private final RandomAccessFile myChannel;
    private final File myFile;

    @SuppressWarnings({"IOResourceOpenedButNotSafelyClosed"})
    public ChannelDescriptor(File file, String accessMode) throws FileNotFoundException {
      myFile = file;
      myChannel = new RandomAccessFile(file, accessMode);
    }

    public void lock() {
      lockCount++;
    }

    public void unlock() {
      lockCount--;
    }

    public boolean isLocked() {
      return lockCount != 0;
    }

    public RandomAccessFile getChannel() {
      return myChannel;
    }
  }
}